PHOTOFIXATION OF CARBON-DIOXIDE IN SEMICONDUCTOR PARTICULATE AND MICROBIAL SYSTEMS

Photocatalytic reduction of CO2 to HCOOH and HCHO was carried out in a Pt/CdS/RuO2 semiconductor particulate system using [Ru(III)(EDTA-H)H2O] complex as catalyst. Upon illumination at 505 nm (band gap energy of CdS), the system produced HCOOH and HCHO at rates equal to 3.05 x 10(-2) M h-1 and 2.0 x 10(-2) M h-1, respectively. Trace amounts of CH2OH, CH4 and CO were also detected in the reaction vessel. Photobiological conversion of CO2 to formic acid was achieved by using Halobacterium halobium MMT22 in aqueous solution at a rate equal to 0.45 M h-1. A one-and-half-fold increase in the rate of formation of formic acid was observed when the photobiological reduction of CO2 was performed in the presence of L-ascorbic acid as electron-donating agent and [Ru(III)(bipy)3]2+ as photosensitizer.