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

MARTIN, CARLOS ALBERTO; BALTANAS, MIGUEL A; CASSANO, ALBERTO E

ENVIRONMENTAL SCIENCE & TECHNOLOGY

AMER CHEMICAL SOC

Año: 1996 vol. 30 p. 2355 - 2364

0013-936X

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 the hole capture by the substrate itself), which are then the rate-determining steps. (iv) The employment of low levels of incident radiation leads to larger quantum efficiencies, the more so if dilute suspensions of the photocatalyst are used.