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

The photocatalytic decomposition of chloroform in aqueous solution was investigated at 23C using suspensions of titanium dioxide of average particle size 30 nm within the wavelength range 310-380 nm. Decomposition was monitored by in-situ chloride measurements by electrode, checked occasionally by ion chromatography, and by automatic titration with sodium hydroxide to maintain stable pH. The latter method was based on the fact that each chlorine atom in an organic molecule released a proton on degradation. The mechanism proposed was the reaction of surface bound hydroxyl radicals with adsorbed chloroform; this was in competition with the recombination of hydroxyl radicals. The quantum efficiency of degradation was inversely proportional to the square root of the incident light intensity. The adsorption of electron donors and acceptors to the titanium dioxide surface was a more important influence on reaction rate than the effect of pH dependent Fermi level shifts.