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

• Published in: Chemistry, an Asian journal an Asian journal, 2016-12, Vol.11 (24), p.3568-3574
• Main Authors: Gong, Yuanzheng, Yang, Chun, Ji, Hongwei, Chen, Chuncheng, Ma, Wanhong, Zhao, Jincai
• Format: Article
• Language: English
• Subjects: Chemistry; hydroxylation of aromatics; NIH shift; Phenols; Photocatalysis; photochemistry; reaction mechanisms; water chemistry
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201601299

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. Radical influences: NIH shift phenomena were observed during the evolution of HO–adduct radicals in TiO2 photocatalysis and Fenton degradations of water‐insoluble aromatics. Results indicate that a mixed mechanism of both the carbocation intermediate pathway and oxygen‐capturing pathway occurs in both reactions (see figure).