Effect of graphene oxidation degree on the catalytic activity of graphene for ozone catalysis

The potential of graphene-based materials, including graphene oxide (GO), over-oxidized graphene oxide (oGO), and non-oxidized graphene (nOG), for catalytic ozonation was investigated, along with the mechanism of ozone catalysis. Increasing the extent of oxidation of graphene led to the formation of hydroxyl and carboxyl groups on the graphene surface, which then partially converted into epoxy groups. The catalytic efficiency of oGO was much higher than that of both GO and nOG. Graphene's extent of oxidation might be a significant factor in catalytic ozonation. The hydroxyl radical exposure to ozone exposure ratio (R_ct) of 25 mg L^-1 ozone/oGO was 75-fold higher than that of an ozone alone process. The ozone decomposition rate and para-chlorobenzoic acid removal efficiency were higher at pH 9 than at any other pH. The R_ct of ozone/oGO at pH 9 was 2.35 × 10^-5. Temperature affected ozone adsorption on the nOG surface. Ozone/graphene experiment with an excess of tert-butyl alcohol was proposed that hydroxyl radicals generated by GO and oGO existed mainly in the solution phase, while those generated by nOG existed in both solution and surface phases.