Efficient Photocatalytic Reduction of CO2 Present in Seawater into Methanol over Cu/C-Co-Doped TiO2 Nanocatalyst Under UV and Natural Sunlight

Photocatalytic reduction of CO2 in seawater into chemical fuel, methanol (CH3OH), was achieved over Cu/C-co-doped TiO2 nanoparticles under UV and natural sunlight. Photocatalysts with different Cu loadings (0, 0.5, 1, 3, 5, and 7 wt%) were synthesized by the sol-gel method and were characterized by XRD, SEM, UV-Vis, FTIR, and XPS. Co-doping with C and Cu into TiO2 remarkably promoted the photocatalytic production of CH3OH. This improvement was attributed to lowering of bandgap energy, specific catalytic effect of Cu for CH3OH formation, and the minimization of photo-generated carrier recombination. Co-doped TiO2 with 3.0 wt% Cu was found to be the most active catalyst, giving a maximum methanol yield rate of 577 mu mol g-cat(-1) h(-1) under illumination of UV light, which is 5.3-fold higher than the production rate over C-TiO2 and 7.4 times the amount produced using Degussa P25 TiO2. Under natural sunlight, the maximum rate of the photocatalytic production of CH3OH using 3.0 wt% Cu/C-TiO2 was found to be 188 mu mol g-cat(-1) h(-1), which is 2.24 times higher than that of C-TiO2, whereas, no CH3OH was observed for P25.