PHOTOCHEMICAL REDUCTION OF CARBON-DIOXIDE BY TRICHLOROBIS(2,2'/6',2''-TERPYRIDYL)VANADIUM(III) AND METHYL VIOLOGEN

Photoreduction of carbon dioxide to formaldehyde and formic acid was carried out using an electron relay system composed of a new complex of trichlorobis(2,2':6',2"-terpyridyl)vanadium(III) (V(III)(TPY)2Cl3; redox photosensitizer), methyl viologen (MV2+; strong electron acceptor) and ethylenediaminetetraacetic acid (EDTA (or TEOA); sacrificial electron donor). By following the action spectrum for formaldehyde formation, it was shown that the photochemical reduction process is sensitized by V(III)(TPY)2Cl3. The best performance of the present system was observed when the complex, MV2+, EDTA and TEOA concentrations were 5 x 10(-4) M, 1 X 10(-2) M, 5 X 10(-3) M and 6 X 10(-2) M respectively. Visible light of 80 mW cm-2 was used for the irradiation experiments at 25-degrees-C. Quantum yields of photoproduction of formaldehyde at lambda = 670 nm and lambda = 470 nm were also determined for both EDTA and TEOA electron donors. The effects of reaction temperature, light intensity, pH and reaction time were also studied. According to the experimental results obtained, a reaction mechanism was proposed.