Enhanced photocatalytic oxidation of NO over g-C3N4-TiO2 under UV and visible light

In this work, graphitic carbon nitride-titanium dioxide (g-C3N4-TiO2) was successfully prepared by a facile calcination route utilizing commercial P25 and melamine as the precursors. The as-prepared g-C3N4/TiO2 photocatalysts were characterized systematically to elucidate their morphological structure and physico-chemical properties. The photocatalytic performance of g-C3N4-TiO2 composites was investigated for the removal of NOx in air. At the optimal g-C3N4 content (∼15 wt%, labeled as M400), the conversion of NOx was 27%, which is higher than that of pure P25 (17%) and g-C3N4 (7%) under visible light. The activity of M400 was also enhanced under UV light. However, a mechanically mixed g-C3N4 and TiO2 sample (with the content of g-C3N4 the same as M400, labeled as M0 + g-C3N4) did not improve the conversion of NOx. Therefore, the interaction of g-C3N4 and P25 is important for the activity. EPR results indicated that O2− is the main active species for NO oxidation to NO3− under visible and UV light, which is responsible for the difference in activity between M400 and M0 + g-C3N4. The present study can improve our understanding of NO removal on the photocatalyst surface and the mechanism for the activity enhancement by the formation of g-C3N4-TiO2.