Role of Water in Methanol Photochemistry on TiO<sub>2</sub> Nanocrystals: An In Situ DRIFTS Study
Cong Fu, Yunshang Zhang, Xiao Sun, Fei Fang, Weixin Huang
Abstract
Effects of adsorbed water on methanol photochemistry on TiO2 surfaces is an interesting and important issue. In this paper, we have studied coadsorption and photochemistry of water and methanol on TiO2 nanocrystals with different predominantly exposed facets using in situ diffuse-reflectance infrared spectroscopy and an isotope labeling technique. Preadsorbed water on TiO2 exerts versatile influences on methanol photochemistry. Water competes with methanol for surface sites on TiO2; meanwhile, surface OH groups are capable of assisting methanol decomposition to methoxy species. Surface OH groups can trap photoexcited electrons, which open up photocatalytic reactions of adsorbed methanol species in the absence of O2; moreover, the acquiring surface •OH radicals can directly participate in photocatalytic conversions of adsorbed methanol species. In the presence of O2, water influences photocatalytic oxidation of adsorbed methanol species on TiO2 NCs mainly by affecting methanol and O2 adsorption. All these effects vary sensitively with exposed facets and surface structures of TiO2 nanocrystals. These results unveil the complex nature of influences of adsorbed water on methanol photochemistry on TiO2 surfaces.