An Investigation into the Stability of Graphitic C 3 N 4 as a Photocatalyst for CO 2 Reduction

The increasing CO 2 concentration in the atmosphere exerts a significant influence on global warming and climate change. The capture and utilization of CO 2 by conversion to useful products is an area of active research. In this work, the photodriven reduction of CO 2 was investigated using graphitic carbon nitride (g-C 3 N 4 ) as a potential photocatalyst. The photocatalytic reduction of CO 2 was investigated with g-C 3 N 4 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-C 3 N 4 in the presence of CO 2 was CO, and the rate of production was observed to decrease over time. Oxygen-doped g-C 3 N 4 was also tested for CO 2 reduction but had efficiency lower than that of the parent g-C 3 N 4 . Repeated cycles of photocatalytic CO 2 reduction showed a decline in the activity of the g-C 3 N 4 . In the absence of CO 2 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-C 3 N 4 as a photocatalyst, this work highlights the important need for replicates and control testing to determine material stability.