Experiment of photochemical reduction and deposition of cupric ion by titanium dioxide photocatalyst was carried out. The TiO2 Particles were suspended in the aqueous solution of copper sulphate where sodium formate was added as a hole scavenger. It was shown that cupric ion can be reduced and deposited on TiO2 surface very rapidly when the TiO2 particles are embedded at adequately higher densities and formic acid is added at moderate concentrations comparative to or higher than that of cupric ion. The deposition rate depends strongly on the concentration of sodium formate: it increases as the concentration increases. The mechanism of reduction reaction was estimated by the elementary reactions and the adsorption of formic anion. The practical deposition rates can be successfully explained by assuming that the oxidation reaction step of adsorbed formic anion is rate controlling, with the remaining steps being all instantaneously fast. Possibility of photochemical reduction of chromium ion(VI) to nontoxic chromium ion(III) or to metal chromium was also investigated. (C) 2003 Elsevier B.V. All rights reserved.