Photocatalyzed decomposition of 4-chlorophenol by Keggin-type heteropolytungstate

The photocatalytic decomposition of 4-chlorophenol with a Keggin-type heteropolytungstate, PW₁₂O₄₀^3-(abbreviated as PW₁₂^3-), 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-cholorophenol exists as a pre-equilibrium step. This complex formation was evidence 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 PW₁₂^3-. 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.