Photocatalytic reduction of CO 2 with H 2 O over graphene oxide-supported oxygen-rich TiO 2 hybrid photocatalyst under visible light irradiation: Process and kinetic studies

Abstract

Abstract The photoreduction of carbon dioxide (CO2) into hydrocarbon fuels was studied in a homemade photocatalytic system over 5 wt.% graphene oxide-doped oxygen-rich TiO2 (5GO-OTiO2) photocatalyst. The CO2 transformation process is a sequential combination of both water oxidation and CO2 reduction. As these processes can be affected by parameters such as radiant flux intensity and the partial pressures of both CO2 and water vapour, these factors were systematically varied and studied in order to determine the most suitable process conditions for achieving high photocatalytic activity. Based on results from the CO2 photoreduction experiments, a total methane (CH4) yield of 3.450 μmol gcat−1 was successfully attained over 5GO-OTiO2 after 8 h of reaction time under visible light irradiation. The experimental data obtained was then fitted into the Langmuir-Hinshelwood surface reaction mechanism, wherein both CO2 and H2O adsorbed simultaneously on the photocatalyst surface to form the CH4 product. Regression fitting was performed to determine the kinetic parameters such as reaction rate constant and adsorption equilibrium constants. The reaction rate as well as CO2 and H2O adsorption equilibrium constants were determined to be 84.42 μmol gcat−1 h−1, 0.019 bar−1 and 8.07 bar−1, respectively. The significantly smaller CO2 adsorption equilibrium constant implied that the adsorption of CO2 was very weak while water strongly adsorbed on the photocatalyst surface.