Photocatalytic activity of low band gap hydrogenated HfO2 doped TiO2 (H-HfO2/TiO2), HfO2 doped TiO2
(HfO2/TiO2) and TiO2 (pristine) were investigated by photocatalytic degradation of five different industrial dyes. The current study envisages the effect of doping hydrogen and HfO2 up on TiO2 for photocatalytic degradation of different chemically structured dyes. Methylene Blue attains fast degradation
efficiency of 90%, within 10 min of the reaction due to high photocatalytic adsorption and degradation
over the rough TiO2 surface. Effect of pH on dye degradation is observed, leading to disintegration and
mineralization.
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%.
This document is from the website www.entechnol.de dated 3/2017. It discusses an article titled "Zinc Oxide–Titania Heterojunction-based Solid Nanospheres as Photoanodes for Electron-Trapping in Dye-Sensitized Solar Cells" which examines using zinc oxide-titania heterojunction solid nanospheres as photoanodes to trap electrons in dye-sensitized solar cells.
Zinc Oxide–Titania Heterojunction-based Solid Nanospheres as Photoanodes for ...Devika Laishram
Agile nanostructure architectures and smart combinations of
semiconducting metal oxide materials are key features of
high-performing dye-sensitized solar cells (DSSCs). Herein,
we synthesize mesoporous solid nanospheres of ZnO–TiO2
with type-II heterojunction and use these as an efficient photoanode material for excellent photoconversion. These polydisperse aggregates doped with 1%, 5%, and 10% of ZnO
exhibit improved solar cell performance with respect to pristine TiO2 under AM 1.5 G. The 1% ZnO doped TiO2 nanosphere possess high specific surface area (84.23 m2
g
@1
) as
a photoanode and shows high photoconversion efficiency of
about 8.07% with ca. 18% improvement in the photocurrent
density (Jsc) compare to TiO2 nanosphere. The improved
solar cell performance (Dh=40%) of ZnO decorated TiO2
nanospheres is ascribed to type-II heterojunction of ZnO–
TiO2
, that reduces the electron recombination and synergistically enhances the electron mobility and charge collection
capability
Nickel and cobalt transfigured natural clay: a green catalyst for low-tempera...Devika Laishram
Soot particulates in engine exhausts pose a severe threat to the environment and human health – causing cancer, affecting the heart and lungs and drives metal processes. This study proposes a practical,
real-world application of transition metal modified natural clay as an environmentally benign, low-cost,
green catalyst for soot oxidation. Ni and Co (NC-Clay) incorporated natural clay catalysts were prepared
by a simple wet impregnation method and meticulously characterized by different characterization
techniques. The catalyst exhibited higher H2 absorption at a lower temperature with similar trends as
observed in O2 TPD that indicated a remarkable redox property, which is useful for applications as a
catalyst in soot oxidation. Excellent catalytic activity with a very low T50 of 358 1C was observed and can
be accredited to the improved surface oxygen vacancies and thermal stability by the metal modification
of clay
Recent advances in ultra-low temperature (sub-zero to 100 8C) synthesis, mech...Devika Laishram
The development of titania (TiO2) nanomaterials for next-generation photonic, optoelectronic, and
catalytic applications necessitates a facile and cost-effective synthetic methodology for precisely tuning
the composition, phase, and morphology at nanometer scales. In this review, an attempt has been made
to comprehend the progress of the emerging and rapidly developing synthesis methods evolved for the
low-temperature synthesis of titania with a particular emphasis on sub-zero temperature. Insights and
understandings of how the temperature affects the characteristic surface properties and morphology of
titania, along with a detailed discussion on the material characteristics for various technological device
applications are dealt with various methods of analysis. Furthermore, the temperature-dependent
morphological (0D–3D) and structural changes and their impact on different energy-harvesting and
storage and water remediation applications are elucidated. Thus, this review specifically opens the
understanding of different TiO2 polymorph syntheses and their physiochemical comprehension for
advanced technological device performance enhancements
Engineered ZnO-TiO2 Nanospheres for High Performing Membrane Assimilated Phot...Devika Laishram
This paper is a study of ZnO doped TiO2 in various percentages
ranging from 0% (undoped) up to 10%. The effect of doping
was observed via the change in morphological, optical,
electrical and physical properties of ZnO-TiO2 nanospheres.
Hydrothermally grown nanospheres are used for removing
contaminants photo-catalytically from waste water and also as
photoanodes in dye-sensitized solar cells (DSSCs) with graphene as counter electrode. Of the many approaches that have
been explored for purification of contaminated water, this work
presents designing of an environmental friendly solution, based
on easily available filter paper membrane and incorporating it
with the synthesized catalyst for photodegradation of the
harmful toxic substances. These reusable membranes assist in
the photodegradation process by creating room for better
light-catalyst-dye interaction via large surface sites. The spherically structured heterojunction of ZnO-TiO2 generates excitons
that oxidize methyl orange (MO) and reduce harmful Cr(VI) to
non-toxic Cr(III) with high efficacy. Additionally, the agile
nanostructures were employed as efficient photoanode material by fabricating dye sensitized solar cells with graphene as
counter electrode.
HfO2 nanodots incorporated in TiO2 and its hydrogenation for high performance...Devika Laishram
Black titania (H-TiO2) as a photoanode material has attracted huge attention due to its extremely high
optical absorption in the visible region. Herein, black TiO2 doped with HfO2 shows 45.7% higher photoconversion efficiency than H-TiO2 under identically similar conditions. The incorporation of HfO2
nanodots increased the optical scattering in H-TiO2 only when it underwent hydrogenation along with
TiO2. Hafnia-doped TiO2 (HfO2/TiO2) is synthesized by a combination of simple sol–gel and
hydrothermal method followed by thermal annealing under controlled hydrogen atmosphere. The
hydrogenated H-(TiO2/HfO2) exhibited very high optical absorption but slightly lower than H-TiO2 due
to light scattering by HfO2 nanodots. We observed a sharp decrease in optical band gap of TiO2/HfO2
from 3.2 to 2.4 eV up on hydrogen annealing, which is important in solar applications as demonstrated
by the fabrication of high efficiency dye sensitized solar cells (DSSC)
High-performance dye-sensitized solar cell using dimensionally controlled tit...Devika Laishram
The subject of the current study is a concoct of anatase and rutile mixed phase titania synthesized at 40 C and
10 C. At these sub-zero temperatures, highly crystalline, phase-oriented nanostructured titania were formed.
At 40 C, nanocrystals of TiO2 consist of the anatase phase while nanorods dominated by the rutile phase form
at 10 C. These samples are remarkable photoanode materials with excellent photon scattering ability in dyesensitized solar cells (DSSCs). On performance optimization of DSSCs, a composition of 0.5 wt% TiO2 (prepared
at 40 C) and P25 improved the photon harvesting by providing a large number of sites for interaction, resulting
in a high photocurrent of 18.46 mA cm2 and 8.6% photoconversion efficiency.
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%.
This document is from the website www.entechnol.de dated 3/2017. It discusses an article titled "Zinc Oxide–Titania Heterojunction-based Solid Nanospheres as Photoanodes for Electron-Trapping in Dye-Sensitized Solar Cells" which examines using zinc oxide-titania heterojunction solid nanospheres as photoanodes to trap electrons in dye-sensitized solar cells.
Zinc Oxide–Titania Heterojunction-based Solid Nanospheres as Photoanodes for ...Devika Laishram
Agile nanostructure architectures and smart combinations of
semiconducting metal oxide materials are key features of
high-performing dye-sensitized solar cells (DSSCs). Herein,
we synthesize mesoporous solid nanospheres of ZnO–TiO2
with type-II heterojunction and use these as an efficient photoanode material for excellent photoconversion. These polydisperse aggregates doped with 1%, 5%, and 10% of ZnO
exhibit improved solar cell performance with respect to pristine TiO2 under AM 1.5 G. The 1% ZnO doped TiO2 nanosphere possess high specific surface area (84.23 m2
g
@1
) as
a photoanode and shows high photoconversion efficiency of
about 8.07% with ca. 18% improvement in the photocurrent
density (Jsc) compare to TiO2 nanosphere. The improved
solar cell performance (Dh=40%) of ZnO decorated TiO2
nanospheres is ascribed to type-II heterojunction of ZnO–
TiO2
, that reduces the electron recombination and synergistically enhances the electron mobility and charge collection
capability
Nickel and cobalt transfigured natural clay: a green catalyst for low-tempera...Devika Laishram
Soot particulates in engine exhausts pose a severe threat to the environment and human health – causing cancer, affecting the heart and lungs and drives metal processes. This study proposes a practical,
real-world application of transition metal modified natural clay as an environmentally benign, low-cost,
green catalyst for soot oxidation. Ni and Co (NC-Clay) incorporated natural clay catalysts were prepared
by a simple wet impregnation method and meticulously characterized by different characterization
techniques. The catalyst exhibited higher H2 absorption at a lower temperature with similar trends as
observed in O2 TPD that indicated a remarkable redox property, which is useful for applications as a
catalyst in soot oxidation. Excellent catalytic activity with a very low T50 of 358 1C was observed and can
be accredited to the improved surface oxygen vacancies and thermal stability by the metal modification
of clay
Recent advances in ultra-low temperature (sub-zero to 100 8C) synthesis, mech...Devika Laishram
The development of titania (TiO2) nanomaterials for next-generation photonic, optoelectronic, and
catalytic applications necessitates a facile and cost-effective synthetic methodology for precisely tuning
the composition, phase, and morphology at nanometer scales. In this review, an attempt has been made
to comprehend the progress of the emerging and rapidly developing synthesis methods evolved for the
low-temperature synthesis of titania with a particular emphasis on sub-zero temperature. Insights and
understandings of how the temperature affects the characteristic surface properties and morphology of
titania, along with a detailed discussion on the material characteristics for various technological device
applications are dealt with various methods of analysis. Furthermore, the temperature-dependent
morphological (0D–3D) and structural changes and their impact on different energy-harvesting and
storage and water remediation applications are elucidated. Thus, this review specifically opens the
understanding of different TiO2 polymorph syntheses and their physiochemical comprehension for
advanced technological device performance enhancements
Engineered ZnO-TiO2 Nanospheres for High Performing Membrane Assimilated Phot...Devika Laishram
This paper is a study of ZnO doped TiO2 in various percentages
ranging from 0% (undoped) up to 10%. The effect of doping
was observed via the change in morphological, optical,
electrical and physical properties of ZnO-TiO2 nanospheres.
Hydrothermally grown nanospheres are used for removing
contaminants photo-catalytically from waste water and also as
photoanodes in dye-sensitized solar cells (DSSCs) with graphene as counter electrode. Of the many approaches that have
been explored for purification of contaminated water, this work
presents designing of an environmental friendly solution, based
on easily available filter paper membrane and incorporating it
with the synthesized catalyst for photodegradation of the
harmful toxic substances. These reusable membranes assist in
the photodegradation process by creating room for better
light-catalyst-dye interaction via large surface sites. The spherically structured heterojunction of ZnO-TiO2 generates excitons
that oxidize methyl orange (MO) and reduce harmful Cr(VI) to
non-toxic Cr(III) with high efficacy. Additionally, the agile
nanostructures were employed as efficient photoanode material by fabricating dye sensitized solar cells with graphene as
counter electrode.
HfO2 nanodots incorporated in TiO2 and its hydrogenation for high performance...Devika Laishram
Black titania (H-TiO2) as a photoanode material has attracted huge attention due to its extremely high
optical absorption in the visible region. Herein, black TiO2 doped with HfO2 shows 45.7% higher photoconversion efficiency than H-TiO2 under identically similar conditions. The incorporation of HfO2
nanodots increased the optical scattering in H-TiO2 only when it underwent hydrogenation along with
TiO2. Hafnia-doped TiO2 (HfO2/TiO2) is synthesized by a combination of simple sol–gel and
hydrothermal method followed by thermal annealing under controlled hydrogen atmosphere. The
hydrogenated H-(TiO2/HfO2) exhibited very high optical absorption but slightly lower than H-TiO2 due
to light scattering by HfO2 nanodots. We observed a sharp decrease in optical band gap of TiO2/HfO2
from 3.2 to 2.4 eV up on hydrogen annealing, which is important in solar applications as demonstrated
by the fabrication of high efficiency dye sensitized solar cells (DSSC)
High-performance dye-sensitized solar cell using dimensionally controlled tit...Devika Laishram
The subject of the current study is a concoct of anatase and rutile mixed phase titania synthesized at 40 C and
10 C. At these sub-zero temperatures, highly crystalline, phase-oriented nanostructured titania were formed.
At 40 C, nanocrystals of TiO2 consist of the anatase phase while nanorods dominated by the rutile phase form
at 10 C. These samples are remarkable photoanode materials with excellent photon scattering ability in dyesensitized solar cells (DSSCs). On performance optimization of DSSCs, a composition of 0.5 wt% TiO2 (prepared
at 40 C) and P25 improved the photon harvesting by providing a large number of sites for interaction, resulting
in a high photocurrent of 18.46 mA cm2 and 8.6% photoconversion efficiency.
Recent Progress in Synthesis of Nano- and Atomic-Sized CatalystsDevika Laishram
Well-defined nano-and atomic-sized heterogeneous catalysts with extremely high
catalytic activities and unique selectivities show promise in addressing the critical
energy- and environment-related challenges of this century. The exceptional
properties of these catalysts, such as their electronic and geometric structures and
the effective interactions between metals and supports, give rise to unprecedented
catalytic efficiency over that of conventional catalysts. The facile prospects for
tuning the active sites of these catalysts pave the way to optimizing their activities,
selectivities, and stabilities, thus offering extensive application possibilities in
significant industry-related catalytic reactions. A prerequisite for synthesizing
nano- and atomic-sized catalyst is to prepare extremely disperse nano- and
subnanoscale atoms on suitable supports. This book chapter summarizes various
synthesis methods employed to synthesize nano- and atomic-scale catalysts.
State of the Art in the Characterization of Nano- and Atomic-Scale CatalystsDevika Laishram
Nanometer and subnanometer particles and films are becoming an essential and
integral part of new technologies and inventions in different areas. Some of the
most common areas include the microelectronic industry, magnetic recordings,
photovoltaic applications, and optical coatings. Because of the ultrasmall size at
atomic levels, the effect of quantum size becomes prominent, and the sensitivity
of size is defined even by a difference of a single atom. Additionally, the effect
is of utmost importance as the single-atom catalysts are far more advantageous
than conventional catalysts as they tend to anchor easily because of their low
coordination. Also, the presence of a single-atom catalyst in reactions creates
efficient charge transfer as it forms a strong interaction with the support.
Furthermore, catalysts in the subnanometer regime exhibit different electronic
states and adsorption capabilities compared to traditional catalysts. Therefore, to
fully appreciate the subnanometer catalysis reactions, it is essential to study the
means of characterizing the prepared subnano catalysts,
Solution Processed Hafnia Nanoaggregates: Influence of Surface Oxygen on Cata...Devika Laishram
Hafnium dioxide (HfO2) nanoaggregates are
synthesized by sol−gel and hydrothermal routes followed by
hydrogen annealing at different time durations. The proposed
study aims to explore the effect of hydrogen annealing time on
the properties of HfO2 and also envisage the catalytic soot
oxidation using HfO2 nanoaggregates. It is observed that
annealing under a hydrogen atmosphere brought about
substantial changes in certain attributes such as chemical and
textural properties with marginal changes in some other
properties like optical activity and band gap. The pristine
HfO2 without hydrogen annealing showed a lower ignition
temperature, whereas hydrogen annealed HfO2 for 2 h showed
the best catalytic performance characterized by the soot
combustion temperature (T50) in contrast to samples prepared at longer duration because of the higher surface adsorbed
oxygen species in its widely distributed pores.
Nitrogen-Enriched Carbon Nanobubbles and Nanospheres for Applications in Ener...Devika Laishram
Multifunctional carbon nanomaterials have attracted remarkable consideration for use in various energy
conversion and storage devices because of their ultrahigh specific
surface area, unique morphology, and excellent electrochemical
properties. Herein, we report the synthesis of highly uniform and
ordered nitrogen-enriched carbon nanospheres (CS) and nanobubbles (CNB) by a modified Stöber reaction using resorcinol and
formaldehyde in the presence of ethylenediamine as a nitrogen
source. A comparative study of the prepared CS and CNB
nanomaterials is presented here with potential use in a wide variety
of applications involving large surface area and electrical
conductivity. As counter electrode materials in solar cells, CNB and CS showed enhanced photoelectrochemical activity for
catalytically reducing I3
− to I− and improved capacitive behavior with a low charge transfer resistance and remarkable power
conversion efficiency (PCE) of 10.40% with improved Jsc (20.20 mA/cm2
) and Voc (0.73 V). The enhanced performance of the
fabricated photoelectrochemical cell is due to the excellent point contact and good conductivity that offered better charge
transportation of electrons with minimum recombination. The enhanced adsorption upon increasing the pressure without an
apparent saturation level signified the large CO2 adsorption with 2 mmol/g for the CS. Additionally, the rectangular-shaped CV
curve indicated the double-layer capacitive behavior, good electrochemical reversibility, and high-power characteristics, prerequisites
for supercapacitor application. This study probes the practical possibility of nitrogen-enriched carbon nanostructures as a
multifunctional material for prospective applications.
Boosting Photocatalytic Activity Using Carbon Nitride Based 2D/2D van der Waa...Devika Laishram
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. Twodimensional 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
Multifunctional materials for clean energy conversionDevika Laishram
With the rapid depletion of fossil fuels, rising environmental concerns,
and population growth, it is inevitable to develop clean energy technologies
to power our future society [1e4]. These energy conversion and storage
technologies are anticipated to be sustainable and also capable of meeting
our long-term energy needs. During the past few years, extensive research
interests have been devoted to the advancement of energy conversion devices, as they play a crucial role in the prosperity and economic growth of
a country. Particularly, the energy conversion technologies such as solar
and fuel cells have proved to be highly reliable and can offer clean and sustainable energy at affordable rate [5e8]. However, the performance potential of these devices, such as output voltage, conversion efficiency, and
stability, are greatly relied on the materials used. The energy conversion process comprises physical and/or chemical reactions at th
Surface fluorination of α-Fe2O3 using selectfluor for enhancement in photoele...Devika Laishram
Fluorinated α-Fe2O3 nanostructures are synthesized via a facile hydrothermal route using Selectfluor™ (F-TEDA)
as a fluorinating as well as growth directing agent. The addition of incrementally increasing amount of F-TEDA
to Fe precursor under hydrothermal conditions resulted in preferential growth of α-Fe2O3 along (110) orientation with respect to (104) direction by ~ 35%, the former being important for enhanced charge transport.
On increasing fluorination, the heirarchical dendritic-type α-Fe2O3 changes to a snow-flake type structure (FTEDA-20%) anisotropically growing along the six directions however, at higher F-TEDA concentrations (≥
30%), loosely held particulate aggregates are seen to be formed. The X-Ray Photoelectron Spectroscopy (XPS)
suggest the maximum fluorinarion of α-Fe2O3 at 1.21 at% in 30% F-TEDA. Further, optical absorption studies
reveal reduction in optical band gap from 2.10 eV in case of pristine to 1.95 eV for fluorinated α-Fe2O3. A
photoanode made by taking 20% fluorinated α-Fe2O3 in a ratio of 10:90 with respect to TiO2 (P-25) showed
improved performance in dye sensitized solar cells with an increase in efficiency by ~16% in comparision to that
of pristine Fe2O3 and TiO2. Furthermore, anode consisting of thin films of fluorinated α-Fe2O3 on FTO also
exhibit enhanced current density on illumination of ~100 W/m2
. The increase in photoelectrochemical activity
seems to be due to the combination of two factors namely preferential growth of α-Fe2O3 along (110) direction
resulting in an improved charge transfer efficiency and reduced recombination losses due to the presence of
fluorine.
On the study of phase and dimensionally controlled titania nanostructures syn...Devika Laishram
The present studies are about surfactant free simple synthesis for titania (TiO2) nanostructures, by which morphology and phase can be tuned through temperature variation. The formation of oval shaped nanocrystals
and nanorods at different temperatures are attributed to the phase transformation between anatase and rutile
by one-step chemical reaction involving titanium tetraisopropoxide and aqueous ethyl alcohol. Categorically,
two different morphologies of TiO2 were observed with respect to variation in temperature with nanorods
formation at −20 °C and −10 °C and oval shape formation at −40 °C and −30 °C with higher surface area.
Crystalline nature and size of nano-TiO2 were determined by transmission electron microscopy (TEM) and
X-ray diffraction (XRD). The energy gap of TiO2 nanoparticles were determined by optical absorption measurement and found to be in the range of ~2.92 to 3.02 eV with an indirect band nature.
Air- and water-stable halide perovskite nanocrystals protected with nearly-m...Devika Laishram
Halide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient
stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a
measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is
compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier
recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr3 nanocrystals was
achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride
protected CsPbBr3 nanocrystals (CNMBr) indicated spherical CsPbBr3 nanoparticles encased in a few nm thick gC3N4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm− 2
. The CNMBr catalyst was successfully deployed for CO2
photoreduction giving carbon monoxide and methane as the reaction products.
Recent Progress in Synthesis of Nano- and Atomic-Sized CatalystsDevika Laishram
Well-defined nano-and atomic-sized heterogeneous catalysts with extremely high
catalytic activities and unique selectivities show promise in addressing the critical
energy- and environment-related challenges of this century. The exceptional
properties of these catalysts, such as their electronic and geometric structures and
the effective interactions between metals and supports, give rise to unprecedented
catalytic efficiency over that of conventional catalysts. The facile prospects for
tuning the active sites of these catalysts pave the way to optimizing their activities,
selectivities, and stabilities, thus offering extensive application possibilities in
significant industry-related catalytic reactions. A prerequisite for synthesizing
nano- and atomic-sized catalyst is to prepare extremely disperse nano- and
subnanoscale atoms on suitable supports. This book chapter summarizes various
synthesis methods employed to synthesize nano- and atomic-scale catalysts.
State of the Art in the Characterization of Nano- and Atomic-Scale CatalystsDevika Laishram
Nanometer and subnanometer particles and films are becoming an essential and
integral part of new technologies and inventions in different areas. Some of the
most common areas include the microelectronic industry, magnetic recordings,
photovoltaic applications, and optical coatings. Because of the ultrasmall size at
atomic levels, the effect of quantum size becomes prominent, and the sensitivity
of size is defined even by a difference of a single atom. Additionally, the effect
is of utmost importance as the single-atom catalysts are far more advantageous
than conventional catalysts as they tend to anchor easily because of their low
coordination. Also, the presence of a single-atom catalyst in reactions creates
efficient charge transfer as it forms a strong interaction with the support.
Furthermore, catalysts in the subnanometer regime exhibit different electronic
states and adsorption capabilities compared to traditional catalysts. Therefore, to
fully appreciate the subnanometer catalysis reactions, it is essential to study the
means of characterizing the prepared subnano catalysts,
Solution Processed Hafnia Nanoaggregates: Influence of Surface Oxygen on Cata...Devika Laishram
Hafnium dioxide (HfO2) nanoaggregates are
synthesized by sol−gel and hydrothermal routes followed by
hydrogen annealing at different time durations. The proposed
study aims to explore the effect of hydrogen annealing time on
the properties of HfO2 and also envisage the catalytic soot
oxidation using HfO2 nanoaggregates. It is observed that
annealing under a hydrogen atmosphere brought about
substantial changes in certain attributes such as chemical and
textural properties with marginal changes in some other
properties like optical activity and band gap. The pristine
HfO2 without hydrogen annealing showed a lower ignition
temperature, whereas hydrogen annealed HfO2 for 2 h showed
the best catalytic performance characterized by the soot
combustion temperature (T50) in contrast to samples prepared at longer duration because of the higher surface adsorbed
oxygen species in its widely distributed pores.
Nitrogen-Enriched Carbon Nanobubbles and Nanospheres for Applications in Ener...Devika Laishram
Multifunctional carbon nanomaterials have attracted remarkable consideration for use in various energy
conversion and storage devices because of their ultrahigh specific
surface area, unique morphology, and excellent electrochemical
properties. Herein, we report the synthesis of highly uniform and
ordered nitrogen-enriched carbon nanospheres (CS) and nanobubbles (CNB) by a modified Stöber reaction using resorcinol and
formaldehyde in the presence of ethylenediamine as a nitrogen
source. A comparative study of the prepared CS and CNB
nanomaterials is presented here with potential use in a wide variety
of applications involving large surface area and electrical
conductivity. As counter electrode materials in solar cells, CNB and CS showed enhanced photoelectrochemical activity for
catalytically reducing I3
− to I− and improved capacitive behavior with a low charge transfer resistance and remarkable power
conversion efficiency (PCE) of 10.40% with improved Jsc (20.20 mA/cm2
) and Voc (0.73 V). The enhanced performance of the
fabricated photoelectrochemical cell is due to the excellent point contact and good conductivity that offered better charge
transportation of electrons with minimum recombination. The enhanced adsorption upon increasing the pressure without an
apparent saturation level signified the large CO2 adsorption with 2 mmol/g for the CS. Additionally, the rectangular-shaped CV
curve indicated the double-layer capacitive behavior, good electrochemical reversibility, and high-power characteristics, prerequisites
for supercapacitor application. This study probes the practical possibility of nitrogen-enriched carbon nanostructures as a
multifunctional material for prospective applications.
Boosting Photocatalytic Activity Using Carbon Nitride Based 2D/2D van der Waa...Devika Laishram
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. Twodimensional 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
Multifunctional materials for clean energy conversionDevika Laishram
With the rapid depletion of fossil fuels, rising environmental concerns,
and population growth, it is inevitable to develop clean energy technologies
to power our future society [1e4]. These energy conversion and storage
technologies are anticipated to be sustainable and also capable of meeting
our long-term energy needs. During the past few years, extensive research
interests have been devoted to the advancement of energy conversion devices, as they play a crucial role in the prosperity and economic growth of
a country. Particularly, the energy conversion technologies such as solar
and fuel cells have proved to be highly reliable and can offer clean and sustainable energy at affordable rate [5e8]. However, the performance potential of these devices, such as output voltage, conversion efficiency, and
stability, are greatly relied on the materials used. The energy conversion process comprises physical and/or chemical reactions at th
Surface fluorination of α-Fe2O3 using selectfluor for enhancement in photoele...Devika Laishram
Fluorinated α-Fe2O3 nanostructures are synthesized via a facile hydrothermal route using Selectfluor™ (F-TEDA)
as a fluorinating as well as growth directing agent. The addition of incrementally increasing amount of F-TEDA
to Fe precursor under hydrothermal conditions resulted in preferential growth of α-Fe2O3 along (110) orientation with respect to (104) direction by ~ 35%, the former being important for enhanced charge transport.
On increasing fluorination, the heirarchical dendritic-type α-Fe2O3 changes to a snow-flake type structure (FTEDA-20%) anisotropically growing along the six directions however, at higher F-TEDA concentrations (≥
30%), loosely held particulate aggregates are seen to be formed. The X-Ray Photoelectron Spectroscopy (XPS)
suggest the maximum fluorinarion of α-Fe2O3 at 1.21 at% in 30% F-TEDA. Further, optical absorption studies
reveal reduction in optical band gap from 2.10 eV in case of pristine to 1.95 eV for fluorinated α-Fe2O3. A
photoanode made by taking 20% fluorinated α-Fe2O3 in a ratio of 10:90 with respect to TiO2 (P-25) showed
improved performance in dye sensitized solar cells with an increase in efficiency by ~16% in comparision to that
of pristine Fe2O3 and TiO2. Furthermore, anode consisting of thin films of fluorinated α-Fe2O3 on FTO also
exhibit enhanced current density on illumination of ~100 W/m2
. The increase in photoelectrochemical activity
seems to be due to the combination of two factors namely preferential growth of α-Fe2O3 along (110) direction
resulting in an improved charge transfer efficiency and reduced recombination losses due to the presence of
fluorine.
On the study of phase and dimensionally controlled titania nanostructures syn...Devika Laishram
The present studies are about surfactant free simple synthesis for titania (TiO2) nanostructures, by which morphology and phase can be tuned through temperature variation. The formation of oval shaped nanocrystals
and nanorods at different temperatures are attributed to the phase transformation between anatase and rutile
by one-step chemical reaction involving titanium tetraisopropoxide and aqueous ethyl alcohol. Categorically,
two different morphologies of TiO2 were observed with respect to variation in temperature with nanorods
formation at −20 °C and −10 °C and oval shape formation at −40 °C and −30 °C with higher surface area.
Crystalline nature and size of nano-TiO2 were determined by transmission electron microscopy (TEM) and
X-ray diffraction (XRD). The energy gap of TiO2 nanoparticles were determined by optical absorption measurement and found to be in the range of ~2.92 to 3.02 eV with an indirect band nature.
Air- and water-stable halide perovskite nanocrystals protected with nearly-m...Devika Laishram
Halide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient
stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a
measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is
compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier
recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr3 nanocrystals was
achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride
protected CsPbBr3 nanocrystals (CNMBr) indicated spherical CsPbBr3 nanoparticles encased in a few nm thick gC3N4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm− 2
. The CNMBr catalyst was successfully deployed for CO2
photoreduction giving carbon monoxide and methane as the reaction products.
Air- and water-stable halide perovskite nanocrystals protected with nearly-m...
Heterostructured HfO2/TiO2 spherical nanoparticles for visible photocatalytic water remediation
1. Heterostructured HfO2/TiO2 spherical nanoparticles for visible
photocatalytic water remediation
Devika Laishram, Kiran P. Shejale, Ritu Gupta, Rakesh K. Sharma ⇑
Department of Chemistry, Indian Institute of Technology Jodhpur, NH-65, Nagaur Road, Karwar, Jodhpur, Rajasthan 342037, India
a r t i c l e i n f o
Article history:
Received 9 May 2018
Received in revised form 7 August 2018
Accepted 10 August 2018
Available online 11 August 2018
Keywords:
HfO2/TiO2
Hydrogenation
Photocatalytic dye degradation
a b s t r a c t
Photocatalytic activity of low band gap hydrogenated HfO2 doped TiO2 (H-HfO2/TiO2), HfO2 doped TiO2
(HfO2/TiO2) and TiO2 (pristine) were investigated by photocatalytic degradation of five different indus-
trial dyes. The current study envisages the effect of doping hydrogen and HfO2 up on TiO2 for photocat-
alytic degradation of different chemically structured dyes. Methylene Blue attains fast degradation
efficiency of 90%, within 10 min of the reaction due to high photocatalytic adsorption and degradation
over the rough TiO2 surface. Effect of pH on dye degradation is observed, leading to disintegration and
mineralization.
Ó 2018 Published by Elsevier B.V.
1. Introduction
Chemical substances used in the textile and dyeing industries
are mostly non-biodegradable which, when left untreated cause
severe pollution to the aquatic ecosystem affecting health and
environment [1]. On an average, 200 L of water is used for dyeing
1 kg of textiles [2]. The waste dyes in the water are either toxic,
carcinogenic or changes the characteristic of water leaving it unfit
for use for all practical purposes [3]. Traditional systems of water
treatment such as flocculation, ion exchange and adsorption of
dyes remain ineffective, costly and transfer nondestructively the
pollution from one phase to another [4–6]. Thus, degradation of
organic impurities into its various constituents like CO2, water
vapour and other inorganic substances via proper utilization of
sunlight is a highly effective, low-cost solution. Recently, effective
utilization of semiconductor photocatalysts has been resurgent of
activity in water remediation [7–11]. TiO2 is a principal semicon-
ductor nanomaterial of choice because of its wide abundance,
non-toxicity, high photocatalytic performance and stability
[12–14]. However, TiO2 suffers from low photocatalytic efficiency
due to its wide band gap of 3.2 eV resulting in improper utilization
of solar spectrum absorbing only in the UV range [15]. Thus, mod-
ification is for enhancing properties by doping various metals and
non-metals, tuning the shape, morphology and particle size [16].
Recently, black TiO2 synthesis has successfully reduced the band
gap, expanding the absorptivity to visible range and increasing
photoactivity [15–17].
In this work, the TiO2 nanomaterial with 1% HfO2 doping having
most favourable structural and optical properties (2.94 eV, Fig. S2)
is synthesized and tested for photo-degradation study of five
different dyes – methyl orange (MO), methyl blue (MB), cresol
red (CR), thymol blue (TB) and solochrome black (SB).
2. Experimental details
2.1. Synthesis of HfO2/TiO2 spherical nanoparticles (SNP)
H-HfO2/TiO2 nano-spherical structures were synthesized by sol-
gel and solvothermal process [18]. Briefly, 1% HfO2 doped TiO2
were prepared by a two-step sol-gel and hydrothermal process
followed by annealing under reducing hydrogen atmosphere. The
detailed procedure is given in SI.
2.2. Characterization
The crystallographic parameters were analyzed by X-ray diffrac-
tometer (Bruker D8 Advance Diffractometer). Elemental composi-
tion analysis was performed using XRF (X-Ray Fluorescence)
analyzer. Morphological analysis was done using TEM (Transmis-
sion Electron Microscopy, FEI Tecnai-G2 T20) operated at 200 kV.
HPLC analysis was performed using Waters 2489 (Fig. S6), BET mea-
surements were performed using Quantachrome Autosorb iQ3.
2.3. Photocatalytic degradation
The dyes – MO, MB, CR, SB and TB were purchased from Acros,
SRL, Sigma and Qualigens. Dye solutions in water (20 mM) were
https://doi.org/10.1016/j.matlet.2018.08.053
0167-577X/Ó 2018 Published by Elsevier B.V.
⇑ Corresponding author.
E-mail address: rks@iitj.ac.in (R.K. Sharma).
Materials Letters 231 (2018) 225–228
Contents lists available at ScienceDirect
Materials Letters
journal homepage: www.elsevier.com/locate/mlblue
2. prepared and 400 mg/L of catalyst was dispersed in 15 mL of each
of the dye solutions. The photocatalytic behavior was observed
under 1 Sun simulated light (SS50AAA Solar Simulator, PET Photo
Emission Tech.) for 50 min under mild stirring. The residual con-
centration of the dye was estimated by a colorimeter.
3. Results and discussion
3.1. Structural and Morphological characterization
The material showed lattice planes distinct to anatase phase of
TiO2 which is identified with JCPDS 021-1272 (Fig. 1a). No extra
peaks were observed in the diffraction pattern of TiO2 SNP and thus
it can be concluded that the material synthesized is highly pure
[19]. HfO2/TiO2 and H-HfO2/TiO2 showed broad hump at 28.3°
and 31.62° ascertained to monoclinic HfO2 [20]. The effect on
strain and crystallite size upon doping HfO2 and eventual hydro-
genation are observed and tabulated in Fig. 1b and Table 1. The
magnified (1 0 1) highest intense peak (Fig. 1b) showed 2 h shift
in the lower angle corresponding to 0.04 and 0.128 after doping
HfO2 and hydrogenation correspondingly. XRF plot in Fig. 1c indi-
cates presence of Hf (La1 and Lb1) and Ti (Ka1 and Kb1) in the syn-
thesized SNP.
Lattice expansion of 0.0738% was observed for H-HfO2/TiO2 due
to incorporation of bigger size HfO2 on the TiO2 lattice [21]. More-
over, annealing under reducing hydrogen atmosphere creates
defects in lattice contributing substantially to lattice expansion
[17]. The XRF spectroscopy is a non-destructive analysis technique
that gives quantitative and qualitative assessment of elements. The
intense peak showed the presence of larger amount of Ti in the sam-
ple and Hf as smaller humps due to 1% doping in the prepared SNP.
The uniformly formed spherical morphology of the materials was
confirmed using TEM (Fig. 2a–c) that showed TiO2 SNP comprising of
smaller grain like TiO2 and HfO2 particles. Fig. 2a–c (inset) revealed
the gradual increase in size of the SNP upon doping, with H-HfO2/
TiO2 being the largest. The average diameter follows the order –
TiO2 (305 nm) HfO2/TiO2 (326 nm) H-HfO2/TiO2 (400 nm).
Also, even distribution of pores was observed by the light and dark
contrast in TEM images. The HR-TEM images (Fig. 2d–f) indicate
lattice spacing corresponding to anatase phase of TiO2 with average
d-spacing value of 0.35 nm consistent to (1 0 1) as observed in the
XRD pattern (Fig. 2a). The bright spots in SAED pattern (Fig. S1a–c)
are fainted upon hydrogen treatment due to slight decrease in poly-
crystalline nature which is understandable.
3.2. Photocatalytic activity
Aqueous solution of various dyes – MB, CR, MO, TB and SB were
photocatalytically degraded using the synthesized materials as cat-
alyst for 50 min (Fig. 3a–c). Amongst all dyes, MB was best
degraded by all the three catalysts within shortest duration
observed for H-HfO2/TiO2 with 90% in 10 min. MB shows strong
absorbance at 664 nm and 292 nm with shoulder peak at 614 nm
and 245 nm (Fig. 3(d–f)). The adsorption of dye upon the catalyst
surface depends on the electrostatic interaction between the dye
and surface of the catalyst [22]. TiO2 is amphoteric and reacts dif-
ferently with pH, e.g. MB is cationic and adsorption is stronger with
TiO2 surface leading to higher degradation efficiency under basic
conditions (Fig. 3d–f). Catalyst containing dye gets degraded when
electron-hole pair generated by the light reacts with water mole-
cules to yield active radicals. The oxidation of dyes lead to cleavage
of bonds and breaking of aromatic rings with formation of smaller
inorganic molecules in three steps–decolourization, degradation
and mineralization. Enhanced degradation activity of H-HfO2/
TiO2 with a band gap of 2.47 eV (Fig. S2) was observed due to
better utilization of solar spectrum, reduced recombination and
suitable tuning of band gap due to annealing under hydrogen
and doping HfO2. Hydrogen annealing leads to formation of defect
and oxygen vacant sites creating superoxide and hydroxyl radicals
useful for dye degradation [17,23]. Thus, H-HfO2/TiO2 showed the
Fig. 1. (a) XRD of the material with JCPDS data (b) XRD of highest intense peak (1 0 1) denoting shift and intensity change. (c) XRF spectra of doped TiO2.
Table 1
Cell parameters of the nanomaterials.
Sl. No. Synthesized SNP Crystallite Size (in nm) Strain Unit cell parameter calculated
a (nm) c (nm)
1. TiO2 3.2018 0.5259 ± 0.2351 0.3789 0.8815
2. HfO2/TiO2 3.0188 0.4137 ± 0.2530 0.3790 0.9710
3. H- HfO2/TiO2 3.4863 0.5272 ± 0.2144 0.3792 0.9715
226 D. Laishram et al. / Materials Letters 231 (2018) 225–228
3. highest degradation rate at 0.216 min 1
among the three catalysts
tested with MB dye (Table S1). Also, the % degradation efficiency
was calculated and plotted (Fig. S4) for each of the five dyes
degraded using all catalysts. Recyclability test was performed for
five cycles for MB with H-HfO2/TiO2, revealed high stability of cat-
alyst (Fig. S5). Obliteration of dye to smaller molecules due to pho-
tocatalytic degradation can be realized by the appearance of new
peaks at lower retention time in the HPLC chromatogram
(Fig. S6). Additionally, the improved degradation efficiency using
H-HfO2/TiO2 is attributed to the HfO2 doping leading to a highly
mesoporous structure with larger surface area for exchange of
mass between the dye and catalyst molecules as confirmed from
the BET analysis (Fig. S3, Table S2) [24,25]. Moreover, doping
induced defects and oxygen vacancies act as trapping sites
Fig. 3. (a–c) Degradation of five different dyes using TiO2, HfO2/TiO2 and H-HfO2/TiO2 at pH 7. (d-f) show the degradation of MB dye at different pH using H-HfO2/TiO2.
Fig. 2. TEM (a), (b), (c) and HR-TEM (d), (e), (f) images of synthesized TiO2, HfO2/TiO2 and H-HfO2/TiO2 respectively. Inset of (a), (b) and (c) shows the corresponding spherical
structure growing in size with doping.
D. Laishram et al. / Materials Letters 231 (2018) 225–228 227
4. decreasing the recombination rate. Thus, the compound effect of
doping HfO2 over TiO2 and subsequent annealing under H2 atmo-
sphere can be a suitable means to synthesize an advanced form
of SNP for using in accelerated photocatalytic dye degradation
applications. The results are compared with literature reports
and tabulated in Table S3.
4. Conclusion
High surface area nanospherical black TiO2 doped with 1% HfO2
are synthesized by sol-gel and hydrothermal method for degrada-
tion of five common textile dyes. The morphological characteriza-
tions using TEM analysis revealed that each nanosphere has an
average size of 500 nm consisting of 15–20 nm size granules of
HfO2 and TiO2 nanoparticles. Such structural assembly greatly
enhances the number of active sites, surface area for dye attach-
ment and enhances the light scattering effect. Degradation study
of the dyes revealed high activity over 90% within 10 min for MB
under illumination at basic pH.
Acknowledgement
The authors would like to thank Indo-UK NERC Water Quality
Project DST/TM/INDO-UK/2K17/52 for financial support and
MRC, MNIT Jaipur, India, for TEM facility and CASE, IIT Jodhpur
for characterization facility. Authors gratefully acknowledge Mr.
Ganpat Choudhary and Mr. Shubham Pandey for XRD and BET
analysis.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at https://doi.org/10.1016/j.matlet.2018.08.053.
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