Functional metal oxide photocatalyst for efficient carbon dioxide reduction

Solar fuels derived from solar energy are envisioned to replace fossil fuels for a sustainable earth and society. Photocatalytic carbon dioxide (CO2) reduction for gaseous or liquid fuels production is one of the most promising processes to not only solve the energy crisis, but also reduce the environmental issues such as greenhouse effect. However, advancement of CO2 reduction for solar fuels production is largely hindered by the lack of efficient photocatalysts. In this thesis, the work was focused on surface modification of semiconductor metal oxide photocatalyst to increase the affinity between CO2 and catalysts as well as preventing the electron hole pair recombination toward optimize the reaction efficiency. Firstly, methanolamine was utilized to functionalize the TiO2 surface by a facile one-step solvothermal method. Surface amine group can greatly increases the affinity of CO2 on TiO2 surfaces through chemisorption by formation of carbamate. This process can also activate the CO2 molecules, which allows more efficient charge transfer from TiO2. As a results, amine-functionalize TiO2 can significantly enhances the CO and CH4 production yield by photocatalytic CO2 reduction. Secondly, to further apply this amine group surface modification method, amine-functionalized ZnO was synthesized via a facile one-step hydrothermal method. The CO2 adsorption ability is greatly increased after surface amine group modification. After activation of CO2 molecules upon chemisorptions, the photoexicited electrons generated under UV-light irradiation can more efficiently reduce the CO2, thus significantly enhance the photocatalytic CO2 reduction rate. Finally, to prevent electron-hole pair recombination of semiconductor, Cu was decorated on ZnO nanowire single crystal by photodeposition method. The Cu exists in Cu2O form and act as a cocatalyst. By trapping the photogenerated electrons, this Cu cocatalyst can effectively reduce electron-hole pair recombination toward efficient CO2 photoreduction. The selectivity towards CO2 reduction is also increased by this Cu cocatalst. DOCTOR OF PHILOSOPHY (MSE)