Photocatalyzed Decomposition of 4-Chlorophenol by Keggin-Type Heteropolytungstate

Abstract The photocatalytic decomposition of 4-chlorophenol with a Keggin-type heteropolytungstate, PW12O403− (abbreviated as PW123−), under aerated conditions has been investigated in an aqueous or water-acetonitrile solution by using a 300 W Xe arc lamp at 303 K. The kinetics of the reaction indicated that the reaction proceeds via a Langmuir–Hinshelwood (or Michaelis–Menten) type mechanism, in which the complexation between the heteropolyanion and 4-chlorophenol exists as a pre-equilibrium step. This complex formation was evidenced by the observation of a new band at λ < 650 nm and the enhancement of the solubility of 4-chlorophenol in water in the presence of PW123−. The intensity of the new band varied in parallel with the reaction rate, depending on the concentrations of 4-chlorophenol and acetonitrile. This fact was consistent with the mechanism proposed.