Graphitic Carbon Nitride for Photocatalytic Air Treatment

Graphitic carbon nitride (g-C₃N₄) is a conjugated polymer, which recently drew a lot of attention as a metal-free and UV and visible light responsive photocatalyst in the field of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability and earth-abundant nature. In the present work, bulk g-C₃N₄ was synthesized by thermal decomposition of melamine. This material was further exfoliated by thermal treatment. S-doped samples were prepared from thiourea or further treatment of exfoliated g-C₃N₄ by mesylchloride. Synthesized materials were applied for photocatalytic removal of air pollutants (acetaldehyde and NO_x) according to the ISO 22197 and ISO 22197-1 methodology. The efficiency of acetaldehyde removal under UV irradiation was negligible for all g-C₃N₄ samples. This can be explained by the fact that g-C₃N₄ under irradiation does not directly form hydroxyl radicals, which are the primary oxidation species in acetaldehyde oxidation. It was proved by electron paramagnetic resonance (EPR) spectroscopy that the dominant species formed on the irradiated surface of g-C₃N₄ was the superoxide radical. Its production was responsible for a very high NO_x removal efficiency not only under UV irradiation (which was comparable with that of TiO₂), but also under visible irradiation.