Photocatalytic splitting of water into hydrogen and oxygen using solar energy has attracted substantial interest in recent years as a potentially clean and renewable source for hydrogen fuel. A recent breakthrough is the discovery of GaN/ZnO, a pseudobinary semiconductor alloy, which has a water splitting efficiency much higher than other oxides under visible light. This high efficiency is partly attributed to its bandgap, which is lower than those of GaN and ZnO. The mechanism of this bandgap lowering is under intense debate. We have studied theoretically the mechanism of this bandgap lowering. We first developed a model to construct GaN/ZnO alloys based on the clustering and octet rule violation concepts. Then the bandgaps and optical properties of the alloys were studied by introducing the many-body effects by means of the GW approach and the Bethe-Salpeter equation. Effective bandgap engineering of different alloy configurations of GaN/ZnO will be discussed.As one of the most effective photocatalysts, TiO2 has been widely studied due to its advantages of high efficiency, low cost, chemical inertness, and photostability. However, the bandgap of TiO2 lies in the UV range, which means that only about 5% of sunlight has the required energy to activate the catalyst. Doping is a promising approach to reduce the absorption threshold of TiO2 and bring it from the UV to the visible region. However, dopants may themselves be recombination centers or generate other defects such as oxygen vacancies. A possible way to improve the photocatalytic performance of doped TiO2 is codoping. We have studied theoretically N-F and N-Cl codoped anatase TiO2based on density functional theory (DFT) calculations. Detailed microscopic information on the structural and electronic properties of the system will be discussed.

Theoretical study on the structural and electronic properties of photocatalytic materials

246th National Meeting (2013)

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