Zinc vanadium oxide coupled carbon nitride nanocomposite for photocatalytic carbon dioxide reduction to methanol

Abstract

Photocatalytic reduction of carbon dioxide (CO2) with water (H2O) into solar fuels is considered as a promising strategy to simultaneously address the global energy and environmental issues. The main objective of this study was to design and fabricate photoreactor system and to synthesize Z-scheme assembly of reduced graphene oxide (RGO) and protonated carbon nitride (pCN) based zinc vanadium oxide (ZnV2O6) nanocomposite for selective photoreduction of CO2 to solar fuels. The pure ZnV2O6, ZnV2O6/RGO, ZnV2O6/pCN and ZnV2O6/RGO/pCN nanocomposites were synthesized by a single step solvothermal method. The performance of nanocomposite catalysts was investigated in a liquid and gas phase photocatalytic systems under UV and visible light irradiations. The most effective catalyst in liquid phase system was ZnV2O6/RGO/pCN which gave a maximum methanol yield of 3726.7 µmol g-cat-1 using photoreactor without reflector and 5207.2 µmol g-cat-1 using photoreactor with reflector. Performance comparison revealed 1.4 times higher yield rate in photoreactor with reflector compared to photoreactor without reflector. Besides, weight percent ratio, effect of time and stability contributed significantly to enhance reactor performances. Using gas phase system, ZnV2O6/RGO/pCN nanocomposite demonstrated excellent photoactivity in the reduction of CO2 into carbon monoxide (CO), hydrogen (H2), methane (CH4) and methanol (CH3OH) under visible light irradiation. The CO evolution rate as a main product over ZnV2O6/RGO/pCN nanocomposite of 3756 µmol g-cat-1 was obtained. The quantum efficiency of 14.2 % was achieved for CH3OH production in a photoreactor with reflector, followed by 10.4 % and 0.25 % in photoreactor without reflector and fixed-bed photoreactor, respectively under visible light irradiation. Finally, Langmuir-Hinshelwood kinetic model was developed to investigate adsorption behaviors and photocatalytic oxidation and reduction process. In conclusion, solar photoreactor with reflector and modified ZnV2O6 nanocatalysts could make markedly higher CO2 reduction to fuels.