| In recent years, driven by increasing energy needs, decreasing fossil fuel resource, and environmental concerns of nuclear energy, the search for clean and renewable energy is attracting massive research interest. Hydrogen is recognized as a kind of efficient fuel and environmentally friendly materials because of its high energy capacity and no polluted byproduct. Utilization of solar energy to produce hydrogen gas from direct photocatalytic water-splitting has long been considered the ultimate solution to energy and environmental problems.Among these photocatalysts, TiO2is one of the most promising catalysts because of its superior photocatalytic performance, easy availability, long-term stability, and nontoxicity. However, its wide band gap (3.2eV for anatase) leads to a low utilization efficiency of sunlight because only the ultraviolet light can meet requirement of the energy for the electron transition between the valence band and conduction band, which hinders its potential practical applications. Therefore it is urgent that another major limitation for achieving high photocatalytic efficiency is the rapid recombination of charge carriers. Therefore, extending the sorption spectrum to visible range and retarding the recombination rate are required to promote the photocatalytic effciency.To solve these problems, graphene and dye are utilized to be incorporated with TiO2-Graphene has attracted a great deal of attention in recent years because of its excellent electronic conductivity and high specific surface area arising from its strictly2D structure. It can withdraw and shuttle electrons because of its ultrahigh electron mobility>1000cm2V-1s-1. Therefore, the quick electron transfer further facilitates excited electron-hole pair separation and retards the charge pair recombination. The activation process of charge separation and migration is as a result of the charges being on the surface of the photocatalyst ready for the desired reduction of proton. Four kinds of photosensitizers are used in the photocatalytic reaction system:1-pyrenebutyric acid (PB), l-amino-2-naphthol-4-sulfonic acid, Copper (II) phthalocyanine and alizarin red (AR). Dyes can further improve the dopment uniformity of graphene and T1O2and extend the absorption in the visible region upon composite formation. We have exploited the different types of catalysts, such as PB-G-TiO2、 G-SO3H-TiO2、 CuPcSOCl-G-P25and AR-G-P25.The composites were characterized by powder X-ray diffraction (XRD), UV-visible absorption spectra, transmission electron microscopy (TEM), and evaluation of photocatalytic water splitting under Xenon lamp illumination. TEM images show that nanoparticles anchored on the surface of graphene, from which we can clearly observe without obvious aggregation by way of an intimate interfacial contact. As-prepared materials with PB and1,2,4-acid do not show the extension of absorption range, but the absorption edge of composites with Copper (II) phthalocyanine and AR are red-shifted compared to others. The photocatalytic activity of all samples was evaluated for the hydrogen evolution. It was found that new composite photocatalysts possessed highly efficient hydrogen evolution from water under UV light irradiation. It is noted that materials with alizarin red exhibited a catalytic efficiency of207.5μmol/(5h·g) under Xenon lamp irradiation. |
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