CO₂ photoreduction using NiO/InTaO₄in 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/InTaO₄layer 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/gh with light intensity of 327mW/cm² at 25°C. Increasing the reaction temperature to 75°C increased the production rate to 21.0μmol/gh. Methanol production rate was 11.30 μmol/gh 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. © 2010 Elsevier B.V. All rights reserved.