PURIFICATION OF WATER WITH NEAR-UV 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 TiO2 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) TiO2 suspensions. The integrated L-H rate expression gives reasonable agreement with observed time-dependent CO2 formation curves. A comparison was made between CO2 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 m2 of sunlight. Formic acid was mineralized at approximately twice the rate of the other solutes. © 1990.