Solar energy fixation of carbon dioxide via cadmium sulphide and other semiconductor photocatalysts

Aqueous carbon dioxide is photochemically reduced in the presence of semiconductor suspensions and colloids. Experiments have been performed using CdS, ZnO, SiC, Ba TiO3, and SrTiO3, dispersions. Product analysis showed the formation of formic acid formaldehyde, sometimes methanol and in the presence of tetramethylammonium chloride, two-carbon products such as glyoxylic and acetic acids and sometimes acetaldehyde. Product yields and photochemical yields were studied as a function of pH, solution composition, added sacrifical electron donors and catalysts, irradiation intensity and irradiation time. A demonstration experiment with a flat-bed solar collector showed the formation of formic acid and formaldehyde using direct sunlight.