ChemInform Abstract: Mechanistic Aspects of the Photooxidation of Water at the n‐TiO2/Aqueous Interface: Optically Induced Transients as a Kinetic Probe.

Abstract

ChemInform Abstract It is demonstrated that the method of optically induced photocurrent transients is a powerful tool for the study of the mechanisms of photoinduced charge transfer at the semiconductor/electrolyte interface. The results obtained for the (001) nTiO2/aqueous electrolyte interface suggest a model for water oxidation which involves two pH sensitive pathways. In the pH range 0-11, water oxidation appears to occur via an outer-sphere channel. From pH 12 to pH 15.5 (10 M NaOH) hydroxide oxidation follows an inner-sphere reaction channel. Based on the transient response as a function of hydrogen isotope, along with the activity of nonelectroactive competitive ligands (e.g., MeCN), the inner-sphere pathway is suggested to occur via a "Ti-OH" surface species as the key intermediate.

Atomic-Scale Surface Local Structure of TiO2 and Its Influence on the Water Photooxidation Process

“…It has long been assumed − that the water photooxidation reaction at the TiO 2 surface is initiated by oxidation of surface Ti–OH group (or OH – ions in an aqueous solution) by photogenerated holes, h + , by an electron-transfer mechanism. , Actually, the formation of • OH radicals in UV-irradiated TiO 2 systems was reported by a spin-trapping ESR , or low-temperature ESR method, diffuse reflection FTIR spectroscopy, and gas-phase emission spectroscopy . However, it was reported that the water photooxidation reaction at the TiO 2 surface did not produce any free • OH radicals but adsorbed • OH (or Ti–O • ) radicals, the latter of which gave ESR signals similar to those reported by the spin-trapping method.…”