Photochemistry on TiO_2: Mechanisms behind the surface chemistry

摘要

Photochemistry from TiO_2 surfaces is described for two cases: The UV-induced photodesorption of O_2 from TiO_2(110) - 1 × 1; and the hydrophilic effect caused by UV irradiation on TiO_2. In both cases fundamental information about how these processes occur has been found. In the case of the O_2 photodesorption kinetics, it has been found that the rate of the process is proportional to the square root of the UV flux, showing that second-order electron-hole pair recombination is dominant in governing the photodesorption rate. In addition these measurements provide an estimate of the concentration of hole traps in the TiO_2 crystal. In other measurements of the UV-induced hydrophilicity, starting with the atomically-clean TiO_2 surface, it has been shown that the effect occurs suddenly at a critical point during irradiation as a result of photooxidation of a monolayer of hydrocarbon (n-hexane) at equilibrium with ppm concentration of n-hexane in O_2 at 1 atmosphere pressure.