Theoretical and Experimental Investigation of Photocatalytic Conversion of CO2 Using Nitrogen-Doped Graphene Oxide Composites under Solar Irradiation Conditions in Nigeria

Photocatalytic conversion of carbon dioxide to value-added fuels using solar energy represents a grand challenge at the intersection of carbon capture, renewable energy, and photochemistry, and theoretical frameworks for predicting photocatalyst performance in tropical high-irradiance conditions such as those prevailing in Northern Nigeria have not been developed. This study combines theoretical quantum chemical analysis, materials synthesis, and experimental investigation of the photocatalytic CO2 reduction activity of nitrogen-doped graphene oxide composites coupled with bismuth vanadate and molybdenum disulphide cocatalysts, evaluated under simulated and real solar irradiation conditions representative of Kano State solar spectrum characteristics. An original theoretical framework is developed to explain observed activity trends based on charge transfer dynamics modelled by time-dependent DFT and non-equilibrium Green's function transport simulations, which predict dominant charge carrier pathways and recombination mechanisms at heterointerfaces in the composite photocatalyst system. Composites were synthesised by a hydrothermal method, characterised by XPS, XRD, HRTEM, BET, PL spectroscopy, and photoelectrochemical analysis. CO2 reduction experiments under one-sun simulated solar irradiation produced methanol and carbon monoxide as primary products, with a maximum methanol production rate of 42.6 micromol/g/h for the optimised composite, representing a 5.8-fold improvement over the bismuth vanadate benchmark. The theoretical charge transfer model predicted product selectivity trends correctly across all composite compositions tested. The study makes original theoretical contributions to solar CO2 conversion science and provides experimental evidence for a locally synthesisable photocatalyst in Nigerian solar energy contexts. Keywords: CO2 photoreduction, graphene oxide, DFT, solar irradiation, nitrogen doping