Purification of water with near—u.v. illuminated suspensions of titanium dioxide

Benzoic acid, salicyclic acid, phenol, 2-chlorophenol, 3-chlorophenol, 4-chlorophenol, nitrobenzene, methanol, ethanol, acetic acid and formic acid in aerated, aqueous suspensions of TiO 2 were illuminated with near u.v. light. Each solute was present over a range of concentration; generally 1–50 mg 1 −1. The rate of oxidation to carbon dioxide was measured at each concentration. The dependence of the rate on concentration obeyed simple Langmuir-Hinshelwood (L-H) kinetics for each solute. Empirical constants have been determined enabling the prediction of mineralization rates at any solute concentration in 0.1% (w/w) TiO 2 suspensions. The integrated L-H rate expression gives reasonable agreement with observed time-dependent CO 2 formation curves. A comparison was made between CO 2 formation rate using 4-chlorophenol illuminated with artificial and natural u.v. light. The results indicate that 90% mineralization of all the solutes except formic acid initially present as 50 mg solute 1 −1 suspension occurs within 2–3 h with 1 m 2 of sunlight. Formic acid was mineralized at approximately twice the rate of the other solutes.