The photocatalytic reduction of CO2 using copper-loaded silicate rocks has been reported. The Cu-silicate rock powders suspended in the solution were illuminated with sunlight. Amphibolite, gneiss, granite, granodiorite, phyllite, quartzdiorite, and shale, which are quite ordinary rocks, were tested as substrates (silicate rock) of the catalyst. These catalysts were specific for the formation of formic acid. The effects of amounts of copper, illumination time, and temperature were investigated on photoreduction of CO2. The 30% Cu-loaded quartzdiorite (0.3 g/g) in these Cu rocks was the best catalyst. The formation of formic acid on the Cu-silicate rock increased with time up to 10 h after which the formation decreased, and then became constant. The formic acid formation decreased with temperature for 10 h sunlight illumination. For the photochemical reduction of CO2, a relatively low temperature was suitable. With photochemical reduction, the maximum yield of formic acid was 54 nmol/g under optimum experimental conditions. The carbon dioxide reduction system developed might well become of practical interest for the photochemical production of raw materials for the photochemical industry.Key words: photocatalytic reduction of carbon dioxide, formic acid, copper-loaded silicate rocks, temperature effect, illumination time.
Photochemical Reduction of Carbon Dioxide to Formic Acid