Active Species in Photocatalytic Reactions of Methanol on TiO2(110) Identified by Surface Sum Frequency Generation Vibrational Spectroscopy

The photocatalytic reactivity of one monolayer of methanol on TiO2(110) was measured with the surface sum frequency generation vibrational spectroscopy in the C-H stretching range, which shows high photon energy dependence. The photocatalytic reactivity was systematically investigated for different active species on TiO2(110), dissociative adsorbed methanol at five-coordinated Ti sites (Ti-5c), methoxy without adsorbed methanol at Ti-5c sites, and methoxy O-b sites. The results show that the methoxy at Ti-5c sites has much higher photocatalytic reactivity than that of dissociative adsorbed methanol at Ti-5c sites, and the methoxy at O-b sites might be inactive. This work demonstrates that methoxy at Ti-5c sites is the most active species on TiO2(110) and suggests that effectively removing surface OH could enhance the photodegradation of surface organics.