The role of non-radical pathway in heterogeneous activation of persulfate and H2O2 by superparamagnetic magnetite-reduced graphene oxide nanocomposite

Abstract

Superparamagnetic magnetite-reduced graphene oxide nanocomposite (Fe3O4-rGO) was synthesized by a one-pot solvothermal method and were characterized by XRD, TEM, FESEM, FTIR, XPS, and VSM analysis. The different systems such as PS/Fe3O4-rGO, H2O2/Fe3O4-rGO, and the combined system of PS + H2O2/Fe3O4-rGO were evaluated for acetaminophen (ACP) degradation under different pH conditions. The study showed the superior activity of PS/ Fe3O4-rGO over the other systems with >98% of ACP removal within 150 min in a wide pH range (3–10). The ACP removal and TOC reduction at acidic pH are as follows; PS/ Fe3O4-rGO > PS + H2O2/ Fe3O4-rGO > H2O2/ Fe3O4-rGO. The investigation of different reactive species involved in these systems showed the predominance of non-radical pathway over the radical pathway for the ACP degradation. The extensively reactive catalyst surface leads to further reactions of radicals to end up with less reactive species. Despite the lower reactivity, the abundance of O2•-, 1O2 are sufficient to carry out the ACP removal with good mineralization. The pathway of ACP degradation in the PS/Fe3O4-rGO system was proposed based on the HR-LC-MS/MS analysis. The applicability of PS/Fe3O4-rGO system was further confirmed by studying the removal of ACP from groundwater. In PS + H2O2/Fe3O4-rGO combined system, the addition of lower polar solvents such as ethanol and t-butanol acted as activity enhancer. Combining PS and H2O2 in the same system to gain more radicals is not a good strategy in terms of economical and reactivity aspects.