Graphene-based semiconductor photocatalysts

Review: 158 refs.

Synthesis of RGO (reduced graphene oxide)-CdS composite material was performed through CBD (chemical bath deposition) method in which graphene oxide served as the support and Cadmium Sulfate Hydrate as the starting material. Graphene-based semiconductor photocatalysts have attracted extensive attention due to their usefulness for environmental and energy applications. The band gap (2.4 eV) of CdS corresponds well with the spectrum of sunlight because the crystalline phase, size, morphology, specic surface area and defects, etc., of CdS can affect its photocatalytic activity. The specific surface structure (morphology) of the photocatalyst can be effective for the suppression of recombination between photogenerated electrons and holes. Graphene (GN) has unique properties such as a high value of Young`s modulus, large theoretical specific surface area, excellent thermal conductivity, high mobility of charge carriers, and good optical transmittance. These excellent properties make GN an ideal building block in nanocomposites. It can act as an excellent electron-acceptor/transport material. Therefore, the morphology, structural characterization and crystal structure were observed using various analytical tools, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. From this analysis, it is shown that CdS particles were well dispersed uniformly in the RGO sheet. Furthermore, the photocatalytic property of the resulting RGO-CdS composite is also discussed in relation to environmental applications such as the photocatalytic degradation of pollutants. It was found that the prepared RGO-CdS nanocomposites exhibited enhanced photocatalytic activity as compared with that of CdS nanoparticles. Therefore, better efficiency of photodegradation was found for water purification applications using RGO-CdS composite.

Enhanced photocatalytic activity of hierarchical macro/mesoporous TiO2–graphene composites for photodegradation of acetone in air

Current energy crisis and environmental issues, including depletion of fossil fuels, rapid industrialization, and undesired CO2 emission resulting in global warming has created havoc for the global population and significantly affected the quality of life. In this scenario the environmental problems in the forefront of research priorities. Development of renewable energy resources particularly the efficient conversion of solar light to sustainable energy is crucial in addressing environmental problems. In this regard, the synthesis of semiconductors-based photocatalysts has emerged as an effective tool for different photocatalytic applications and environmental remediation. Among different photocatalyst options available, graphene and graphene derivatives such as, graphene oxide (GO), highly reduced graphene oxide (HRG), and doped graphene (N, S, P, B-HRG) have become rising stars on the horizon of semiconductors-based photocatalytic applications. Graphene is a single layer of graphite consisting of a unique planar structure, high conductivity, greater electron mobility, and significantly very high specific surface area. Besides, the recent advancements in synthetic approaches have led to the cost-effective production of graphene-based materials on a large-scale. Therefore, graphene-based materials have gained considerable recognition for the production of semiconducting photocatalysts involving other semiconducting materials. The graphene-based semiconductors photocatalysts surpasses electron-holes pairs recombination rate and lowers the energy band gap by tailoring the valence band (VB) and conduction band (CB) leading to the enhanced photocatalytic performance of hybrid photocatalysts. Herein, we have summarized the latest developments in designing and fabrication of graphene-based semiconducting photocatalysts using a variety of commonly applied methods such as, post-deposition methods, in-situ binding methods, hydrothermal and/or solvothermal approaches. In addition, we will discuss the photocatalytic properties of the resulting graphene-based hybrid materials for various environmental remediation processes such as; (i) clean H2 fuel production, photocatalytic (ii) pollutants degradation, (iii) photo-redox organic transformation and (iv) photo-induced CO2 reduction. On the whole, by the inclusion of more than 300 references, this review possibly covered in detail the aspects of graphene-based semiconductor photocatalysts for environmental remediation processes. Finally, the review will conclude a short summary and discussion about future perspectives, challenges and new directions in these emerging areas of research.

Efficient photocatalysts for hydrogen production and pollutant degradation are crucial to address energy and environmental challenges. metal–organic framework (MOF)‐derived Cu x O/TiO 2 /C (TCC) composites are synthesized from Cu‐doped NH 2 ‐MIL‐125(Ti) and their performance in photodegradation of pollutants and photocatalytic hydrogen generation are evaluated. These porous TCC composites demonstrate rapid adsorption capacities and greatly enhance photocatalytic degradation of organic pollutants under visible light, with TCC‐1 achieving complete pollutants removal in 90 min due to adsorption and photocatalysis. Moreover, these Cu x O/TiO 2 /C composites exhibit superior photocatalytic hydrogen evolution performance, and TCC‐2 achieves the highest hydrogen production rate of 2339 μmol g −1 h −1 , 13 times greater than TiO 2 /C. The enhanced activity is attributed to the formation of type‐II band alignment between the coexisted anatase and rutile TiO 2 phases, the presence of Cu 2 O/CuO heterojunctions that facilitate p–n charge separation, and Cu 0 clusters as electron sinks to accelerate proton reduction. Porous carbon boosts adsorption and also provides rapid electron transport pathways. Additionally, the coexistence of multiple Cu species (Cu 2+ /Cu + ) facilitates reversible redox shuttling, suppressing electron–hole recombination. The synergistic effects of these structural and electronic features lead to superior hydrogen generation and pollutant degradation activity of TCC composites, demonstrating the promise of MOF‐derived photocatalysts for sustainable energy and environmental applications.

Graphene, have two-dimensional structure with high conductivity, extremely high specific surface area and superior electron mobility etc. It has been regarded as an important synthesis material for various composite materials used in many applications. Especially, graphene-based semiconductor photo catalysts have attracted extensive attention because of their usefulness in environmental applications such as air cleanup, water disinfection, hazardous waste remediation, and water purification. The present study involves the photo catalytic degradation of methyl orange by photo catalytic process using different concentrations of ZrO2/graphene synthesized at different annealing temperature. A series of zirconium oxide (ZrO2, zirconia) and graphene (Gr) composites with different contents of Gr (5.7, 7.3, 8.3 %) in the composite were synthesized using zirconium oxychloride (ZrOCl2·8H2O) and graphene oxide as the starting materials. The photocatalytic activities of the synthesized composites were measured for the degradation of methyl orange dye with UV spectroscopy. The rate of decolorization was recorded with respect to the change in intensity of absorption peaks for methyl orange. The absorption peaks, diminished and finally disappeared during reaction, indicating that the dye had been degraded. The photocatalytic activity is strongly affected by the concentration of graphene in the ZrO2. The synthesized ZrO2/graphene photocatalysts are characterized by X-ray diffraction, TGA, Raman spectroscopy and UV–Visible spectroscopy. Finally, it has been concluded that graphene when employed as catalytic support for ZrO2 boost its photo catalytic efficiency. Effect of graphene on photo catalytic activity of ZrO2 anneal at 1,000 °C.

Graphene is a single layer of graphite with a unique two-dimensional structure with high conductivity, superior electron mobility, absorptivity, and specific surface area. The extraordinary mechanical, thermal, and electrical properties of graphene are due to long-range π conjugation. Due to these properties, graphene can be used in nanosystems and nano- devices. The photocatalytic efficiency of composites (semiconductor-based metal oxides and graphene-based photocatalysts) can be improved under visible light. Graphene behaves as an electron acceptor in these types of composite photocatalysts. Different types of graphene-based composites (graphene (G)-semiconductor, graphene oxide (GO)-semiconductor, and reduced graphene oxide (RGO)-semiconductor, where the semiconductor is TiO2 , ZnO, CdS, Zn2SnO4 , etc.) can be prepared through simple mixing and/or sonication, sol-gel process, liquid-phase, hydrothermal, and solvothermal methods. This chapter includes the most recent advances in different applications of graphene-based semiconductor photocatalysts for degrading various contaminants (treatment of waste water) and producing hydrogen (fuel of future) by photosplitting water, and photo-catalytically reducing carbon dioxide to energy-rich synthetic fuels (combating against global warming and energy crisis), etc<br>

Graphitic carbon nitride (g-C(3)N(4)), as an intriguing earth-abundant visible light photocatalyst, possesses a unique two-dimensional structure, excellent chemical stability and tunable electronic structure. Pure g-C(3)N(4) suffers from rapid recombination of photo-generated electron-hole pairs resulting in low photocatalytic activity. Because of the unique electronic structure, the g-C(3)N(4) could act as an eminent candidate for coupling with various functional materials to enhance the performance. According to the discrepancies in the photocatalytic mechanism and process, six primary systems of g-C(3)N(4)-based nanocomposites can be classified and summarized: namely, the g-C(3)N(4) based metal-free heterojunction, the g-C(3)N(4)/single metal oxide (metal sulfide) heterojunction, g-C(3)N(4)/composite oxide, the g-C(3)N(4)/halide heterojunction, g-C(3)N(4)/noble metal heterostructures, and the g-C(3)N(4) based complex system. Apart from the depiction of the fabrication methods, heterojunction structure and multifunctional application of the g-C(3)N(4)-based nanocomposites, we emphasize and elaborate on the underlying mechanisms in the photocatalytic activity enhancement of g-C(3)N(4)-based nanocomposites. The unique functions of the p-n junction (semiconductor/semiconductor heterostructures), the Schottky junction (metal/semiconductor heterostructures), the surface plasmon resonance (SPR) effect, photosensitization, superconductivity, etc. are utilized in the photocatalytic processes. Furthermore, the enhanced performance of g-C(3)N(4)-based nanocomposites has been widely employed in environmental and energetic applications such as photocatalytic degradation of pollutants, photocatalytic hydrogen generation, carbon dioxide reduction, disinfection, and supercapacitors. This critical review ends with a summary and some perspectives on the challenges and new directions in exploring g-C(3)N(4)-based advanced nanomaterials.

14 - Conductive polymer-based composite photocatalysts for environment and energy applications

Graphene-based photocatalysts for degradation of organic pollution

Graphene-based materials receive attention in the field of energy and environmental application. The unique physiochemical assets such as the high surface area, high thermal stability, chemical flexibility, high electron mobility and mechanical solidity make it a highly versatile material for different applications. In this critical review, the application of graphene-based material in energy and environmental remediation is discussed in detail. More specifically, the role of graphene in thought-provoking research fields, viz. solar cell, photocatalytic water splitting, photocatalytic degradation of organic pollutants and heavy metal removal, is focused. As graphene possesses very good carrier mobility, it enhances the photocatalytic performance of semiconducting materials. Very interestingly, graphene is being used in both hole transport layer and electron transport layer in solar cell. Similarly, high surface area of graphene assists in heavy metal removal by adsorption. The challenges and recent achievements in these fields are highlighted in this review.

Graphitic carbon nitride (g-C3N4), since the pioneering work on visible-light photocatalytic water splitting in 2009, has emerged as a highly promising advanced material for environmental and energetic applications, including photocatalytic degradation of pollutants, photocatalytic hydrogen generation, and carbon dioxide reduction. Due to its distinctive two-dimensional structure, excellent chemical stability, and distinctive optical and electrical properties, g-C3N4 has garnered a considerable amount of interest in the field of biomedicine in recent years. This review focuses on the fundamental properties of g-C3N4, highlighting the synthesis and modification strategies associated with the interfacial structures of g-C3N4-based materials, including heterojunction, band gap engineering, doping, and nanocomposite hybridization. Furthermore, the biomedical applications of these materials in various domains, including biosensors, antimicrobial applications, and photocatalytic degradation of medical pollutants, are also described with the objective of spotlighting the unique advantages of g-C3N4. A summary of the challenges faced and future prospects for the advancement of g-C3N4-based materials is presented, and it is hoped that this review will inspire readers to seek further new applications for this material in biomedical and other fields.

Atomic Layer Deposition for Energy and Environmental Applications

In the pursuit towards the use of sunlight as a sustainable source for energy generation and environmental remediation, photocatalytic water splitting and photocatalytic pollutant degradation have recently gained significant importance. Research in this field is aimed at solving the global energy crisis and environmental issues in an ecologically-friendly way by using two of the most abundant natural resources, namely sunlight and water. Over the past few years, carbon-based nanocomposites, particularly graphene and graphitic carbon nitride, have attracted much attention as interesting materials in this field. Due to their unique chemical and physical properties, carbon-based nanocomposites have made a substantial contribution towards the generation of clean, renewable and viable forms of energy from light-based water splitting and pollutant removal. This review article provides a comprehensive overview of the recent research progress in the field of energy generation and environmental remediation using two-dimensional carbon-based nanocomposites. It begins with a brief introduction to the field, basic principles of photocatalytic water splitting for energy generation and environmental remediation, followed by the properties of carbon-based nanocomposites. Then, the development of various graphene-based nanocomposites for the above-mentioned applications is presented, wherein graphene plays different roles, including electron acceptor/transporter, cocatalyst, photocatalyst and photosensitizer. Subsequently, the development of different graphitic carbon nitride-based nanocomposites as photocatalysts for energy and environmental applications is discussed in detail. This review concludes by highlighting the advantages and challenges involved in the use of two-dimensional carbon-based nanocomposites for photocatalysis. Finally, the future perspectives of research in this field are also briefly mentioned.

Engineering the plasmonic nanohybrid structures to provide the advancement in their optical and photocatalytic profiles is one of the important aspects for the development of several environmental and energy applications. Plasmonic nanohybrids, integration of semiconductors and noble nanoparticles provide efficient charge separation due to Schottky junction and plasmon nanoparticle induced electromagnetic field. Effective charge separation and electromagnetic features make plasmonic nanohybrids a promising candidate for SERS-based detection environmental detoxification and energy harvesting applications. In the present chapter, we will summarize and elaborate the different strategies and modification techniques to enhance photocatalytic-driven environmental and energy applications. Moreover, the current chapter also includes the detection of various harmful pollutant molecules and their decomposition under sunlight using several plasmonic nanohybrids. This chapter also reveals the origins of morphological, optical, and plasmonic variations on TiO2 nanostructures for enhanced photocatalytic efficiency. We have also highlighted the probable mechanism due to the plasmonic nanoparticles’ aspects over TiO2 nanostructures and their future perspectives of advanced photocatalysis. This chapter provides the fundamental synthesis aspects of plasmonic nanohybrid and their possible usage in energy and environmental applications significantly. This chapter will provide a basic understanding for the readers to develop several plasmonic nanostructures for environmental applications.