Jiaguo Yu

Highly Efficient Visible-Light-Driven Photocatalytic Hydrogen Production of CdS-Cluster-Decorated Graphene Nanosheets

The production of clean and renewable hydrogen through water splitting using photocatalysts has received much attention due to the increasing global energy crises. In this study, a high efficiency of the photocatalytic H(2) production was achieved using graphene nanosheets decorated with CdS clusters as visible-light-driven photocatalysts. The materials were prepared by a solvothermal method in which graphene oxide (GO) served as the support and cadmium acetate (Cd(Ac)(2)) as the CdS precursor. These nanosized composites reach a high H(2)-production rate of 1.12 mmol h(-1) (about 4.87 times higher than that of pure CdS nanoparticles) at graphene content of 1.0 wt % and Pt 0.5 wt % under visible-light irradiation and an apparent quantum efficiency (QE) of 22.5% at wavelength of 420 nm. This high photocatalytic H(2)-production activity is attributed predominantly to the presence of graphene, which serves as an electron collector and transporter to efficiently lengthen the lifetime of the photogenerated charge carriers from CdS nanoparticles. This work highlights the potential application of graphene-based materials in the field of energy conversion.

Synergetic Effect of MoS2 and Graphene as Cocatalysts for Enhanced Photocatalytic H2 Production Activity of TiO2 Nanoparticles

The production of H(2) by photocatalytic water splitting has attracted a lot attention as a clean and renewable solar H(2) generation system. Despite tremendous efforts, the present great challenge in materials science is to develop highly active photocatalysts for splitting of water at low cost. Here we report a new composite material consisting of TiO(2) nanocrystals grown in the presence of a layered MoS(2)/graphene hybrid as a high-performance photocatalyst for H(2) evolution. This composite material was prepared by a two-step simple hydrothermal process using sodium molybdate, thiourea, and graphene oxide as precursors of the MoS(2)/graphene hybrid and tetrabutylorthotitanate as the titanium precursor. Even without a noble-metal cocatalyst, the TiO(2)/MoS(2)/graphene composite reaches a high H(2) production rate of 165.3 μmol h(-1) when the content of the MoS(2)/graphene cocatalyst is 0.5 wt % and the content of graphene in this cocatalyst is 5.0 wt %, and the apparent quantum efficiency reaches 9.7% at 365 nm. This unusual photocatalytic activity arises from the positive synergetic effect between the MoS(2) and graphene components in this hybrid cocatalyst, which serve as an electron collector and a source of active adsorption sites, respectively. This study presents an inexpensive photocatalyst for energy conversion to achieve highly efficient H(2) evolution without noble metals.

Polymeric Photocatalysts Based on Graphitic Carbon Nitride

Semiconductor-based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g-C3N4) for visible-light photocatalytic water splitting, g-C3N4 -based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g-C3N4 -based photocatalysts, including the fabrication and nanostructure design of pristine g-C3N4 , bandgap engineering through atomic-level doping and molecular-level modification, and the preparation of g-C3N4 -based semiconductor composites. Also, the photo-catalytic applications of g-C3N4 -based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non-noble-metal cocatalysts, and Z-scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g-C3N4 -based photocatalysts are highlighted.

Tunable Photocatalytic Selectivity of Hollow TiO2 Microspheres Composed of Anatase Polyhedra with Exposed {001} Facets

A fluoride mediated self-transformation method is proposed for the synthesis of hollow TiO(2) microspheres (HTS) composed of anatase polyhedra with exposed ca. 20% {001} facets. Importantly, HTS exhibit tunable photocatalytic selectivity in decomposing azo dyes in water. The fluorinated HTS show preferential decomposition of methyl orange (MO) in comparison to methylene blue (MB). In contrast, the surface-modified HTS by either NaOH washing or calcinations at 600 degrees C favor decomposition of MB over MO. The surface chemistry and the surface structure at the atomic level are key factors in tuning the adsorption selectivity and, consequently, photocatalytic selectivity of HTS toward azo dyes.

All‐Solid‐State Z‐Scheme Photocatalytic Systems

The current rapid industrial development causes the serious energy and environmental crises. Photocatalyts provide a potential strategy to solve these problems because these materials not only can directly convert solar energy into usable or storable energy resources but also can decompose organic pollutants under solar-light irradiation. However, the aforementioned applications require photocatalysts with a wide absorption range, long-term stability, high charge-separation efficiency and strong redox ability. Unfortunately, it is often difficult for a single-component photocatalyst to simultaneously fulfill all these requirements. The artificial heterogeneous Z-scheme photocatalytic systems, mimicking the natural photosynthesis process, overcome the drawbacks of single-component photocatalysts and satisfy those aforementioned requirements. Such multi-task systems have been extensively investigated in the past decade. Especially, the all-solid-state Z-scheme photocatalytic systems without redox pair have been widely used in the water splitting, solar cells, degradation of pollutants and CO2 conversion, which have a huge potential to solve the current energy and environmental crises facing the modern industrial development. Thus, this review gives a concise overview of the all-solid-state Z-scheme photocatalytic systems, including their composition, construction, optimization and applications.

Noble Metal-Free Reduced Graphene Oxide-ZnxCd1–xS Nanocomposite with Enhanced Solar Photocatalytic H2-Production Performance

Design and preparation of efficient artificial photosynthetic systems for harvesting solar energy by production of hydrogen from water splitting is of great importance from both theoretical and practical viewpoints. ZnS-based solid solutions have been fully proved to be an efficient visible-light driven photocatalysts, however, the H(2)-production rate observed for these solid solutions is far from exciting and sometimes an expensive Pt cocatalyst is still needed in order to achieve higher quantum efficiency. Here, for the first time we report the high solar photocatalytic H(2)-production activity over the noble metal-free reduced graphene oxide (RGO)-Zn(x)Cd(1-x)S nanocomposite prepared by a facile coprecipitation-hydrothermal reduction strategy. The optimized RGO-Zn(0.8)Cd(0.2)S photocatalyst has a high H(2)-production rate of 1824 μmol h(-1) g(-1) at the RGO content of 0.25 wt % and the apparent quantum efficiency of 23.4% at 420 nm (the energy conversion efficiency is ca. 0.36% at simulated one-sun (AM 1.5G) illumination). The results exhibit significantly improved photocatalytic hydrogen production by 450% compared with that of the pristine Zn(0.8)Cd(0.2)S, and are better than that of the optimized Pt-Zn(0.8)Cd(0.2)S under the same reaction conditions, showing that the RGO-Zn(0.8)Cd(0.2)S nanocomposite represents one of the most highly active metal sulfide photocatalyts in the absence of noble metal cocatalysts. This work creates a green and simple way for using RGO as a support to enhance the photocatalytic H(2)-production activity of Zn(x)Cd(1-x)S, and also demonstrates that RGO is a promising substitute for noble metals in photocatalytic H(2)-production.

Engineering heterogeneous semiconductors for solar water splitting

There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

Visible Light Photocatalytic H2-Production Activity of CuS/ZnS Porous Nanosheets Based on Photoinduced Interfacial Charge Transfer

Visible light photocatalytic H(2) production through water splitting is of great importance for its potential application in converting solar energy into chemical energy. In this study, a novel visible-light-driven photocatalyst was designed based on photoinduced interfacial charge transfer (IFCT) through surface modification of ZnS porous nanosheets by CuS. CuS/ZnS porous nanosheet photocatalysts were prepared by a simple hydrothermal and cation exchange reaction between preformed ZnS(en)(0.5) nanosheets and Cu(NO(3))(2). Even without a Pt cocatalyst, the as-prepared CuS/ZnS porous nanosheets reach a high H(2)-production rate of 4147 μmol h(-1) g(-1) at CuS loading content of 2 mol % and an apparent quantum efficiency of 20% at 420 nm. This high visible light photocatalytic H(2)-production activity is due to the IFCT from the valence band of ZnS to CuS, which causes the reduction of partial CuS to Cu(2)S and thus enhances H(2)-production activity. This work not only shows a possibility for substituting low-cost CuS for noble metals in the photocatalytic H(2) production but also for the first time exhibits a facile method for enhancing H(2)-production activity by photoinduced IFCT.

g-C3N4-Based Photocatalysts for Hydrogen Generation.

Graphitic carbon nitride (g-C3N4)-based photocatalysts have attracted dramatically increasing interest in the area of visible-light-induced photocatalytic hydrogen generation due to the unique electronic band structure and high thermal and chemical stability of g-C3N4. This Perspective summarizes the recent significant advances on designing high-performance g-C3N4-based photocatalysts for hydrogen generation under visible-light irradiation. The rational strategies such as nanostructure design, band gap engineering, dye sensitization, and heterojunction construction are described. Finally, this Perspective highlights the ongoing challenges and opportunities for the future development of g-C3N4-based photocatalysts in the exciting research area.

Effect of surface structure on photocatalytic activity of TiO2 thin films prepared by sol-gel method

TiO2 thin films with different surface structures are prepared from alkoxide solutions containing polyethylene glycol (PEG) via the sol-gel method. The effects of PEG addition to the precursor solution on the surface structures and photocatalytic activity of the resultant thin films are studied. The larger the amount of PEG added to the precursor solution, the larger the size and number of pores produced in the resultant films when PEG added to the gel films decomposed completely during heat-treatment. The adsorbed hydroxyl content of such porous thin films is found to increase with increasing amount of PEG. However, the transmittance of the films decreases due to the scattering of light by pores of larger size and bigger number in the films. Photocatalytic degradation experiments show that methyl orange is efficiently decolorized in the presence of the TiO2 thin films by exposing its aqueous solution to ultraviolet light and the suitable surface structures remarkably enhance the photocatalytic activity of TiO2 films.