Combined treatment process of Fenton-like and peroxymonosulfate catalyzed by Fe(III)-reduced graphene oxide for efficient removal of isoprothiolane: Fe(III)/Fe(II) cycle and mechanism study

Abstract

Reduced graphene oxide supported with ferric ion (Fe(III)-rGO) was successfully prepared, and performed as an excellent catalyst to activate hydrogen peroxide (H2O2) and peroxymonosulfate (PMS) for isoprothiolane (IPT) degradation. IPT removal efficiency was proven to be better in the Fe(III)-rGO/H2O2/PMS system (96.2%) than in the Fenton-like reaction (72.6%) and PMS-AOP (80.0%) individually. X-ray photoelectron spectroscopy showed that Fe(III) was reduced in Fenton-like reaction, and the reduced Fe(II) played a crucial role in the subsequent PMS-AOP. The combination of the Fenton-like reaction and PMS-AOP involved the valence state conversion of Fe, which consequently improved Fe(III)-rGO utilization rate and IPT removal efficiency. Fe(III)-rGO remarkably boosted the Fe(III)/Fe(II) cycle and generated superoxide radical (O2−•) and singlet oxygen (1O2) in the Fe(III)-rGO/H2O2/PMS system. Fe(III)-rGO acts as the electron transfer mediator; thus, promoting electron transfer from IPT to H2O2 and PMS and accelerating the generation of active species. Fe(IV) with high oxidation performance was formed in PMS-AOP and efficiently removed some of the IPT. IPT removal efficiency was more than 90% at a pH range of 3–11; this efficiency could be maintained above 50% even after five consecutive degradation experiments, exhibiting excellent stability and reusability of Fe(III)-rGO. Additionally, iron sludge formation was greatly reduced because of the stable chemical bonding of iron ions to the rGO surface. Therefore, this study provides a new multisystem and synergistic approach for the efficient removal of organic micro-pollutants from water.