Metal-free graphene-based catalytic membrane for degradation of organic contaminants by persulfate activation

Abstract

The persulfate (PS) activation can be successfully applied in water treatment and the use of carbon materials to activate PS has been thoroughly described in the literature. Nevertheless, the prospect of employing a metal-free catalytic membrane as the single activator of PS has to be better studied. In the present work, graphite oxide was prepared by the modified Hummers' method and different nitrogen precursors (melamine, urea and gaseous ammonia) were investigated to produce N-doped graphene oxide catalysts. The material prepared with melamine presented the highest nitrogen content (23.78 wt%) and the highest catalytic activity for the degradation of phenol in aqueous solution. The membrane fabricated with this catalyst was applied in filtration experiments for the degradation of phenol and oxalic acid. The catalytic mechanism is governed by both the radical and the non-radical degradation of the pollutants, but a more notorious contribution of singlet oxygen species was observed. It was demonstrated that the membrane lost the N-pyridinic groups during the reaction and, as consequence, part of its catalytic activity, whereas N-quaternary species remained in the used membrane. An important advantage associated with the application of this metal-free catalytic membrane, instead of a catalyst in powder form, is to avoid the final catalyst separation step.