Visible light photocatalytic oxidation of NO using g-C₃N₄ nanosheets: stability, kinetics, and effect of humidity

Heterogeneous photocatalysis is a promising technology for the degradation of environmental pollutants. In this work, g-C₃N₄ nanosheets were employed as a visible light photocatalyst to investigate the stability, kinetics and to understand the impact of humidity on the photocatalytic oxidation of nitric oxide (NO). Graphitic carbon nitride (g-C₃N₄) with unique physicochemical properties proves to be a promising photocatalytic material. Visible light active g-C₃N₄ nanosheets were successfully synthesized by thermal polycondensation of melamine followed by thermal exfoliation. Compared with the bulk carbon nitride, g-C₃N₄ nanosheets show significant NO removal efficiency (68%), followed by excellent stability after 5 cycles of photocatalytic oxidation under visible LED light illumination. Furthermore, photocatalytic oxidation of NO at various humidity levels revealed the significant role of humidity in photocatalytic NO removal. Finally, the initial uptake coefficients γ_0,geo, and γ_0,BET of NO on g-C₃N₄ nanosheets were determined to be 1.0 × 10^{− 5} and 1.58 × 10^{− 9}, respectively, and were found to decrease with increasing humidity. It appears that the photocatalytic removal of NO happens primarily on the surface of the g-C₃N₄ nanosheet.