Photocatalyst For Hydrogen Generation Research Articles

Co–TiO2 supported on reduced graphene oxide as a highly active and stable photocatalyst for hydrogen generation

We have developed a highly active and stable catalyst based on Co and TiO2 nanoparticles anchored on reduced graphene oxide (rGO) sheets for the photocatalytic hydrogen generation from water splitting. The catalyst was prepared using a novel methodology involving the modified Hummers approach followed by pyrolysis. The crystallinities, morphologies, optical properties, and chemical structures of the synthesized catalysts were investigated using different characterization techniques. The photocatalytic activity was investigated under UV–vis spectroscopy in solutions containing different Na2S + Na2SO3 concentrations and methanol as hole scavengers. The optimized composite that comprises Co: TiO2:rGO (1:6:10) shows a 2.5-fold improvement in the catalyst efficiency under UV–vis compared to bare TiO2, and it was recycled with the same activity for three cycles. This remarkable improvement in the photocatalytic activity of the developed nanocomposites compared to TiO2 can be attributed to the improved capacity of the nanocomposites to absorb visible light and efficiently separate charge carriers at the interface.

The synthesis of Cu-TCPP MOF/g-C3N4 heterojunctions as efficient photocatalysts for hydrogen generation

Semiconductor photocatalysis is a potential solution to meet energy needs with green and inexhaustible solar energy.

Au@CdS Nanocomposites as a Visible-Light Photocatalyst for Hydrogen Generation from Tap Water

The Au@CdS nanocomposites have been synthesized using a combination of wet chemical and hydrothermal approaches at lower reaction temperatures. The concentrations of CdS precursors and reaction temperature can be essential in influencing photocatalytic water splitting under blue-LED light excitation. The optimized Au@CdS nanocomposites (5 mM CdS precursors and 100 °C) exhibited the highest hydrogen evolution rate of 1.041 mmolh−1 g−1, which is 175.3 times higher than CdS nanoparticles for de-ionized water under blue-LED light excitation. This result is ascribed to separate photogenerated charge carriers and increased light absorption by the Au core. The Au@CdS nanocomposites (1.204 mmolh−1 g−1) revealed significant applications in photocatalytic tap water splitting under blue-LED light excitation, which is 512.3 times higher than CdS nanoparticles. In addition, reusability experiments demonstrate that Au@CdS nanocomposites exhibit excellent stability for the long-term photocatalytic tap water splitting process. Furthermore, this research shows that Au nanoparticles decorated with CdS shells effectively achieve high-efficiency conversion from light to hydrogen energy.

Efficient Visible-Light Driven Photocatalytic Hydrogen Production by Z-Scheme ZnWO4/Mn0.5Cd0.5S Nanocomposite without Precious Metal Cocatalyst

How to restrain the recombination of photogenerated electrons and holes is still very important for photocatalytic hydrogen production. Herein, Z-scheme ZnWO4/Mn0.5Cd0.5S (ZWMCS) nanocomposites are prepared and are applied as visible-light driven precious metal cocatalyst free photocatalyst for hydrogen generation. The ZnWO4/Mn0.5Cd0.5S nanocomposites with 30 wt% ZnWO4 (ZWMCS-2) can reach a photocatalytic hydrogen evolution rate of 3.36 mmol g−1 h−1, which is much higher than that of single ZnWO4 (trace) and Mn0.5Cd0.5S (1.96 mmol g−1 h−1). Cycling test reveals that the ZMWCS-2 nanocomposite can maintain stable photocatalytic hydrogen evolution for seven cycles (21 h). The type of heterojunction in the ZWMCS-2 nanocomposite can be identified as Z-scheme heterojunction. The Z-scheme heterojunction can effectively separate the electrons and holes, so that the hydrogen generation activity and stability of the ZWMCS-2 nanocomposite can be enhanced. This work provides a highly efficient and stable Z-scheme heterojunction photocatalyst for hydrogen generation.

Metal Sulfide Photocatalysts for Hydrogen Generation: A Review of Recent Advances

Metal-sulfide nanostructures have piqued the interest of researchers for decades due to their intriguing optoelectronic properties. Indeed, significant advances and improvements have been made in various fundamental aspects for cutting-edge applications, such as water splitting and hydrogen production. Furthermore, rising demand for low-dimensional materials due to lower material consumption and improved performance due to quantum size effects has spurred research on semiconducting metal sulfides. Consequently, size-controllable nanostructures with diverse morphologies have been fabricated and studied for potential applications. However, the photocatalytic hydrogen evolution rate is still limited mainly by fast recombination rate, poor solar energy utilization and lack of surface-active sites for H2 reduction. This review will highlight particularly recent findings in metal-sulfide-based photocatalysts for hydrogen evolution reactions, considering the swift development and excellent research in this field. Following a brief overview of fundamental properties, we will explore state-of-the-art strategies for enhancing H2 generation efficiencies over the pristine, heterostructured and co-catalayzed metal-sulfide photocatalysts.

Laser-Based Synthesis of TiO2-Pt Photocatalysts for Hydrogen Generation.

The development of visible-light active titanium dioxide is one of the key challenges in photocatalysis that stimulates the development of TiO2-based composite materials and methods for their synthesis. Here, we report the use of pristine and Pt-modified dark titanium dioxide prepared via pulsed laser ablation in liquid (Nd:YAG laser, 1064 nm, 7 ns) for photocatalytic hydrogen evolution from alcohol aqueous solutions. The structure, textural, optical, photoelectrochemical, and electrochemical properties of the materials are studied by a complex of methods including X-ray diffraction, low-temperature nitrogen adsorption, electrophoretic light scattering, diffuse reflection spectroscopy, photoelectrochemical testing, and electrochemical impedance spectroscopy. Both the thermal treatment effect and the effect of modification with platinum on photocatalytic properties of dark titania materials are studied. Optimal compositions and experimental conditions are selected, and high photocatalytic efficiency of the samples in the hydrogen evolution reaction (apparent quantum yield of H2 up to 0.38) is demonstrated when irradiated with soft UV and blue LED, i.e., 375 and 410 nm. The positive effect of low platinum concentrations on the increase in the catalytic activity of dark titania is explained.

Omnidirectional Hydrogen Generation Based on a Flexible Black Gold Nanotube Array.

Solar-driven hydrogen generation is emerging as an economical and sustainable means of producing renewable energy. However, current photocatalysts for hydrogen generation are mostly powder-based or rigid-substrate-supported, which suffer from limitations, such as difficulties in catalyst regeneration or poor omnidirectional light-harvesting. Here, we report a two-dimensional (2D) flexible photocatalyst based on elastomer-supported black gold nanotube (GNT) arrays with conformal CdS coating and Pt decoration. The highly porous GNT arrays display a strong light-trapping effect, leading to near-complete absorption over almost the entire range of the solar spectrum. In addition, they offer high surface-to-volume ratios promoting efficient photocatalytic reactions. These structural features result in high H2 generation efficiencies. Importantly, our elastomer-supported photocatalyst displays comparable photocatalytic activity even when being mechanically deformed, including bending, stretching, and twisting. We further designed a three-dimensional (3D) tree-like flexible photocatalytic system to mimic Nature's photosynthesis, which demonstrated omnidirectional H2 generation. We believe our strategy represents a promising route in designing next-generation solar-to-fuel systems that rival natural plants.

Bromide‐Mediated Reduction Kinetics and Oxidative Etching for Manipulating the Twin Structure and Facet of Pd Nanocrystals for Catalysis

AbstractWith Pd as an example, a set of quantitative analyses is designed to shed light on the bromide‐mediated reduction kinetics and oxidative etching in determining the twin structure and facet of Pd nanocrystals. The success of this work relies on the kinetic measurements of Pd(II) precursor reduction and the close examinations of resultant Pd seeds and nanocrystals at different stages of synthesis. We observe there is a clear trend where low, moderate, and high initial Pd(II) reduction rates regulated by Br− ions correspond to the formation of Pd seeds with singly‐twinned, multiply‐twinned, and single‐crystal structures in the nucleation stage, respectively. Our quantitative analyses also suggest the oxidative etching induced by oxygen/Br− pair can selectively remove the multiply‐twinned Pd seeds from the products in the growth stage while leaving behind singly‐twinned or single‐crystal Pd seeds for the evolution into Pd nanocrystals with well‐defined facets in high purity. The mechanistic insights obtained in this work can be extended to the synthesis of Pd@Pd−Pt core−shell nanocubes with high‐index facets, which can be used as excellent electrocatalysts and photocatalysts for hydrogen generation.

Designing Nanoengineered Photocatalysts for Hydrogen Generation by Water Splitting and Conversion of Carbon Dioxide to Clean Fuels.

Semiconductor photocatalysis has received tremendous attention in the past decade as it has shown great promise in the context of clean energy harvesting for environmental remediation. Sunlight is an inexhaustible source of energy available to us throughout the year, although it is rather dilutely dispersed. Semiconductor based photocatalysis presents one of the best ways to harness this source of energy to carry out chemical reactions of interest that require external energy input. Photocatalytic hydrogen generation by splitting of water, CO2 mitigation, and CO2 conversion to green fuel have therefore become the highly desirable clean and sustainable processes for a better tomorrow. Although numerous efforts have been made and continue to be expended to search and develop new classes of photocatalyst materials in recent years, several significant challenges still remain to be resolved before photocatalysis can reach its commercial potential. Therefore, major attention is required towards improving the efficiencies of the existing photocatalysts by further manipulating them and parallelly employing newer strategies for novel photocatalyst designs. This personal account aims to provide a broad overview of the field primarily invoking examples of our own research contributions in the field, which include photocatalytic hydrogen generation and CO2 reduction to value added chemicals. This account reviews the state-of-the-art research activities and scientific possibilities which a functional material can offer if its properties are put to best use through goal-oriented design by combining with other compatible materials. We have addressed fundamental principles of photocatalysis, different kind of functional photocatalysts, critical issues associated with them and various strategies to overcome the related hurdles. It is our hope that this current personal account will provide a platform for young researchers to address the bottleneck issues in the field of photocatalysis and photocatalysts with a sense of clarity, and to find innovative solutions to resolve them by a prudent choice of materials, synthesis protocols, and approaches to boost the photocatalysis output. We emphasize that a targeted or goal-directed photocatalyst nanoengineering as perhaps the only way to realize an early success in this multiparametric domain.

Metal Halide Perovskite Heterojunction for Photocatalytic Hydrogen Generation: Progress and Future Opportunities

AbstractPhotocatalytic hydrogen generation paves a promising way to mitigate the global energy crisis and deteriorative environmental issues. Among different materials, metal halide perovskites (MHPs) have recently emerged as a promising class of inexpensive and easy‐to‐make semiconductors for various photocatalytic applications such as organic contaminant degradation, CO2 reduction, H2 evolution, and N2 fixation. Although MHPs‐based standalone photocatalysts offer architectural simplicity, they provide restricted control over recombination processes and spatial separation of redox half‐reactions. Meanwhile, heterojunction systems are of growing interest due to their ability to control energy‐consuming redox processes and effectively suppress charge carrier recombination. In this review, the authors elaborately discuss perovskite‐based heterojunction photocatalysts for hydrogen generation both from a material chemistry point of view and band alignment perspective. They discuss the design principle of MHP heterostructures necessary for H2 evolution and the underlying photo‐physics behind process optimization. Moving forward, they conclude by meticulously outlining the ongoing challenges, opportunities, and future outlooks for MHP‐based heterojunction photocatalysts for H2 evolution.

Controlled synthesis of Pt-loaded yolk-shell TiO2@SiO2 nanoreactors as effective photocatalysts for hydrogen generation

Controlled synthesis of Pt-loaded yolk-shell TiO2@SiO2 nanoreactors as effective photocatalysts for hydrogen generation

Opto-electrochemical characteristics of synthesized BaFe2O4 nanocomposites: Photocatalytic degradation and hydrogen generation investigation

We report on this study the optical and photo-electrochemical properties of BaFe2O4 (BFO) nanoparticles and their role in photocatalytic degradation of an organic pollutant and hydrogen generation. The spinel BFO was synthesized by the sol-gel route and formed at 900 °C, the phase was identified by the X-ray diffraction (XRD) analysis, confirmed by the Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The morphology was investigated by scanning electron microscopy (SEM). The optical and dielectric properties of BFO were investigated by the photoluminescence (PL) and the diffuse reflectance spectrum (DRS); An optical gap of 2.10 eV was found. The cyclic voltammetry of BFO has shown promising outcomes in the generation of hydrogen under visible light with a potential of (∼- 0.91 VSCE). The electrochemical impedance spectroscopy (EIS) was also undertaken in the dark and under illumination. In order to support the results, we tested the activity of this spinel for the degradation of Rhodamine B (Rh B), 93% of Rh B was oxidized after 3 h with a quantum efficiency of 0.32% by the BFO/ZnO. The use of the new BFO/ZnO hetero-system by adding ZnO nanoparticles was performed to enhance the photocatalytic activity which generates radicals for the Rh B degradation and hydrogen liberation. The degradation radicals were determined by scavenger tests, both O2•−and •OH were the main reactive species. Moreover, the stability of BFO/ZnO hetero-system was demonstrated for four consecutive cycles. Hence, the hetero-system was found to be an efficient photocatalyst for hydrogen generation by facilitation of the photo-electron transfer with the deference potential (Ered – EZnO–CB = ∼0.14 VSCE); This opens up new opportunities for hydrogen production as we can say that energy supply has a high priority in our time due to its importance.

Precursor self-derived Cu@TiO2 hybrid Schottky junction for enhanced solar-to-hydrogen evolution

Solar-to-hydrogen production has attracted increasing attention since it possesses great potential in alleviating energy and environmental crises to some extent. The key issue is to develop efficient photocatalysts exhibiting superior hydrogen production capability. In this work, Cu@TiO 2 hybrid (Cu nanoparticles encapsulated in TiO 2 ) has been successfully prepared by Cu 2 O self-template reduction through solvothermal treatment in ethylene glycol-water mixed solvent. When octahedral Cu 2 O is involved in the reaction system, the Cu 2 O@Ti-precursor octahedral structure is first formed and subsequently the Cu@TiO 2 hybrid is prepared with the reduction of ethylene glycol (EG). The Cu@TiO 2 hybrid derived with different mass of Cu exhibits improved photocatalytic hydrogen production performance compare to pure TiO 2 and P25. Among those photocatalysts, the Cu@TiO 2 -10% (the copper content is 10 wt%) shows the highest hydrogen evolution rate of 4336.7 μmol g −1 h −1 , and it is twice as much as the pure TiO 2 and 1.9 times as much as P25, respectively. Based on the photo/electrochemical results, an efficient photo-generated electron-hole separation contributes to the enhancement of photocatalytic H 2 evolution upon the Cu@TiO 2 hybrid. When replacing octahedral Cu 2 O with cubic and truncated octahedrons ones, the Cu@TiO 2 hybrid photocatalysts are also obtained and they also display superior solar-to-hydrogen evolution than pure TiO 2 and P25. It is expected this work could develop an approach to design Cu-encapsulated hybrid photocatalysts for hydrogen generation. •Cu@TiO 2 hybrid photocatalyst was prepared by a facile solvothermal method. •Different structured Cu 2 O were employed to prepare Cu@TiO 2 hybrid nanostructures. •The formed Schottky junction between Cu and TiO 2 facilitated the charge separation. • The Cu@TiO 2 hybrid Schottky junction showed enhanced photocatalytic hydrogen evolution.

Metal–organic frameworks with mixed-anion secondary building units as efficient photocatalysts for hydrogen generation

Three new CPs (Cu-X-bpy, X = Cl/Br, Cl/I or Br/I; bpy = 4,4′-bipyridine) with mixed-anion secondary building units (SBUs) were successfully synthesized and their structures were confirmed by X-ray crystallography, PXRD, far-IR and Raman spectroscopy, EXAFS, EDX, element analysis and ICP-MS. Their photocatalytic H2 productivities were systematically investigated and compared with corresponding single-anion Cu-X-bpy (X = Cl, Br, I). It was found that the CPs possess excellent H2 productivity even without additional photosensitizer and cocatalyst, and their activities can be significantly enhanced from 2.79 (Cu-I-bpy) to 10.04 mmol/gh (Cu-Cl/I-bpy) by simply varying the anions, μ-X-, in SBUs. Mechanistic investigations indicate that the water dissociation and hydrogen adsorption energies during water splitting can be regulated by just varying μ-X- in SBUs, which majorly accounts for their great discrepancy in H2 productivity rather than the light harvesting, charge separation and transfer efficiency of Cu-X-bpy. This finding enlightens a new approach for designing water splitting and related catalytic materials.

ZnO-based heterostructures as photocatalysts for hydrogen generation and depollution: a review

ZnO-based heterostructures as photocatalysts for hydrogen generation and depollution: a review

Electron-Rich and Hole-Rich Sites on Graphene Oxide for the Hydrogen Evolution from Formic Acid; Gold Supported on Graphene Oxide/Silica Photocatalyst for Hydrogen Generation

Electron-Rich and Hole-Rich Sites on Graphene Oxide for the Hydrogen Evolution from Formic Acid; Gold Supported on Graphene Oxide/Silica Photocatalyst for Hydrogen Generation

Au@Cds Nanocomposites as a Visible-Light Photocatalyst for Hydrogen Generation from Tap Water

Au@Cds Nanocomposites as a Visible-Light Photocatalyst for Hydrogen Generation from Tap Water

A review on the visible light active modified photocatalysts for water splitting for hydrogen production

There are various methods to produce hydrogen from water splitting as a substitute energy resource for fossil fuels in accordance with the global environmental crisis. Among these, water photocatalysis is considered one of the most renewable and sustainable processes simulated the solar energy utilized system in nature. During a half century, different kinds of photocatalysts were developed to convert photon energy into chemical energy to induce redox potential under visible light irradiation condition. In the beginning step, semiconductor materials, such as transition metal oxides, were explored extensively to use as a photocatalyst for hydrogen generation. However, semiconductor has limitations to act as an effective photocatalyst for water splitting due to the large band gap and recombination of charge carriers. Therefore, several kinds of modifications of structure or components have been studied to design visible light active photocatalysts for water splitting to generate hydrogen. Their performance was improved substantially by adding a noble metal or sensitizer to adjust the band gap and reduce the recombination of photoinduced charge carriers. Considering solar light-induced photocatalytic hydrogen generation, various visible light active photocatalysts have been derived from carbon chain organic compounds and lattice crystals. This review classifies the visible light active photocatalysts as follows: (a) structural and chemical components of modified graphitic carbon nitride (g-C3N4), (b) exfoliated perovskites, and (c) π-bond conjugated polymers to produce hydrogen from water splitting. The hydrogen evolution efficiency of photocatalysts shows a great difference under visible light (λ > 400 nm) irradiation according to the three-dimensional structure and electron transfer pathway. This is because the capability of restricting the recombination of photoinduced charge carriers and the band gap between the valence band and the conduction band of photocatalysts is dependent on the morphology and electrostatic interactions among components. This paper reviews visible light photocatalysts, that is, g-C3N4 based materials, layered perovskites, and conjugated polymers, to provide integrated insight into photocatalytic water splitting to obtain hydrogen.

TiO2@ZnFe2O4 heterojunctions for effecicent photocatalytic degradation of persistent pollutants and hydrogen evolution

Designing and fabricating the double-capability photocatalysts with the capability of producing hydrogen from the splitting of water and degrading environmental organic pollutants under visible light irradiation are significant in environmental treatment and new energy preparation. As a proof of concept, TiO2@ZnFe2O4 heterojunctions with high performance and stability were prepared by a one-step hydrothermal method, in which TiO2 nanosheets successfully grew on the main body of ZnFe2O4 nanorods. The microstructures and morphologies of the as-produced composites as well as their photocatalytic hydrogen generation rate and photocatalytic degradation performances towards humic acid, florfeniol, tetracyclines, and bisphenol A were investigated. The results indicate that TiO2@ZnFe2O4 heterojunctions possessed the higher photocatalytic activities towards hydrogen production and contaminants degradation ability than that of only TiO2 and ZnFe2O4. Especially, TiO2@ZnFe2O4 heterojunctions with the molar ratio of 1:4 have the best activities and manifest good stability. Significant enhancement of visible light absorption and photogenerated charge separation of TiO2@ZnFe2O4 were achieved. This work paves a way to construct a low-cost, environment-friendly, recyclable, and non-poisonous photocatalysts for hydrogen generation and the degradation of pollutants.

Electrospinning Preparation of GaN:ZnO Solid Solution Nanorods with Visible-Light-Driven Photocatalytic Activity toward H2 Production

The development of a facile method for the synthesis of GaN:ZnO solid solution, an attractive material with a wurtzite-type structure, is vital to enhance its photocatalytic activity toward H2 evolution. Herein, GaN:ZnO solid solution nanorods with diameters of around 180 nm were fabricated by combining the electro-spun method with a sequentially calcinating process. Photocatalytic water-splitting activities of the as-obtained samples loaded with Rh2−yCryO3 co-catalyst were estimated by H2 evolution under visible-light irradiation. The as-prepared GaN:ZnO nanorods at a nitridation temperature of 850 °C showed the optimal performance. Careful characterization of the GaN:ZnO solid solution nanorods indicated that the nitridation temperature is an important parameter affecting the photocatalytic performance, which is related to the specific surface area and the absorbable visible-light wavelength range. Finally, the mechanism of the GaN:ZnO solid solution nanorods was also investigated. The proposed synthesis strategy paves a new way to realize excellent activity and recyclability of GaN:ZnO solid solution nanorod photocatalysts for hydrogen generation.