The effect of the functional ionic group of the viologen derivative on visible-light driven CO2 reduction to formic acid with the system consisting of water-soluble zinc porphyrin and formate dehydrogenase

The effect of the functional ionic group of 4,4 '-bipyridinium salt derivatives (4,4 '-BPs) as the electron carrier on the visible-light driven conversion of CO2 to formic acid with the system consisting of water-soluble zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) and formate dehydrogenase (FDH) in the presence of triethanolamine (TEOA) as an electron donor was investigated. 1,1 '-Diaminoethyl-(DAV), 1-aminoethyl-1 '-methyl-(AMV), 1-carboxymethyl-1 '-methyl-(CMV) and 1,1 '-dicarboxymethyl-4,4 '-bipyridinium salt (DCV) were prepared as the 4,4 '-BPs with the functional ionic group. Irradiation of a CO2 saturated buffer solution containing TEOA, ZnTPPS, 4,4 '-BP and FDH with visible light irradiation resulted in the production of formic acid. By using 4,4 '-BPs with the cationic aminoethyl-group, DAV or AMV as an electron carrier, the effective visible-light driven formic acid production based on the CO2 reduction was observed compared to the 4,4 '-BPs with the anionic carboxymethyl-group, CMV or DCV. The formic acid production rate with DAV was approximately 3.2 times higher than that of the system with DCV.