Adsorptive interaction of peroxymonosulfate with graphene and catalytic assessment via non-radical pathway for the removal of aqueous pharmaceuticals.

Abstract

Graphene has been applied as a catalyst in peroxymonosulfate (PMS) activation for the removal of pharmaceuticals in water. Firstly, a kinetic adsorption study of PMS was developed, fitting the results to the Elovich s equation. Moreover, the influence of the main variables in the adsorptive process such as pH, initial PMS concentration, and graphene dose were assessed. Secondly, the degradation of diclofenac as a target compound was studied comparing PMS-catalytic versus adsorption processes. PMS-catalytic process enhanced the removal of the micropollutant if compared to adsorption when using a low dose of graphene (less than 50\u202fmg\u202fL-1) or after surface saturation. Studies using radical scavengers suggested the lack of radicals in the process, suggesting the non-radical activation of PMS. Thirdly, the adsorption versus PMS-catalytic processes were also compared for the oxidation of a mixture of three antibiotics (norfloxacin, tetracycline and sulfamethoxazole) with different chemical structure. PMS-catalytic activation was more effective for the removal of those compounds that presented less affinity towards adsorption onto the graphene surface. Finally, characterization of the fresh and PMS-treated material was performed. Graphene demonstrated to be stable after its use as catalysts in PMS activation, suffering only slight transformation of the surface oxidation groups.