With a global increase in energy demand, it becomes urgent to develop effective techniques to make use of renewable energy. Although conversions of solar energy to electric and chemical energy attract numerous attention, several key issues are of great importance to be solved for the semiconductor-based photocatalytic process: i) increase the density of photogenerated charge carriers; ii) utilize of visible light for higher photoconversion efficiencies; and iii) reduce the recombination of charge carriers. Different strategies have been taken to realize the manipulation of photogenerated charge carriers to enhance the photocatalysis activities. First, morphology control of different semiconductors, such as TiO2, ZnO and Ta3N5, has been performed. The obtained branched TiO2 nanorod arrays, ZnO nanopencil and stronly adhered Ta3N5 nanotube arrays on FTO substrates have shown enhanced photocurrents as a result of increased charge carrier densities. Second, increasing the visible-light responsiveness of photocatalysts with large band gaps is an effective way to increase their photocatalytic efficiencies. Nitrogen-doped TiO2 hollow spheres, which show the absorption under visible-light irradiation, have a higher photodegradation rate of organic dyes compared with the undoped ones. TiO2 branched nanorod arrays integrated with CdS nanoparticles can response to visible-light and has an increased and stable photocurrent for photoelectrochemical solar water splitting. Composition of plasmonic metal is also employed to enhance the photocatalytic properties of semiconductors. Au-TiO2 branched nanorods, Au-TiO2 nanocups and Au-ZnO nanopencils show improved photocatalytic properties under visible-light irradiation. Additionally, semiconductors with suitable band gaps, such as WO3 nanomultilayers and C3N4 nanotubes, are synthesized which have high photocatalytic activities. Furthermore, construction of heterojunctions is conducted to enhance the separation of photogenerated charge carriers. BiVO4 with preferentially composited Ag3PO4 nanoparticles on its (040) facets showed a much higher photocatalytic activity since the photogenerated electrons and holes could be effectively separated at the interface of BiVO4 and Ag3PO4. BiVO4 with surface C3N4 islands shows enhanced separation of charge carriers with an increased activity. With all the effort to better manipulate photogenerated electrons and holes in semiconductors, the era of highly effective photocatalysis process for practical applications will be promising.

Manipulating photogenerated electrons and holes in semiconductors for solar hydrogen production

248th National Meeting (2014)

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