Mechanistic Studies of TiO2 Photocatalysis and Fenton Degradation of Hydrophobic Aromatic Pollutants in Water

Yuanzheng Gong; Chun Yang; Hongwei Ji; Chuncheng Chen; Wanhong Ma; Jincai Zhao

doi:10.1002/asia.201601299

Mechanistic Studies of TiO₂ Photocatalysis and Fenton Degradation of Hydrophobic Aromatic Pollutants in Water

Chem Asian J. 2016 Dec 19;11(24):3568-3574. doi: 10.1002/asia.201601299. Epub 2016 Nov 22.

Authors

Yuanzheng Gong^{1

2}, Chun Yang^{1

2}, Hongwei Ji^{1

2}, Chuncheng Chen^{1

2}, Wanhong Ma^{1

2}, Jincai Zhao^{1

2}

Affiliations

¹ Key Laboratory of Photochemistry, National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, P.R. China.
² University of Chinese Academy of Sciences, Beijing, 100049, P.R. China.

PMID: 27759949
DOI: 10.1002/asia.201601299

Abstract

HO-adduct radicals have been investigated and confirmed as the common initial intermediates in TiO₂ photocatalysis and Fenton degradations of water-insoluble aromatics. However, the evolution of HO-adduct radicals to phenols has not been completely clarified. When 4-d-toluene and p-xylene were degraded by TiO₂ photocatalysis and Fenton reactions, respectively, a portion of the 4-deuterium or 4-CH₃ group (18-100 %) at the attacked ipso position shifted to the adjacent position of the ring in the formed phenols (NIH shift; NIH is short for the National Institutes of Health, to honor the place where this phenomenon was first discovered). The results, combined with the observation of a key dienyl cationic intermediate by in situ attenuated total reflectance FTIR spectroscopy, indicate that, for the evolution of HO-adduct radicals, a mixed mechanism of both the carbocation intermediate pathway and O₂ -capturing pathway occurs in both aqueous TiO₂ photocatalysis and aqueous Fenton reactions.

Keywords: NIH shift; hydroxylation of aromatics; photochemistry; reaction mechanisms; water chemistry.