| Since Fujishima and Honda’s first report on Ti O2 photoelectrode in 1972, semiconductor-mediated photocatalytic technology has attracted much attention for many years, because it is a vital step in using solar energy to purify polluted air and wastewater, or to split water for green-energy hydrogen production. So far, Ti O2 is the most promising photocatalysts for its superiority in the oxidation capacity, chemical inertness, nontoxicity, cost effectiveness, and long-term stability. Unfortunately, owing to its wide electronic band gap, Ti O2 absorbs only the ultraviolet fraction of the solar spectrum, which accounts for just 4% of solar irradiation. Therefore, development of photocatalysts activated by visible light would have a profound impact and would lead to many applications of practical relevance to society.Bi VO4 is a well-known photoelectrode material, which absorbs part of the visible light due to its relatively small band gap(~2.4 e V). Although water splitting using Bi VO4 is promising for hydrogen generation, the short carrier diffusion length and poor charge transport property limit the efficiency. To solve these problems, various methods have been employed including doping Bi VO4 with ions, heterojunction structure formation, and decorating with noble metal. Alternatively, nano-structuring the Bi VO4 is believed to be another possible technology for overcoming the disadvantages of Bi VO4 due to the geometric–dependence of its properties. Most recently, Three-dimensional inverse opal structure is of tremendous value because it not only provides high specific surface area and porosity, but also improves light harvesting due to multiple scattering. Moreover, the periodical structure can provide an additional photonic bandgap effect(slow light effect), which enhances light-matter interactions by reducing the propagation of light. There are two mainly chapter in this thesis:(1) Fabrication of carbon quantum dots/Bi VO4 inverse opal and its enhanced photoelectrochemical properties.Carbon quantum dots(CQDs) coated Bi VO4 inverse opal(io-Bi VO4) structure that shows dramatic improvement of photoelectrochemical hydrogen generation has been fabricated using electrodeposition with a template. The io-Bi VO4 maximizes photon trapping through slow light effect, while maintaining adequate surface area for effective redox reactions. CQDs are then incorporated to the io-Bi VO4 to further improve the photoconversion efficiency. Due to the strong visible light absorption property of CQDs and enhanced separation of the photoexcited electrons, the CQDs coated io-Bi VO4 exhibit a maximum photo-to-hydrogen conversion efficiency of 0.35%, which is 6 times higher than that of the pure Bi VO4 thin films. This work was published in Applied Physics Letters, 2015, 106, 153901.(2) Fabrication of Ag/Bi VO4 inverse opal and its enhanced photoelectrochemical properties.We developed a pulsed current deposition method to fabricate Bi VO4 inverse opals with highly dispersed Ag nanoparticles as a visible light driven photoelectrode. It is observed that the incorporation of Ag nanoparticles can significantly improve the photocurrent density of Bi VO4 inverse opals in all light spectrums. With an appropriated deposition time of 35 s, the measured photocurrent density of the sample is the highest. Since the localized surface plasmon resonance property of the Ag nanoparticles can be observed in the Ag/Bi VO4 sample, the mechanism of the enhanced photoelectrochemical properties is still unclear, which should be studied in the future. |
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