title: H2O-involved two-electron pathway for photooxidation of aldehydes on TiO2: an isotope labeling study.
abstract: Aldehyde pollution has been receiving increasing environmental concern recently. In this study, the photooxidation of aldehydes to carboxylates on the TiO2 surface was studied by an oxygen-isotope-labeling method. The solvent H2O was found to contribute much to the oxygen source of the formed carboxylate, which cannot be explained if the conventional O2-involved free radical chain reaction is the only mechanism for the photocatalytic oxidation of aldehydes. We also observed that, unlike in the TiO2 photocatalytic system, the aldehyde oxidation in homogeneous solutions initiated by single electron oxidant (•)OH and SO4(•-) radicals inserted a small O atom of H2O into the product acids. The detailed experiments, combined with DFT calculation, revealed the existence of a new pathway for the oxidation of aldehyde on TiO2, in which, analogous to oxidation of aldehyde by dehydrogenase, the aldehyde undergoes a hydration first and subsequently is oxidized through a two-electron transfer process. The present study highlights the multielectron characteristic of TiO2 photocatalytic oxidation and can have implications for the oxidation of aldehyde in the environment.
authors: Beijing National Laboratory for Molecular Sciences, Key Laboratory of Photochemistry Institution Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
authors: Tao
authors: T
authors: Shi
authors: Wei
authors: W
authors: Chang
authors: Hongna
authors: H
authors: Zhang
authors: Hongwei
authors: H
authors: Ji
authors: Wanhong
authors: W
authors: Ma
authors: Chuncheng
authors: C
authors: Chen
authors: Jincai
authors: J
authors: Zhao
mesh_terms: D000447:Aldehydes / Q000032:analysis* / Q000737:chemistry*; D004785:Environmental Pollutants / Q000737:chemistry*; D007553:Isotope Labeling; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000447:Aldehydes; D004785:Environmental Pollutants; D014867:Water; C009495:titanium dioxide; D014025:Titanium