Semiconductor-based photocatalysis has dramatically increased interest in the field of photocatalysis, because of
its ability to directly utilize solar energy into fuels and for the degradation of various pollutants. However, the
photocatalytic performance of semiconductor-based photocatalys still lower due to the quick recombination
photogenerated electron–hole pairs and low visible light utilization. Therefore, numerous efforts have been made
to solve these complications. Particularly, cocatalysts supported semiconductor have been extensively applied in
designing and developing highly effective composite photocatalysts for hydrogen photocatalytic application.WS2
has attracted enormous attention in photocatalysis due to its unusual properties like enhancing visible lightharvesting,
charge transfer dynamics and surface reactions of a photocatalytic system. In this review, we
begin by describing synthesis route, different morphologies and brief sketch properties of WS2. A brief discussion
of the WS2 supported metal oxide, metal sulphide, carbon based materials, silver based materials and bismuth
based materials photocatalysts is then provided. While various plausible photocatalytic mechanisms of
photogenerated-electrons and holes in WS2 composite should be proposed. The applications of WS2 as cocatalyst
in the Photocatalytic hydrogen production, organic contaminant degradation and Cr(VI) removal. This review
may offer motivation for designing and fabricating novel and efficient WS2 based composite photocatalysts for
highly efficient photocatalytic applications.
Review on Synthesis and Applications of Nanomaterial Molybdenum Disulphide (M...IRJET Journal
This document reviews the synthesis and applications of the nanomaterial molybdenum disulfide (MoS2) and its use in photocatalysis. It discusses MoS2's desirable properties including its band gap, mobility, and hexagonal structure. The document outlines challenges to chalcogenide-based photocatalysis like limited visible light absorption and reviews approaches to address these, such as doping MoS2 with metals or creating heterostructures. It examines MoS2's optical and structural characteristics and its use as a photocatalyst, noting efforts to improve its performance. Finally, it discusses using MoS2 and MoS2-based materials for the photocatalytic treatment of pollutants
IRJET-A Review on Utilization of Waste Heat from Automobile Based on Thermoel...IRJET Journal
This document discusses using metal-doped zinc oxide nanoparticles for water treatment in industries. It begins by introducing zinc oxide nanoparticles and the need to dope them with metals like magnesium to modify their properties. It then describes how magnesium-doped zinc oxide nanoparticles were synthesized using a sol-gel method. Characterization of the nanoparticles showed they were uniform in size and distribution. Experiments were conducted using these nanoparticles to degrade methylene blue dye in water via a photocatalytic process when exposed to light. The mechanism of photocatalysis is explained where light generates electron-hole pairs that initiate degradation reactions on the nanoparticle surfaces. The goal is to use this process to treat wastewater from industries in an efficient and environmentally friendly
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
Reduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
tReduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Visible light solar photocatalytic degradation of pulp and paper wastewater u...eSAT Journals
Abstract
With the growing number of industries there are large volumes of wastewater generated every day. Pulp and paper mills are highly polluting as they release effluents containing organic pollutants, and high levels of Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). Even though well-established processes exist to treat these effluents, there are only a few processes which are energy efficient. Conventional treatment methods are not effective for the degradation of toxic organic pollutants, hence other treatment techniques are necessary. One of the recent developments in this field is the Advanced Oxidation Process (AOP). Solar photocatalysis is a type of AOP which utilises UV light to activate semiconductor photocatalyst in order to produce highly reactive radical species. TiO2 is a widely used catalyst for this purpose, to oxidise or reduce the organic pollutants in industrial wastewater. However, photocatalysis using visible light has been receiving increased attention hence, modification of TiO2 is necessary for its enhanced response to visible light. There are many methods for modifying TiO2, such as doping and photo-sensitisation. This study focusses on the modification of TiO2 using the method of dye-sensitisation (photo-sensitisation) with the dyes rhodamine B and methylene blue. Solar photocatalytic experiments were carried out for the degradation of pulp and paper wastewater, at different conditions like varying catalyst loading (500mg, 600mg, 750mg and 1000mg of catalyst for 300ml of aqueous wastewater) and effluent concentration (20ml, 25ml, 30ml and 35ml of wastewater). Preliminary tests were done to determine the best conditions for photocatalytic degradation, and these were applied for final tests. Keywords - Solar Photocatalysis, Visible Light, Dye Sensitisation, Pulp and paper, Methylene blue, Rhodamine B, TiO2 catalyst.
Review on Synthesis and Applications of Nanomaterial Molybdenum Disulphide (M...IRJET Journal
This document reviews the synthesis and applications of the nanomaterial molybdenum disulfide (MoS2) and its use in photocatalysis. It discusses MoS2's desirable properties including its band gap, mobility, and hexagonal structure. The document outlines challenges to chalcogenide-based photocatalysis like limited visible light absorption and reviews approaches to address these, such as doping MoS2 with metals or creating heterostructures. It examines MoS2's optical and structural characteristics and its use as a photocatalyst, noting efforts to improve its performance. Finally, it discusses using MoS2 and MoS2-based materials for the photocatalytic treatment of pollutants
IRJET-A Review on Utilization of Waste Heat from Automobile Based on Thermoel...IRJET Journal
This document discusses using metal-doped zinc oxide nanoparticles for water treatment in industries. It begins by introducing zinc oxide nanoparticles and the need to dope them with metals like magnesium to modify their properties. It then describes how magnesium-doped zinc oxide nanoparticles were synthesized using a sol-gel method. Characterization of the nanoparticles showed they were uniform in size and distribution. Experiments were conducted using these nanoparticles to degrade methylene blue dye in water via a photocatalytic process when exposed to light. The mechanism of photocatalysis is explained where light generates electron-hole pairs that initiate degradation reactions on the nanoparticle surfaces. The goal is to use this process to treat wastewater from industries in an efficient and environmentally friendly
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
Reduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Reduced graphene oxide–CuO nanocomposites for photocatalyticconversion of CO2...Pawan Kumar
tReduced graphene oxide (rGO)–copper oxide nanocomposites are prepared by covalent grafting of CuOnanorods on the rGO skeleton. Chemical and structural features of rGO–CuO nanocomposites are probedby FTIR, XPS, XRD and HRTEM analyses. Photocatalytic potential of rGO–CuO nanocomposites is exploredfor reduction of CO2into the methanol under the visible light irradiation. The breadth of CuO nanorods andthe oxidation state of Cu in the rGO–CuO/Cu2O nanocomposites are systematically varied to investigatetheir photocatalytic activities. The pristine CuO nanorods exhibited very low photocatalytic activity owingto fast recombination of charge carriers and yielded 175 mol g−1methanol, whereas rGO–Cu2O andrGO–CuO exhibited significantly improved photocatalytic activities and yielded five (862 mol g−1) andseven (1228 mol g−1) folds methanol, respectively. The superior photocatalytic activity of CuO in therGO–CuO nanocomposites was attributed to slow recombination of charge carriers and efficient transferof photo-generated electrons through the rGO skeleton. This study further excludes the use of scavengingdonor.
Visible light solar photocatalytic degradation of pulp and paper wastewater u...eSAT Journals
Abstract
With the growing number of industries there are large volumes of wastewater generated every day. Pulp and paper mills are highly polluting as they release effluents containing organic pollutants, and high levels of Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). Even though well-established processes exist to treat these effluents, there are only a few processes which are energy efficient. Conventional treatment methods are not effective for the degradation of toxic organic pollutants, hence other treatment techniques are necessary. One of the recent developments in this field is the Advanced Oxidation Process (AOP). Solar photocatalysis is a type of AOP which utilises UV light to activate semiconductor photocatalyst in order to produce highly reactive radical species. TiO2 is a widely used catalyst for this purpose, to oxidise or reduce the organic pollutants in industrial wastewater. However, photocatalysis using visible light has been receiving increased attention hence, modification of TiO2 is necessary for its enhanced response to visible light. There are many methods for modifying TiO2, such as doping and photo-sensitisation. This study focusses on the modification of TiO2 using the method of dye-sensitisation (photo-sensitisation) with the dyes rhodamine B and methylene blue. Solar photocatalytic experiments were carried out for the degradation of pulp and paper wastewater, at different conditions like varying catalyst loading (500mg, 600mg, 750mg and 1000mg of catalyst for 300ml of aqueous wastewater) and effluent concentration (20ml, 25ml, 30ml and 35ml of wastewater). Preliminary tests were done to determine the best conditions for photocatalytic degradation, and these were applied for final tests. Keywords - Solar Photocatalysis, Visible Light, Dye Sensitisation, Pulp and paper, Methylene blue, Rhodamine B, TiO2 catalyst.
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
This document describes the large scale photochemical synthesis of M@TiO2 nanocomposites (M = Ag, Pd, Au, Pt) and investigates their optical properties, catalytic activity for CO oxidation, and antibacterial effects. Well-dispersed M@TiO2 nanocomposites with particle diameters of 200-400 nm were synthesized using a clean photochemical method without additives. The sizes of the noble metal nanoparticles formed on the TiO2 support were approximately 1 nm for Pt, 5 nm for Au and Pd, and 2-20 nm for Ag. The nanocomposites exhibited excellent catalytic activity for CO oxidation at low temperatures. Tests also showed the nanocomposites had antibacterial effects against E
This document summarizes manipulation strategies for two-dimensional amorphous nanomaterials (2D ANMs) to enhance their performance in electrochemical energy storage and conversion applications. It discusses two main categories of manipulation: 1) geometric configuration design, including spatial structure design (e.g. creating porous structures) and coordination environment design (e.g. defect creation); and 2) component interaction, including elemental doping/coupling and heterophase compositing. Recent examples manipulating 2D ANMs through these approaches for applications in batteries, supercapacitors and electrocatalysis are reviewed. The document concludes by discussing opportunities to further optimize manipulation of 2D ANMs.
This document describes the synthesis and characterization of a core-shell structured reduced graphene oxide wrapped magnetically separable rGO@CuZnO@Fe3O4 microspheres photocatalyst and its use for the photoreduction of carbon dioxide to methanol under visible light irradiation. The photocatalyst takes advantage of the high photocatalytic efficiency of zinc oxide, the high surface area and charge carrier mobility of reduced graphene oxide, and the magnetic properties of an iron oxide core. Experimental results showed the rGO@CuZnO@Fe3O4 photocatalyst had higher catalytic activity than other possible combinations, with a methanol yield of 2656 μmol/gcat under visible light, and could be readily recovered and
Recent progress on reduced graphene oxide....suresh kannan
The document summarizes recent progress on using reduced graphene oxide (rGO)-based materials as counter electrodes for dye-sensitized solar cells (DSSCs) as a cost-effective alternative to platinum. It discusses how rGO on its own is not effective as a counter electrode but that adding metal nanoparticles to rGO composites improves their catalytic activity and performance in DSSCs. The document reviews various rGO composites that have been studied, including those with silver, nickel, tungsten and platinum nanoparticles, as well as metal oxides and dichalcogenides. It compares the photovoltaic parameters of DSSCs using these rGO composite counter electrodes to those using conventional platinum counter electrodes
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%.
HYDROGEN GENERATION FROM WASTE WATER BY USING SOLAR ENERGY | J4RV3I11004Journal For Research
Objective of this paper is to produce hydrogen which is an ideal fuel for the next generation because it is abundantly available in nature, energy efficient and clean. Wide varieties of technologies are available to produce hydrogen but only few of them are considered environmental friendly. Solar water splitting via photo catalytic reaction is one of them which have attracted tremendous attention. In this paper we are working on hydrogen production via solar splitting. Photo catalytic water splitting is one of the promising technologies to produce pure and clean hydrogen. Since it is reasonable having low process cost and has a small reactor, it can be made for house hold application and hence has a huge market potential. Generation of hydrogen under visible irradiation is the main area of work. Based on the literature reported here, visible irradiation can be achieved by doping of TiO2 with metal or non-metal. We have used Fe doping to increase the efficiency. The result indicates that Fe doped sieves produce more hydrogen than the normal TiO2 coated sieve and the efficiency can be increased if we increase the number of doped sieves and surface area.
This document discusses hydrogen production from photocatalytic water splitting using semiconductor materials. It begins by introducing alternative energies and hydrogen as an ideal fuel. It then discusses various methods of hydrogen production, focusing on solar-driven processes like thermochemical, photobiological, and photocatalytic water splitting. The document examines using titanium dioxide (TiO2) as a photocatalyst for water splitting and methods to improve its photoactivity, such as metal loading and doping. It also discusses high-efficiency photocatalytic systems and the types of photocatalytic water splitting reactions. In the end, it emphasizes the need for further research to develop new technologies for low-cost, environmentally friendly hydrogen production.
IRJET- Study of Single Chamber and Double Chamber Efficiency and Losses o...IRJET Journal
This document summarizes research on the efficiency and losses of single chamber and double chamber wastewater treatment using microbial fuel cells (MFCs). MFCs can concurrently treat wastewater and generate electricity by using microorganisms to break down organic matter and release electrons. The document compares different MFC designs, including single chamber and double chamber systems. Single chamber MFCs are simpler but have lower columbic efficiency due to oxygen diffusion into the anode chamber, while double chamber MFCs can maintain separate conditions in each chamber to improve efficiency. The document also discusses standard electrode potentials, treatment efficiencies, columbic efficiencies, and factors that affect MFC performance.
Sustainable Strategies for the Exploitation of End-of-Life Permanent MagnetsNOMADPOWER
Rare Earth Magnets (REM), especially the NdFeB type, are essential components in high-performance electric motors and wind turbines, playing an important role in the shift towards a low-carbon energy matrix. However, little work has been done to understand how the production of REM can be in line with the global sustainable transition. To overcome this lack and help with future research, as well as decision-making, this paper provides a literature overview of which aspects of sustainability are being investigated in the REM supply chain, and how each of them contributes to achieving Sustainable Development Goals (SDG). This research is developed through a consistent analysis of 44 peer-reviewed publications, followed by an analysis of strengths, weaknesses, opportunities, and threats. Four main subjects of studies were identified: environmental impact; social impact; economic aspects and circular economy. Most of the studies focus on computing the environmental impact through life cycle assessment and discussing techniques towards exploring the circular economy concept. In addition to contributing to a greener economy, the majors identified strengths of REM are the great potential of its supply chain in reducing primary resource extraction, since REM recovery and recycling seem to be viable, and the promising techniques to minimize environmental impacts along the rare earth elements production chain.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
The effect of band engineering of semiconductors on photocatalyic water split...eSAT Journals
Abstract
The direct conversion of solar energy using a photocatalyst in a water splitting reaction is a source of a sustainable and clean hydrogen supply. In general, photocatalysts are semiconductors that possess valence and conduction bands. These energy bands permit the absorption of photon energy to excite electrons in the outer orbitals of the photocatalysts. Photoexcited electron and hole pairs can subsequently induce a watersplitting reaction to produce hydrogen and oxygen. Photocatalytic water splitting is affected by the band level and crystallinity of the photocatalyst. Therefore, band engineering using chemical modifications such as cationic and anionic modification could createa photocatalyst suitable for the large-scale production of hydrogen. In this paper, cationic and anionic modifications of photocatalysts and the effects of these modifications onphotocatalytic water splitting are reviewed. Keywords: Water splitting; Photocatalysis; Hydrogen
Synthesis MgO nanopowder using Sol-gel technique: A critical reviewPratish Rawat
During the last decade, it has realized that when materials are synthesized to nanoscale dimensions, they will show new and remarkably improved physical and chemical properties. Due to its wide and major applications, in-depth investigations have been carried out on metal oxide nanomaterials. A significant amount of research is going on in synthesis and characterization of MgO/PVA nanocomposites. Some of the literature has been reviewed to get the idea about the synthesis and characterization of MgO/PVA nanocomposites using sol-gel technique.
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
This document summarizes the synthesis and characterization of halogen-doped carbon nitride nanosheets and BiOI heterojunctions for use in photoelectrochemical water splitting. Specifically:
1) Fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) nanosheets were synthesized using thermal annealing to improve light absorption and charge separation.
2) CNF-Cl nanosheets were combined with bismuth oxyiodide (BiOI) nanoplates via a hydrothermal method to form heterojunctions.
3) Characterization using TEM, XRD, Raman and EDS mapping confirmed the formation of CNF-Cl
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression of charge recombination in bulk gC 3 N 4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm− 2 under AM1. 5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV …
This document summarizes a research paper on dye sensitized solar cells (DSSCs). It provides background on the development of DSSCs since 1991 and their advantages over traditional silicon solar cells in terms of lower cost and simpler preparation. However, liquid electrolytes used in early DSSCs limited long-term performance. Recent research has focused on improving electrolytes, particularly developing quasi-solid state electrolytes, to enhance photoelectric performance and stability for practical applications of DSSCs. The document reviews progress on quasi-solid state electrolytes and their advantages over liquid electrolytes for DSSCs.
The Use of Artificial Photosynthesis to Power Hydrogen Fuel CellsJacob Saletsky
This document summarizes a student paper about using artificial photosynthesis to power hydrogen fuel cells. It discusses how artificial photosynthesis works by using solar energy, water, and catalysts like titanium oxide to split water into hydrogen and oxygen. It then explains how hydrogen fuel cells can use the hydrogen to generate electricity. The document argues that artificial photosynthesis is a promising renewable energy source because, like natural photosynthesis, its byproducts are harmless and materials are reusable. It also discusses the components and processes involved in artificial photosynthesis and hydrogen fuel cells.
This study is define on the nanotechnology with energy application. In this technology explain the energy conversion, generation, storage and transportation.it is in unique technique, capacity, great potential to fabricate new structure at atomic scale has produced novel material and devices. Its technique have great potential applications with wide fields.to required large no. of energy in the world.in present available energy is not sufficient for comparison on world requirement energy. That’s vision of fulfillment the required no. of energy by through this new technique.in hence present advance of the nanotechnology to suitable useful energy generation, production, storage and use. The main function and aim of this technology working from different fields, areas and points, to find out the better solutions. Which is the great challenge of our life?
Thermal Stability Investigation and Improvement: A Gateway to High Efficiency...IRJET Journal
This document summarizes research into improving the thermal stability and power conversion efficiency of organometal trihalide perovskite solar cells. The researchers used modeling software to simulate cell performance at different temperatures. They achieved a promising power conversion efficiency of 29.31% for their cell model. The simulations showed that higher temperatures negatively impact carrier concentration, band gaps, and mobilities, reducing efficiency. Unlike typical models that peak at 300K, this model's efficiency increased above 300K, peaking at 29.34% at 325K and remaining high up to 355K. This suggests improved thermal stability. The findings provide a useful reference for fabricating thermally stable, high-efficiency perovskite solar cells.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
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
This document describes the large scale photochemical synthesis of M@TiO2 nanocomposites (M = Ag, Pd, Au, Pt) and investigates their optical properties, catalytic activity for CO oxidation, and antibacterial effects. Well-dispersed M@TiO2 nanocomposites with particle diameters of 200-400 nm were synthesized using a clean photochemical method without additives. The sizes of the noble metal nanoparticles formed on the TiO2 support were approximately 1 nm for Pt, 5 nm for Au and Pd, and 2-20 nm for Ag. The nanocomposites exhibited excellent catalytic activity for CO oxidation at low temperatures. Tests also showed the nanocomposites had antibacterial effects against E
This document summarizes manipulation strategies for two-dimensional amorphous nanomaterials (2D ANMs) to enhance their performance in electrochemical energy storage and conversion applications. It discusses two main categories of manipulation: 1) geometric configuration design, including spatial structure design (e.g. creating porous structures) and coordination environment design (e.g. defect creation); and 2) component interaction, including elemental doping/coupling and heterophase compositing. Recent examples manipulating 2D ANMs through these approaches for applications in batteries, supercapacitors and electrocatalysis are reviewed. The document concludes by discussing opportunities to further optimize manipulation of 2D ANMs.
This document describes the synthesis and characterization of a core-shell structured reduced graphene oxide wrapped magnetically separable rGO@CuZnO@Fe3O4 microspheres photocatalyst and its use for the photoreduction of carbon dioxide to methanol under visible light irradiation. The photocatalyst takes advantage of the high photocatalytic efficiency of zinc oxide, the high surface area and charge carrier mobility of reduced graphene oxide, and the magnetic properties of an iron oxide core. Experimental results showed the rGO@CuZnO@Fe3O4 photocatalyst had higher catalytic activity than other possible combinations, with a methanol yield of 2656 μmol/gcat under visible light, and could be readily recovered and
Recent progress on reduced graphene oxide....suresh kannan
The document summarizes recent progress on using reduced graphene oxide (rGO)-based materials as counter electrodes for dye-sensitized solar cells (DSSCs) as a cost-effective alternative to platinum. It discusses how rGO on its own is not effective as a counter electrode but that adding metal nanoparticles to rGO composites improves their catalytic activity and performance in DSSCs. The document reviews various rGO composites that have been studied, including those with silver, nickel, tungsten and platinum nanoparticles, as well as metal oxides and dichalcogenides. It compares the photovoltaic parameters of DSSCs using these rGO composite counter electrodes to those using conventional platinum counter electrodes
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%.
HYDROGEN GENERATION FROM WASTE WATER BY USING SOLAR ENERGY | J4RV3I11004Journal For Research
Objective of this paper is to produce hydrogen which is an ideal fuel for the next generation because it is abundantly available in nature, energy efficient and clean. Wide varieties of technologies are available to produce hydrogen but only few of them are considered environmental friendly. Solar water splitting via photo catalytic reaction is one of them which have attracted tremendous attention. In this paper we are working on hydrogen production via solar splitting. Photo catalytic water splitting is one of the promising technologies to produce pure and clean hydrogen. Since it is reasonable having low process cost and has a small reactor, it can be made for house hold application and hence has a huge market potential. Generation of hydrogen under visible irradiation is the main area of work. Based on the literature reported here, visible irradiation can be achieved by doping of TiO2 with metal or non-metal. We have used Fe doping to increase the efficiency. The result indicates that Fe doped sieves produce more hydrogen than the normal TiO2 coated sieve and the efficiency can be increased if we increase the number of doped sieves and surface area.
This document discusses hydrogen production from photocatalytic water splitting using semiconductor materials. It begins by introducing alternative energies and hydrogen as an ideal fuel. It then discusses various methods of hydrogen production, focusing on solar-driven processes like thermochemical, photobiological, and photocatalytic water splitting. The document examines using titanium dioxide (TiO2) as a photocatalyst for water splitting and methods to improve its photoactivity, such as metal loading and doping. It also discusses high-efficiency photocatalytic systems and the types of photocatalytic water splitting reactions. In the end, it emphasizes the need for further research to develop new technologies for low-cost, environmentally friendly hydrogen production.
IRJET- Study of Single Chamber and Double Chamber Efficiency and Losses o...IRJET Journal
This document summarizes research on the efficiency and losses of single chamber and double chamber wastewater treatment using microbial fuel cells (MFCs). MFCs can concurrently treat wastewater and generate electricity by using microorganisms to break down organic matter and release electrons. The document compares different MFC designs, including single chamber and double chamber systems. Single chamber MFCs are simpler but have lower columbic efficiency due to oxygen diffusion into the anode chamber, while double chamber MFCs can maintain separate conditions in each chamber to improve efficiency. The document also discusses standard electrode potentials, treatment efficiencies, columbic efficiencies, and factors that affect MFC performance.
Sustainable Strategies for the Exploitation of End-of-Life Permanent MagnetsNOMADPOWER
Rare Earth Magnets (REM), especially the NdFeB type, are essential components in high-performance electric motors and wind turbines, playing an important role in the shift towards a low-carbon energy matrix. However, little work has been done to understand how the production of REM can be in line with the global sustainable transition. To overcome this lack and help with future research, as well as decision-making, this paper provides a literature overview of which aspects of sustainability are being investigated in the REM supply chain, and how each of them contributes to achieving Sustainable Development Goals (SDG). This research is developed through a consistent analysis of 44 peer-reviewed publications, followed by an analysis of strengths, weaknesses, opportunities, and threats. Four main subjects of studies were identified: environmental impact; social impact; economic aspects and circular economy. Most of the studies focus on computing the environmental impact through life cycle assessment and discussing techniques towards exploring the circular economy concept. In addition to contributing to a greener economy, the majors identified strengths of REM are the great potential of its supply chain in reducing primary resource extraction, since REM recovery and recycling seem to be viable, and the promising techniques to minimize environmental impacts along the rare earth elements production chain.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
The effect of band engineering of semiconductors on photocatalyic water split...eSAT Journals
Abstract
The direct conversion of solar energy using a photocatalyst in a water splitting reaction is a source of a sustainable and clean hydrogen supply. In general, photocatalysts are semiconductors that possess valence and conduction bands. These energy bands permit the absorption of photon energy to excite electrons in the outer orbitals of the photocatalysts. Photoexcited electron and hole pairs can subsequently induce a watersplitting reaction to produce hydrogen and oxygen. Photocatalytic water splitting is affected by the band level and crystallinity of the photocatalyst. Therefore, band engineering using chemical modifications such as cationic and anionic modification could createa photocatalyst suitable for the large-scale production of hydrogen. In this paper, cationic and anionic modifications of photocatalysts and the effects of these modifications onphotocatalytic water splitting are reviewed. Keywords: Water splitting; Photocatalysis; Hydrogen
Synthesis MgO nanopowder using Sol-gel technique: A critical reviewPratish Rawat
During the last decade, it has realized that when materials are synthesized to nanoscale dimensions, they will show new and remarkably improved physical and chemical properties. Due to its wide and major applications, in-depth investigations have been carried out on metal oxide nanomaterials. A significant amount of research is going on in synthesis and characterization of MgO/PVA nanocomposites. Some of the literature has been reviewed to get the idea about the synthesis and characterization of MgO/PVA nanocomposites using sol-gel technique.
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
This document summarizes the synthesis and characterization of halogen-doped carbon nitride nanosheets and BiOI heterojunctions for use in photoelectrochemical water splitting. Specifically:
1) Fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) nanosheets were synthesized using thermal annealing to improve light absorption and charge separation.
2) CNF-Cl nanosheets were combined with bismuth oxyiodide (BiOI) nanoplates via a hydrothermal method to form heterojunctions.
3) Characterization using TEM, XRD, Raman and EDS mapping confirmed the formation of CNF-Cl
Heterojunctions of halogen-doped carbon nitride nanosheets and BiOI for sunli...Pawan Kumar
A fluorine-doped, chlorine-intercalated carbon nitride (CNF-Cl) photocatalyst has been synthesized for simultaneous improvements in light harvesting capability along with suppression of charge recombination in bulk gC 3 N 4. The formation of heterojunctions of these CNF-Cl nanosheets with low bandgap, earth abundant bismuth oxyiodide (BiOI) was achieved, and the synthesized heterojunctions were tested as active photoanodes in photoelectrochemical water splitting experiments. BiOI/CNF-Cl heterojunctions exhibited extended light harvesting with a band-edge of 680 nm and generated photocurrent densities approaching 1.3 mA cm− 2 under AM1. 5 G one sun illumination. Scanning Kelvin probe force microscopy under optical bias showed a surface potential of 207 mV for the 50% BiOI/CNF-Cl nanocomposite, while pristine CNF-Cl and BiOI had surface photopotential values of 83 mV and 98 mV …
This document summarizes a research paper on dye sensitized solar cells (DSSCs). It provides background on the development of DSSCs since 1991 and their advantages over traditional silicon solar cells in terms of lower cost and simpler preparation. However, liquid electrolytes used in early DSSCs limited long-term performance. Recent research has focused on improving electrolytes, particularly developing quasi-solid state electrolytes, to enhance photoelectric performance and stability for practical applications of DSSCs. The document reviews progress on quasi-solid state electrolytes and their advantages over liquid electrolytes for DSSCs.
The Use of Artificial Photosynthesis to Power Hydrogen Fuel CellsJacob Saletsky
This document summarizes a student paper about using artificial photosynthesis to power hydrogen fuel cells. It discusses how artificial photosynthesis works by using solar energy, water, and catalysts like titanium oxide to split water into hydrogen and oxygen. It then explains how hydrogen fuel cells can use the hydrogen to generate electricity. The document argues that artificial photosynthesis is a promising renewable energy source because, like natural photosynthesis, its byproducts are harmless and materials are reusable. It also discusses the components and processes involved in artificial photosynthesis and hydrogen fuel cells.
This study is define on the nanotechnology with energy application. In this technology explain the energy conversion, generation, storage and transportation.it is in unique technique, capacity, great potential to fabricate new structure at atomic scale has produced novel material and devices. Its technique have great potential applications with wide fields.to required large no. of energy in the world.in present available energy is not sufficient for comparison on world requirement energy. That’s vision of fulfillment the required no. of energy by through this new technique.in hence present advance of the nanotechnology to suitable useful energy generation, production, storage and use. The main function and aim of this technology working from different fields, areas and points, to find out the better solutions. Which is the great challenge of our life?
Thermal Stability Investigation and Improvement: A Gateway to High Efficiency...IRJET Journal
This document summarizes research into improving the thermal stability and power conversion efficiency of organometal trihalide perovskite solar cells. The researchers used modeling software to simulate cell performance at different temperatures. They achieved a promising power conversion efficiency of 29.31% for their cell model. The simulations showed that higher temperatures negatively impact carrier concentration, band gaps, and mobilities, reducing efficiency. Unlike typical models that peak at 300K, this model's efficiency increased above 300K, peaking at 29.34% at 325K and remaining high up to 355K. This suggests improved thermal stability. The findings provide a useful reference for fabricating thermally stable, high-efficiency perovskite solar cells.
Similar to Recent progress in Tungsten disulphide based Photocatalyst for Hydrogen Production and Environmental Remediation.pdf (20)
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
Electric vehicle and photovoltaic advanced roles in enhancing the financial p...IJECEIAES
Climate change's impact on the planet forced the United Nations and governments to promote green energies and electric transportation. The deployments of photovoltaic (PV) and electric vehicle (EV) systems gained stronger momentum due to their numerous advantages over fossil fuel types. The advantages go beyond sustainability to reach financial support and stability. The work in this paper introduces the hybrid system between PV and EV to support industrial and commercial plants. This paper covers the theoretical framework of the proposed hybrid system including the required equation to complete the cost analysis when PV and EV are present. In addition, the proposed design diagram which sets the priorities and requirements of the system is presented. The proposed approach allows setup to advance their power stability, especially during power outages. The presented information supports researchers and plant owners to complete the necessary analysis while promoting the deployment of clean energy. The result of a case study that represents a dairy milk farmer supports the theoretical works and highlights its advanced benefits to existing plants. The short return on investment of the proposed approach supports the paper's novelty approach for the sustainable electrical system. In addition, the proposed system allows for an isolated power setup without the need for a transmission line which enhances the safety of the electrical network
Embedded machine learning-based road conditions and driving behavior monitoringIJECEIAES
Car accident rates have increased in recent years, resulting in losses in human lives, properties, and other financial costs. An embedded machine learning-based system is developed to address this critical issue. The system can monitor road conditions, detect driving patterns, and identify aggressive driving behaviors. The system is based on neural networks trained on a comprehensive dataset of driving events, driving styles, and road conditions. The system effectively detects potential risks and helps mitigate the frequency and impact of accidents. The primary goal is to ensure the safety of drivers and vehicles. Collecting data involved gathering information on three key road events: normal street and normal drive, speed bumps, circular yellow speed bumps, and three aggressive driving actions: sudden start, sudden stop, and sudden entry. The gathered data is processed and analyzed using a machine learning system designed for limited power and memory devices. The developed system resulted in 91.9% accuracy, 93.6% precision, and 92% recall. The achieved inference time on an Arduino Nano 33 BLE Sense with a 32-bit CPU running at 64 MHz is 34 ms and requires 2.6 kB peak RAM and 139.9 kB program flash memory, making it suitable for resource-constrained embedded systems.
Optimizing Gradle Builds - Gradle DPE Tour Berlin 2024Sinan KOZAK
Sinan from the Delivery Hero mobile infrastructure engineering team shares a deep dive into performance acceleration with Gradle build cache optimizations. Sinan shares their journey into solving complex build-cache problems that affect Gradle builds. By understanding the challenges and solutions found in our journey, we aim to demonstrate the possibilities for faster builds. The case study reveals how overlapping outputs and cache misconfigurations led to significant increases in build times, especially as the project scaled up with numerous modules using Paparazzi tests. The journey from diagnosing to defeating cache issues offers invaluable lessons on maintaining cache integrity without sacrificing functionality.
Understanding Inductive Bias in Machine LearningSUTEJAS
This presentation explores the concept of inductive bias in machine learning. It explains how algorithms come with built-in assumptions and preferences that guide the learning process. You'll learn about the different types of inductive bias and how they can impact the performance and generalizability of machine learning models.
The presentation also covers the positive and negative aspects of inductive bias, along with strategies for mitigating potential drawbacks. We'll explore examples of how bias manifests in algorithms like neural networks and decision trees.
By understanding inductive bias, you can gain valuable insights into how machine learning models work and make informed decisions when building and deploying them.
Harnessing WebAssembly for Real-time Stateless Streaming PipelinesChristina Lin
Traditionally, dealing with real-time data pipelines has involved significant overhead, even for straightforward tasks like data transformation or masking. However, in this talk, we’ll venture into the dynamic realm of WebAssembly (WASM) and discover how it can revolutionize the creation of stateless streaming pipelines within a Kafka (Redpanda) broker. These pipelines are adept at managing low-latency, high-data-volume scenarios.
DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELgerogepatton
As digital technology becomes more deeply embedded in power systems, protecting the communication
networks of Smart Grids (SG) has emerged as a critical concern. Distributed Network Protocol 3 (DNP3)
represents a multi-tiered application layer protocol extensively utilized in Supervisory Control and Data
Acquisition (SCADA)-based smart grids to facilitate real-time data gathering and control functionalities.
Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
Presentation of IEEE Slovenia CIS (Computational Intelligence Society) Chapte...University of Maribor
Slides from talk presenting:
Aleš Zamuda: Presentation of IEEE Slovenia CIS (Computational Intelligence Society) Chapter and Networking.
Presentation at IcETRAN 2024 session:
"Inter-Society Networking Panel GRSS/MTT-S/CIS
Panel Session: Promoting Connection and Cooperation"
IEEE Slovenia GRSS
IEEE Serbia and Montenegro MTT-S
IEEE Slovenia CIS
11TH INTERNATIONAL CONFERENCE ON ELECTRICAL, ELECTRONIC AND COMPUTING ENGINEERING
3-6 June 2024, Niš, Serbia
Batteries -Introduction – Types of Batteries – discharging and charging of battery - characteristics of battery –battery rating- various tests on battery- – Primary battery: silver button cell- Secondary battery :Ni-Cd battery-modern battery: lithium ion battery-maintenance of batteries-choices of batteries for electric vehicle applications.
Fuel Cells: Introduction- importance and classification of fuel cells - description, principle, components, applications of fuel cells: H2-O2 fuel cell, alkaline fuel cell, molten carbonate fuel cell and direct methanol fuel cells.
2. Chemical Engineering Journal 424 (2021) 130393
2
field of photocatalysis [22].
In 1972, Fujishima and Honda reported the photoelectrocalalytic
splitting of water by using the TiO2 electrode as a photoanode and Pt
cathode under UV light [23]. In 1976 Carey et al. discovered the
degradation of organic pollutants on powdered TiO2 photocatalyst [24].
Some metal oxide semiconductor such as TiO2 [25–28], ZnO [29–33],
ZrO2 [34–37]and CeO2 [38–41] can act as photocatalyts for solar energy
conversion and environmental remediation, this wide band gap metal
oxide materials absorb only UV light. In terms of solar spectrum ac
counts 5% of UV light, 45% of visible light (400–700 nm) and 50% of
Infrared light (above 700 nm), Therefore, the photocatalytic activity of
metal oxide semiconductor under solar light irradiation is not sufficient
[42–44]. Additionally, metal sulphide (CdS [45–47], and ZnInS4
[48–50]), carbon-based materials [51–55] and metal organic frame
works [56,57] are widely used to utilize more visible light from the solar
energy in the field of photocalysis, but their photocatalytic efficiencies
are quite limited due to its quick recombination of photo-generated
charge carrier. When cocatalyst loaded on the surface semiconductor
photocatalyst surface significantly accelerate the visible light absorption
and reduce the charge recombination rate and enhance the efficiency of
the photocatalytic system [58,59]. These cocatalysts are classified into
two types (i) noble metal-based cocatalyst, (ii) non-noble-metal based
cocatalyst [60–62]. Noble metal cocatalyst such as Ag [63], Au [64,65],
Pt [66–69] and Ru [70–72] are highly desirable to enhance the photo
catalytic activity of semiconductor-based photoctalyst. However, the
low abundance and high cost of noble metals significantly hindered their
practical applications. Therefore, the development of earth abundant
and low-cost co-catalyst combined semiconductor photocatalyst along
with high visible light absorpion and high stability is still a big challenge
for its practical application.
During the past few years, many transition metal sulphide and metal
oxide has been used as a noble metal-free co-catalyst for semiconductor
photocatalysis, which includes NiS [73–76], Cu2O [77,78], NiCo2O4
[79–81], and WS2 [82]. Among these, WS2 has attracted much attention
due to its excellent optical absorption properties, good stability, low
cost, and environmental friendliness. However, WS2 exhibit excellent
performance under visible light and infra-red radiation due to their good
photogenerated electron-hole pair transportation capacity, boosting the
lifetime of photogenerated carriers [83,84]. Additionly, modifications of
semiconductor photocatalyst by WS2 is much meaningful strategy to
improve the photocatalytic activities of semiconductor based photo
catalysis, which can reduce the fast recombination of photogenerated
electrons of semiconductor photocatalyst. From Fig. 1, the number of
articles on WS2 catalyst and WS2 photocatalyst has increased
dramatically over the past 8 years, and more than 150 papers has been
published. With respect to catalysis and photocatalysis in WS2, there is
significant improvement in number of publications since 2018. Notably
WS2 serve as a new research direction for the development of a novel
photocatalytic system for energy conversion and environmental
remediation.
Herein, we begin by describing synthesis route, different morphol
ogies and brief sketch properties of WS2. A brief discussion of the WS2
supported metal oxide, metal sulphide, carbon based materials, silver-
based materials and bismuth-based materials photocatalysts is then
provided. While various plausible photocatalytic mechanisms of
photogenerated-electrons and holes in WS2 composite should be pro
posed. The applications of WS2 cocatalyst in the photocatalytic
hydrogen production, organic contaminant degradation and Cr(VI)
removal. This review may offer motivation for designing and fabricating
novel and efficient WS2 based composite photocatalysts for highly effi
cient photocatalytic applications.
2. Synthesis of WS2 based composites
The synthesis method plays an essential role in the fabrication of the
photocatalyst. As well known, the photocatalytic efficiency of different
photocatalyst suffers from their morphology, crystallite size, and shape,
which can be controlled by changing their synthesis parameter [85–87].
Therefore, in this section, we reviewed the important strategies for the
synthesis of WS2 and WS2 based composites. The key to the successful
synthesis of WS2 composites is to control the sulfurization by different
reaction condition for preferential morphologies and uniform growth.
The synthesis methods and properties of WS2 and composites are shown
in Table 1. Till to date, a variety of synthetic methods have been
established, which can be categories into (i) hydrothermal method [88].
(ii) solvothermal method and (iii) calcination method
2.1. Hydrothermal method
The hydrothermal method is a very powerful approach to synthesize
various nanoscale materials. Such a method operates on elevated tem
peratures and water as a solvent in confined volume to create high
pressure. The product crystal growth is widely depends on the solubility
of the precursor [89,90]. By carefully analysing the previous reports on
the synthesis of WS2 and WS2 based composite material by the hydro
thermal route, we can understand that the hydrothermal approach could
be used to prepared WS2 nanomaterials with various morphologies,
nanowire, nanoflower and nanosphere. Cao et al., prepared WS2 with
different morphologies via hydrothermal route, by changing the amount
of CTAB. This result showed that many irregular nanosheets are formed
in the reaction time for 4 hrs. The reaction time extended to 24 h, a
number of nanosheets assembled to provide flowerlike morphology.
Additionally, CTAB molecules also help to assemble the sheet like
morphology into 3D flowerlike morphology. Furthermore, the
morphology of the prepared WS2 can be controlled by the primary fac
tors, reaction temperature, and reaction duration. This results demon
strated that changing the experimental conditions has a crucial role in
the morphology of WS2 [91]. Hydrothermal growth of WS2 based
composites preparation classified into two types; i) In situ hydrothermal
growth ii) solution based mixing method.
2.1.1. In-situ hydrothermal growth
In-situ the strategy involves the growth of WS2 on other semi
conductors under hydrothermal condition, which can help to the uni
form growth of WS2. Wu et al., have revealed that the uniform coating of
layered WS2 (~4 layers) on TiO2 nanosheets by using sodium tungstate
and L- cysteine as a precursor. During the hydrothermal reaction, the W
= O bonds connected with plate-to-plate stacked structured TiO2
nanosheets. The hydrothermal synthesis bare WS2 exist microsphere
structure and it has petal-like features, which can be achieved by WS2
Fig. 1. Number of scientific articles published on WS2 based material over the
past decade ((source: http://www.Sciencedirect.com; Search term: “WS2 cata
lyst” and “WS2 photocatalyst”).
M. Sridharan and T. Maiyalagan
3. Chemical Engineering Journal 424 (2021) 130393
3
nanosheets are combined together. When the hydrothermal growth of
WS2 on TiO2 nanosheets, the TiO2 surface changed to rough. The loading
amount of WS2 can be controlled by changing the ratio of TiO2 and W
source concentration [92].
2.1.2. Solution based mixing method
Almost all the solution mixing methods follows the two-step process.
WS2 nanocrystals are usually prepared by using a hydrothermal
approach and then using other methods to combine WS2 cocatalyst with
other semiconductors to form composites. Gopannagari et al., prepared
the few-layer WS2-CdS composite. In this composite preparation first
step is the hydrothermal synthesis of few-layer WS2 by using thio
acetamide and tungsten chloride precursors. Here thioacetamide plays
dual role as a reducing agent and sulphur source. The second step pre
pared WS2 and CdS dispersed in DMF then exfoliated by ultrasonication
the scheme was predicted in Fig. 2 (a) [93]. J. Zhou et al. reported the
fabrication of WS2 sheets- ZnIn2S4 particles. The sheet like WS2 was first
synthesized, and then these nanosheets were dispersed with water by
using ultrasonication. Next, the WS2 sheets were linked to these ZnIn2S4
via simple hydrothermal method. Finally, the loading amounts of WS2
were controlled by changing the WS2:ZnIn2S4 ratio [94].
2.2. Solvothermal method
The solvothermal method was established from the hydrothermal
method, the solvent usage is one of the main differences between the
two methods. While hydrothermal method using water as a solvent but
the solvothermal method is organic solvents are used to disperse the
reaction precursor, this organic solvent act as a reducing agent and also
inhibit the aggregation of nanoparticle, due to their high viscosity [95].
Xiao et al., prepared the WS2 quantum dots by sonication solvothermal
method using bulk WS2, and then the hydrothermally prepared BiOCl
dispersion was mixed with the WS2 quantum dots in ethanol solvent, the
obtained mixture stirring 24 h at room temperature to form the WS2/
BiOCl composite (Fig. 2(b)). Similarly, WS2 was also synthesized by a
sonicatication solvothermal method using bulk WS2 as a precursor and
DMF is solvent. Then obtained WS2 coupled with BiOCl through the one-
pot hydrothermal method, during this one-step reaction, the Bi3+
was
hydrolyzed to produce the BiO+
ions. Then, layered structured
[Bi2O2]2+
obtained through BiO+
and Cl-
was inserted into the layered
structure. Simultaneously, the negative charged WS2 QDs were inter
acted by the positive charged BiO+
ions, resulting in a uniform and tight
distribution of WS2 quantum dots on BiOCl [96]. Guiping et al., reported
Table 1
Synthesis method and properties of WS2.
S.No Catalyst WS2 Synthesis method Morphology of WS2 Surface area (m2
/g) Band gap (eV) References
1 WS2/CdS Hydrothermal nanosheet 93
2 WS2/WO3 Solvothermal 3D flower 97
3 WS2/g-C3N4 Calcination method nanoparticles 25 98
4 WS2/g-C3N4 Calcination method nanosheet 1.35 99
5 WS2/g-C3N4 Calcination method sandwich 40.64 1.44 100
6 WS2/In2.77S4 Calcination method nanosheet 99.8 1.66 102
7 WS2/MoS2 Calcination method nanoparticles 1.7 103
8 WS2/AgI Calcination method nanosheet 1.6 104
9 WS2 Hydrothermal flower-like nanosphere 1.35 91
10 WS2 Solvothermal flower like nanorod 115
11 WS2 Hydrothermal mesoporous 197 1.44 114
12 WS2 Hydrothermal hexagonal platelets 94.6 1.91 113
13 WS2 Hydrothermal nanosheet 7.5 1.99 116
14 WS2 Hydrothermal nanorod 10.8 1.92 116
Fig. 2. Schematic representation of synthesis of WS2 composites (a)WS2/CdS (Reprinted with permission from Ref [93] copyright from Elsevier), (b) WS2/BiOBr
(Reprinted with permission from Ref [96] copyright from RSC), (c) WS2/WO3 (Reprinted with permission from Ref [97] copyright from MDPI), (d) WS2/g-C3N4
(Reprinted with permission from Ref [100] copyright from Elsevier), (e) β-Bi2O3/ WS2 (Reprinted from Ref [111] with permission from the Chinese Chemical Society
(CCS), Peking University (PKU), and the Royal Society of Chemistry).
M. Sridharan and T. Maiyalagan
4. Chemical Engineering Journal 424 (2021) 130393
4
WS2 coupled with WO3 can be obtained by the solvothermal synthesis of
WS2, N-methyl-2-pyrrolidone was used as the solvent to enhance the
vulcanization of tungstic chloride, and followed by partial oxidation
method introduced to produce WS2/WO3 hybrid material, the schematic
representation of WS2/WO3 are shown in Fig. 2(c) [97].
2.3. Calcination method
The calcination method has been widely used to prepare WS2 and its
composite photocatalysts. For example, Yidong et al., reported the
mesoporous graphitic carbon nitride–WS2 composite. They used
(NH4)2WS4 as a precursor and impregnation combined calcination
method to produce the WS2/g-C3N4 composite under the flowing of 10%
H2S–90% H2 gas mixture [98]. Huu et al., reported the synthesis of WS2/
g-C3N4 composite by solid state calcination of tungstic acid and thio
urea. In this case, thiourea acted as a sulphur source for WS2 and pre
cursor of g-C3N4. The loading amount of WS2 in the composites
controlled by changing the concentration of thiourea [99]. Dongyao et
al., also fabricated sandwich-structured WS2/g-C3N4 composite by one-
pot calcination process, during this process WO3 and thiourea as starting
material for WS2 and g-C3N4, then uniformly grinded mixture calcinated
under Ar atmosphere, the synthesis scheme of WS2/g-C3N4 are shown in
Fig. 2(d) [100]. Similarly, Zhou et al., reported WS2/g-C3N4 composite
prepared by one step calcination method using sodium tungstate and
thiourea, during this one-step reaction, changing the concentration of
sodium tungstate to altering the WS2 content [101]. Wu Xiang-Feng et
al., reported the fabrication of WS2/In2.77S4. The Wrinkled WS2 nano
sheets were synthesized by calcination of WO3 and thiourea under N2
atmosphere, and then these nanosheets linked to In2.77S4 through the in-
situ hydrothermal method [102]. Li et al., synthesized a composite of
dual-petals nanostructured WS2@MoS2, Firstly, ball milling combined
calcination of WO3 and S to produce WS2, and then these WS2 coupled
with MoS2 by hydrothermal method [103]. Finally, Xieng-Feng et al.,
reported WS2/AgI hybrid. They used calcination of WO3 and thiourea to
produce WS2, and then coupled with AgI by in-situ method [104].
Dongmei et al., designed WS2/TiSi2 composites, in this work ball-milled
TiSi2 and (NH4)2WS4 calcinated under Ar atmosphere to produce WS2/
TiSi2 composites by changing the weight ratio of (NH4)2WS4 and TiSi2 to
control the content of WS2 [105].
2.4. Sonication assisted method
Recently, the sonication method has been widely used for the
fabrication of novel nanomaterials with unusual properties. The chem
ical effects of sonication arise from acoustic cavitation. When, the liq
uids are irradiated through sonication, the compressive and alternating
expansive acoustic waves generate bubbles and the bubbles are oscil
lated. The oscillated bubbles can effectively store ultrasonic energy, very
short time implosive collapse of bubbles producing concentrated energy,
using this extreme condition to prepare various nanomaterials [106]. Xu
et al., have employed ultrasound-assisted liquid exfoliation method to
produce ultrathin WS2. The bulkWS2 dispersed in NMP and then soni
cated (150 W output power) to obtain ultrathin WS2 NSs, The growth of
Cu on the surface of the WS2 through the photochemical method [107].
Yajun et al., also reported the preparation of CdS/WS2/CN composite.
They used Bulk WS2 as a starting materials and 1-methyl-2-pyrrolidine
(NMP) as a dispersion medium. The NMP dispersed bulk WS2 soni
cated for 5 h resulted in the WS2 sheets and then coupled with g-C3N4
and CdS [108]. Yueyao et al., used a similar strategy and water as a
dispersion medium to prepare the WS2 then coupled with ZnS [109].
Furthermore, some sonication methods can use a mixture of solvent as a
dispersion medium for exfoliated WS2 from bulk WS2. For example Atkin
et al., fabricated WS2/carbon dot composite, the 2D WS2 was first syn
thesized by grinding sonication of bulk WS2 and mixture of water and
ethanol solution as a dispersion medium and then coupled with carbon
dot to obtain WS2/carbon dot composite [110]. Similarly, Li et al et al.,
synthesized the WS2@Bi2O3 heterojunction. The n-type ultrathin WS2
nanosheets exfoliated from a mixture of solvent methanol and water
dispersed bulk WS2 through 48 h sonication (Fig. 2(e)). Then ultrathin
WS2 nanosheets loaded on solvothermal prepared β-Bi2O3 hollow mi
crospheres through a simple stirring method [111].
3. Properties of WS2
WS2 exhibit excellent photocatalytic properties and good visible
light absorption capacity, and it is enormously used as a cocatalyst for
photocatalysis, such as photocatalytic dye degradation and photo
catalytic hydrogen production. Tungsten disulfide (WS2) has layered
structure, which is analogy to graphite-like structure, this layer consist
of unit S–W–S atomic trilayers. Each layer constructed by W atoms
sandwiched between two sulphur atoms. Bulk WS2 has a layered
structure stacked together by van der Waals force. The W-S covalent
interaction within the layer is stronger than van der Waals interaction
between neighbouring unit, therefore plane sliding is allowed [91]. WS2
nanosheets have large surface area, which helps to enhance the binding
or loading of nanoparticles. Bulk WS2 (which contain less than five
monolayer) are reduced to a single monolayers, which undergoes
indirect-to-direct gap transition [107,108]. Its narrow band gap of 1.5
eV is highly encouraging to absorb visible light. WS2 have excellent
visible light absorption ability compared with metal oxide (TiO2 [25],
ZnO [29], CeO2 [41]), metal sulphide (CdS [45], ZnInS4 [48],) carbon
based materials (g-C3N4 [53]). A detailed understanding of the funda
mental properties of WS2 and WS2 based composite is quite necessary for
the further improvement of related photocatalytic applications [112].
Unique properties of WS2 are described in the following section,
including the morphology, optical properties, and photo corrosion in
hibition ability.
3.1. Morphology
The morphology of WS2 has a significant role in their electrical and
optical properties, thus determining their photocatalytic efficiency. In
the following section, the morphological feature of WS2 photocatalyst
was briefly summarized. Scrutinizing the specific morphological rela
tion between the WS2 photocatalysts and its photocatalytic performance
not only plays an essential role in boosting the performance of WS2
photocatalysts but also helps to induce the potential utilization of WS2
based composite photocatalysts [83]. Many researchers have reported
the photocatalytic behavior of WS2 photocatalysts with specific
morphology. Cao et al., synthesized Flower-like WS2 nanosphere (Fig. 3
(a,b)) via hydrothermal method using CTAB as a surfactant. They also
reported that CTAB was considered to be a crucial role in growing the
flower like morphology. The interaction forces of inside the CTAB helps
to made uniformly grown flower like morphology. The obtained flower
like sphere shows excellent light absorption ability and it may have
potential applications as a visible light active catalyst [91]. Same group
prepared nanospheres (Fig. 3 (c,d)), nanorods (Fig. 3(e,f)) and nanobelts
(Fig. 3 (g,h)) by hydrothermal method using CTAB as a surfactant. The
three different morphologies were obtained by changing the concen
tration of CTAB. The light absorption properties of the prepared nano
structure were investigated by UV–Visible spectroscopy analysis, this
result shows all WS2 have blue shift compared to bulk WS2, which in
dicates the presence of strong quantum confinement effect in the WS2
nanostructure [84]. Vattikuti et al., reported group reported the prepa
ration of hexagonal WS2 platelets (Fig. 3(i,j)) by hydrothermal method.
The reaction time and temperature influence the uniform morphology of
WS2. Through FESEM results, they found that when the reaction tem
perature is 150 ◦
C, only hexagonal WS2 platelets were obtained. They
have demonstrated the WS2 platelets results in good photocatalytic ac
tivity, due to their good stability and open reactive sites [113].
Numerous efforts have been devoted to synthesize a 2-dimensional
metal sulphide semiconductor for its various applications. Moreover,
M. Sridharan and T. Maiyalagan
5. Chemical Engineering Journal 424 (2021) 130393
5
most researchers to date reported that the morphology dependence of 2-
dimensional nanosheets materials for photocatalytic application. The
nanosheet like structured WS2 can be prepared by using various
methods. Vattikuti et al., reported the synthesis of mesoporous WS2
nanosheets by a hydrothermal approach with cetyltrimethylammonium
bromide (CTAB) used as a surfactant. The mesoporous WS2 nanosheets
exhibit high photocatalytic activity, due to their higher surface area
(197 m2
g− 1
) [114]. A hydrothermal method was reported by Yong-
Chuan et al., for hyacinth flower-like WS2 nanorods synthesis in the
presence of L-cysteine as a sulphur source at 200 ◦
C. The hydrothermally
synthesized flower-like WS2 nanorods (Fig. 3(k,l)) showed a length in
the range of 2.00 μm and diameters 0.42 μm, which exhibit good pho
tocatalytic performance [115]. Waseem et al., prepared WS2 nanorods
and nanosheets by using hydrothermal technique and thiourea as a
sulphur source. In this study, the authors have come up with an inter
esting result as they have synthesized nanorods and nanosheets both
under the hydrothermal condition and CTAB as a surfactant. The WS2
nanosheets were formed at pH 6.15 and WS2 nanosheets at pH 7.25. WS2
nanosheet has shown better photocatalytic performance than WS2
nanorod, due to their enhanced pore size [116].
3.2. Optical absorption property
Light absorption is the primary step in the photocatalytic reaction,
measuring the efficiency of a photocatalyst by absorbing light energy to
create efficient electron-holepairs for the catalytic reaction. The ab
sorption of visible and NIR regions in the solar spectrum is playing an
essential role in photocatalysis. Different types of metal oxide, metal
sulphide, and metal carbide have been used as a photocatalyst for
environmental pollution remediation. Unfortunately, most of the semi
conductor is absorbing only UV light, and these materials not effective
under visible and NIR region. More recently WS2 is widely used as a
UV–Visible and NIR absorbing materials for solar cell and photocatalytic
applications [117]. To understand the effect of WS2 deposited semi
conductor on light-harvesting ability, optical band gap, valance band
(VB), and conduction band (CB) edges of the semiconductor. For
example, WS2 nanosheet composited with g-C3N4, the UV–Visible
diffuse reflectance spectroscopy was used to demonstrate that WS2 helps
to enhance the UV–Visible and NIR absorption ability of bare g-C3N4.
Accordingly, UV–vis DRS spectra and Tauc’s plot employed to measure
the optical band gap of semiconductor photocatalyst [99]. Moreover,
the flat band potential is helpful to estimate the electronic band struc
tures of photocatalyst, which can be measured through the Mott-
Schottky plot. Basically, the plot band potential of P-type semi
conductor is located to their VB edge and n-type semiconductor plot
band potential value is located to their CB edge. In fact, such an
enhanced Visible and NIR light absorption has also been comprehen
sively studied in other works on the WS2 based photocatalysts. For
example, Xiang-Feng and co-workers designed that the fabrication of p-n
heterojunction through the combination of In2.77S4 and WS2, Moreover
WS2 enhance the visible and NIR light absorption of In2.77S4 [102]. In
similar cases, the WS2 quantum dots coupled with Bi2S3 [118], and WS2
nanosheet combined with ZnS. This finding shows a sensitive response
to visible light [109]. Zhang et al., designed WS2/CdS composite, bare
CdS shows the absorption edge at 520 nm (Fig. 4 (a)). But WS2 nano
sheets combined CdS exhibit remarkable light absorption at a higher
wavelength than 520 nm. Fig. 4 (b) shows the after mixing of WS2 and
CdS to minimize the emission intensity of pure CdS [119].
3.3. Photocorrosion stability
To date, the researcher focused on improves the photocorrosion in
hibition of semiconductors for photocatalytic application. However, the
photocatalytic system affects from photocorrosion under illumination,
photogenerated electron and hole involve the decomposition of a pho
tocatalyst, which result in the photocatalytic activity steadily decreased
with increases the irradiation time. Basically, the photocorrosion of
semiconductor photocatalys depends on the arrangement of conduction
band minimum relates to reduction potential or valance band maximum
relates to oxidation potential [120]. When, photocatalyst with a valance
band maximum lower than oxidation potential (O2/H2O) will deterio
rate from oxidation by unconsumed holes (for example. ZnS). Likewise,
the photocatalyst with conduction band minimum higher than reduction
potential (H+
/H2) will affect from reduction by unconsumed electrons
(CdS) [121]. Zhong et al., designed broad spectrum responded WS2/ZnS
photocatalyst for hydrogen production. The lower photocatalytic
hydrogen production of bare ZnS is lower, due to their higher band gap
(3.8 eV), the fast recombination of photogenerated charge carriers, and
the photo corrosion occurred by photogenerated holes. The band gap
value and valence band edge of WS2 is 1.18 eV and 1.76 eV respectively.
Thus, WS2/ZnS composite, CB position of WS2 is lower than that of ZnS.
The VB of ZnS is more positive than WS2. Therefore, WS2/ZnS composite
follow type-I heterojunction mechanism, which means that, the photo
genrated electron transfer from ZnS CB to photocatalytic hydrogen
production active sites on WS2 surface. The photogenrated holes transfer
from ZnS VB to WS2 VB. Then, the WS2 VB having photogenerated holes
are depleted by sacrificial agent, and protecting the ZnS nanoparticle
corrosion [109].
Zhong et al., introduced the CdS/WS2 heterostructure for H2 pro
duction. Under illumination, CdS dissolved to Cd2+
and S2-
, due to the
photocorrosion. When increase the illumination time with Cd2+
and S2-
concentration also increased in the solvent. Under irradiation, CdS/WS2
Fig. 3. (a&b) SEM image of nanoflower (Reprinted with permission from Ref [91]copyright from Springer), (c&d) nanosphere, (e&f) nanowire, (g&h) nanobelt
(Reprinted with permission from Ref [84] copyright from IET), (i&j) hexagonal WS2 platelets (Reprinted with permission from Ref [113] copyright from Elsevier), (k)
SEM image of flower like nanorod and (l) TEM image of flower like nanorod (Reprinted with permission from Ref [115] copyright from Elsevier).
M. Sridharan and T. Maiyalagan
6. Chemical Engineering Journal 424 (2021) 130393
6
having large size CdS dissolved to Cd2+
and S2-
and then S2-
easily
connects with the sulphur vacancies of WS2. According to the rate-
theory analysis of surface roughness, the CdS recrystallization rate is
lower. It produces smaller size and uniformly distributed CdS nano
particles on WS2 surface. After 100 h recycling reaction dissolution and
recrystallization reaches equilibrium and the H2 production rate remain
unchanged. This results in accordance with Inductively Coupled Plasma-
atomic emission spectroscopy (ICP-AES) analysis result, the concentra
tion of W4+
, Cd2+
and S2-
are 15.2, 51.52 and 12.66 ppm (Fig. 4(c,d)) in
solution respectively, after 90 h recycling reaction. CdS/WS2 having
Cd2+
and S2-
concentration is lower than pure CdS concentration in
solution. This results demonstrate that photocorrosion- recrystallization
led to enhance the photocatalytic activity. The recrystallization process
and photocorrosion effect of CdS/WS2 composites are schematically
shown in Fig. 4(e) [122].
4. Basic principles of photocatalytic activity
In semiconductor photocatalysis, Initiate or accelerate the reduction
and oxidation reaction by the photocatalyst under illumination.
Generally the photocatalytic mechanism involves the following steps
(Fig. 5), Firstly generating photoelectrons from the excitation of valance
band to conduction band, holes are generated in the valance band.
Secondly, photogenrated electrons and holes move to the surface.
Thirdly, The CB electrons have +0.5 to 1.5 V chemical reduction po
tential versus normal hydrogen electrode (NHE) and reveal strong
reduction ability, VB holes having strong oxidative potential. Both
photogenerated electrons and holes can acts as a oxidant and reductant
Fig. 4. (a) UV–Visible spectra, (b) Photoluminescence spectra of CdS/WS2 (Reprinted with permission from Ref [119] copyright from ACS), (c) The amount of Cd2+
and S2-
decomposed from CdS, (d) The amount of Cd2+
and S2-
decomposed from CdS/WS2, (e) Schematic representation of photo corrosion effect of CdS and
recrystallization of CdS on WS2 nanosheet (Reprinted with permission from Ref [122] copyright from Elsevier).
M. Sridharan and T. Maiyalagan
7. Chemical Engineering Journal 424 (2021) 130393
7
and its react with semiconductor surface desorbed electron donar and
electron acceptor. The excited state electron and holes can recombine
and deplete the input energy is released in the form of light or heat. The
excited electron involve different reactions for phohocatalytic hydrogen
production, Cr(VI) reduction and organic dye degradation. (i) The
excited electrons involve the reduction of H+
to H2 (For photocatalytic
hydrogen producton), (ii) The excited electron undergo the reduction of
Cr(VI) to Cr(III) (For photocatalytic Cr(VI) reduction), (iii) The excited
electron reduce the surface adsorbed oxygen species to .
O2
–
, subse
quently, active anion radical degraded the pollutants. The crystal defects
or scavengers are served as a recombination centre for electron and
holes. The crystal defects not only acted as active site and also induce the
recombination. Therefore, good crystalinity with controlled defect is
reducing the recombination and combined with other cocatalyst, which
involves the enrichment in separation of photogenerated electron-hole
pairs and electrical conductivity. Based on the photocatalysis working
principle, the recombination of photogenerated electron and the hole is
adverse effect on the efficiency of a semiconductor based photocatalysis
[20,27,123,124]. For good photocatalytic efficiency, the effective sep
aration of photogenerated charge carrier and reduce the fast recombi
nation of photogenerated electrons. To develop the photocatalyst
activity and visible light absorption, the access that has mostly applied
to form semiconductor photocatalyst coupled with cocatalyst.
5. WS2 based composites
Coupling WS2 with other semiconductor materials including, metal
oxide, metal sulphide, carbon-based nanomaterials and Ag, Bi-based
materials can affect the photocatalytic activity in comparison with
pure semiconductor photocatalyst. The, construction of WS2 hybrids and
their nanocomposites is a suitable approach for the future development
of WS2-based photocatalysts. This review describes the WS2 based
hybrid nanostructures which were applied to investigate the photo
catalytic activity. The photocatalytic dye degradation and hydrogen
production efficiency of WS2 based composites are shown in Tables 2
and 3.
Fig. 5. The schematic representation of cocatalyst supported semiconductor
photocatalytic mechanism.
Table 2
Summary of WS2 Based Composites for Photocatalytic Dye Degradation.
S.
no
Catalyst Catalyst loading
(mg)
Contaminant
concentration
Light source Contaminant Reaction
duration
Degradation
efficiency
References
1 WS2 100 30 ppm UV and Sunlight malachite
green
120 mins 71.20% 83
2 Hexagonal WS2 5 10 ppm 300 W Xe lamp/Visible
light
Rhodamine-B 300 mins 97% 113
3 Mesoporus WS2 100 100 mL of 4 ppm 150 W UV lamp Rhodamine-B 30 mins 97% 114
4 Flower like WS2 50 50 mL of 20 ppm 500 W Xe lamp/Visible
light
Rhodamine-B 270 mins 91% 115
5 WS2 nanosheet 50 100 mL of 5 ppm 100 W Xe lamp Methylene
blue
60 mins 99.83% 116
6 WS2 nanodots/
TiO2
20 100 mL of 20 ppm 300 W Xe lamp Rhodamine-B 120 mins 86.10% 127
7 WS2/N-doped
TiO2
50 100 mL of 20 ppm 500 W Tungsten lamp Congo red 300 mins 94% 128
8 WS2/Bi2O3 40 40 mL of 10 ppm 500 W/Visible light ofloxacin 60 mins 85% 111
9 WS2/MoS2 100 100 mL of 40 ppm 500 W/Visible light Methylene
blue
120 mins 95% 103
10 WS2Q.Dots/
BiOCl
20 100 mL of 20 ppm 300 W Xe lamp/Visible
light
Rhodamine-B 20 mins 80.10% 96
11 WS2/g-C3N4 100 90 mL of 30 ppm 100 W/Visible light methylene
blue
6 h 85.30% 99
12 WS2/AgI 50 150 mL of 10 ppm 300 W/Visible light Rhodamine-B 30 mins 91.2 104
13 2D WS/Carbon
dots
0.24 1 ppm 150 W Xe lamp/Visible
light
Congo red 10 mins 12% 110
14 Bi2S3/WS2 20 100 mL of 5 ppm 300 W Xe lamp Methyl orange 90 mins 88.40% 147
15 WS2/MoS2 25 50 mL of 10 ppm 300 W Xe lamp Rhodamine-B 40 mins 93% 150
16 WS2/BiOCl 50 100 mL of 10 ppm 500 W Xe lamp Malachite
green
45 mins 98.4% 160
17 WS2/BiOCl 50 100 mL of 10 ppm 500 W Xe lamp Cr(VI) 120 mins 94.90% 160
18 WS2/BiOBr 40 40 mL of 10 ppm 500 W Xe lamp/visible
light
Lanasol red 5B 40 mins 99% 164
19 WS2/BiOBr 40 40 mL of 20 ppm 500 W Xe lamp/visible
light
Lanasol red 5B 60 mins 99% 165
20 WS2/In2.77S4 50 150 mL of 50 ppm 300 W Xe lamp/visible
light
Cr(VI) 60 mins 86.60% 102
21 WS2/ZnIn2S4 100 200 mL of 10 ppm 150 W Xe lamp/visible
light
Cr(VI) 120 mins 93.60% 148
M. Sridharan and T. Maiyalagan
8. Chemical Engineering Journal 424 (2021) 130393
8
5.1. Metal oxide-WS2 composites
During the past few years, many researchers have reported various
types of heterostructured composites of WS2 with metal oxides showing
improved efficiencies relative to their bare materials. The earth-
abundant and non-noble metal oxides such as TiO2, ZrO2, WO3 and
Fe3O4 were the most widely used photocatalyst and it has been
employed as a promising candidate for constructing WS2 based
composite.
5.1.1. WS2/TiO2
Several studies on the fabrication of TiO2/WS2 composite have been
reported to induce photocatalytic activities. Jing et al., fabricate nano
sized WS2 coupled mesoporous TiO2 to enhance the visible light
adsorption of bare TiO2. It was observed that the nanosized WS2 loaded
on TiO2 resulted in fluorescence quenching of the TiO2 emission. An
obvious enhancement of hydrogen production rate 2.13 μmol g− 1
h− 1
was also observed [125]. Similarly, Zheng et al., reported TiO2 nano
sheets integrated with layered WS2 by hydrothermal reaction. The as-
prepared TiO2/WS2 composites exhibited excellent photocatalytic
Methyl orange degradation activity than TiO2 and WS2, due to the well
visible light absorption and minimized the charge carrier recombination
[126]. Wu et al., reported Layered WS2/TiO2 nanocomposites synthe
sized via the hydrothermal method, As synthesized novel Layered WS2/
TiO2 nanocomposites exhibited high photocatalytic performance for the
degradation of RhB under visible light irradiation as compared to bare
WS2 and TiO2 nanosheets [92]. Wu et al., synthesized WS2/TiO2 for
photocatalytic activity. The WS2 nanodots were loaded on the inner wall
of TiO2 nanotubes. Under light irradiation for 120 min achieved
degradation rate of 86.1% by 10% WS2 nanodots loaded different TiO2,
which is mainly due to the synergistic effect between WS2 and TiO2, high
specific surface area, the low recombination rate of the photogenerated
electron-hole pairs [127].
Similarly, nitrogen doped TiO2 nanosheets were synthesized by hy
drothermal and calcination method using urea as a nitrogen source.
Elangovan et al., reported N-TiO2/WS2 for photocatalytic dye degrada
tion. Such composite can effectively enhance the visible light response.
The photocatalytic activities for congo red degradation were carried out
under visible light. Compared with N doped TiO2, N doped TiO2/WS2
executed the photocatalytic performance, which could remove 90% of
Congo Red in 300 min. In this case, the composite was introduced WS2,
resulting in utilization of visible light. The photogenerated electrons
could be effectively separated. Accordingly, the possible photocatalytic
mechanisms of N-TiO2/WS2 were proposed as illustrated in Fig. 6 (a)
The photocatalytic durability of N-TiO2/WS2 are show in Fig. 6 (b)
[128].
5.1.2. WS2/ZrO2
Zirconium oxide is an n-type semiconductor photocatalyst with a
bandgap of 5 eV and it exhibits good photocatalytic activity under UV
irradiation and also the photogenerated charge carriers have high redox
behaviour due to their wide-band gap. ZrO2 has three different types of
crystal structure i) monoclinic ii) tetragonal and iii) Cubic. It has good
thermal and chemical stability, and low cost. ZrO2 photocatalytic ac
tivity is still limited under visible light irradiation. Thus, ZrO2 is coupled
with cocatalyst in order to improve the photocatalytic performance
[129]. Opoku et al., reported reported tuning the electronic properties
and interfacial interactions of WS2 and ZrO2 (001). The calculated work
functions of ZrO2(001) 6.02 eV (Fig. 7 (a)) were smaller than ZrO2
(101) surface (6.31 eV), Similarly WS2 single layer, WS2 double layer
and WS2 triple layer sheets were 5.40, 5.04, and 4.79 eV (Fig. 7 (b-d)).
Monolayer and few–layer WS2 sheets work function was lower than the
(001) surface, the potential difference between the two phases are very
large. Thus electron transfer from 2D layered WS2 to the ZrO2 (001)
surface and Fermi level of the two monolayers aligned. ZrO2 electron-
rich environment would be negatively charged, and WS2 would be
positively charged. The work function of WS2 single layer/ZrO2 (001),
WS2 double layer/ZrO2 (001) and WS2 triple-layer/ZrO2 (001) reduced
due to transfer and separation charge carrier creates on surface dipole
pointing towards the ZrO2. In Fig. 7 (e-g) shows the number of layer in
the WS2 sheets increase with gradually reduced in the work function of
the WS2/ ZrO2 (001) hetero structures and this signifies the movement
of electron WS2 to ZrO2 (001) [130]. Vattukutti et al., reported WS2/
ZrO2 hybrid for photocatalytic activity. The WS2/ZrO2 hybrid catalysts
exhibited significantly higher H2 production activities and CV degra
dation performances than pure WS2 and ZrO2 photocatalyst under
simulated solar light and UV irradiation, which is due to intimate in
teractions between the ZrO2 NPs (0D), and layered (2D) WS2 nanosheets
and also enhance UV vis light-absorption capacity. The WS2/ZrO2
hybrid H2 production was 7311.44 µmol h− 1
g− 1
, which was 8.3 and
5.28 times higher than those for ZrO2 (872.32 µmol h− 1
g− 1
) and WS2
(1383.61 µmol h− 1
g− 1
) respectively, additionally the hybrid catalyst
exhibited excellent photocatalytic and chemical stabilities [131].
5.1.3. WS2/WO3
Tungsten oxide is an important material in photocatalytic applica
tions. WO3 can absorb visible light irradiation and thus can be widely
used as a visible-light-driven photocatalys. Many research teams pre
pared Tungsten oxide composite by various methods for photocatalytic
applications. Because Tungsten oxide composite reduces the fast pho
togenerated charge carrier recombination and enhances the potocata
lytic activity of WO3. Paola et al., fabricated WS2/WO3 composites
fabricated via oxidation of WS2 and sulfidation of WO3. This WS2/WO3
composite effectively degrades the organic pollutant. The degradation
efficiency of the WS2/WO3 composite was higher than bare WS2 and
WO3 [132].
Huo et al., prepared WS2 nanosheets by thiourea reduction method
using vacuum tube furnace, and then WS2 nanosheets were surface-
Table 3
Summary of WS2 Based Composites for Photocatalytic Hydrogen Production.
S.
no
Catalyst Catalyst
loading
Light source H2 production
rate µmol⋅h− 1
g− 1
References
1 WS2/g-
C3N4
20 300 W Xe
lamp/visible
light
599.7 100
3 WS2/g-
C3N4
100 300 W Xe
lamp/visible
light
154 101
4 WS2/Cu 3 Xe lamp/
visible light
6400 107
5 WS2/ZnS 10 300 W Xe
lamp/visible
light
308 109
6 WS2/CdS 3 Xe lamp/
visible light
1410 119
7 WS2/CdS 100 300 W Xe
lamp/visible
light
373.41 122
8 WS2/CdS 100 350 W Xe
lamp/visible
light
420 138
9 WS2/CdS 20 mg Xe lamp/
visible light
6110 140
10 WS2/CdS 50 mg 300 W Xe
lamp/visible
light
1773 141
11 WS2/g-
C3N4
50 mg 300 W Xe
lamp/visible
ligh
101 152
12 WS2/g-
C3N4
10 mg 300 W Xe
lamp/visible
ligh
331 153
13 WS2/g-
C3N4
25 mg 300 W Xe
lamp/visible
ligh
350.75 154
M. Sridharan and T. Maiyalagan
9. Chemical Engineering Journal 424 (2021) 130393
9
functionalized with tetragonal WO3 nanoparticles. This type-II struc
ture, which favours the transfer and separation of photogenerated
electron-hole pairs, resulting good photocatalytic activity [133].
Sumantha et al., fabricated WS2/WO3 via electrodeposition and air
annealing. Under illumination, The photogenerated WS2 CB electrons
transferred to the WO2 conduction band and holes in the valance band of
WO3 transfer to WS2 VB. The photogenerated electron reacts with O2 to
O2−
, photogenerated hole reacts with OH−
to form OH*. Then reactive
species react with organic contaminant to produce small molecules. The
photodegradation of phenol under different conditions are shown in
Fig. 8 (a) and photocatalytic mechanism are illustrated in Fig. 8 (b)
[134].
5.1.4. WS2/Fe3O4
Fe3O4 is a p-type semiconductor and it is non-toxic and low cost. Bare
Fe3O4 photocatalyst possesses quite smaller photocatalytic activity.
Fe3O4 combines with other semiconductors to form composites, It
favorable for separation of charge carrier and recyclability. The KIT-6/
Fig. 6. (a) Proposed photocatalytic mechanism of N-TiO2/WS2, (b) Photocatalytic durability of N-TiO2/WS2 (Reprinted with permission from Ref [128] copyright
from ASP).
Fig. 7. (a) The calculated electrostatic potential of ZrO2 (001), (b) Monolayer WS2, (c) double-layer WS2, (d) Three layer WS2, (e) WS2-single layer/ZrO2, (f) WS2-
doublr layer/ZrO2 and (g) WS2-three layer/ZrO2 (Reprinted with permission from Ref [130] copyright from Elsevier).
M. Sridharan and T. Maiyalagan
10. Chemical Engineering Journal 424 (2021) 130393
10
WS2-Fe3O4 nanocomposite was prepared by in situ growth of WS2
nanoparticles on the pores of mesoporous KIT-6 material through the
hydrothermal method. This KIT-6/WS2-Fe3O4 nanocomposite shows
well a photodegradation efficiency of chlorpyrifos under visible light.
The higher photocatalytic activity was achieved to its high specific area
and low recombination rate due to the synergic effect between WS2,
Fe3O4 and KIT-6 [135].
Based on the previous studies, it can be concluded that incorporation
of WS2 to metal oxides mainly take advantage of the enhanced visible
light absorption. Compared to bare metal oxides, WS2 incorporated
metal oxides shows excellent photocatalytic performance due to the
effective transportation and separation of photogenerated electrons.
This WS2 incorporation into metal oxides is highly appreciable for
fabrication of various visible light active photocatalyst.
5.2. WS2/metal sulphide composites
Very recently, many researchers have designed and reported various
types metal sulphides combined with WS2 showing improved effi
ciencies compared to their bare materials. The earth-abundant metal
sulphides such as CdS, ZnS, ZnInS4 and MoS2 were the most widely used
photocatalyst and it has been employed as suitable materials for
developing WS2 based composite.
5.2.1. WS2/CdS
Cadmium sulphide as a kind of II-VI transition metal dichalcogenide
has extensively studied photocatalyst in the past few years. It has been
devoted more attention because of its unique properties like high elec
tronic mobility and excellent charge transport properties. Based on the
advantages, CdS have been widely used as photocatalyst on the removal
of organic contaminants. WS2 incorporating with other semiconductor
material, which can enhance the light absorption capacity of the pho
tocatalysts and also enhance the photogenerated electrons transfer and
separation [136,137]. In some recent work, a new approach to synthe
size CdS/WS2 nanocomposites was developed, and the relationship be
tween the WS2 and the respective visible light photoactivity was studied.
Gopannagari et al., investigated the effect of WS2 on the optical prop
erties and photocatalytic activity of CdS, The optimized WS2 loaded
photocatalyst shows the rate of H2 production of 185.79 mmol h− 1
g− 1
under simulated solar light irradiation, which is 33 times higher than
that of pristine CdS [93].
Zhong et al.,obtained the best results for a nanocomposite containing
40% WS2 with CdS to show enhanced hydrogen production (373.41
mmol g-1
h− 1
) compared with WS2 and CdS photocatalysts. Under visible
light irradiation the photocorrosion and recrystallization of CdS on WS2
surface to be favorable to for enhance hydrogen generation and reduce
the photocorrosion effect [122]. Zong et al., prepared WS2 loaded CdS
that showed increased activity under light irradiation. The 1.0 wt% of
WS2 loaded structure demonstrated enhanced visible light harvesting
and hydrogen production. Which is 28 times higher than bare CdS
[138]. Su et al., used hemispherical shell-thin lamellar WS2 porous
structures hybridized CdS and demonstrated enhanced visible light ab
sorption due to the highsurface area and good electron transport ability,
resulting in improved photo-conversion and a better hydrogen produc
tion [139]. He et al., synthesized CdS nanorods coupled with WS2
nanosheets by solvothermal/exfoliation method; it showed enhanced
hydrogen production of 61.1 mmol/g/h.
The possible photocatalytic mechanism of CdS nanorods coupled
with WS2 nanosheets in visible light irraditionare shown Fig. 9 (a,b)
[140]. Danyun et al., obtained exfoliated WS2 nanosheeets/CdS com
posites (Fig. 9 (c)) and compared their hydrogen evolution rate and
stability with those of bare CdS. It was originate that the exfoliation of
WS2 crystal and facilitated visible light absorption due to the strong
interaction of the WS2 and CdS, which eventually led to reduce recom
bination of the photoexcited charge carriers, WS2/CdS shows higher
hydrogen production rate compared with CdS and WS2 (Fig. 9 (d))
[141]. Zhang et al., reported that a (2D)-2D heterostructured CdS/WS2
photocatalyst liberated 8-fold more H2 production than CdS; this was
mainly because of the efficient separation of photogenerated charge
carrier due to large contact region. the photoexcited elctrons from CdS
CB transferred to CB of WS2 because its CB potential is higher than that
of CdS also the 2D WS2 acted as a good electron collector [119]. Vat
tukutti et al., prepared CdS anchored porous WS2 hybrid show the ab
sorption of Visible light. This unique porous WS2 hybrid design
displayed enhanced photocatalytic activity, which was attributed to the
facile electron transfer path from CdS to WS2 [142]. Velpandian et al.,
synthesized CdS@WS2 heterostructure. It was found that the excitance
of WS2 enhanced the visible light absorption and reduce charge
recombination of CdS. This composite shows enhanced Cr(VI) reduction
and RhB degradation compared with bare CdS [143].
5.2.2. WS2/ZnS
ZnS is an important II-VI group semiconductor and it has been
extensively researched due to its excellent physicochemical and optical
properties. It exhibits in two forms i) sphalerite ii) wurtzite and their
calculated bandgap 3.72 eV and 3.77 eV respectively. Up to the present
ZnS was applied in many research areas due to high energy conversion
efficiency. Under illumination, ZnS mostly working in the UV region for
photo-generated electron-hole pair separation also decomposed into the
component in the absence of sacrificial electron donor [14,144,145]. In
Fig. 8. (a) Photodegradation of phenol under different conditions, and (b) schematic representation for photocatalytic mechanism of WS2/WO3 (Reprinted with
permission from Ref [134] copyright from Elsevier).
M. Sridharan and T. Maiyalagan
11. Chemical Engineering Journal 424 (2021) 130393
11
order to solve this concern, ZnS was successfully synthesized in com
posite fabrication features. Zhong et al., reported WS2/ZnS hetero
structures show good photocatalytic performance. By combining ZnS
with WS2 sheets, the visible light absorption property of ZnS was
enhanced and reduces the quick recombination of photoinduced
electron-hole pairs. The 0.5 wt% WS2 NSs loaded ZnS shows highest H2
evolution rate of 308 μmol h− 1
g− 1
(Fig. 10 (a)). This efficiency is 3 times
higher than pure ZnS photocatalyst and also shows good catalytic
activity under 50 h irradiation (Fig. 10 (b)) [109].
5.2.3. WS2/Bi2S3
Bismuth sulfide is a type of lamellar structure semiconductor and
their bandgap is 1.3–1.6 eV [146]. Nanostructures of Bismuth sulfide
have numerous attentions in photocatalysis due to their visible light
absorption capacity. However, the photocatalytic activity of bare Bi2S3
remains limited because the material shows lower efficiency and
Fig. 9. (a) Schematic representation of the photcatalytic mechanism of CdS/WS2 in lactic acid solution (Reprinted with permission from Ref [140] copyright from
ACS), (b) schematic illustration of visible light induced photocatalytic mechanism of CdS/WS2 [140], (c) Schematic representation of the 1–2 layered 2H-WS2/CdS
and its photocatalytic hydrogen production mechanism [141] and (d) The photocatalytic hydrogen production rate of CdS/WS2 under visible and simulated sunlight
(Reprinted with permission from Ref [141] copyright from ACS).
Fig. 10. (a) Rate of photocatalytic H2 evolution on ZnS loading with different amount of WS H2, (b) Cyclic runs for the photocatalytic H2 evolution WS2/ZnS
(Reprinted from Ref [109] with permission from the Centre National de la Recherche Scientifique (CNRS) and the Royal Society of Chemistry).
M. Sridharan and T. Maiyalagan
12. Chemical Engineering Journal 424 (2021) 130393
12
stability, showing quick recombination of photogenerated charge
carrier. Vattikuti et al reported Bi2S3 nanorod/2D exfoliated WS2
nanosheet heterojunction for photocatalytic activity. as prepared com
posites exhibits1.42 and 1.19 times higher photocatalytic activity than
pure and Bi2S3 and WS2. The enhanced performance can be attributed to
1D/2D porous structure, large specific surface area, enhanced charge
separation, and transfer efficiency, reduced photoelectron–hole recom
bination [147].
5.2.4. WS2/ZnInS4
ZnIn2S4 is an emerging celebrity ternary sulfide semiconductor
photocatalyst recent years, such as non-toxicity, good chemical stability,
and good chemical crystallinity. The photocatalytic performance of
ZnIn2S4 itself is low; therefore, ZnIn2S4
-
based composite fabrication have
received more attention [67]. Pudkon et al., synthesized hetero
structures through hydrothermal method the composite of WS2 loaded
on ZnIn2S4 achieved the highest photocatalytic performance Different
concentration of WS2 loaded ZnIn2S4 photocatalytic hydrogen produc
tion efficiency is shown in Fig. 11 (a) which is higher than bare ZnIn2S4
and WS2.
In this work, ZnIn2S4/WS2 composites shows good photocatalytic
performance under UV–visible irradiation compared with visible irra
diation (Fig. 11 (b)). moreover photocatalytic Cr(VI) reduction effi
ciency of WS2, ZnIn2S4, and WS2/ZnIn2S4 composites are 4.2%, 78.4%
and 93.6% respectively [148] Zhou et al., synthesized WS2/ZnIn2S4
composites by hydrothermal method. The obtained WS2/ZnIn2S4 com
posites resulted in much higher photocatalytic performance for
hydrogen evolution than bare ZnIn2S4, and the photocatalytic perfor
mance of ZnIn2S4 was significantly affected by the cocatalyst WS2
loading amount. 3% of WS2 cocatalyst loaded ZnIn2S4 composite ach
ieved the best hydrogen production rate of 199.1 mmol/h/g, which was
higher than conventional Pt/ZnIn2S4 photocatalysts. The enhanced
photocatalytic performance of WS2/ZnIn2S4 composites could be fav
oured to the efficient photogenerated electron-hole pair’s migration and
separation [94].
5.2.5. WS2/MoS2
Molybdenum disulfide (MoS2) is a layered structured transition
metal dichalcogenide. It has enormous attention for various fields of
dye-sensitized solar cells, photocatalytic hydrogen production and
degradation of organic and inorganic contaminants, Because of its
structural similarities to graphene. MoS2 shows high charge carrier
transport and high wear resistance, those physical properties similar to
that of graphene. Moreover, MoS2 has excellent properties over gra
phene such as good visible light absorption capacity, earth-abundant
and low cost [149]. Li et al., prepared WS2@MoS2 composites by 2-
step an approach involving ball-milling, annealing, and hydrothermal
method, this composite provided a higher efficiency than pure WS2 and
MoS2. Under illumination, it follows the type II heterojunction electron
transfer mechanism. Photogenerated electron could be injected into the
conduction band of MoS2 from that of WS2 [117]. Similarly, Luo et al.,
coupled WS2 with MoS2 to increase the visible light absorption capacity
of the photocatalyst. After being illuminated, MoS2/WS2 shows the
highest photodegradation rate constant, which is almost five times
higher than pure MoS2 [150].
To sum up, introducing WS2 to metal sulphides (CdS, ZnS, Bi2S3,
ZnInS4 and MoS2) can form composites, which can enhance the sepa
ration and transfer the photogenerated electrons. In addition, the WS2
incorporation effectively inhibits the photocorrosion effect of metal
sulphides. The composite fabrication of WS2 with metal sulphides may
be a hopeful strategy for potential application of Photocatalytic dye
degradation, Cr(VI) reduction and hydrogen production
5.3. WS2/Carbon based materials
During the past few years, carbon materials have attracted intensive
attention to enhance photocatalytic activity. Carbon materials such as
carbon quantum dots and g-C3N4 enhancing the performance of metal-
free semiconductor based photocatalysis.
5.3.1. WS2/g-C3N4
Graphitic carbon nitride (g-C3N4) has much attention as metal-free
polymer n-type semiconductor photocatalysis because of its intrinsic
features, high activity and unique 2D layered structure, non-toxicity and
efficient visible-light absorption. It accommodates only the earth-
abundant carbon and nitrogen, good chemical and thermal stability
due to the conjugated layer structure containing a strong covalent bond
between carbon and nitrogen atoms. g-C3N4 bandgap value 2.7 eV (460)
nm, which is helpful to harvest the visible light as well as conduction
band and valance band edge position suitable for both water reduction
and oxidation. Moreover, the photoactivity performance of bare g-C3N4
is low due to its high photogenerated charge carrier’s recombination.
Various methods have been used to overcome these problems such as
doping with metals and non-metals, composites formation with some
other metal oxides and metal sulphides [54,151].
Hou et al., employed WS2 as the co-photocatalyst hybridizing WS2/
mesoporous g-C3N4 composite by impregnation–sulfidation approach.
When controlling the content of WS2 as 0.3 wt%, the composite showed
the greatest photocatalytic hydrogen production. In the photocatalytic
reaction, WS2 obviously encouraged charge separation and transfer,
Fig. 11. (a) Rate of photocatalytic H2 production on ZnInS4 loading with different amount of WS2, (b) photocatalytic H2 production rate of ZnInS4, ZnInS4/WS2
under UV–visible and visible light irradiation (Reprinted with permission from Ref [148] copyright from RSC).
M. Sridharan and T. Maiyalagan
13. Chemical Engineering Journal 424 (2021) 130393
13
thus inhibiting the photoelectron-hole pair’s recombination [98]. Lin
et al., used one pot calcination method to prepare sandwich-structured g-
C3N4/WS2 composite, When 7.49 wt% of W having WS2 was deposited
on g-C3N4, the composite exhibited the excellent photocatalytic activity
(599.7 μmol h-1
g− 1
), which is around 25 times higher than that of pure
g-C3N4 [100].
Maxwell et al., used a gas–solid reaction to synthesize WS2/g-C3N4
composites. Different ratios of WS2 were growth on g-C3N4 to form the
heterojunction and the composite revealed enhanced photocatalytic H2
production under visible light irradiation. The 0.01 wt% WS2 loaded
composite shows the highest H2-production rate of 101 μmol g− 1
h− 1
,
which is higher than Pt deposited g-C3N4. The enhanced photocatalytic
H2 production was attributed to the heterojunction formation between
g-C3N4 and WS2 cocatalyst [152]. Jianjian et al., synthesized 1T- WS2
and then coupled with g-C3N4 and used it as a photocatalyst for the H2
production reaction. 1T-WS2 play a dual role in photocatalytic reaction
(i) The better electrical conductivity of 1T-WS2 helps to transfer the
photogenerated electron. (ii) 1T- WS2 can provide more active sites for
hydrogen production reactions on the basal plane (Fig. 12 (a)), more
over, it helps to reduce electron travel length and recombination of
photogenerated holes. High hydrogen production rate of 331.09 µmolg-
1
h− 1
was achieved by WS2/g-C3N4, which is 43.3 times higher than bare
g-C3N4 [153]. Zhou et al., prepared WS2/g-C3N4 photocatalysts through
one-pot synthesis. The 0.3 wt% WS2 loaded g-C3N4 achieved the highest
photocatalytic H2 production rate of 154 mmol h-1
g− 1
. Which is higher
than 0.3 wt% Pt loaded g-C3N4 and 34 times higher than Pure g-C3N4
[101]. Huang et al., reported the colloidal synthesis of 1T/2H-WS2
nanoflakes growth on 2D g-C3N4. This composite shows that the pho
tocatalytic H2 production 350.75 µmolg-1
h− 1
, Which is higher than 1T/
2H- WS2 and 2D g-C3N4 as well as other WS2/g-C3N4 composites without
Pt. The photocatalytic hydrogen production mechanism of WS2/g-C3N4
is shown in Fig. 12 (b). This composite could be expressively beneficial
for the separation of the electron-hole pairs, prevent the charge
recombination [154]. Similarly, Tran et al., reported WS2/g-C3N4 com
posites for photocatalytic degradation of methylene blue. The concen
tration of WS2 to g-C3N4 affects photocatalytic degradation efficiency of
the composites. 1:7 wt ratio WS2 to g-C3N4 shows the highest photo
catalytic activity compared with bare g-C3N4 and WS2 [99].
5.3.2. WS2/Carbon dots
Carbon dots (CDs) have attracted attention in photocatalysis due to
their fascinating properties including biocompatibility, less toxicity,
solubility in water, and easy surface modification and surface func
tionalization [155,156]. Nowadays, numerous effort has been devoted
to CDs coupled with other material and employed for both photo
catalytic and electrocatalytic applications. Atkin et al., designed 2D
tungsten disulfide nanoflakes hybridized with carbon dots for photo
catalytic applications. The CDs strongly adhered to the WS2 basal plane
through van der Waals attraction forces. The composite material was
then shown higher photocatalytic Congo Red degradation efficiency.
The assessment of the electronic band structures of CDs, 2D WS2 and
Congo Red was suggested that the improvement is due to induced the
affinity of Congo Red onto the surface of the WS2 flakes rather than a 2D
WS2/CD [110].
In summary, WS2 can be introduced into Carbon based materials to
form WS2/Carbon based composites. This WS2 incorporation into these
composite photocatalyst can induce them with unique properties of WS2
possibly produce new properties, such as extended visible light ab
sorption, and effective separation of photogenerated electrons, which
boosted the overall photocatalytic activity. These carbon based mate
rials are low cost and less toxic. Therefore, WS2/Carbon materials based
composite provide invigorating way on the noble metal free and visible
light active photocatalyst fabrication.
5.4. WS2 with Bismuth based materials
Bismuth-based materials have considerable attention in photo
catalytic activity because of its excellent visible light absorption prop
erties. Several Bi3+
containing materials have narrow bandgap and
enhanced visible light absorption due to the hybridization of O 2p and Bi
6s2
valence bands [157,158]. Various Bi based materials such as Bi
based oxides and Bi based oxyhalides (BiOCl and BiOBr) are widely used
in photocatalytic activity. However, the photocatalytic activity of bare
Bi based materials is still limited because of the quick recombination of
photogenerated charge carrier.
5.4.1. WS2/BiOCl
BiOCl photocatalysts have received great attention due to its UV and
Solar irradiation absorption ability, because of their indirect bandgap
(3.2 eV) and VB is mainly composed of O 2p states and Cl 3P states. But
bare BiOCl not efficient to visible light photocatalysis. BiOCl photo
catalyst coupling with co-photocatalysts is one of the effective methods
to enhance the visible light photocatalytic activity [159]. The lower
active oxygen species production hindered the electron-hole pair
Fig. 12. (a) Schematic illustration of charge transfer mechanism of WS2/ g-C3N4 (Reprinted with permission from Ref [153] copyright from Elsevier), (b) Photo
catalytic H2 production mechanism of 3D composite structured WS2/ g-C3N4 (Reprinted with permission from Ref [154] copyright from Elsevier).
M. Sridharan and T. Maiyalagan
14. Chemical Engineering Journal 424 (2021) 130393
14
formation and separation in BiOCl photocatalytic activity. Xiao et al.,
reported that WS2 incorporated BiOCl for photocatalytic activity. Under
visible light, the photogenerated electrons could transfer from CB of WS2
to BiOCl due to the suitable band alignment. This promoted charge
carrier separation leading to an enhance RhB degradation efficiency
[96]. Similarly, Ashraf et al., designed 2D/2D BiOCl/WS2 heterojunction
by solution-based sonication method (Fig. 13 (a)). The content of the
WS2 nanosheets in the composite can affect the efficiency of MG
removal. ECB and EVB edges of bare WS2 nanosheets are about 0.165 eV
and 2.15 eV respectively. And for bare BiOCl nanosheets, 0.195 eV and
3.525 eV, respectively. EVB and ECB edge of WS2 higher than EVB and
ECB edge of bare BiOCl respectively. So, under illumination, the
photoexcited WS2 conduction band electrons can easily transfer to BiOCl
conduction band and BiOCl VB having holes easily moves to the WS2
nanosheets (Fig. 13 (b)). An enhanced efficiency degradation of MG is
observed when the WS2 content is increased from 1% to 2%. However,
further raising the concentration of WS2 leads to hinder MG degradation
efficiency. The possible reason for the negative impact of excess amount
of WS2 could be the decrease active sides of the BiOCl [160].
5.4.2. WS2/BiOBr
BiOBr is now paid attention in photocatalysis field due to its high
photocorrosion stability, non-toxicity and good chemical stability. The
visible-light photocatalytic activity of BiOBr is still limited in practical
application, due to its lower visible light absorption and fast recombi
nation of photogenerated electrons [161–163]. The extensive researcher
has shown that the heterojunction formation with other materials,
improved the electron hole pair separation, extend the lifetime of pho
togenerated electron and enhance the photocatalytic activity. Fu et al.,
reported a WS2/BiOBr for the long-term photocatalytic removal of
organic and inorganic pollutant removal. Based on their results, the
organic and inorganic contaminant degradation feature is highly WS2
concentration dependent. 10 mL of WS2 quantum dots loaded BiOBr
heterostructure shows outstanding photocatalytic performance. To
wards normally, the catalyst concentration, dye concentration and
presence of secondary effluents or organic contaminants affect the
photocatalytic efficiency of the catalyst. The high CIP concentration and
low catalyst concentration and addition of various ions (PO4
3-
, Cu2+
and
Ca2+
) reduce the degradation of CIP. The other organic pollutant
degradation efficiency of organic pollutant also studied. The coexistence
of other organic contaminants (LR5B, RhB and TC) also, reduce the
photocatalytic activity of the catalyst. The removal of various pollutant
including Ciprofloxacin (92%), 99% (Lanasol Red 5B), 95% (Rhodamine
B), 96% (tetracycline), 41% (Bisphenol A), and 85% (metronidazole)
was obtained under visible light irradiation [164]. Same group have
investigated the photocatalytic activity of flower-like WS2/BiOBr het
erojunction. The formation of heterojunction between BiOBr and WS2
enhance the light absorption capacity. Under Visible light irradiation,
photogenerated electrons and holes are formed on the surface of WS2
and BiOBr. The WS2 CB having photogenerated electrons transferred to
the CB of BiOBr, while photogenerated holes are moved from the VB of
BiOBr to WS2. The photogenerated holes in the VB of WS2 could not
react with H2O, because VB potential of WS2 more negative than the
redox potential of •OH/H2O (+2.38 eV vs. NHE). The WS2 introduction
into BiOBr could enhance photogenerated electron and hole pair
transfer and separation (Fig. 14 (a)). Based on their results,The degra
dation efficiencies of a various contaminant in the following order:
Lanasol Red 5B (99%), metronidazole (97%), tetracycline (92%),
oxytetracycline (92%), rhodamine B (90%), CIP (83%), methylene blue
(78%), methyl orange (62%), bisphenol (42%) and phenol (40%)
(Fig. 14 (b)).
The photocatalytic degradation of ciprofloxacin was explored under
different conditions, and that result demonstrated that high concentra
tion of ciprofloxacin, lower pH and concentrations of ions (PO4
3−
,
HPO4
2-
, H2
PO4−
, and Cu2+
) reduced the photocatalytic degradation ef
ficiency [165].
5.4.3. WS2/(BiO)2CO3
Most of the Bi-based oxide, catalyst possesses strong visible light
absorption capacity and good photocatalytic activity. However the
practical usage of individual catalyst is still limited because of their fast
recombination of photogenerated charge carriers [166]. (BiO)2CO3 is an
n-type semiconductor, it’s a typical silane phase and belongs to
Aurivillius-related oxide family. In recent years, the number of re
searchers reported (BiO)2CO3 in the field of photocatalysis due to its
advantages like 2D layered crystal structure, good stability and low
toxicity. But the large bandgap (ca. 3.4 eV) of (BiO)2CO3 limited their
visible light activity. To further enhance the visible light absorption and
charge carrier separation of (BiO)2CO3 by the fabrication of hetero
junction with other materials [167]. Li et al., reported flower like Z-
scheme WS2/(BiO)2CO3 composites synthesized by one-pot hydrother
mal method. Under illumination both WS2 and (BiO)2CO3 excited,
subsequently the photogenerated electrons and holes are stimulated.
Because of both higher VB and CB potentials of WS2 than those of
(BiO)2CO3. Therefore it follows Z-scheme mechanism, CB electrons of
WS2 react with O2 to form .
O2
−
and the hole in the VB of (BiO)2CO3 react
with H2O to produce OH. The average life time of (BiO)2CO3 and WS2/
(BiO)2CO3 were 3.5 and 3.2. The decrement of life time indicates that
some non-radiative process occurs in WS2/(BiO)2CO3 heterojuction after
the deposition of WS2 (Fig. 15(a)). The active trapping experiments were
Fig. 13. (a) Schematic representation of the synthesis procedure of BiOCl/WS2 composite, (b) Schematic representation of the photocatalytic mechanism of BiOCl/
WS2 (Reprinted with permission from Ref [160] copyright from RSC).
M. Sridharan and T. Maiyalagan
15. Chemical Engineering Journal 424 (2021) 130393
15
shown in (Fig. 15 (b)). The obtained active species react with organic
pollutant to form smaller molecules. This result demonstrated that
flower-like Z-scheme WS2/(BiO)2CO3 composites show 3.23 times better
Lanasol Red 5B degradation efficiency than bare (BiO)2CO3, moreover
95% ciprofloxacin removal efficiency within 90 min [168].
Fig. 14. (a) Schematic diagram of band level with possible photocatalytic mechanism of WS2/BiOBr, (b) Photocatalytic degration efficiency of WS2/BiOBr
(Reprinted with permission from Ref [165] copyright from Elsevier).
Fig. 15. (a) Time-resolved emission decay of (BiO)2CO3 and WS2/(BiO)2CO3, (b) degradation efficiency of WS2/(BiO)2CO3 using different active species (Reprinted
with permission from Ref [168] copyright from Elsevier).
Fig. 16. (a) Photocatalytic mechanism of WS2/Bi2MoO6, (b) The XRD pattern of WS2/Bi2MoO6 before and after durability test (Reprinted with permission from Ref
[170] copyright from Springer).
M. Sridharan and T. Maiyalagan
16. Chemical Engineering Journal 424 (2021) 130393
16
5.4.4. WS2/Bi2MoO6
Bismuth molybdate (Bi2MoO6) is an n-type semiconductor with layer
structure which is assembled by Bi2O2
2+
layers and perovskite-like
layered [MoO4]2−
. It is widely used in photocatalysis because of their
advantages like narrow bandgap (2.4–2.8 eV), high visible-light absor
bance and high chemical stability [169]. The lower quantum yield and
fast recombination of photogenerated charge carrier still restrict its
photocatalytic activity. Recently, Bi2MoO6 composite fabrication shown
great potential for emerged and advanced in the field of photocatalysis.
Under visible-light irradiation both WS2 and Bi2MoO6 are excited,
the photoexcited Bi2MoO6 conduction band electrons easily transfer to
WS2, because the conduction band potential of Bi2MoO6 (− 0.31 eV) is
more negative than WS2 conduction band potential. CB of Bi2MoO6
having a few electrons reacted with dissolved oxygen to form O2−
. The
main active species like holes and O2−
react with pollutant to form CO2
and H2O (Fig. 16 a). Enhanced efficiency in RhB degradation is observed
when the concentration of WS2 is increased from 1% to 5%. However,
further increasing concentration of WS2 to 7% leads to a decrease in RhB
degradation. The promising reason for the opposite effect of the excess
amount could be the blocking of active sides of Bi2MoO6, although 5% of
WS2 exhibits remarkably enhanced photocatalytic activity and good
stability. After four cycles, the XRD pattern of WS2/Bi2MoO6 shows
similar XRD pattern to initial XRD pattern (Fig. 16 (b)) [170].
5.4.5. WS2/Bi2O3
Bi2O3 as an efficient visible light active material for photocatalysis
[171]. Li et al., reported the synthesis of WS2@Bi2O3 composite for
photocatalytic application. The synthesized composite optimized by
changing the concentration of WS2 (1% to 12%) to WS2@Bi2O3 com
posite. The 8% WS2 loaded WS2@Bi2O3 composites shows higher pho
tocatalytic activity compared with bare WS2 and Bi2O3. The calculated
band gap value of WS2 and β-Bi2O3 are 1.41 eV and 2.36 eV respectively
and the band structure are shown in the Fig. 17(a,b). The noticeable
difference between the bandgap of both WS2 and β-Bi2O3 would be
useful for the harvesting of visible irradiation. p-type and n-type semi
conducting nature of β-Bi2O3 and WS2 confirmed through the fermi level
position (0.797 eV and 1.023 eV VB of WS2 and β-Bi2O3). The calculated
work functions of β-Bi2O3 and WS2 are shown in Fig. 17(c–g). The CB of
WS2 having photogenerated electrons easily transferred to the conduc
tion band of β-Bi2O3, because the conduction band edges of WS2 higher
than β-Bi2O3. At the same time, photogenerated hole is transfers from
valance band of β-Bi2O3 to VB of WS2 [111].
In conclusion, the incorporation of WS2 to Bi-based materials to
achieve higher quantum yields and enhanced visible light absorption
capacity. Therefore, these substantial developments and methods for
customization of photocatalyst show potential activity for their real time
application toward photocatalysis for clean environment and sustain
able energy production.
5.5. WS2/Ag based materials
Silver-based materials have been widely used in photocatalytic ac
tivity, due to their superior utilization of visible light. Among the various
silver-based materials, AgI [172–175] and Ag3PO4 [176–179] have
proved the most important materials to utilize the visible light irradia
tion and good photocatalytic activity. However both AgI and Ag3PO4
suffer from photo corrosion at long time under light irradiation.
Therefore, most of the researcher reported that Ag3PO4 and AgI coupled
with other co-photocatalysts or conductive materials. Researchers take
concern of WS2 as a suitable co-catalyst due to its unique property like
high photocorrsion stability. Wu et al., synthesized AgI/WS2 composites
by a simple in situ growth of AgI on WS2 nanosheet. AgI nanoparticles
were uniformly distributed on the WS2 nanosheets, both component
very close contact with each other. The optimized photocatalytic ac
tivity of AgI/WS2 composite on RhB was 91.2% on 30 min. The possible
photocatalytic mechanism of the synthesized composites shown in
Fig. 18 (a). Under the illumination, VB electron in WS2 and AgI can be
excited to CB, VB forming the photogenerated holes. CB of AgI photo
generated electrons moves to CB of WS2. This electron reacts with O2 to
form ⋅O2−
. Finally, ⋅O2−
can react with RhB to produce small molecule
[104].
WS2 can be also combined with Ag3PO4 for photocatalytic applica
tions. Hongjian et al. prepared WS2/Ag3PO4 heterostructures by pho
tocatalytic degradation of RhB. The theoretically calculated valance
bands of Ag3PO4 and WS2 are 2.9 eV and 2.11 eV respectively, similarly
the conduction band of Ag3PO4 and WS2 are 0.45 eV and 0.21 eV.
Because the photogenerated electrons transferred from the conduction
band of WS2 to Ag3PO4 (Fig. 18 (b)) and also hole in the valance band of
Ag3PO4 migrates to WS2. The photogenerated holes react with
contaminant to produce small molecules. Bare Ag3PO4 can completely
degrade the contaminant after 33 min. But Ag3PO4 deposited on WS2
degrade within 9 min, The results show that the existence of WS2 sheets
can expressively enhance the photocatalytic performance of Ag3PO4
[180].
In conclusion, introduction of WS2 into Ag based materials can
promote photocatalytic performance, being attributed to minimize the
fast recombination of photogenerated electron and holes. More impor
tantly, the WS2 afford high specific area, which helps to enhance the
deposition of nanostructured Ag based materials.
Fig. 17. (a&b) The geometries of WS2 and β- Bi2O3, (c&d) The band structure of β- Bi2O3 and WS2 (c,d), the band edge placement of valence band minimum, (e)
fermi level, (f) conduction band minimum β- Bi2O3 and WS2 (Reprinted from Ref [111] with permission from the Chinese Chemical Society (CCS), Peking University
(PKU), and the Royal Society of Chemistry).
M. Sridharan and T. Maiyalagan
17. Chemical Engineering Journal 424 (2021) 130393
17
6. Conclusion
Photocatalyst are probable to be an upcoming trend, since nano
structured photocatalysts have shown considerable superior perfor
mance than their bulk counterparts. Over the past decades different
methods have been used to enhance the photocatalyst optimizing the
photons and electrons prominent to enriched catalytic activity such as
(i) fabrication of both Inorganic and/or organic semiconductors heter
ojunctions, (ii) band-gap engineering strategies, (iii) usage dye molecule
as a sensitizer, (iv) Usage of the cocatalyst. Among the various ap
proaches, cocatalyst loading has emerged as an innovative type for
photocatalysis, In fact, WS2 loaded on TiO2, WO3, MoS2, CdS and g-
C3N4, have been proven to be highly efficient catalysts for photocatalytic
applications. Although noticeable progress has been reached, the studies
in WS2 based photocatalysis are the primary stage and further im
provements are needed. First, new synthesis methods introduced to
improve WS2 or WS2 based composites. Second, the catalytic perfor
mance of WS2 is lowered by the quantity of these materials and their
structures. Innovative synthesis methods and computational help are
essential towards the design of site-selective loading of WS2 on another
semiconductor photocatalyst for enhanced performance. Additionally,
more studies are needed to develop the understanding of WS2 based
photocatalytic mechanism. During the photocatalytic reaction, the sta
bility of the photocatalyst is a major concern in metal sulphide based
photocatalysis, because the stability of the metal sulphide composites
remains outstanding issues. Before forwarding to the large scale syn
thesis and application of metal sulphide composite, the analysis of any
secondary pollution from its composites is a serious consideration for
photocatalysis.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgement
The authors acknowledge the financial support from the Scheme for
Promotion of Academic and Research Collaboration (SPARC) of the
Ministry of Human Resource Development (MHRD), Government of
India, SPARC Grant No. SPARC/2018-2019/P1122/SL.
References
[1] J. Baxter, Z. Bian, G. Chen, D. Danielson, M.S. Dresselhaus, A.G. Fedorov, T.
S. Fisher, C.W. Jones, E. Maginn, U. Kortshagen, A. Manthiram, A. Nozik, D.
R. Rolison, T. Sands, L. Shi, D. Sholl, Y. Wu, Nanoscale design to enable the
revolution in renewable energy, Energy Environ. Sci. 2 (2009) 559–588, https://
doi.org/10.1039/b821698c.
[2] Q. Chen, X. Tan, Y. Liu, S. Liu, M. Li, Y. Gu, P. Zhang, S. Ye, Z. Yang, Y. Yang,
Biomass-derived porous graphitic carbon materials for energy and environmental
applications, J. Mater. Chem. A. 8 (2020) 5773–5811, https://doi.org/10.1039/
c9ta11618d.
[3] F.A. Rahman, M.M.A. Aziz, R. Saidur, W.A.W.A. Bakar, M.R. Hainin, R. Putrajaya,
N.A. Hassan, Pollution to solution: Capture and sequestration of carbon dioxide
(CO2) and its utilization as a renewable energy source for a sustainable future,
Renew. Sustain. Energy Rev. 71 (2017) 112–126, https://doi.org/10.1016/j.
rser.2017.01.011.
[4] X. Shi, X. Zhang, F. Bi, Z. Zheng, L. Sheng, J. Xu, Z. Wang, Y. Yang, Effective
toluene adsorption over defective UiO-66-NH2: an experimental and
computational exploration, J. Mol. Liq. 316 (2020), 113812, https://doi.org/
10.1016/j.molliq.2020.113812.
[5] S. Hyok Ri, F. Bi, A. Guan, X. Zhang, Manganese-cerium composite oxide
pyrolyzed from metal organic framework supporting palladium nanoparticles for
efficient toluene oxidation, J. Colloid Interface Sci. 586 (2021) 836–846, https://
doi.org/10.1016/j.jcis.2020.11.008.
[6] E. Barea, C. Montoro, J.A.R. Navarro, Toxic gas removal-metal-organic
frameworks for the capture and degradation of toxic gases and vapours, Chem.
Soc. Rev. 43 (2014) 5419–5430, https://doi.org/10.1039/c3cs60475f.
[7] R.J. Detz, J.N.H. Reek, B.C.C. Van Der Zwaan, The future of solar fuels: when
could they become competitive? Energy Environ. Sci. 11 (2018) 1653–1669,
https://doi.org/10.1039/c8ee00111a.
[8] W. Pa, Indonesia solar power study using secondary data, J. Climatol. Weather
Forecast. 05 (2017) 3–6, https://doi.org/10.4172/2332-2594.1000191.
[9] J. Charles Rajesh Kumar, M.A. Majid, Renewable energy for sustainable
development in India: current status, future prospects, challenges, employment,
and investment opportunities, Energy. Sustain. Soc. 10 (2020) 1–36, https://doi.
org/10.1186/s13705-019-0232-1.
[10] Y. Wang, L. Yu, R. Wang, Y. Wang, X. Zhang, A novel cellulose hydrogel coating
with nanoscale Fe0 for Cr(VI) adsorption and reduction, Sci. Total Environ. 726
(2020), 138625, https://doi.org/10.1016/j.scitotenv.2020.138625.
[11] Y. Yang, Z. Zheng, W. Ji, J. Xu, X. Zhang, Insights to perfluorooctanoic acid
adsorption micro-mechanism over Fe-based metal organic frameworks:
combining computational calculation with response surface methodology,
J. Hazard. Mater. 395 (2020), 122686, https://doi.org/10.1016/j.
jhazmat.2020.122686.
[12] Y. Wang, L. Yu, R. Wang, Y. Wang, X. Zhang, Reactivity of carbon spheres
templated Ce/LaCo0.5Cu0.5O3 in the microwave induced H2O2 catalytic
degradation of salicylic acid: characterization, kinetic and mechanism studies,
J. Colloid Interface Sci. 574 (2020) 74–86, https://doi.org/10.1016/j.
jcis.2020.04.042.
[13] Y. Wang, R. Wang, L. Yu, Y. Wang, C. Zhang, X. Zhang, Efficient reactivity of
LaCo0.5Cu0.5O3 perovskite intercalated montmorillonite and g-C3N4
nanocomposites in microwave-induced H2O2 catalytic degradation of bisphenol
A, Chem. Eng. J. 401 (2020), 126057, https://doi.org/10.1016/j.
cej.2020.126057.
[14] C. Xu, P. Ravi Anusuyadevi, C. Aymonier, R. Luque, S. Marre, Nanostructured
materials for photocatalysis, Chem. Soc. Rev. 48 (2019) 3868–3902, https://doi.
org/10.1039/c9cs00102f.
[15] C. Gao, J. Wang, H. Xu, Y. Xiong, Coordination chemistry in the design of
heterogeneous photocatalysts, Chem. Soc. Rev. 46 (2017) 2799–2823, https://
doi.org/10.1039/c6cs00727a.
[16] J. Kou, C. Lu, J. Wang, Y. Chen, Z. Xu, R.S. Varma, Selectivity enhancement in
heterogeneous photocatalytic transformations, Chem. Rev. 117 (2017)
1445–1514, https://doi.org/10.1021/acs.chemrev.6b00396.
[17] A. Reynal, F. Lakadamyali, M.A. Gross, E. Reisner, J.R. Durrant, Parameters
affecting electron transfer dynamics from semiconductors to molecular catalysts
for the photochemical reduction of protons, Energy Environ. Sci. 6 (2013)
3291–3300, https://doi.org/10.1039/c3ee40961a.
Fig. 18. (a) The photocatalytic mechanism of AgI/WS2 (Reprinted with permission from Ref [104] copyright from IET), (b) Schematic representation of the
photcatalytic mechanism of WS2/Ag3PO4 (Reprinted with permission from Ref [180] copyright from RSC).
M. Sridharan and T. Maiyalagan
18. Chemical Engineering Journal 424 (2021) 130393
18
[18] T. Hisatomi, K. Takanabe, K. Domen, Photocatalytic water-splitting reaction from
catalytic and kinetic perspectives, Catal. Lett. 145 (2015) 95–108, https://doi.
org/10.1007/s10562-014-1397-z.
[19] T. Hisatomi, T. Minegishi, K. Domen, Kinetic assessment and numerical modeling
of photocatalytic water splitting toward efficient solar hydrogen production, Bull.
Chem. Soc. Jpn. 85 (2012) 647–655, https://doi.org/10.1246/bcsj.20120058.
[20] S. Zhu, D. Wang, Photocatalysis: basic principles, diverse forms of
implementations and emerging scientific opportunities, Adv. Energy Mater. 7
(2017) 1–24, https://doi.org/10.1002/aenm.201700841.
[21] M. Muringa Kandy, A.K. Rajeev, M. Sankaralingam, Development of proficient
photocatalytic systems for enhanced photocatalytic reduction of carbon dioxide,
Sustain. Energy Fuels. 5 (2021) 12–33, https://doi.org/10.1039/d0se01282c.
[22] H. Zhou, Y. Qu, T. Zeid, X. Duan, Towards highly efficient photocatalysts using
semiconductor nanoarchitectures, Energy Environ. Sci. 5 (2012) 6732–6743,
https://doi.org/10.1039/c2ee03447f.
[23] L. Finegold, J.L. Cude, Biological sciences: one and two-dimensional structure of
alpha-helix and beta-sheet forms of poly(L-Alanine) shown by specific heat
measurements at low temperatures (1.5-20 K), Nature 238 (1972) 38–40, https://
doi.org/10.1038/238038a0.
[24] J.H. Carey, J. Lawrence, H.M. Tosine, Photodechlorination of PCB’s in the
presence of titanium dioxide in aqueous suspensions, Bull. Environ. Contam.
Toxicol. 16 (1976) 697–701, https://doi.org/10.1007/BF01685575.
[25] K. Nakata, A. Fujishima, TiO2 photocatalysis: design and applications,
J. Photochem. Photobiol. C Photochem. Rev. 13 (2012) 169–189, https://doi.
org/10.1016/j.jphotochemrev.2012.06.001.
[26] J. Schneider, M. Matsuoka, M. Takeuchi, J. Zhang, Y. Horiuchi, M. Anpo, D.
W. Bahnemann, Understanding TiO2 photocatalysis: mechanisms and materials,
Chem. Rev. 114 (2014) 9919–9986, https://doi.org/10.1021/cr5001892.
[27] Q. Guo, C. Zhou, Z. Ma, X. Yang, Fundamentals of TiO2 photocatalysis: concepts,
mechanisms, and challenges, Adv. Mater. 31 (2019) 1–26, https://doi.org/
10.1002/adma.201901997.
[28] X. Zhang, J. Chen, S. Jiang, X. Zhang, F. Bi, Y. Yang, Y. Wang, Z. Wang, Enhanced
photocatalytic degradation of gaseous toluene and liquidus tetracycline by
anatase/rutile titanium dioxide with heterophase junction derived from materials
of Institut Lavoisier-125 (Ti) Degradation pathway and mechanism studies,
J. Colloid Interface Sci. 588 (2021) 122–137, https://doi.org/10.1016/j.
jcis.2020.12.042.
[29] C.B. Ong, L.Y. Ng, A.W. Mohammad, A review of ZnO nanoparticles as solar
photocatalysts: synthesis, mechanisms and applications, Renew. Sustain. Energy
Rev. 81 (2018) 536–551, https://doi.org/10.1016/j.rser.2017.08.020.
[30] D. Kim, K. Yong, Boron doping induced charge transfer switching of a C3N4/ZnO
photocatalyst from Z-scheme to type II to enhance photocatalytic hydrogen
production, Appl. Catal. B Environ. 282 (2021), 119538, https://doi.org/
10.1016/j.apcatb.2020.119538.
[31] M.T. Uddin, M.E. Hoque, M. Chandra Bhoumick, Facile one-pot synthesis of
heterostructure SnO2/ZnO photocatalyst for enhanced photocatalytic
degradation of organic dye, RSC Adv. 10 (2020) 23554–23565, https://doi.org/
10.1039/d0ra03233f.
[32] M. Aqeel, M. Rashid, M. Ikram, A. Haider, S. Naz, J. Haider, A. Ul-Hamid,
A. Shahzadi, Photocatalytic, dye degradation, and bactericidal behavior of Cu-
doped ZnO nanorods and their molecular docking analysis, Dalt. Trans. 49 (2020)
8314–8330, https://doi.org/10.1039/d0dt01397h.
[33] T. Munawar, S. Yasmeen, F. Hussain, K. Mahmood, A. Hussain, M. Asghar,
F. Iqbal, Synthesis of novel heterostructured ZnO-CdO-CuO nanocomposite:
characterization and enhanced sunlight driven photocatalytic activity, Mater.
Chem. Phys. 249 (2020), 122983, https://doi.org/10.1016/j.
matchemphys.2020.122983.
[34] Q. Wang, K. Edalati, Y. Koganemaru, S. Nakamura, M. Watanabe, T. Ishihara,
Z. Horita, Photocatalytic hydrogen generation on low-bandgap black zirconia
(ZrO2) produced by high-pressure torsion, J. Mater. Chem. A. 8 (2020)
3643–3650, https://doi.org/10.1039/c9ta11839j.
[35] S. Polisetti, P.A. Deshpande, G. Madras, Photocatalytic activity of combustion
synthesized ZrO2 and ZrO2-TiO2 mixed oxides, Ind. Eng. Chem. Res. 50 (2011)
12915–12924, https://doi.org/10.1021/ie200350f.
[36] M.A. Wahba, S.M. Yakout, W.A.A. Mohamed, H.R. Galal, Remarkable
photocatalytic activity of Zr doped ZnO and ZrO2/ZnO nanocomposites:
structural, morphological and photoluminescence properties, Mater. Chem. Phys.
256 (2020), 123754, https://doi.org/10.1016/j.matchemphys.2020.123754.
[37] K. Anandan, K. Rajesh, K. Gayathri, S. Vinoth Sharma, S.G. Mohammed Hussain,
V. Rajendran, Effects of rare earth, transition and post transition metal ions on
structural and optical properties and photocatalytic activities of zirconia (ZrO2)
nanoparticles synthesized via the facile precipitation process, Phys. E Low-
Dimensional Syst. Nanostruct. 124 (2020), 114342, https://doi.org/10.1016/j.
physe.2020.114342.
[38] R.A.C. Amoresi, R.C. Oliveira, N.L. Marana, P.B. De Almeida, P.S. Prata, M.
A. Zaghete, E. Longo, J.R. Sambrano, A.Z. Simões, CeO2 nanoparticle
morphologies and their corresponding crystalline planes for the photocatalytic
degradation of organic pollutants, ACS Appl. Nano Mater. 2 (2019) 6513–6526,
https://doi.org/10.1021/acsanm.9b01452.
[39] M. Sridharan, P. Kamaraj, Y.S. Huh, S. Devikala, M. Arthanareeswari, J.A. Selvi,
E. Sundaravadivel, Quaternary CZTS nanoparticle decorated CeO2 as a noble
metal free p-n heterojunction photocatalyst for efficient hydrogen evolution,
Catal. Sci. Technol. 9 (2019) 3686–3696, https://doi.org/10.1039/c9cy00429g.
[40] M. Sridharan, P. Kamaraj, R. Vennila, Y.S. Huh, M. Arthanareeswari, Bio-inspired
construction of melanin-like polydopamine-coated CeO2 as a high-performance
visible-light-driven photocatalyst for hydrogen production, New J. Chem. 44
(2020) 15223–15234, https://doi.org/10.1039/d0nj02234a.
[41] Z. Cui, H. Zhou, G. Wang, Y. Zhang, H. Zhang, H. Zhao, Enhancement of the
visible-light photocatalytic activity of CeO2 by chemisorbed oxygen in the
selective oxidation of benzyl alcohol, New J. Chem. 43 (2019) 7355–7362,
https://doi.org/10.1039/c9nj01098j.
[42] H. Xu, S. Ouyang, L. Liu, P. Reunchan, N. Umezawa, J. Ye, Recent advances in
TiO2-based photocatalysis, J. Mater. Chem. A. 2 (2014) 12642–12661, https://
doi.org/10.1039/c4ta00941j.
[43] X. Wang, F. Wang, Y. Sang, H. Liu, Full-spectrum solar-light-activated
photocatalysts for light–chemical energy conversion, Adv. Energy Mater. 7
(2017) 1–15, https://doi.org/10.1002/aenm.201700473.
[44] Y. Sang, H. Liu, A. Umar, Photocatalysis from UV/Vis to near-infrared light:
towards full solar-light spectrum activity, ChemCatChem 7 (2015) 559–573,
https://doi.org/10.1002/cctc.201402812.
[45] X. Deng, C. Wang, H. Yang, M. Shao, S. Zhang, X. Wang, M. Ding, J. Huang, X. Xu,
One-pot hydrothermal synthesis of CdS decorated CuS microflower-like structures
for enhanced photocatalytic properties, Sci. Rep. 7 (2017) 32–36, https://doi.
org/10.1038/s41598-017-04270-y.
[46] Q. Wang, J. Lian, Q. Ma, S. Zhang, J. He, J. Zhong, J. Li, H. Huang, B. Su,
Preparation of carbon spheres supported CdS photocatalyst for enhancement its
photocatalytic H2 evolution, Catal. Today. 281 (2017) 662–668, https://doi.org/
10.1016/j.cattod.2016.05.013.
[47] B. He, R. Liu, J. Ren, C. Tang, Y. Zhong, Y. Hu, One-step solvothermal synthesis of
petalous carbon-coated Cu+ doped CdS nanocomposites with enhanced
photocatalytic hydrogen production, Langmuir 33 (2017) 6719–6726, https://
doi.org/10.1021/acs.langmuir.7b01450.
[48] Y. Chen, S. Hu, W. Liu, X. Chen, L. Wu, X. Wang, P. Liu, Z. Li, Controlled syntheses
of cubic and hexagonal ZnIn2S4 nanostructures with different visible-light
photocatalytic performance, Dalt. Trans. 40 (2011) 2607–2613, https://doi.org/
10.1039/c0dt01435d.
[49] H. Liu, Z. Jin, Z. Xu, Z. Zhang, D. Ao, Fabrication of ZnIn2S4-g-C3N4 sheet-on-
sheet nanocomposites for efficient visible-light photocatalytic H2-evolution and
degradation of organic pollutants, RSC Adv. 5 (2015) 97951–97961, https://doi.
org/10.1039/c5ra17028a.
[50] N. Ding, Y. Fan, Y. Luo, D. Li, Q. Meng, Enhancement of H2 evolution over new
ZnIn2S4/RGO/MoS2 photocatalysts under visible light, APL Mater. 3 (2015),
https://doi.org/10.1063/1.4930213.
[51] S. Kundu, K. Bramhaiah, S. Bhattacharyya, Carbon-based nanomaterials: in the
quest of alternative metal-free photocatalysts for solar water splitting, Nanoscale
Adv. 2 (2020) 5130–5151, https://doi.org/10.1039/d0na00569j.
[52] N. Syed, J. Huang, Y. Feng, X. Wang, L. Cao, Carbon-based nanomaterials via
heterojunction serving as photocatalyst, Front. Chem. 7 (2019) 1–7, https://doi.
org/10.3389/fchem.2019.00713.
[53] J. Fu, J. Yu, C. Jiang, B. Cheng, g-C3N4-based heterostructured photocatalysts,
Adv. Energy Mater. 8 (2018) 1–31, https://doi.org/10.1002/aenm.201701503.
[54] X. Zhang, Y. Yang, W. Huang, Y. Yang, Y. Wang, C. He, N. Liu, M. Wu, L. Tang, g-
C3N4/UiO-66 nanohybrids with enhanced photocatalytic activities for the
oxidation of dye under visible light irradiation, Mater. Res. Bull. 99 (2018)
349–358, https://doi.org/10.1016/j.materresbull.2017.11.028.
[55] J. Wen, J. Xie, X. Chen, X. Li, A review on g-C3 N4 -based photocatalysts, Appl.
Surf. Sci. 391 (2017) 72–123, https://doi.org/10.1016/j.apsusc.2016.07.030.
[56] J. Chen, X. Zhang, F. Bi, X. Zhang, Y. Yang, Y. Wang, A facile synthesis for
uniform tablet-like TiO2/C derived from Materials of Institut Lavoisier-125(Ti)
(MIL-125(Ti)) and their enhanced visible light-driven photodegradation of
tetracycline, J. Colloid Interface Sci. 571 (2020) 275–284, https://doi.org/
10.1016/j.jcis.2020.03.055.
[57] J. Chen, X. Zhang, X. Shi, F. Bi, Y. Yang, Y. Wang, Synergistic effects of octahedral
TiO2-MIL-101(Cr) with two heterojunctions for enhancing visible-light
photocatalytic degradation of liquid tetracycline and gaseous toluene, J. Colloid
Interface Sci. 579 (2020) 37–49, https://doi.org/10.1016/j.jcis.2020.06.042.
[58] A. Of, J. Yang, L. Berkeley, C. Physics, C.L. Guiyang, Roles of cocatalysts in
photocatalysis and, Acc. Chem. Res. 46 (2013) 1900–1909.
[59] J. Ran, J. Zhang, J. Yu, M. Jaroniec, S.Z. Qiao, Earth-abundant cocatalysts for
semiconductor-based photocatalytic water splitting, Chem. Soc. Rev. 43 (2014)
7787–7812, https://doi.org/10.1039/c3cs60425j.
[60] L.Z. Qin, Y.Z. Lin, Y.C. Dou, Y.J. Yang, K. Li, T. Li, F.T. Liu, Toward enhanced
photocatalytic activity of graphite carbon nitride through rational design of noble
metal-free dual cocatalysts, Nanoscale. 12 (2020) 13829–13837, https://doi.org/
10.1039/c9nr10044j.
[61] N. Chen, Z. Zhu, H. Ma, W. Liao, H. Lü, Catalytic upgrading of biomass-derived 5-
hydroxymethylfurfural to biofuel 2,5-dimethylfuran over Beta zeolite supported
non-noble Co catalyst, Mol. Catal. 486 (2020), 110882, https://doi.org/10.1016/
j.mcat.2020.110882.
[62] Y. Zheng, J. Dong, C. Huang, L. Xia, Q. Wu, Q. Xu, W. Yao, Co-doped Mo-Mo2C
cocatalyst for enhanced g-C3N4 photocatalytic H2 evolution, Appl. Catal. B
Environ. 260 (2020), 118220, https://doi.org/10.1016/j.apcatb.2019.118220.
[63] D. Gao, W. Liu, Y. Xu, P. Wang, J. Fan, H. Yu, Core-shell Ag@Ni cocatalyst on the
TiO2 photocatalyst: One-step photoinduced deposition and its improved H2-
evolution activity, Appl. Catal. B Environ. 260 (2020), 118190, https://doi.org/
10.1016/j.apcatb.2019.118190.
[64] M. Song, Y. Wu, G. Zheng, C. Du, Y. Su, Junction of porous g-C3N4 with BiVO4
using Au as electron shuttle for cocatalyst-free robust photocatalytic hydrogen
evolution, Appl. Surf. Sci. 498 (2019), 143808, https://doi.org/10.1016/j.
apsusc.2019.143808.
M. Sridharan and T. Maiyalagan