Multifunctional sites on reduced graphene oxide synergistically improving the degradation of diclofenac in peroxydisulfate systems

Abstract

Carbonaceous catalysts are highly efficient in activation of persulfate thus attracting much attention in pollutant control. A reduced graphene oxide (rGO600) was carefully prepared via thermal annealing graphene oxide to activate peroxydisulfate (PDS) for generating nonradical and radical degradation pathways of diclofenac (DCF) in this study. The rGO600 had multifunctional groups, high defective degree (vacancies, CO and C−O−C; abundant reactive sites to activate PDS) and specific surface area. In the rGO600/PDS/DCF system, DCF was fast adsorbed on the surface and degraded via 1O2, electron transfer complex and O2•−. The rGO600/PDS/DCF system was resistant to the presence of Cl−and NO3−. Reductive NO2− and humic acid significantly retarded the absorption and activation of PDS by rGO600. Ten intermediate products from DCF were tentatively identified and proposed by using high-resolution mass spectrometry. The major adsorption sites for DCF and major catalytic sites for PDS were not exactly the same sites. The coexist of abundant reactive oxygen species (ROS)-generation sites and adsorbed DCF on the adsorption sites should favor the quick utilization of the generated ROS. The multifunctional sites on rGO600 improved the activation of PDS with pseudo first-order kinetics and the degradation of DCF.