PHOTOCHEMICAL OXIDATION OF BENZOTHIOPHENE IN SEAWATER

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Photochemical oxidation of benzothiophene in seawater

Kinetic investigation into the photochemical oxidation of benzothiophene in seawater showed that photo-oxidation rates of benzothiophene were influenced by the medium, pH, heavy metal ion, dissolved oxygen, and light intensity. The photo-oxidation of benzothiophene followed the first order reaction law, with the rate constants ranging from 1.21×10⁻⁵/s to 5.38×10⁻⁵/s. An interesting observation was that the presence of Hg²⁺ could markedly enhance the photo-oxidation rate of benzothiophene in seawater; and that the photo-oxidation rate of benzothiophene increased with light intensity. The effect of oxygen on the rate constant for benzothiophene photolysis was also observed. Compared with purging with nitrogen, purging seawater with oxygen evidently increased the photolysis rate of benzothiophene. Based on this observation, a benzothiophene photo-oxidation mechanism including singlet oxygen (O₂ ¹Δ_g) was suggested. Two photolysis products of benzothiophene were identified. The photolysis of benzothiophene is considered to be important in the removal of this compound in seawater. Project 49706070 supported by NSFC and also supported by Shandong Province NSF (No. Q97E04145).