Photochemical stability of g-C3N4 in the gas phase

For the successful environmental applications of g-C3N4 photocatalyst, sufficient photochemical stability is an important parameter. The present work is thus devoted to the investigation of the photostability of g-C3N4 materials in terms of production of organic compounds under UV and VIS light irradiation; for the purpose of comparison, TiO2 material was also investigated. The measurement of total organic compounds in air shows the production of organic compounds when g-C3N4 materials are irradiated with UV or VIS light. Detailed analysis of organic compounds present in the air was performed using GC-MS. When both materials (TiO2 and g-C3N4) were exposed in the dark, the air contained traces of ordinary solvents (acetone, hexane, ethyl acetate). In the case of TiO2, after 1 day of UV irradiation, all organic compounds were removed. Contrary to it, in the case of exfoliated g-C3N4, the concentration of acetone after UV or VIS irradiation increased. The solid-state measurements indicate that after UV/VIS light exposure, there are no changes either in the surface layers or in the bulk of the g-C3N4 photocatalyst. However, based on the observed mass decrease and elemental analysis, the material is oxidised on the surface, and it seems that this surface reaction leads to the disruption of the C-N bonds and the formation of organic compounds, which are released into the atmosphere. But, no compounds containing nitrogen were determined by MS, so nitrogen is most probably released in the form of NOx.