Photolysis of chloroform and other organic molecules in aqueous titanium dioxide suspensions

Abstract

The photocatalytic degradation of chloroform has been \ninvestigated in aqueous suspensions of TiO_2 over the \nwavelength range of 310-380 nm. A detailed reaction \nmechanism has been proposed in which the rate-determining \nstep is the reaction of surface-bound *OH with \nadsorbed CHCl_3. A pH-stat titration technique was developed \nfor the measurement of the rates of degradation \nof chlorinated hydrocarbons. The quantum efficiency (Ф \n= 0.56 at ⋋ = 330 nm) of the degradation of CHCl_3, was \nfound to be inversely proportional to the square root of \nthe incident light intensity. This relationship can be explained in terms of a direct competition between a second-order recombination of surface-bound 'OH and the \nrate-determining reaction of surface-bound 'OH with \nCHCl_3. The rates of degradation of several electron donors \nhave been correlated with their computed surface speciation. \nThe results of this study show that the adsorption \nof electron donors and acceptors to the TiO_2 surface plays \na more important role in determining the rate of the \nphotocatalytic reactions than the effect of pH-dependent \nFermi-level shifts.