Photoreduction of CO2 to fuels under sunlight using optical-fiber reactor

An optical-fiber reactor is employed to photocatalytically reduce CO₂ with H₂O to fuels under UVA artificial light and concentrated natural sunlight. The optical fiber is coated with gel-derived TiO₂–SiO₂ mixed oxide-based photocatalysts. Fe atom is found to insert into the TiO₂–SiO₂ 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/TiO₂ catalyst with the quantum yield of 0.0235%, whereas Cu–Fe/TiO₂–SiO₂ 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/TiO₂–SiO₂ (0.0182%) than on its Cu–Fe/TiO₂ counterpart (0.0159%). There is only methane evolved over both bare TiO₂–SiO₂ and Cu–Fe/TiO₂–SiO₂ 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 TiO₂–SiO₂–acac catalyst, whereas the superior photoactivity of Cu–Fe/TiO₂–SiO₂ catalyst under natural sunlight could be ascribed to its full absorption of visible light.