Photocatalytic Reactors. 3. Kinetics of the Decomposition of Chloroform Including Absorbed Radiation Effects

Abstract

The rate of decomposition of water pollutants by means of photocatalytic processes can be quantitatively evaluated by using a fully irradiated photoreactor in which the rate of energy absorption is precisely quantified. Using a suspension of titanium dioxide as the active photocatalyst, excess oxygen over the stoichiometric demand, and a mercury arc lamp, we have found that (i) The rate of photocatalytic decomposition of chloroform in water is of first order with respect to [HCCl3], zero order with respect to [O2], and about one-half order with respect to the volumetric rate of energy absorption (VREA). (ii) The effects due to catalyst concentration are accounted for within the VREA dependence. (iii) These findings coincide with a reaction pathway in which, at moderate to high irradiation conditions and in the absence of mass transport limitations, the recombination rate of the photogenerated charge carriers is much faster than the hole trapping by hydroxyl groups attached to surface TiIV atoms (and/or th...