The influence of synthesis conditions on the visible-light triggered photocatalytic activity of g-C3N4/TiO2 composites used in AOPs

Different synthesis temperatures (450–550 °C) were applied to synthesize g-C3N4 with the highest visible-light triggered photocatalytic activity. The best performing g-C3N4 photocatalyst was synthesized at 550 °C due to the created favourable structure that expressed the lowest band gap and charge carrier recombination rate. To further improve the photocatalytic activity of g-C3N4, different g-C3N4/TiO2 (gCN/TNP) composites with varying weight concentrations of g-C3N4 and TiO2 were prepared. Charge carrier separation was enabled due to the injection of photogenerated electrons from the g-C3N4 conduction band (CB) to the TiO2 CB, where they reacted with water-dissolved oxygen to form reactive oxygen species. The best performing composite was 0.50gCN/TNP 2 h with 50 wt% of g-C3N4 and 2 h calcination at 350 °C. The improved photocatalytic activity is due to an appropriate ratio between the shielding effect of TiO2, higher contact area and the consecutive improvement of the charge carrier separation, which is the key determining factor.