The temporal behavior of the photocatalytic reduction of carbonate in aqueous solution by the UV/TiO2 process was studied under various conditions. The photocatalytic reduction of carbonate proceeded faster in acidic solutions than in alkaline solutions. The reaction rate increased with the UV light intensity and the amount of TiO2 present in solution. However, the presence of excessive amounts of TiO2 hindered the UV light penetration. The main products of the photocatalytic reduction of carbonate by the UV/TiO2 reduction process were found to be methanol and methane. A Langmuir-Hinshelwood type kinetic equation was developed for modeling the photocatalytic reduction of carbonate. (C) 2003 Elsevier B.V. All rights reserved.