Photochemistry of Ethanol on Rutile TiO2(110): Breaking Two Bonds with One Hole

Understanding the mechanism of ethanol (EtOH) photochemistry is of significance for photocatalytic H2 production. Here, we reported a systematical study of EtOH photochemistry on rutile (R)-TiO2(110), aiming to illustrate how photogenerated holes and electrons are involved in bond breaking. We found that the yields of aldehyde from the ethoxy group and EtOH photooxidation on R- TiO2(110) are proportional to the square root of the photon flux, demonstrating that one hole can induce molecular EtOH decomposition to aldehyde. The initial O-H bond cleavage occurs mainly via a proton-coupled hole transfer process, and the C-H bond cleavage is a hole-mediated process, leaving two electrons on the surface, in agreement with the "current doubling effect". In addition, the rate of aldehyde formation from the ethoxy group is about 3 orders of magnitude faster than that from EtOH, suggesting that the O-H bond cleavage determines the rate of EtOH photochemistry. The results may considerably broaden our understanding of TiO2 photocatalysis.