Efficiency and stability of metal-free carbon nitride in the photocatalytic ozonation of oxamic acid under visible light

The photocatalytic ozonation of oxamic acid (OMA) on an aqueous solution in the presence of carbon nitride was investigated as an efficient process of water treatment. Several techniques were used to characterize the fresh and used catalysts. The bulk material, labeled as gCN, was thermally post-treated at 500 degrees C (gCN-T), and a significant enhancement in the surface area was observed. Photocatalytic ozonation in the presence of carbon nitride proved to be effective in removing OMA, especially using gCN-T, owing to a complete OMA degradation after 120 min of reaction. The combined performance of photocatalytic ozonation in the presence of gCN-T allowed to confirm a synergetic effect between the two processes. The decrease in the OMA removal rate observed in the presence of scavengers suggested that the photogeneration of holes on the catalyst surface is predominant for the oxidation mechanism when compared to the hydroxyl radicals. A slight decrease in the degradation performance was observed in the recycling tests, probably owing to the modifications on gCN-T exposed structure; the other physical-chemical properties remained constant after several runs of photocatalytic ozonation.