CATALYSIS BY HETEROPOLY COMPOUNDS .33. PHOTOCATALYZED DECOMPOSITION OF 4-CHLOROPHENOL BY KEGGIN-TYPE HETEROPOLYTUNGSTATE

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 s olution by using a 300 W Xe are lamp at 303 K. The kinetics of the rea ction indicated that the reaction proceeds via a Langmuir-Hinshelwood (or Michaelis-Menten) type mechanism, in which the complexation betwee n the heteropolyanion and 4-chlorophenol exists as a pre-equilibrium s tep. This complex formation was evidenced by the observation of a new band at lambda < 650 nm and the enhancement of the solubility of 4-chl orophenol in water in the presence of PW123-. The intensity of the new band varied in parallel with the reaction rate, depending on the conc entrations of 4-chlorophenol and acetonitrile. This fact was consisten t with the mechanism proposed.