CO2 photoreduction using NiO/InTaO4 in optical-fiber reactor for renewable energy

The photocatalytic reduction of CO2 into fuels provides a direct route to produce renewable energy from sunlight. NiO loaded InTaO4 photocatalyst was prepared by a sol–gel method. Aqueous-phase CO2 photoreduction was performed in a quartz reactor to search for the highest photoactivity in a series of NiO/InTaO4 photocatalysts. Thereafter, the best NiO/InTaO4 was dip coated on optical fibers and calcined at 1100 °C. A uniform NiO/InTaO4 layer of 0.14 μm in thickness was observed on the optical fiber. An optical-fiber photoreactor, comprised of ∼216 NiO/InTaO4-coated fibers, was designed to transmit and spread light uniformly inside the reactor. The UV–vis spectra of powder InTaO4 as well as NiO loaded InTaO4 prepared via the same procedure indicated that both photocatalysts could absorb visible light. XRD confirmed that InTaO4 was in single phase. Vapor-phase CO2 was photocatalytically reduced to methanol using the optical-fiber reactor under visible light and real sunlight irradiation in a steady-state flow system. The rate of methanol production was 11.1 μmol/g h with light intensity of 327 mW/cm2 at 25 °C. Increasing the reaction temperature to 75 °C increased the production rate to 21.0 μmol/g h. Methanol production rate was 11.30 μmol/g h by utilizing concentrated sunlight which was comparable to the result of using artificial visible light. The quantum efficiencies were estimated to be 0.0045% and 0.063% in aqueous-phase and optical-fiber reactors, respectively, per gram NiO/InTaO4 photocatalyst. The quantum efficiency increased due to the superior light-energy utilization of NiO/InTaO4 thin film in the optical-fiber reactor