Hydrothermal synthesis of FeS2 as a highly efficient heterogeneous electro-Fenton catalyst to degrade diclofenac via molecular oxygen effects for Fe(II)/Fe(III) cycle

In this study, we demonstrated that hydrothermal synthesized FeS2 was highly efficient to catalyze the H2O2 decomposition for diclofenac sodium (DCF) degradation in a wide range of initial pH (3–9) by heterogeneous electro-Fenton (EF) process, and this “Pyrite-EF” showed a better performance for the mineralization of DCF in comparison with the classic EF process. Effect of pyrite content on the hydroxyl radicals generation and iron dissolution produced by the decomposition of hydrogen peroxide (H2O2), and applied current density on the degradation kinetics and mineralization efficiency were studied. Moreover, toxicity assessment by means of microtox method showed the solution toxicity was removed after treatment. Experimental results revealed that the enhancement of DCF degradation rate in the Pyrite-EF process was attributed to the molecular oxygen activation induced by more surface bound ferrous ions on FeS2, generating superoxide anions to accelerate the Fe(II)/Fe(III) cycle on the FeS2 surface, which favored the H2O2 decomposition to generate more hydroxyl radicals for the DCF degradation via a heterogeneous EF-like process. These findings could provide some new insights into the molecular oxygen activation induced by FeS2 and the subsequent heterogeneous Pyrite-EF degradation of organic pollutants from wastewater.