Photoreduction of CO 2 to fuels under sunlight using optical-fiber reactor

Abstract

An optical-fiber reactor is employed to photocatalytically reduce CO 2 with H 2O to fuels under UVA artificial light and concentrated natural sunlight. The optical fiber is coated with gel-derived TiO 2–SiO 2 mixed oxide-based photocatalysts. Fe atom is found to insert into the TiO 2–SiO 2 lattice during sol–gel process, resulting in the full visible light absorption as well as the effect on product selectivity of the derived catalyst. Under UVA, ethylene is mainly produced on Cu–Fe/TiO 2 catalyst with the quantum yield of 0.0235%, whereas Cu–Fe/TiO 2–SiO 2 catalyst is observed to favor methane production with the quantum yield of 0.05%. Meanwhile, the overall energy efficiency is found to be much higher on Cu–Fe/TiO 2–SiO 2 (0.0182%) than on its Cu–Fe/TiO 2 counterpart (0.0159%). There is only methane evolved over both bare TiO 2–SiO 2 and Cu–Fe/TiO 2–SiO 2 catalysts under natural sunlight with the production rates of 0.177 and 0.279 μmol/g-cat h, respectively. For the former catalyst, the increase in light intensity is not found to compensate the inherent electron–hole recombination in the TiO 2–SiO 2–acac catalyst, whereas the superior photoactivity of Cu–Fe/TiO 2–SiO 2 catalyst under natural sunlight could be ascribed to its full absorption of visible light.