Ozonation of carbamazepine in the presence of sulfur-dopped graphene: Effect of process parameters and formation of main transformation products

The stability of graphene structure in sulfur-doped graphene catalyst is demonstrated to be a key aspect during the ozonation process. Enhancing the stability of the sulfur-doped graphene structure is therefore important to improve its catalytic activity during the ozonation process. However, this has remained a challenge so far. Therefore, we adopted a low-energy microwave plasma technique to synthesize a high purity sulfur-doped graphene (S _ Gr) catalyst for the ozonation process. The effect of S _ Gr in the ozonation process was tested using carbamazepine (CBZ; 0.05 mM) as a probe compound. A complete CBZ removal was obtained at an ozone concentration of 0.08 mM while in comparison with single O3, similar to 1.5 and 2.5 times decrease in the formation of the two important in-termediate transformation products i.e., BQM (1-(2-benzaldehyde) - 4-hydroxy (1H, 3H)-quinazoline-2-one) and BQD (1-(2-benzaldehyde) -(1H, 3H)-quinazoline-2, 4-dione) was observed. Radical scavenging experiments confirmed the formation of HO center dot. The XPS results showed that the activity of S _ Gr towards the formation of HO center dot was positively related to S-bearing carbon atoms at the edge of the graphene structure. Therefore, the addition of S _ Gr is directly linked with the formation of HO center dot, which further contributed to the improved elimination of intermediate transforma-tion products. With a low sulfur loss of 1 %, the microwave plasma synthesized S _ Gr catalyst remained stable during ozonation, implying its feasibility in practical application.