An Investigation into the Stability of Graphitic C₃N₄ as a Photocatalyst for CO₂ Reduction

The increasing CO₂ concentration in the atmosphere exerts a significant influence on global warming and climate change. The capture and utilization of CO₂ by conversion to useful products is an area of active research. In this work, the photodriven reduction of CO₂ was investigated using graphitic carbon nitride (g-C₃N₄) as a potential photocatalyst. The photocatalytic reduction of CO₂ was investigated with g-C₃N₄ powder immobilized on a glass support in a batch gas-phase photoreactor. The experiments were carried out under UV–vis irradiation at 70 °C and an initial pressure of 2.5 bar. The only gas-phase product detected during the irradiation of the g-C₃N₄ in the presence of CO₂ was CO, and the rate of production was observed to decrease over time. Oxygen-doped g-C₃N₄ was also tested for CO₂ reduction but had efficiency lower than that of the parent g-C₃N₄. Repeated cycles of photocatalytic CO₂ reduction showed a decline in the activity of the g-C₃N₄. In the absence of CO₂ some CO generation was also observed. Characterization of used and unused materials, using FTIR and XPS, showed an increase in the oxygen functional groups following UV–vis irradiation or thermal treatment. While others report the use of g-C₃N₄ as a photocatalyst, this work highlights the important need for replicates and control testing to determine material stability.