CO 2 photoreduction using NiO/InTaO 4 in optical-fiber reactor for renewable energy

Abstract

The photocatalytic reduction of CO 2 into fuels provides a direct route to produce renewable energy from sunlight. NiO loaded InTaO 4 photocatalyst was prepared by a sol–gel method. Aqueous-phase CO 2 photoreduction was performed in a quartz reactor to search for the highest photoactivity in a series of NiO/InTaO 4 photocatalysts. Thereafter, the best NiO/InTaO 4 was dip coated on optical fibers and calcined at 1100 °C. A uniform NiO/InTaO 4 layer of 0.14 μm in thickness was observed on the optical fiber. An optical-fiber photoreactor, comprised of ∼216 NiO/InTaO 4-coated fibers, was designed to transmit and spread light uniformly inside the reactor. The UV–vis spectra of powder InTaO 4 as well as NiO loaded InTaO 4 prepared via the same procedure indicated that both photocatalysts could absorb visible light. XRD confirmed that InTaO 4 was in single phase. Vapor-phase CO 2 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/cm 2 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/InTaO 4 photocatalyst. The quantum efficiency increased due to the superior light-energy utilization of NiO/InTaO 4 thin film in the optical-fiber reactor.