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 CO 2 in seawater into chemical fuel, methanol (CH 3 OH), was achieved over Cu/C-co-doped TiO 2 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 TiO 2 remarkably promoted the photocatalytic production of CH 3 OH. This improvement was attributed to lowering of bandgap energy, specific catalytic effect of Cu for CH 3 OH formation, and the minimization of photo-generated carrier recombination. Co-doped TiO 2 with 3.0 wt% Cu was found to be the most active catalyst, giving a maximum methanol yield rate of 577 μmol g-cat −1 h −1 under illumination of UV light, which is 5.3-fold higher than the production rate over C-TiO 2 and 7.4 times the amount produced using Degussa P25 TiO 2 . Under natural sunlight, the maximum rate of the photocatalytic production of CH 3 OH using 3.0 wt% Cu/C-TiO 2 was found to be 188 μmol g-cat −1 h −1 , which is 2.24 times higher than that of C-TiO 2 , whereas, no CH 3 OH was observed for P25.