Nickel and Platinum Modified Exfoliated Carbon Nitride as Photo-Thermal Catalysts for CO2 Hydrogenation

Abstract

The photocatalytic conversion of carbon dioxide into value-added fuels and chemicals is a promising route to mitigate greenhouse gas emissions while enabling sustainable energy storage. This study investigates the use of catalysts composed of exfoliated graphitic carbon nitride modified with either single-atom Ni sites or Pt nanoparticles for photo-thermal CO2 hydrogenation under combined light irradiation and thermal activation. The photocatalysts have been extensively characterized by different physico-chemical techniques, allowing the study of structure-activity relationships. Both metal-modified catalysts exhibit significantly enhanced CO2 conversion compared to pristine g-C3N4, which is attributed to improved light absorption, reduced charge recombination, and the role of metals as catalytically active sites. However, the catalytic behaviour varies markedly depending on the metal. Pt nanoparticles promote a thermally driven pathway assisted by light, enhancing overall activity and favouring CO formation, whereas Ni single-atom sites preserve the photocatalytic character of the support and shift the selectivity of hydrogenation towards methanol rather than methane primarily obtained over metal-free C3N4. These findings indicate that the combined photonic and thermal energy inputs efficiently activate both CO2 and H2, accelerating reaction kinetics and modifying reaction pathways beyond those achieved in purely thermal or purely photocatalytic systems.