Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward
exploiting alternative energy resources such as solar energy. Here, we
report the successful low-cost and easily accessible synthesis of hybrid
semiconductor@TiO2 nanotube photocatalysts. In order to realize its
maximum potential in harvesting photons in the visible-light range, TiO2
nanotubes have been loaded with earth-abundant, low-band-gap fibrous
red and black phosphorus (P). Scanning electron microscopy− and
scanning transmission electron microscopy−energy-dispersive X-ray
spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV−vis measurements have been performed,
substantiating the deposition of fibrous red and black P on top and
inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and
TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in
1.5−2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared
with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge
separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier
dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate
the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band
potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results
demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in
optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular …
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO 2...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP …
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Vapor growth of binary and ternary phosphorusbased semiconductors into TiO2 n...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with
the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12)
were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing
vapor phase reaction deposition, the cavities of 100 mm long TiO2 nanotubes were infiltrated;
approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive
characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman
spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the
substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water
splitting performance compared to pristine materials and were found to be more active at higher
wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The
improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge
transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
The document summarizes research into using InGaN nanowire devices for hydrogen production via water splitting. It finds that InGaN alloys have an appropriate band structure but that nanowires are needed to accommodate lattice strain. Initial tests show some nanowire samples exhibiting photocatalytic hydrogen production from water, with production rates increasing for lower nanowire density samples and higher light intensities. Further optimization of indium composition, nanowire morphology, doping, and co-catalysts is suggested to improve the efficiency of hydrogen generation from water using InGaN nanowire devices.
The document summarizes research on modifying the bandgap of n-TiO2 through carbon doping to enable its use in photoelectrochemical water splitting using visible light. Carbon-modified n-TiO2 (CM-n-TiO2) films were synthesized using spray pyrolysis. Increased carbon doping was achieved by calcining in inert atmosphere. CM-n-TiO2 exhibited photoresponse in the visible spectrum due to carbon doping reducing the bandgap and introducing an intragap band. This modified the band structure of n-TiO2 to extend utilization of solar energy into the visible region.
Synthesis and Characterization of Zinc Phthalocyanine-Cellulose Nanocrystal (...Pawan Kumar
We report highly fluorescent cellulose nanocrystals (CNCs) formed by conjugating a carboxylated zinc phthalocyanine (ZnPc) to two different types of CNCs. The conjugated nanocrystals (henceforth called ZnPc@CNCs) were bright green in color and exhibited absorption and emission maxima at ∼690 and ∼715 nm, respectively. The esterification protocol employed to covalently bind carboxylated ZnPc to surface hydroxyl group rich CNCs was expected to result in a monolayer of ZnPc on the surface of the CNCs. However, dynamic light scattering (DLS) studies indicated a large increase in the hydrodynamic radius of CNCs following conjugation to ZnPc, which suggests the binding of multiple ZnPc molecular layers on the CNC surface. This binding could be through co-facial π-stacking of ZnPc, where ZnPc metallophthalocyanine rings are horizontal to the CNC surface. The other possible binding mode would give rise to conjugated systems where ZnPc metallophthalocyanine rings are oriented vertically on the CNC surface. Density functional theory based calculations showed stable geometry following the conjugation protocol that involved covalently attached ester bond formation. The conjugates demonstrated superior performance for potential sensing applications through higher photoluminescence quenching capabilities compared to pristine ZnPc.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular …
Vapor growth of binary and ternary phosphorus-based semiconductors into TiO 2...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12) were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing vapor phase reaction deposition, the cavities of 100 μm long TiO2 nanotubes were infiltrated; approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water splitting performance compared to pristine materials and were found to be more active at higher wavelengths. SnIP …
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Vapor growth of binary and ternary phosphorusbased semiconductors into TiO2 n...Pawan Kumar
We report successful synthesis of low band gap inorganic polyphosphide and TiO2 heterostructures with
the aid of short-way transport reactions. Binary and ternary polyphosphides (NaP7, SnIP, and (CuI)3P12)
were successfully reacted and deposited into electrochemically fabricated TiO2 nanotubes. Employing
vapor phase reaction deposition, the cavities of 100 mm long TiO2 nanotubes were infiltrated;
approximately 50% of the nanotube arrays were estimated to be infiltrated in the case of NaP7. Intensive
characterization of the hybrid materials with techniques including SEM, FIB, HR-TEM, Raman
spectroscopy, XRD, and XPS proved the successful vapor phase deposition and synthesis of the
substances on and inside the nanotubes. The polyphosphide@TiO2 hybrids exhibited superior water
splitting performance compared to pristine materials and were found to be more active at higher
wavelengths. SnIP@TiO2 emerged to be the most active among the polyphosphide@TiO2 materials. The
improved photocatalytic performance might be due to Fermi level re-alignment and a lower charge
transfer resistance which facilitated better charge separation from inorganic phosphides to TiO2.
Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
The document summarizes research into using InGaN nanowire devices for hydrogen production via water splitting. It finds that InGaN alloys have an appropriate band structure but that nanowires are needed to accommodate lattice strain. Initial tests show some nanowire samples exhibiting photocatalytic hydrogen production from water, with production rates increasing for lower nanowire density samples and higher light intensities. Further optimization of indium composition, nanowire morphology, doping, and co-catalysts is suggested to improve the efficiency of hydrogen generation from water using InGaN nanowire devices.
The document summarizes research on modifying the bandgap of n-TiO2 through carbon doping to enable its use in photoelectrochemical water splitting using visible light. Carbon-modified n-TiO2 (CM-n-TiO2) films were synthesized using spray pyrolysis. Increased carbon doping was achieved by calcining in inert atmosphere. CM-n-TiO2 exhibited photoresponse in the visible spectrum due to carbon doping reducing the bandgap and introducing an intragap band. This modified the band structure of n-TiO2 to extend utilization of solar energy into the visible region.
Synthesis and Characterization of Zinc Phthalocyanine-Cellulose Nanocrystal (...Pawan Kumar
We report highly fluorescent cellulose nanocrystals (CNCs) formed by conjugating a carboxylated zinc phthalocyanine (ZnPc) to two different types of CNCs. The conjugated nanocrystals (henceforth called ZnPc@CNCs) were bright green in color and exhibited absorption and emission maxima at ∼690 and ∼715 nm, respectively. The esterification protocol employed to covalently bind carboxylated ZnPc to surface hydroxyl group rich CNCs was expected to result in a monolayer of ZnPc on the surface of the CNCs. However, dynamic light scattering (DLS) studies indicated a large increase in the hydrodynamic radius of CNCs following conjugation to ZnPc, which suggests the binding of multiple ZnPc molecular layers on the CNC surface. This binding could be through co-facial π-stacking of ZnPc, where ZnPc metallophthalocyanine rings are horizontal to the CNC surface. The other possible binding mode would give rise to conjugated systems where ZnPc metallophthalocyanine rings are oriented vertically on the CNC surface. Density functional theory based calculations showed stable geometry following the conjugation protocol that involved covalently attached ester bond formation. The conjugates demonstrated superior performance for potential sensing applications through higher photoluminescence quenching capabilities compared to pristine ZnPc.
Remarkable self-organization and unusual conductivity behavior in cellulose n...Pawan Kumar
Aqueous suspensions of cellulose nanocrystals were blended with Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) [PEDOT:PSS], and cast into thin films. The morphology, structure and electrical properties of the resulting nanocomposite thin films were thoroughly characterized. We found that the CNC–PEDOT:PSS blends self-organize into a layered vertical stack with a pitch of 100–200 nm while retaining a continuous percolation network for PEDOT. Atomic force microscopy, dynamic light scattering and multi-angle light scattering measurements confirmed the wrapping of polymer chains around the rod-like CNCs. The blended films exhibited improved molecular ordering of the PEDOT chains with concomitant improvement in the carrier mobility. The remarkable self-organization and enhanced structural order enabled the CNC–PEDOT:PSS blends to exhibit a high conductivity typical of PEDOT:PSS even when the content of the insulating CNCs in the nanocomposite was as high as 50 wt%.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
Quantum dots for optoelectronic devices - phdassistancePhD Assistance
Nanometre-scale semiconductor chips have been imagined as next-generation technology with high functionality and convergence. Quantum dots, also known as artificial atoms, have special properties owing to their quantum confinement in all three dimensions. Quantum dots have a lot of interest in optoelectronic systems because of their special properties.
For decades, self-assembled nanostructures have been a topic of considerable concern and significance.
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Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
This document discusses the effect of morphology on the photoelectrochemical performance of nanostructured Cu2O photocathodes. It summarizes that:
1) Different deposition methods including electroreduction, anodization, thermal oxidation, and chemical oxidation were used to deposit planar and 1D nanostructured Cu2O thin films on copper foil with varying morphologies.
2) Mesoscopic and planar Cu2O morphologies exhibited large differences in carrier density and charge transfer resistance, but these differences did not strongly influence their photoelectrochemical performance.
3) Planar Cu2O deposited via electroreduction provided the highest photocurrent density of 5.0 mA cm−2 at 0 V vs RHE,
The document discusses the origin of radiation-induced degradation in polymer solar cells. It finds that charge accumulation at the interface is the primary reason for degradation, affected by the donor-acceptor mixing ratio in the bulk heterojunction. In situ measurements of polymer solar cell performance and recombination lifetimes under X-ray radiation show that devices with high acceptor concentrations experience a significant decrease in open-circuit voltage and fill factor due to radiation, while devices with low acceptor concentrations are more resistant to these changes. The findings provide a quantitative understanding and physical model of the degradation mechanism.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...Pawan Kumar
The overwhelming challenge of depleting fossil fuels and anthropogenic carbon emissions has driven research into alternative clean sources of energy. To achieve the goal of a carbon neutral economy, the harvesting of sunlight by using photocatalysts to split water into hydrogen and oxygen is an expedient approach to fulfill the energy demand in a sustainable way along with reducing the emission of greenhouse gases. Even though the past few decades have witnessed intensive research into inorganic semiconductor photocatalysts, their quantum efficiencies for hydrogen production from visible photons remain too low for the large scale deployment of this technology. Visible light absorption and efficient charge separation are two key necessary conditions for achieving the scalable production of hydrogen from water. Two-dimensional carbon based nanoscale materials such as graphene oxide, reduced graphene oxide, carbon nitride, modified 2D carbon frameworks and their composites have emerged as potential photocatalysts due to their astonishing properties such as superior charge transport, tunable energy levels and bandgaps, visible light absorption, high surface area, easy processability, quantum confinement effects, and high photocatalytic quantum yields. The feasibility of structural and chemical modification to optimize visible light absorption and charge separation makes carbonaceous semiconductors promising candidates to convert solar energy into chemical energy. In the present review, we have summarized the recent advances in 2D carbonaceous photocatalysts with respect to physicochemical and photochemical tuning for solar light mediated hydrogen evolution.
This document discusses X-ray diffraction (XRD) spectroscopy and provides examples of applying XRD principles to characterize different materials. It describes the basic principles of how XRD works using Bragg's law and Miller indices to identify crystal planes. Examples are given for characterizing silver nanoparticles, graphite, graphene oxide, and zinc oxide nanoparticles using XRD, including estimating particle sizes from XRD peak widths and identifying functional groups from infrared spectroscopy. References are also provided for further reading.
This document is a resume for Dr. Elena A. Guliants seeking a research or program management position involving renewable and alternative energy technologies. She has over 23 years of experience in fields such as photovoltaics, energy storage, hydrogen generation, and nanoenergetics. Her educational background includes a Ph.D. in Electrical Engineering and an M.B.A. She is fluent in English and Russian.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Boosting Photocatalytic Activity Using Carbon Nitride Based 2D/2D van der Waa...Pawan Kumar
The surging demand for energy and staggering pollutants in the environment have geared the scientific community to explore sustainable pathways that are economically feasible and environmentally compelling. In this context, harnessing solar energy using semiconductor materials to generate charge pairs to drive photoredox reactions has been envisioned as a futuristic approach. Numerous inorganic crystals with promising nanoregime properties investigated in the past decade have yet to demonstrate practical application due to limited photon absorption and sluggish charge separation kinetics. Two-dimensional semiconductors with tunable optical and electronic properties and quasi-resistance-free lateral charge transfer mechanisms have shown great promise in photocatalysis. Polymeric graphitic carbon nitride (g-C3N4) is among the most promising candidates due to fine-tuned band edges and the feasibility of optimizing the optical properties via materials genomics. Constructing a two-dimensional (2D)/2D van der Waals (vdW) heterojunction by allies of 2D carbon nitride sheets and other 2D semiconductors has demonstrated enhanced charge separation with improved visible photon absorption, and the performance is not restricted by the lattice matching of constituting materials. With the advent of new 2D semiconductors over the recent past, the 2D/2D heterojunction assemblies are gaining momentum to design high performance photocatalysts for numerous applications. This review aims to highlight recent advancements and key understanding in carbon nitride based 2D/2D heterojunctions and their applications in photocatalysis, including small molecules activation, conversion, and degradations. We conclude with a forward-looking perspective discussing the key challenges and opportunity areas for future research.
Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive ApplicationsIOSR Journals
This document summarizes a study on a nonvolatile resistive random access memory device based on the heterojunction of silver nanoparticles and aluminum oxide. The device structure consists of aluminum-aluminum oxide-silver nanoparticles-aluminum. Current-voltage measurements show the device transitions between two states in two steps - a major transition with a resistance ratio of 105 and a minor transition with a ratio of about 101. The memristor operates at low voltages with good uniformity. Scanning electron microscopy, X-ray diffraction and optical absorption characterization confirm the formation of aluminum oxide and silver nanoparticles.
Enhanced charge separation in gC 3 N 4–BiOI heterostructures for visible ligh...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting. HR-TEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical performance is observed …
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM
and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of g-
C3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
Nanostructured composite materials for CO2 activationPawan Kumar
This document discusses nanostructured composite materials for CO2 activation, specifically for the photocatalytic reduction of CO2 to valuable products. It provides background on the increasing energy crisis and climate change caused by fossil fuel use. It then summarizes the basic principles and challenges of using semiconductor photocatalysts for CO2 reduction, including appropriate band gap positions and preventing electron-hole recombination. The document discusses various approaches to overcoming these challenges, such as forming heterojunction composites and using co-catalysts to facilitate charge separation and transfer.
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of gC3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and …
Remarkable self-organization and unusual conductivity behavior in cellulose n...Pawan Kumar
Aqueous suspensions of cellulose nanocrystals were blended with Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) [PEDOT:PSS], and cast into thin films. The morphology, structure and electrical properties of the resulting nanocomposite thin films were thoroughly characterized. We found that the CNC–PEDOT:PSS blends self-organize into a layered vertical stack with a pitch of 100–200 nm while retaining a continuous percolation network for PEDOT. Atomic force microscopy, dynamic light scattering and multi-angle light scattering measurements confirmed the wrapping of polymer chains around the rod-like CNCs. The blended films exhibited improved molecular ordering of the PEDOT chains with concomitant improvement in the carrier mobility. The remarkable self-organization and enhanced structural order enabled the CNC–PEDOT:PSS blends to exhibit a high conductivity typical of PEDOT:PSS even when the content of the insulating CNCs in the nanocomposite was as high as 50 wt%.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems...Pawan Kumar
Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.
Quantum dots for optoelectronic devices - phdassistancePhD Assistance
Nanometre-scale semiconductor chips have been imagined as next-generation technology with high functionality and convergence. Quantum dots, also known as artificial atoms, have special properties owing to their quantum confinement in all three dimensions. Quantum dots have a lot of interest in optoelectronic systems because of their special properties.
For decades, self-assembled nanostructures have been a topic of considerable concern and significance.
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Polymeric carbon nitride-based photocatalysts for photoreforming of biomass d...Pawan Kumar
Photoreforming of biomass to value-added chemicals and fuels is a chemical approach to extract photosynthetically-trapped energy in complex biomolecules which otherwise disintegrate naturally in the environment. Designing precise photocatalytic materials that can selectively break the sturdy, nature-designed biomass with multiplex chemical composition/bonding and inaccessible sites is central to deploying this technology. Polymeric carbon nitride (CN) comprised of a 2D network of condensed heptazine/triazine (C6N7/C3N3) core has shown great promise for photoreforming of biomass derivatives due to intriguing physicochemical and optical properties. This review comprehensively summarizes the state-of-the-art applications of CN-based photocatalysts for the conversion of lignocellulosic biomass derivatives. Various chemical and structural modifications in CN structure such as doping, surface functionalization, hybridization entailing to higher selectivity and conversion have been discussed aiming at providing valuable guidance for future CN-based materials design.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
This document discusses the effect of morphology on the photoelectrochemical performance of nanostructured Cu2O photocathodes. It summarizes that:
1) Different deposition methods including electroreduction, anodization, thermal oxidation, and chemical oxidation were used to deposit planar and 1D nanostructured Cu2O thin films on copper foil with varying morphologies.
2) Mesoscopic and planar Cu2O morphologies exhibited large differences in carrier density and charge transfer resistance, but these differences did not strongly influence their photoelectrochemical performance.
3) Planar Cu2O deposited via electroreduction provided the highest photocurrent density of 5.0 mA cm−2 at 0 V vs RHE,
The document discusses the origin of radiation-induced degradation in polymer solar cells. It finds that charge accumulation at the interface is the primary reason for degradation, affected by the donor-acceptor mixing ratio in the bulk heterojunction. In situ measurements of polymer solar cell performance and recombination lifetimes under X-ray radiation show that devices with high acceptor concentrations experience a significant decrease in open-circuit voltage and fill factor due to radiation, while devices with low acceptor concentrations are more resistant to these changes. The findings provide a quantitative understanding and physical model of the degradation mechanism.
Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Co...Pawan Kumar
We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C3N5 is a low-band-gap (Eg = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C3N5 nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C3N5 heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm2 V–1 s–1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm2 V–1 s–1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J–V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C3N5 in CdS-MHP. C3N5, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core–shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.
Sunlight-driven water-splitting using two-dimensional carbon based semiconduc...Pawan Kumar
The overwhelming challenge of depleting fossil fuels and anthropogenic carbon emissions has driven research into alternative clean sources of energy. To achieve the goal of a carbon neutral economy, the harvesting of sunlight by using photocatalysts to split water into hydrogen and oxygen is an expedient approach to fulfill the energy demand in a sustainable way along with reducing the emission of greenhouse gases. Even though the past few decades have witnessed intensive research into inorganic semiconductor photocatalysts, their quantum efficiencies for hydrogen production from visible photons remain too low for the large scale deployment of this technology. Visible light absorption and efficient charge separation are two key necessary conditions for achieving the scalable production of hydrogen from water. Two-dimensional carbon based nanoscale materials such as graphene oxide, reduced graphene oxide, carbon nitride, modified 2D carbon frameworks and their composites have emerged as potential photocatalysts due to their astonishing properties such as superior charge transport, tunable energy levels and bandgaps, visible light absorption, high surface area, easy processability, quantum confinement effects, and high photocatalytic quantum yields. The feasibility of structural and chemical modification to optimize visible light absorption and charge separation makes carbonaceous semiconductors promising candidates to convert solar energy into chemical energy. In the present review, we have summarized the recent advances in 2D carbonaceous photocatalysts with respect to physicochemical and photochemical tuning for solar light mediated hydrogen evolution.
This document discusses X-ray diffraction (XRD) spectroscopy and provides examples of applying XRD principles to characterize different materials. It describes the basic principles of how XRD works using Bragg's law and Miller indices to identify crystal planes. Examples are given for characterizing silver nanoparticles, graphite, graphene oxide, and zinc oxide nanoparticles using XRD, including estimating particle sizes from XRD peak widths and identifying functional groups from infrared spectroscopy. References are also provided for further reading.
This document is a resume for Dr. Elena A. Guliants seeking a research or program management position involving renewable and alternative energy technologies. She has over 23 years of experience in fields such as photovoltaics, energy storage, hydrogen generation, and nanoenergetics. Her educational background includes a Ph.D. in Electrical Engineering and an M.B.A. She is fluent in English and Russian.
TiO2-HfN Radial Nano-Heterojunction: A Hot Carrier Photoanode for Sunlight-Dr...Pawan Kumar
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace
plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and costeffective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of
atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity
for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) a
large bandgap between optical and acoustic phonon modes (2) and no electronic bandgap, which
allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in
this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing
plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that
extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active
HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Boosting Photocatalytic Activity Using Carbon Nitride Based 2D/2D van der Waa...Pawan Kumar
The surging demand for energy and staggering pollutants in the environment have geared the scientific community to explore sustainable pathways that are economically feasible and environmentally compelling. In this context, harnessing solar energy using semiconductor materials to generate charge pairs to drive photoredox reactions has been envisioned as a futuristic approach. Numerous inorganic crystals with promising nanoregime properties investigated in the past decade have yet to demonstrate practical application due to limited photon absorption and sluggish charge separation kinetics. Two-dimensional semiconductors with tunable optical and electronic properties and quasi-resistance-free lateral charge transfer mechanisms have shown great promise in photocatalysis. Polymeric graphitic carbon nitride (g-C3N4) is among the most promising candidates due to fine-tuned band edges and the feasibility of optimizing the optical properties via materials genomics. Constructing a two-dimensional (2D)/2D van der Waals (vdW) heterojunction by allies of 2D carbon nitride sheets and other 2D semiconductors has demonstrated enhanced charge separation with improved visible photon absorption, and the performance is not restricted by the lattice matching of constituting materials. With the advent of new 2D semiconductors over the recent past, the 2D/2D heterojunction assemblies are gaining momentum to design high performance photocatalysts for numerous applications. This review aims to highlight recent advancements and key understanding in carbon nitride based 2D/2D heterojunctions and their applications in photocatalysis, including small molecules activation, conversion, and degradations. We conclude with a forward-looking perspective discussing the key challenges and opportunity areas for future research.
Aluminum Oxide-Silver Nanoparticle Interfaces for Memristive ApplicationsIOSR Journals
This document summarizes a study on a nonvolatile resistive random access memory device based on the heterojunction of silver nanoparticles and aluminum oxide. The device structure consists of aluminum-aluminum oxide-silver nanoparticles-aluminum. Current-voltage measurements show the device transitions between two states in two steps - a major transition with a resistance ratio of 105 and a minor transition with a ratio of about 101. The memristor operates at low voltages with good uniformity. Scanning electron microscopy, X-ray diffraction and optical absorption characterization confirm the formation of aluminum oxide and silver nanoparticles.
Enhanced charge separation in gC 3 N 4–BiOI heterostructures for visible ligh...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting. HR-TEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical performance is observed …
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM
and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of g-
C3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
Nanostructured composite materials for CO2 activationPawan Kumar
This document discusses nanostructured composite materials for CO2 activation, specifically for the photocatalytic reduction of CO2 to valuable products. It provides background on the increasing energy crisis and climate change caused by fossil fuel use. It then summarizes the basic principles and challenges of using semiconductor photocatalysts for CO2 reduction, including appropriate band gap positions and preventing electron-hole recombination. The document discusses various approaches to overcoming these challenges, such as forming heterojunction composites and using co-catalysts to facilitate charge separation and transfer.
Enhanced charge separation in g-C3N4–BiOI heterostructures for visible light ...Pawan Kumar
Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered
graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are
synthesized and investigated as an active photoanode material for sunlight driven water splitting. HRTEM and elemental mapping reveals formation of a unique heterostructure between BiOI platelets and
the carbon nitride (g-C3N4 and g-C3N4-S) network that consisted of dendritic BiOI nanoplates
surrounded by g-C3N4 sheets. The presence of BiOI in g-C3N4-S/BiOI and g-C3N4-S/BiOI
nanocomposites extends the visible light absorption profile from 500 nm up to 650 nm. Due to excellent
charge separation in g-C3N4/BiOI and g-C3N4-S/BiOI, evident from quenching of the carbon nitride
photoluminescence (PL) and a decrease in the PL lifetime, a significant increase in photoelectrochemical
performance is observed for both types of g-C3N4–BiOI heterojunctions. In comparison to
heterojunctions of bulk g-C3N4 with BiOI, the nanocomposite consisting of few layered sheets of gC3N4 and BiOI exhibits higher photocurrent density due to lower recombination in few layered sheets. A
synergistic trap passivation and charge separation is found to occur in the g-C3N4-S/BiOI
nanocomposite heterostructure which results in a higher photocurrent and a lower charge transfer
resistance.
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and …
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO2 nanorods exhibited a strong photoelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots
Optical Control of Selectivity of High Rate CO2 Photoreduction Via Interband-...Pawan Kumar
Photonic crystals consisting of TiO2 nanotube arrays (PMTiNTs) with periodically modulated diameters were fabricated using a precise charge-controlled pulsed anodization technique. The PMTiNTs were decorated with gold nanoparticles (Au NPs) to form plasmonic photonic crystal photocatalysts (Au-PMTiNTs). A systematic study of CO2 photoreduction performance on as-prepared samples was conducted using different wavelengths and illumination sequences. A remarkable selectivity of the mechanism of CO2 photoreduction could be engineered by merely varying the spectral composition of the illumination sequence. Under AM1.5 G simulated sunlight (pathway#1), the Au-PMTiNTs produced methane (302 µmol h-1) from CO2 with high selectivity (89.3%). When also illuminated by a UV-poor white lamp (pathway#2), the Au-PMTiNTs produced formaldehyde (420 µmol h-1) and carbon monoxide (323 µmol h-1) with almost no methane evolved. We confirmed the photoreduction results by 13C isotope labeling experiments using GC-MS. These results point to optical control of the selectivity of high-rate CO2 photoreduction through selection of one of two different mechanistic pathways. Pathway#1 implicates electron-hole pairs generated through interband transitions in TiO2 and Au as the primary active species responsible for reducing CO2 to methane. Pathway#2 involves excitation of both TiO2 and surface plasmons in Au. Hot electrons produced by plasmon damping and photogenerated holes in TiO2 proceed to reduce CO2 to HCHO and CO through a plasmonic Z-scheme.
Carbon-cuprous oxide composite nanoparticles
were chemically deposited on surface of thin glass tubes of spent
energy saving lamps for solar heat collection. Carbon was
obtained from fly ash of heavy oil incomplete combustion in
electric power stations. Impurities in the carbon were removed by
leaching with mineral acids. The mineral free-carbon was then
wet ground to have a submicron size. After filtration, it was
reacted with concentrated sulfuric/fuming nitric acid mixture on
cold for 3-4 days. Potassium chlorate was then added drop wise on
hot conditions to a carbon slurry followed by filtration.
Nanocarbon sample was mixed with 5% by weight PVA to help
adhesion to the glass surface. Carbon so deposited was doped with
copper nitrate solution. After dryness, the carbon/copper nitrate
film was dipped in hydrazine hydrate to form cuprous oxide -
carbon composite, It was then roasted at 380-400 °C A heat
collector testing assembly was constructed of 5 glass coils
connected in series with a total surface area of 1250 cm2
. Heat
collection was estimated by water flowing in the glass coils that
are coated with the carbon/copper film,. Parameters affecting the
solar collection efficiency such as time of exposure and mass flow
rate of the water were studied. Results revealed that the prepared
glass coil has proven successful energy collector for solar heat.
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst for the visible light‐driven transformation of 4‐nitrobenzenethiol (4‐NBT) to dimercaptoazobenzene (DMAB), producing reaction completion at a laser power of 1 mW (532 nm) while Ag NP/TNA and Ag NP/STNA photocatalysts cannot complete this transformation even at 10 mW laser power. The results point the way forward for photochemically robust, noble metal free, visible light harvesting photoacatalysts based on nanostructured heterojunctions of graphenic frameworks with TiO2.
A perovskite solar cell is a type of solar cell which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Devika Laishram
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ
(BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2
reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar
energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo),
exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse
up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo
and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using
dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by
wrapping on perovskite established an effective heterojunction between the materials for charge
separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased
photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed
optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven
water-splitting with a Faradaic efficiency as high as ∼88%.
Noble Metal Free, Visible Light Driven Photocatalysis Using TiO2 Nanotube Arr...Pawan Kumar
Bulk g‐C3N4 is an earth‐abundant, easily synthesizable, and exceptionally stable photocatalyst with an electronic bandgap of 2.7 eV. Herein, the concepts of P‐doping and size quantization are combined to synthesize highly fluorescent P‐doped carbon nitride quantum dots (CNPQDs) with a bandgap of 2.1 eV. CNPQDs are hosted on anatase‐phase and rutile‐phase TiO2 nanotube array scaffolds, and examined as photoanodes for sunlight‐driven water‐splitting and as photocatalysts for surface catalytic reactions. Square‐shaped rutile phase TiO2 nanotube arrays (STNAs) decorated with CNPQDs (CNPQD‐STNA) generate 2.54 mA cm−2 photocurrent under AM1.5 G simulated sunlight. A champion hydrogen evolution rate of 22 µmol h−1 corresponds to a Faradaic efficiency of 93.2%. In conjunction with Ag nanoparticles (NPs), the CNPQD‐STNA hybrid is also found to be an excellent plexcitonic photocatalyst …
This document describes a study on developing a novel nanocomposite structure for dye-sensitized solar cells (DSSCs) consisting of zinc oxide (ZnO) nanorods coated with titanium dioxide (TiO2) nanoparticles. The ZnO nanorods provide fast electron transport while the TiO2 nanoparticles add high surface area for dye adsorption. Transient measurements show the composite film can transport electrons over 100 times faster than TiO2 nanoparticle films alone. When tested with an alternative redox couple that has fast recombination (ferrocene/ferrocenium), the ZnO-TiO2 films generate higher currents than TiO2 films, demonstrating their ability to better collect injected electrons. However, not all charges successfully transfer from TiO2 to Z
This document summarizes research on using electrodeposited manganese dioxide (MnO2) coatings on porous carbon substrates for capacitive deionization (CDI) applications. Two carbon substrates with different surface areas and morphologies were coated with MnO2 using galvanostatic and cyclic voltammetric deposition. Characterization of the coated electrodes found mixed MnO2 phases present. Testing in half-cell configurations showed that maximum ion uptake per mass was not necessarily optimal for practical CDI applications, where performance per electrode area is more important. The results suggest the structure and deposition method can impact how effectively the electrode volume participates in ion removal reactions.
Nano Tailoring of MnO2 Doped Multiwalled Carbon Nanotubes as Electrode Materi...IRJET Journal
This document describes research on synthesizing manganese dioxide (MnO2) decorated multiwalled carbon nanotubes (MCNT) for use as an electrode material in supercapacitors. MnO2/MCNT nanocomposites were prepared through a simple solvo thermal method. Characterization of the materials was done using XRD, FESEM, TEM, EDS, UV-visible spectroscopy, FTIR, and Raman spectroscopy. The analyses revealed a porous, hierarchical structure of MnO2 coated on the MCNT surface. Increasing the annealing temperature improved the crystallinity and reduced the band gap of the MnO2/MCNT nanocomposite. The synthesized nanocomposite showed potential for high performance
A highly stable CuS and CuS–Pt modified Cu2O/ CuO heterostructure as an effic...Taame Abraha Berhe
This document summarizes the development and characterization of a Cu2O/CuO heterostructure photocathode modified with CuS and Pt nanoparticles for efficient solar hydrogen production. The Cu2O/CuO heterostructure was synthesized via electrodeposition and annealing of copper, then modified with CuS using SILAR and Pt via sputtering. Characterization with Raman, XPS and XANES/EXAFS showed CuS interacted with Cu2O/CuO at the interface. The optimized Cu2O/CuO/CuS photocathode provided a photocurrent density of -5.4 mA cm-2, over 2.5 times higher than bare Cu2O/CuO. Adding both CuS
Nanophotonic enhancement and improved electron extraction in perovskite solar...Pawan Kumar
While vertically oriented metal oxide nanowires have been intensely researched for use as electron transport layers (ETLs) in halide perovskite solar cells (HPSCs), horizontal nanowires (oriented roughly parallel to the substrate) have received much less attention despite their higher photonic strength due to overlapping electric and magnetic dipolar Mie resonance modes. Herein, we demonstrate the fabrication of an assembly of horizontally aligned TiO2 nanorods (HATNRs) on FTO substrates via a facile hydrothermal route. The HATNRs are employed as the ETL to achieve 15.03% power conversion efficiency (PCE) in HPSCs which is higher than the PCE of compact TiO2 based devices (10.12%) by a factor of nearly 1.5. A mixed halide, mixed cation organometal perovskite FA0.83MA0.17Pb(Br0.17I0.83)3 with optimized composition is used as the active layer. The excellent refractive index matching between the perovskite and TiO2, coupled with strong Mie scattering in the nanorod geometry results in broadband near-zero backscattering and high forward scattering, upon coating of HATNRs with perovskite. The maximum suppression of backscattering is found at ∼600 nm. The HATNRs ETL also improves the extraction of electrons from the perovskite layer and results in superior blocking of carrier recombination at the perovskite layer/FTO interface.
Nanophotonic enhancement and improved electron extraction in perovskite solar...Pawan Kumar
While vertically oriented metal oxide nanowires have been intensely researched for use as electron transport layers (ETLs) in halide perovskite solar cells (HPSCs), horizontal nanowires (oriented roughly parallel to the substrate) have received much less attention despite their higher photonic strength due to overlapping electric and magnetic dipolar Mie resonance modes. Herein, we demonstrate the fabrication of an assembly of horizontally aligned TiO2 nanorods (HATNRs) on FTO substrates via a facile hydrothermal route. The HATNRs are employed as the ETL to achieve 15.03% power conversion efficiency (PCE) in HPSCs which is higher than the PCE of compact TiO2 based devices (10.12%) by a factor of nearly 1.5. A mixed halide, mixed cation organometal perovskite FA0.83MA0.17Pb(Br0.17I0.83)3 with optimized composition is used as the active layer. The excellent refractive index matching between the …
Band edge engineering of composite photoanodes for dye sensitized solar cellsvenkatamanthina
This document discusses engineering the band edges of composite photoanodes for dye-sensitized solar cells through doping. Specifically, it doped ZnO nanorods with cobalt to lower its conduction band minimum and doped TiO2 nanoparticles with zirconium to raise its conduction band minimum in order to overcome an energy barrier preventing electron transfer. Characterization with diffuse reflectance spectroscopy and open circuit voltage measurements under illumination confirmed the doping shifted the band edges as intended. However, dye-sensitized solar cells fabricated with the composite nanostructures did not show improved performance. The paper details a methodology for producing and measuring band edge shifts but notes limitations in applying it to improve device operation.
Zr doped TiO2 nanocomposites for dye sensitized solar cellsvenkatamanthina
This document discusses engineering the band edges of a composite photoanode for dye-sensitized solar cells through doping. ZnO nanorods were doped with cobalt to lower their conduction band minimum energy, and TiO2 nanoparticles were doped with zirconium to raise their conduction band minimum energy. This was done to overcome an energy barrier that previously prevented electron transfer from TiO2 to ZnO in the composite. Characterization showed the doping incorporated into the materials as desired without other changes. Open circuit photovoltage measurements indicated the doping shifted the band energies to enable electron transfer, but devices using the materials did not show improved performance. The methodology for producing and measuring band edge shifts through doping is detailed.
High rate CO2 photoreduction using flame annealed TiO2 nanotubesPawan Kumar
The photocatalytic reduction of CO2 into light hydrocarbons using sunlight and water is a challenging reaction involving eight electron transfer steps; nevertheless, it has great potential to address the problem of rising anthropogenic carbon emissions and enable the use of fossil fuels in a sustainable way. Several decades after its first use, TiO2 remains one of the best performing and most durable photocatalysts for CO2 reduction albeit with a poor visible light absorption capacity. We have used flame annealing to improve the response of TiO2 to visible photons and engineered a nanotubular morphology with square-shaped cross-sections in flame-annealed nanotubes. An enhanced CH4 yield was achieved in the photoreduction of CO2 using flame annealed TiO2 nanotubes, and isotope labeled experiments confirmed the reaction products to originate from the CO2 reactant. Flame-annealed TiO2 nanotubes formed in aqueous electrolyte (FANT-aq) yielded 156.5 μmol gcatalyst–1.hr–1 of CH4, which is in the top tier of reported performance values achieved using TiO2 as a stand-alone photocatalyst. This performance resulted because appreciable amounts of CH4 were generated under visible light illumination as well. TiO2 nanotubes exhibited CO2 photoreduction activity up to a wavelength of 620 nm with visible light driven photocatalytic activity peaking at 450 nm for flame annealed TiO2 nanotubes. Isotope labelling studies, using GC–MS and gas-phase FTIR, indicated photoreduction of 13CO2 to 13CH4. The detection of 13CO in the product mixture, and the absence of HCHO and HCOOH provides strong support for the photoreduction proceeding along a carbene pathway. The enhanced CO2 photoreduction performance of FANT-aq is attributed to increased visible light absorption, square morphology, and the presence of rutile as the only crystalline phase with (110) as the dominant plane.
High rate CO2 photoreduction using flame annealed TiO2 nanotubesPawan Kumar
The photocatalytic reduction of CO2 into light hydrocarbons using sunlight and water is a challenging reaction involving eight electron transfer steps; nevertheless, it has great potential to address the problem of rising anthropogenic carbon emissions and enable the use of fossil fuels in a sustainable way. Several decades after its first use, TiO2 remains one of the best performing and most durable photocatalysts for CO2 reduction albeit with a poor visible light absorption capacity. We have used flame annealing to improve the response of TiO2 to visible photons and engineered a nanotubular morphology with square-shaped cross-sections in flame-annealed nanotubes. An enhanced CH4 yield was achieved in the photoreduction of CO2 using flame annealed TiO2 nanotubes, and isotope labeled experiments confirmed the reaction products to originate from the CO2 reactant. Flame-annealed TiO2 nanotubes
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Similar to Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube Arrays for Photoelectrocatalytic Water Splitting (20)
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Recent advancements in tuning the electronic structures of transitional metal...Pawan Kumar
The smooth transition from finite non-renewables to renewable energy conversion technologies will require efficient electrocatalysts which can harness intermittent energies to store in the form of chemical bonds. The oxygen evolution reaction (OER) impedes the widespread usage of water electrolyzers to convert H2O into H2 and persists as a bottleneck, including other energy conversion devices with sluggish four H+/e− kinetics. In this context, designing highly active and stable catalysts capable of driving a lower overpotential in the OER to produce continuous hydrogen (H2) is a primary demanded. This chapter discussed the mechanism of the OER in conventional adsorbate oxygen and lattice oxygen participation in transition metal oxides (TMOs). Further, the influences of surface engineering, doping, and defects in the TMOs and understanding the electronic structure to screen electrodes towards the structure–activity relationship are highlighted. Specifically, the adsorption strength of O 2p is understood in detail as its binding ability over the surface of TMOs can be correlated directly to the OER activity. The iterative development of TMOs in terms of understanding electronic structural attributes is essential for the commercial deployment of energy conversion technologies. The comprehensive outlook of this chapter investigates thoroughly how TMOs can be used as significant materials for the OER in the near future.
Hole transport materials (HTMs) have a significant impact on the effectiveness of organic electronic devices; therefore, we present a molecular architecture of pyrazino[2,3-g]quinoxaline (PQ10)-based room-temperature organic liquid crystalline semiconductor (OLCS) as an alternative HTM. The PQ10 compound exhibits three different rectangular columnar (Colr) phases offering an impressive hole mobility of 8.8 × 10−3 cm2V−1s−1 which is found to be dexterous than most of existing polymeric hole transport materials. The charge transport mechanism is governed by the hole polarons hopping through H-aggregates of the PQ10 molecules and the hole mobility remains nearly constant throughout the mesophase range, but it decreases with increasing applied electric field. The current-voltage characteristics of the PQ10 have also been investigated in all three Colr phases and explained via the Poole-Frenkel conduction mechanism. The dielectric spectroscopy has been eventually carried out to understand the nature of dielectric permittivity and conductivity as a function of temperature and a correlation is established between the molecular architecture of the Colr phases and aforementioned physical properties. Solar cell simulation has been additionally performed to demonstrate that the PQ10 material can be a better choice as HTM for organic electronics and photovoltaic applications.
Multifunctional carbon nitride nanoarchitectures for catalysisPawan Kumar
Catalysis is at the heart of modern-day chemical and pharmaceutical industries, and there is an urgent demand to develop metal-free, high surface area, and efficient catalysts in a scalable, reproducible and economic manner. Amongst the ever-expanding two-dimensional materials family, carbon nitride (CN) has emerged as the most researched material for catalytic applications due to its unique molecular structure with tunable visible range band gap, surface defects, basic sites, and nitrogen functionalities. These properties also endow it with anchoring capability with a large number of catalytically active sites and provide opportunities for doping, hybridization, sensitization, etc. To make considerable progress in the use of CN as a highly effective catalyst for various applications, it is critical to have an in-depth understanding of its synthesis, structure and surface sites. The present review provides an overview of the recent advances in synthetic approaches of CN, its physicochemical properties, and band gap engineering, with a focus on its exclusive usage in a variety of catalytic reactions, including hydrogen evolution reactions, overall water splitting, water oxidation, CO2 reduction, nitrogen reduction reactions, pollutant degradation, and organocatalysis. While the structural design and band gap engineering of catalysts are elaborated, the surface chemistry is dealt with in detail to demonstrate efficient catalytic performances. Burning challenges in catalytic design and future outlook are elucidated.
Production of Renewable Fuels by the Photocatalytic Reduction of CO2 using Ma...Pawan Kumar
The photo-reductive performance of natural ilmenite was boosted and the production of renewable fuels from the reduction of CO2 was enhanced by doping the natural mineral with magnesium. The doping was achieved by high energy ball milling in the presence of MgO and Mg(NO3)2. The photo-reduction of CO2 in aqueous solution led to the evolution of H2, CH4, C2H4, and C2H6, and the insertion of Mg in the structure of ilmenite enabled increases of up to 1245% in the fuel production yield, reaching total production of 210.9 µmol h-1 gcat-1. Displacements of the conduction band to more negative potentials were evidenced for the samples doped with magnesium. Indirect effects such as increases in the valence band maximum, and the introduction of intermediate energy levels were also evidenced through the measurement of the crystallite size and the determination of the band structure of the materials. Mott-Schottky analyses of the samples showed the n-type nature of the semiconductor materials and enabled the estimation of the density of charge carriers, which strongly influenced the photocatalytic performance. The strong potential of the application of natural ilmenite in gas phase artificial photosynthesis was proved by the evaluation of CO2 reduction in gas conditions, which allowed the enhancement in the selectivity and significantly increased the production of CH4 as compared to aqueous solution, reaching an important yield of CH4 of 16.1 µmol h-1 gcat-1.
Nanoengineered Au-Carbon Nitride Interfaces Enhance PhotoCatalytic Pure Water...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Nanoengineered Au-Carbon Nitride Interfaces Enhance Photo-Catalytic Pure Wate...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Cooperative Copper Single Atom Catalyst in Two-dimensional Carbon Nitride for...Pawan Kumar
This document summarizes a study that investigated copper single atom catalysts supported on two-dimensional carbon nitride materials for enhancing the electrochemical reduction of carbon dioxide to methane. Specifically, copper ions were incorporated into the nanoporous structures of poly(heptazine imide) and poly(triazine imide) using a room temperature ion exchange process. This allowed for high loading densities of isolated copper sites. The proximity of copper atoms within the nanopores was found to enable cooperative catalysis that boosted the selectivity and efficiency of the multi-electron conversion of CO2 to CH4. Density functional theory calculations helped explain how the copper-copper distance and coordination environment modulated the binding of reaction intermediates. Optimized copper loading in the
Bioinspired multimetal electrocatalyst for selective methane oxidationPawan Kumar
Selective partial electrooxidation of methane (CH4) to liquid oxygenates has been a long-sought goal. However, the high activation energy of C–H bonds and competing oxygen evolution reaction limit product selectivity and reaction rates. Inspired by iron (IV)-oxo containing metalloenzymes’ functionality to activate the C–H bond, here we report on the design of a copper-iron-nickel catalyst for selective oxidation of CH4 to formate via a peroxide-assisted pathway. Each catalyst serves a specific role which is confirmed via electrochemical, in situ, and theoretical studies. A combination of electrochemical and in situ spectroelectrochemical studies revealed that H2O2 oxidation on nickel led to the formation of active oxygen species which trigger the formation of iron (IV) at low voltages. Density functional theory analysis helped reveal the role of iron (IV)-oxo species in reducing the activation energy barrier for CH4 deprotonation and the critical role of copper to suppress overoxidation. Our multimetal catalyst exhibits a formate faradaic efficiency of 42% at an applied potential of 0.9 V versus a reversible hydrogen electrode.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
ESPP presentation to EU Waste Water Network, 4th June 2024 “EU policies driving nutrient removal and recycling
and the revised UWWTD (Urban Waste Water Treatment Directive)”
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...AbdullaAlAsif1
The pygmy halfbeak Dermogenys colletei, is known for its viviparous nature, this presents an intriguing case of relatively low fecundity, raising questions about potential compensatory reproductive strategies employed by this species. Our study delves into the examination of fecundity and the Gonadosomatic Index (GSI) in the Pygmy Halfbeak, D. colletei (Meisner, 2001), an intriguing viviparous fish indigenous to Sarawak, Borneo. We hypothesize that the Pygmy halfbeak, D. colletei, may exhibit unique reproductive adaptations to offset its low fecundity, thus enhancing its survival and fitness. To address this, we conducted a comprehensive study utilizing 28 mature female specimens of D. colletei, carefully measuring fecundity and GSI to shed light on the reproductive adaptations of this species. Our findings reveal that D. colletei indeed exhibits low fecundity, with a mean of 16.76 ± 2.01, and a mean GSI of 12.83 ± 1.27, providing crucial insights into the reproductive mechanisms at play in this species. These results underscore the existence of unique reproductive strategies in D. colletei, enabling its adaptation and persistence in Borneo's diverse aquatic ecosystems, and call for further ecological research to elucidate these mechanisms. This study lends to a better understanding of viviparous fish in Borneo and contributes to the broader field of aquatic ecology, enhancing our knowledge of species adaptations to unique ecological challenges.
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
Or: Beyond linear.
Abstract: Equivariant neural networks are neural networks that incorporate symmetries. The nonlinear activation functions in these networks result in interesting nonlinear equivariant maps between simple representations, and motivate the key player of this talk: piecewise linear representation theory.
Disclaimer: No one is perfect, so please mind that there might be mistakes and typos.
dtubbenhauer@gmail.com
Corrected slides: dtubbenhauer.com/talks.html
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
2. junction formation, etc., and morphological engineering are
enticing approaches to improve the quantum efficiency.8−11
One-dimensional (1D) TiO2 nanostructures like nanorods,
nanotubes, nanocones, etc., are particularly interesting because
of their large accessible surface areas, vectorial charge-transport
pathways, and a carrier retrieval length comparable to that of
the smallest dimension of the nanostructure. Thus, they have
emerged as excellent candidates for heterojunction formation
with low-band-gap semiconductors.12−17
Low-cost TiO2 nanotube layers fabricated via electro-
chemical anodization present varied applications in photo-
catalytic, photovoltaic, and optoelectronic sensing devi-
ces.18−20
By maximization of the specific surface area from
bulk to nanoparticulate TiO2, improvement of the photo-
electrochemical water-splitting performance using solar light
can be achieved.21
To broaden the application spectrum and
overcome key drawbacks of TiO2 nanotubes, our intention is
band-gap engineering and semiconductor/electrolyte contact
optimization, which play a major role in efficient photocatalytic
water splitting.22,23
Therefore, we utilize a hybrid system of
semiconductor materials between highly ordered self-organized
TiO2 nanotube membranes and inexpensive phosphorus (P)
allotropes, 1D fibrous red P and two-dimensional (2D) black
P, which leads to higher-efficiency composite photocatalysts.
As-prepared hollow nanosized cylinders of TiO2 nanotubes
were formed by electrochemical, field-aided, three-step
anodization of titanium (Ti) films or foils in electrolytes
containing F−
/I−
/ClO3
−
ions. Both P allotropes were
deposited via low-pressure chemical vapor deposition
(CVD).24,25
In order to prevent the semiconductor−semi-
conductor hybrid from material degradation during long
thermal treatment processes, the vapor deposition or so-called
mineralization technique allows crystallization of amorphous
TiO2 to anatase. At the same time, the desirable growth of P
nanorods inside and onto the nanotubes in one annealing step
(at ∼500 °C) takes place. The intrinsic band gap for the n-type
semiconductor anatase TiO2 in the UV range at 3.2 eV limits
light absorption to only <5% of the solar spectrum.26
To much
better exploit the solar spectrum, heterojunction systems with
two P allotropes were investigated: (a) fibrous red P, exhibiting
a band gap of 2.25 eV based on our experimental results and
(b) p-type semiconducting black P due to a direct band gap of
0.3 eV for bulk material in the near-IR region. The latter is
characterized by a high, layer-dependent hole-carrier mobility
of ca. 105
cm2
/(V s).27−29
Fibrous red P is being investigated
regarding its potential as a water-splitting agent and black P as
a field-effect transistor, a photodetector, and a sensor.30−32
In a
heterojunction system, the photogenerated carrier mechanism
can induce the formation of a built-in potential (Vbi) and
hinder electron−hole pair recombination.33−36
The dense
hybrid structure supports the fast charge separation of carriers,
created inside the nanorods, and migration of a short distance
equal to the nanotube radius to cross the heterojunction
interface. Excellent quantum yields can be obtained from the
suitable nanotube structure because of a high aspect ratio,
which ensures efficient photon harvesting, orthogonalized
processes of charge separation and light absorption, and
improved light trapping by Mie scattering.37−39
Modification
of the TiO2 nanotubes has been approached by the decoration
of surfaces with noble-metal nanoparticles, such as gold, silver,
and platinum. A solid interface occurs, in which a Schottky
contact is formed that is less preferable than a p/n-
semiconductor contact in terms of charge-carrier recombina-
tion loss.23,38,40,41
Recently, the desired Z-scheme junction
formation has been successfully carried out with CdS, g-C3N4,
MoS2, ZnIn2S4, Fe2O3, halide perovskites, etc., for use in
extensive photocatalytic applications such as CO2 photo-
reduction, high-performance photoanodes for water-splitting
devices, selective gas sensors, and high-efficiency solar
cells.42−47
In this work, we introduce a vapor-transport process
to grow hybrid semiconductor−semiconductor 1D and 2D
materials to form heterojunctions capable of realizing
enhanced photoelectrochemical water splitting.
■ RESULTS AND DISCUSSION
This section is divided into two main chapters: (1) structural
characterization of fibrous red and black P deposited into and
onto the TiO2 nanotube arrays and (2) the photocatalytic
activity of the P allotrope@TiO2 hybrid materials. Spectro-
scopic [X-ray photoelectron spectroscopy (XPS), UV−vis,
Raman, and Kelvin probe force microscopy (KPFM) studies in
the Supporting Information, SI] and X-ray diffraction (XRD;
see the SI) experiments were applied to characterize the bare
and hybrid materials. A brief photoelectrocatalytic inves-
tigation of the P allotrope@TiO2 hybrid materials contains the
full electrochemical characterization [hydrogen and oxygen
evolution and calculation of the efficiencies, i.e., ABPE, IPCE,
APCE, and Faradaic efficiency (FE) in the SI], including a
plausible mechanism for the water-splitting activity of the title
compounds.
Structural Characterization of P Allotrope@TiO2
Nanotube Hybrids. In order to fabricate hybrid semi-
conducting materials, we succeeded in filling the anatase-type
TiO2 nanotubes with fibrous red and black P using a short-way
transport reaction (Figure 1; experimental details are given in
the SI). This reaction is adapted from the so-called
mineralization principle used for the synthesis of a plethora
of P-containing compounds, as in fibrous solely, binary, and
ternary P compounds like NaP7 and SnIP.48−50
The TiO2 nanotube structure could be preserved after the
deposition of P allotropes via thermal treatment during the
transport reactions.
Fibrous Red P@TiO2 Nanotubes. The mineralization
method can be applied to prepare element allotropes and
binary and ternary compounds. An example is the successful
deposition of fibrous red P onto and into TiO2 nanotube
membranes via the gas phase, as shown in Figure 2. Pure
fibrous P exhibits photocatalytic activity and has the potential
for water-splitting applications.20
Fibrous red P has been
formed everywhere on the TiO2 nanotube membrane (Figure
2b). Noticeably, fibrous P is distributed on the whole surface
of the membranes, as scanning electron microscopy−energy-
Figure 1. (a) Fibrous P (purple pellet) reacted onto and into TiO2
nanotube membranes (pink). Representative SEM pictures of the
electrochemically prepared TiO2 nanotube membranes used in a
mineralizer-driven short-way transport reaction along the (b) bottom,
(c) top, and (d) normal side views.
ACS Applied Nano Materials Article
DOI: 10.1021/acsanm.9b00221
ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
B
3. dispersive X-ray spectroscopy (SEM−EDS) measurements
exhibit in Figure 2c,d and Table S1. According to powder XRD
data, the growth of fibrous red P on top of the TiO2 nanotube
membranes was confirmed (Figure S1).
Scanning transmission electron microscopy (STEM) images
taken after separation of the TiO2 nanotubes by an
ultrasonication process show a bundle of nanotubes with
diameters of ∼90−100 nm. Elemental mapping confirms Ti,
oxygen (O), and P with a distribution of P along the full tube
length (Figure 3).
The successful growth of a fibrous red P structure up to a
certain depth into the TiO2 nanotube arrays can be verified via
Raman measurements. Therefore, TiO2 nanotube membranes
were cut along the cross section after CVD of fibrous red P,
and imaging at specific spots from the surface of a TiO2
nanotube array downward along a vertical line was acquired.
The laser has a standard mode spot size of 1.5 μm (at 50×
magnification). Raman spectra were recorded at several spots
along the 65-μm-long cross section of the membranes. The
experimental frequencies of bulk fibrous red P match the
significant modes between 352 and 462 cm−1
recorded up to
20 μm in distance to the surface from the top side and 15 μm
in distance to the surface from the bottom side along the cross
section of the membranes (shown in Figure S2). A systematic
detection of spots further into the 65-μm-long tubes shows the
expected modes for pure anatase and the additional character-
istic modes of fibrous P up to 15 μm recorded from the top
side of the nanotube array and 15 μm from the bottom side
(Figure 4). A reduction of the crystallinity of fibrous red P
upon going deeper into the tubes can be observed.
After the successful growth of fibrous red P onto and into
TiO2 nanotube arrays was demonstrated via powder XRD,
SEM−EDS, Raman spectroscopy, and STEM−EDS analysis,
the growth of partially crystalline fibrous P into the membrane
was realized, whereas nicely crystallized fibrous P was found at
the surface of the membranes.
Black P@TiO2 Nanotubes. A similar successful gas-phase
deposition has been performed with black P, another element
allotrope of P. Black P is characterized by a structure (on the
number of neighboring P layers)-dependent band-gap value
covering a wide range of the electromagnetic spectrum.51
Thus, black P has potential in applications such as field-effect
transistors, p−n junctions, photodetectors, etc.52
This
orthorhombic allotrope of P crystallizes in space group Cmca
(crystal structure in Figure 5a) shows a high carrier mobility
and in-plane anisotropy, playing a role in hydrogen and oxygen
generation in photocatalytic water splitting.51
Moreover, a
broadening of the absorption fraction toward the visible-light
range of 3.2 eV TiO2 anatase can be provided by a
heterojunction formation with the narrow-band-gap semi-
conductor black P. Depending on the number of neighboring
layers stacked onto each other, a band gap of 0.3 eV in bulk
black P to ∼2 eV for the monolayer (called phosphorene) can
be realized. The overall efficiency of the existing narrow-band-
gap water-splitting photocatalysts is affected by photo-
corrosion, which results from the chemical bond strength of
the given system.53
This fact can be avoided by the fabrication
of a heterojunction hybrid system between black P and TiO2
nanotube arrays, where the chemical bond strength of the bulk
material (TiO2 anatase) will remain and only an alignment of
the Fermi levels between the materials during charge-carrier-
Figure 2. (a) Crystal structure of fibrous red P. (b) TiO2 nanotube
membrane covered with fibrous red P after reaction via gas phase. (c
and d) SEM images of the cross section and surface of fibrous P@
TiO2 nanotube membranes. Fibrous P covers the surface of the
membrane. EDS of the cross section shows P all along the nanotubes
(Table S1).
Figure 3. (a) STEM bright-field image of TiO2 nanotubes separated
from a membrane by an ultrasonication procedure. (b) Elemental
mapping of the overlaid elements Ti, O, and P. (c and d) Ti and O of
the TiO2 nanotubes, (e) with P distributed along the full length of the
tubes.
Figure 4. Raman spectroscopy on fibrous red P@TiO2 membranes.
From the top down: reference Raman spectrum of fibrous red P and
spectra of a fibrous red P@TiO2 membrane cross section measured at
approximately 5, 15, and 20 μm in distance to the surface (membrane
top side) and at approximately 5, 10, and 15 μm in distance to the
surface (membrane bottom side) and a blank TiO2 membrane
(anatase, brown).
ACS Applied Nano Materials Article
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ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
C
4. transport reactions within the hybrid occurs.23
A visual
deposition of characteristic flat metallic-colored needles,
spreading out gradually on the TiO2 nanotube membranes
(reversed side), can be seen in Figure 5b. A SEM image in
Figure 5c shows the successful deposition of a thick black P
layer covering the surface of this cut cross-sectional part of a
TiO2 nanotube membrane. The second SEM image in Figure
5d is displaying a gradual growth of small horizontally aligned
black P crystals between the two arrows, which is confirmed by
EDS measurements (Table S2). A reason for this unusual
growth can be the unique 2D structure of black P. Powder
XRD data can confirm the formation of black P on top of the
TiO2 nanotube arrays (Figure S3).
After separation of the TiO2 nanotubes in an ultrasonication
process, STEM imaging displays a singular tube with a width of
∼150 nm. P was detected inside the tube besides Ti from the
TiO2 membrane after elemental mapping. Furthermore,
analysis of tin (Sn) and iodine (I) inside the tubes was carried
out because of the fact that SnI4 was used during the transport
reaction for synthesis. The formation of SnIP, as a possible side
product, in such a transport reaction was ruled out (Figure
6).50
To verify the successful growth of black P into TiO2
nanotubes, several Raman spectra were recorded after cutting
the nanotube membranes at the cross section after synthesis. A
simultaneous presence at the membrane surface of black P
(main phase), with the most prominent modes at 360, 436,
and 464 cm−1
next to anatase with a characteristic mode at 145
cm−1
, can be confirmed. A gradual change is detectable when
the laser is pointed down to a depth of 7 μm into the
nanotubes, where black P next to anatase (main phase) still can
be confirmed (Figure 7). The crystallinity of the black P phase
remains unchanged, in comparison to Raman imaging of
fibrous red P@TiO2 nanotubes. This is an additional proof of
the assumption of distinct P needles in the SEM image in
Figure 5d.
XPS. Characterization of the surface composition, binding
energies, and oxidation states of fibrous red and black P next to
blank TiO2 samples, hybrid fibrous red P@TiO2, and black P@
TiO2 was investigated via high-resolution XPS studies. The
heterostructure systems reveal consistent oxidation states along
with the pure samples. A shift of the binding energies in the O
1s region of fibrous red P@TiO2 and black P@TiO2 compared
to pristine TiO2 can be primarily attributed to the formation of
P−O bonds in the heterostructure system (Figures S5 and S6).
UV−Vis Spectroscopy. The optical properties of the
samples were determined using UV−vis in diffuse-reflectance
mode (Figure S4). A sharp peak around 320 nm in the UV−vis
spectrum of TiO2 with a band tailing up to 380 nm arises from
a O 2p → Ti 3d transition of electrons, demonstrating a VB to
CB transition. The absorption spectrum of fibrous red P shows
a broad absorption band extending to the visible range. Fibrous
red P deposited on wide-band-gap TiO2 shows improved
absorption in the visible region because of the presence of
moderate-band-gap fibrous red P. The UV−vis spectrum of
black P shows three absorption bands at 315, 374, and 438 nm,
with broadening of the absorption bands in the IR region. This
is in line with findings in the published literature.54,55
After the
deposition of black P on TiO2 nanotubes, the visible-light and
Figure 5. (a) Crystal structure of black P. (b) TiO2 nanotube
membranes with black P needles on the front and back sides after
reaction via the gas phase. (c and d) SEM images of the cross section
and covered surface of black P@TiO2 nanotube membranes. There is
visible horizontal growth along the vertical tube axis between white
arrows. EDS of the cross section shows P all along the nanotubes.
Figure 6. (a) STEM bright-field image of TiO2 nanotubes separated
from a membrane by an ultrasonication procedure. (b) Elemental
mapping of overlaid elements Ti (representing TiO2), P, Sn, and I.
(c) Ti and (d) P substantiating P distributed along the full length of a
TiO2 nanotube, with (e) Sn and (f) I coming from the mineralizer
only present in small amounts.
Figure 7. Raman spectroscopy on black P@TiO2 membranes. From
the top down: reference Raman spectrum of black P, spectra of a
black P@TiO2 membrane cross section measured at the surface and
approximately 3, 5, and 7 μm in distance to the surface (membrane
top side), and a fresh TiO2 membrane (anatase, brown).
ACS Applied Nano Materials Article
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D
5. IR absorption range was increased, which demonstrates a
better visible-light response of the samples.
Visible-light absorption of the samples was investigated in
detail using Tauc plots by plotting a graph of (αhν)1/2
versus
hν, followed by extrapolation of a linear tangent to the X axis,
where α is the absorption coefficient, h is the Planck constant,
and ν is the light frequency (Figure S4). The values of the
optical band gaps from the Tauc plots were found to be 2.97
eV for TiO2, 1.97 eV for fibrous red P, 2.1 eV for fibrous red
P@TiO2, 1.67 eV for black P, and 1.54 eV for black P@TiO2,
respectively, which are in close agreement with the reported
values and clearly demonstrate absorption in the visible region
by the heterojunction hybrids (Figure S4).
Photocatalytic Activity of P Allotrope@TiO2 Nano-
tube Hybrids. The photoelectrochemical water splitting
performance of all compounds was tested using a three-
electrode system. In this setup, the specimens, deposited on
fluorine-doped tin oxide, formed the anode (working
electrode), while platinum and Ag/AgCl were used as the
cathodes (counter electrode) and reference electrode,
respectively. The photoanode was irradiated with AM1.5 G
simulated sunlight with a power density of 100 mW cm−2
(1
sun) at the sample surface. The current density (mA cm−2
)
was measured using linear-sweep voltammetry (LSV) by
sweeping the applied voltage from −0.1 to +0.8 V versus
Ag/AgCl at a scan rate of 0.1 V s−1
. To compare the
photoresponses, the dark current was also measured. The
photocurrent response during light on−off cycles shows a rise
and drop in the photocurrent, which substantiates the
photogeneration of charge carriers in the samples under light
irradiation (Figure 8a,b). The photocurrent densities for TiO2,
fibrous red P, fibrous red P@TiO2, black P, and black P@TiO2,
at 0.6 V versus Ag/AgCl (1.23 V vs RHE; water oxidation
potential), were measured to be 0.22, 0.25, 0.60, 0.19, and 0.20
mA cm−2
respectively (Figure 8c). Under dark conditions, a
negligible current was observed. The photocurrent densities of
pristine black P, bare TiO2, and pristine fibrous red P were
almost identical because of the poor carrier separation in P and
the lack of visible-light absorption in TiO2. Further, black P@
TiO2 does not show a noticeable increase in the photocurrent
density, which can be attributed to the lack of a synergistic
photocatalytic process, which is likely due to the higher degree
of oxidation of P in black P to PxOy, which was evident in the
XPS data (Figure S5). Interestingly, the fibrous red P@TiO2
hybrid exhibited a relatively high photocurrent density (0.60
mA cm−2
), suggesting the successful formation of a
heterojunction and better charge transfer between fibrous red
P and TiO2 (Figure 8a). The viability of the photocatalytic
system to perform under visible light was tested by irradiating
the specimens with a 425 nm LED light and a power density of
54.15 mW cm−2
. The increase in the photocurrent under 425
nm of irradiation clearly demonstrates the applicability of the
system to perform at longer wavelengths (Figure S11). The
highest applied bias photon-to-current efficiency percentage
(ABPE %; calculation details are given in the SI) was found for
a fibrous red P@TiO2 nanohybrid, which was approximately
3.0 times higher than that for TiO2 and pristine fibrous red P,
and demonstrates that heterojunction formation with TiO2
increases the photoelectrocatalytic performance significantly
(Figure 8d).56,57
Further, action spectra, showing IPCE and
APCE % of materials as a function of the wavelength,
demonstrate that a fibrous red P@TiO2 nanohybrid out-
performed and calculated IPCE and APCE % at 450 nm were
found to be 1.30 and 1.65%, respectively (see the SI). To verify
that the generated photocurrent originated from the photo-
electrochemical water splitting and not from side reactions or
Figure 8. (a and b) Linear-sweep voltammograms of TiO2, fibrous red P, fibrous red P@TiO2, black P, and black P@TiO2, under dark conditions
and 1 solar simulated AM1.5 G light irradiation (100 mW cm−2
) showing the photoresponse during on−off and (c) standard mode cycling. (d)
ABPE % versus RHE plot under AM1.5 G light irradiation (100 mW cm−2
). Color code: TiO2 under dark conditions, black; TiO2 under AM1.5 G
light irradiation, grey; fibrous red P, red; fibrous red P@TiO2, brown; black P, blue; black P@TiO2, light blue.
ACS Applied Nano Materials Article
DOI: 10.1021/acsanm.9b00221
ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
E
6. photocorrosion of the electrodes, evolved hydrogen at the
platinum counter electrode was collected to calculate the
Faradaic efficiency (FE; see section 2.6 in the SI). The black
P@TiO2 hybrid displayed the highest FE (90.61%), demon-
strating the origin of the photocurrent from water splitting and
negligible photocorrosion of the materials.
The band-edge energies with respect to the vacuum levels of
all samples were determined from the work function (WF) and
VB spectra acquired using ultraviolet photoelectron spectros-
copy (UPS; Figure 9). The WF was calculated by subtracting
the energy of the emitted secondary electrons (cutoff energy
Ecutoff) from the energy of the incident UV light (He I line of a
He discharge lamp: 21.21 eV) using the expression WF(Φ) =
21.21 − Ecutoff. The extrapolation of the linear region of the WF
spectrum on the X and Y scales and their point of intersection
gave the value of the cutoff energy. The Ecutoff values of TiO2,
fibrous red P@TiO2, and black P@TiO2 were found to be
16.40, 16.24, and 16.11 eV, respectively. Hence, the values of
WF were calculated to be 4.81, 4.97, and 5.10 eV (Figure 9a,c
and insets). The increase of the WF value demonstrates
depletion region formation with concomitant band bending at
the solid-state heterointerface, which leads to a deepening of
the Fermi level of TiO2 in P@TiO2 hybrids. Additionally, the
valence-band maximum (VBmax) values calculated via linear
extrapolation of the leading edges of the UPS VB spectra for
fibrous red P, fibrous red P@TiO2 black P, and black P@TiO2
were found to be 0.82, 1.49 1.41, and 1.45 eV below the Fermi
level. The small difference in the energies between the Fermi
level and VBmax (EF − EVBmax
) for fibrous red P (0.82 eV) and
black P (1.41 eV) reveals that the Fermi level was close to
VBmax and the samples were moderately p-type. Further, XPS
VB spectra of TiO2 gave the value of VBmax as 3.15 eV below
the Fermi level (Figure S4). The increase in VBmax in black P@
TiO2 and fibrous red P@TiO2 implies a slightly uplifted Fermi
level of P in the heterojunction during Fermi-level alignment
and band bending (Figure 10). From the WF and VBmax
results, it can be concluded that heterojunction formation
between P and TiO2 was facilitated by upward band bending in
TiO2 and downward band bending in P allotropes (black P and
fibrous red P), as expected for a p−n heterojunction. Further,
surface potential measurement of materials under dark and
light conditions provides evidence of Fermi-level alignment
and better charge transport due to the formation of a
heterojunction (see section 2.8 in the SI for more details).
Plausible Mechanism. The water-splitting process
proceeds via the absorption of light by the semiconductors,
generating electron−hole pairs, which drive proton reduction
and water oxidation reactions. In photoelectrochemical water
splitting, electrons in the CB of the semiconductors move
toward the platinum cathode, where they reduce protons, while
holes in the VB of the semiconductors oxidize water to
produce oxygen at the anode. Wide band gaps (>1.23 eV) and
aligned positions of the CB and VB (CB < 0.00 eV and VB >
+1.23 eV vs NHE at pH 0) are required to achieve proton
reduction and water oxidation, respectively. TiO2 has a large
band gap, and electron−hole pairs can only be produced under
UV irradiation, which demonstrates the origin of very small
photocurrent density in LSV. However, from DR UV−vis, the
Figure 9. UPS WF spectra of (a) TiO2 and fibrous red P@TiO2 and (c) TiO2 and black P@TiO2. Inset: Ecutoff. The value of the WF was
determined from the UPS WF spectra by using the equation WF(Φ) = 21.21 − Ecutoff, where 21.21 eV is the energy of the incident He I line of a
He discharge lamp used for UPS. UPS VB spectra of (b) fibrous red P and fibrous red P@TiO2 and (d) black P and black P@TiO2 Color code:
TiO2, black; fibrous red P, red; fibrous red P@TiO2, purple; black P, blue; black P@TiO2, light blue.
ACS Applied Nano Materials Article
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ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
F
7. value of the optical band gap was found to be 2.97 eV, which
corresponds to 417 nm; in other words, a small visible-light
fraction can be absorbed by TiO2. The decrease in the band
gap of TiO2 might be explained as the presence of a few Ti3+
defects, oxygen vacancies, and trap sites. Moreover, because of
the low band gaps of pristine black P and fibrous red P, the
generation of sufficient reductive and oxidative electrons and
holes to facilitate the water-splitting reaction can be
affected.58,59
However, a hybrid material, consisting of fibrous
red P with TiO2, was found to be an efficient photocatalyst as a
result of the formation of a heterojunction and efficient charge
transfer between fibrous red P and TiO2. Heterojunction
formation leads to Fermi-level alignment. During Fermi-level
alignment, electrons flow from one semiconductor to another,
which equilibrates the Fermi-level position between the
semiconductors. Measurements of the flat-band potential for
TiO2, pristine fibrous red P, and black P were carried out via
Mott−Schottky analysis (Figure S12b), and the positions were
found to be −0.70, −0.37, and −0.56 V versus Ag/AgCl
(−4.00, −4.14, and −4.33 eV on the Evac scale); however, we
note that the n-type behavior found for pristine fibrous red P
and black P is attributed to a compact TiO2 layer used during
measurements and should be discounted. This indicates an
electron transfer from TiO2 to black P or fibrous red P,
respectively, during Fermi-level alignment. After hybrid
heterojunction formation and equilibrium was reached, the
positions of the flat-band potentials of fibrous red P@TiO2 and
black P@TiO2 were found to be −0.54 and −0.66 V versus
Ag/AgCl (−4.16 and −4.04 eV at the Evac scale; Figure 10).
The downshifting of the flat-band potential of TiO2 in hybrid
systems suggests downward band bending of the CB edge of
fibrous red and black P while upward band bending in TiO2
occurs. This clearly demonstrates the formation of a p−n-type
heterojunction between P allotropes and TiO2. These
observations were also supported by WF values (position of
the Fermi level in a vacuum), where the WF of TiO2 changed
from 4.97 versus vacuum in fibrous red P@TiO2 to 4.81−5.10
eV in black P@TiO2 (Figure 10), which is a sufficiently
positive potential for water oxidation to occur (−5.72 eV vs
Evac or +1.23 V vs NHE at pH 0). The increase in the WF
value in hybrid materials demonstrates lower shifting of the
Fermi level, which agrees well with heterojunction formation.
Additionally, a deeper VBmax in hybrid P allotrope@TiO2
compounds than in pristine P allotropes suggests the successful
formation of a heterojunction and generation of more oxidative
holes to facilitate water splitting. On the basis of the above
findings, we have sketched a band-structure diagram of the
hybrid materials, which demonstrates that more efficient water
splitting was possible because of p−n heterojunction formation
and better charge separation (Figure 10). Further, Nyquist
plots demonstrate that charge-transfer resistance and charge-
transport resistance of hybrids are lower in comparison to
Figure 10. Energy-level diagrams illustrating a plausible charge-separation mechanism in P allotrope@TiO2 heterojunctions.
ACS Applied Nano Materials Article
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ACS Appl. Nano Mater. XXXX, XXX, XXX−XXX
G
8. pristine TiO2, which suggests better charge transfer and
transport in hybrid materials (Figure S12). The cavities of the
TiO2 nanotube membranes are evidently filled with visible-
light-absorbing P allotropes. Thus, generated electron−hole
pairs can be transferred to TiO2. Because of a short path
distance and TiO2 exhibiting a high carrier mobility, carrier
recombination can be prevented and a fast transit of the charge
carriers toward the semiconductor−electrolyte interface is
enabled.
■ CONCLUSION
Hybrid heterojunction systems for optoelectronic applications
were designed, fabricated, characterized, and tested. The so-
called mineralization principle for short-way gas-phase trans-
port of solids was performed to grow semiconductors on TiO2
nanotube arrays. Fibrous red and black P were successfully
deposited onto and into electrochemically produced TiO2
nanotube membranes. The formation of hybrid nanostructures
was analyzed with several spectroscopic and diffraction
methods such as XRD, STEM−EDS, Raman spectroscopy,
UV−vis, and XPS. The effectiveness of the vapor transport was
verified through SEM, STEM, and elemental mapping of the
surface and cross section of nanohybrids, showing deposition
of the materials inside the tubes.
Raman spectroscopy taken at the surface and along the
razor-cut cross section of the nanotubes confirmed the
penetration and growth of fibrous red P up to 15 μm (65
μm in length) and black P up to 7 μm into the nanotubes (60
μm in length). The fibrous red P@TiO2 and black P@TiO2
hybrid materials displayed an improved photoelectrochemical
performance for water splitting in the visible-light regime
because of successful p−n heterojunction formation. UPS WF
spectra demonstrate band alignment, the Fermi level of TiO2
gets downshifted, and an upshift was observed for the P
allotropes during heterojunction formation. This formation
enables carrier transportation from the VB of downshifted
TiO2 to P allotropes, resulting in successful oxidation in the
water splitting. At the same time, Mott−Schottky plots
corroborate the occurrence of more reductive flat bands in
hybrid P allotrope@TiO2 materials, which facilitate the
effective reduction of hydrogen. The increased charge-carrier
mobility, lower charge-transfer resistance, and lower charge-
transport resistance of such hybrid materials lead to better
charge separation and an improved photoelectrochemical
performance.
■ ASSOCIATED CONTENT
*S Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsanm.9b00221.
Experimental details on the synthesis and physicochem-
ical and photoelectrochemical characterization, addi-
tional characterization on powder XRD, Raman and
EDS analyses, DR UV−vis, high-resolution XPS, photo-
current density, electrochemical impedance spectrosco-
py, Nyquist and Mott−Schottky plots, and XPS VB
spectra (PDF)
■ AUTHOR INFORMATION
Corresponding Authors
*E-mail: kshankar@ualberta.ca.
*E-mail: tom.nilges@lrz.tum.de.
ORCID
Pawan Kumar: 0000-0003-2804-9298
Ryan Kisslinger: 0000-0003-2456-396X
Karthik Shankar: 0000-0001-7347-3333
Tom Nilges: 0000-0003-1415-4265
Author Contributions
§
These authors contributed equally.
Author Contributions
E.Ü. and R.K. performed the synthesis and characterization of
P/hybrid materials. P.Ku. was involved in the XPS, UPS, and
photoelectrochemical studies and compiled the results. P.Ka.
performed the electrochemical characterizations. K.S. and T.N.
planned and supervised the research. All authors were involved
in writing their respective parts.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work has been performed as part of the international
graduate school ATUMS (IRTG 2022) funded by Deutsche
Forschungsgemeinschaft and Natural Sciences and Engineering
Research Council of Canada (NSERC). The performance and
assistance in STEM−EDS by Peng Li, Shihong Xu, and
Anqiang He from nanoFAB at the University of Alberta are
gratefully acknowledged. We thank Anna Vogel for Raman
spectroscopy of the samples. K.S. acknowledges NSERC,
National Research Council Canada, Future Energy Systems
(FES). and CMC Microsystems for research funding and
allowances for tool usage. P.Ku. is thankful to FES for a
postdoctoral research fellowship. We kindly acknowledge Dr.
Kazi Alam for DR UV−vis measurements.
■ ABBREVIATIONS
black P@TiO2 = hybrid of black phosphorus and TiO2
CB = conduction band
DR UV−vis = diffuse-reflectance ultraviolet−visible spec-
troscopy
fibrous red P@TiO2 = hybrid of fibrous red phosphorus and
TiO2
IR = infrared radiation
KPFM = Kelvin probe force microscopy
LSV = linear sweep voltammetry
NHE = normal hydrogen electrode
SEM = scanning electron microscopy
STEM−EDS = scanning transmission electron microscopy−
energy-dispersive X-ray spectroscopy
VB = valence band
UPS = ultraviolet photoelectron spectroscopy
WF = work function
XPS = X-ray photoelectron spectroscopy
XRD = X-ray diffraction
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