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 × l0⁻² Mh⁻¹ and 2.0 × 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 usingHalobacterium 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.