Water Steam Bathed FeS₂ for Highly Efficient Fenton Degradation of Alachlor

Abstract

Fenton-like activity of iron sulfides for the generation of reactive oxygen species and degradation of various organic pollutants has been extensively investigated due to its abundance in the natural environment. However, their Fenton-like activity is usually unsatisfactory due to the limited exposure of surface ferrous reactive sites. In this work, a new strategy to enhance the Fentonlike activity of iron sulfides, using pyrite (FeS2) as a model, was developed based on the heat treatment of FeS2 by water steam. It was found that the FeS2 heat-treated by water steam (Heat-FeS2) exhibited much higher heterogeneous Fenton activity in the degradation of alachlor (ACL) than its parent FeS2 prepared from hydrothermal reaction (Fresh-FeS2). At an initial pH of 6.3, the rate of degradation of ACL by Heat-FeS2 Fenton system was 0.48 min −1 , which is ~23 times higher than that of Fresh-FeS2 Fenton system. Electron spin resonance analysis and benzoic acid probe experiments confirmed the production of more hydroxyl (•OH) and superoxide radicals (•O2 − ) in Heat-FeS2 Fenton system than Fresh-FeS2 Fenton system. The increased Fenton-like activity of Heat-FeS2 can be attributed to the increased content of highly reactive surface bonded Fe 2+ /Fe 3+ species, higher amount of leached Fe 2+ , and optimal reaction pH due to stronger acidification of Heat-FeS2. Characterization studies by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy showed that heat treatment remarkably promoted the transformation of lattice Fe 2+ to surface reactive Fe 2+ , allowing the exposure of more surface reactive Fe 2+ and leaching of Fe 2+ ; simultaneously, heat treatment enhanced the generation of surface SO4 2− , creating a highly acidic surface. The surface Fe 2+ percentage in the surface total iron was raised from 13% in Fresh-FeS2 to 29% in Heat-FeS2. Fe 2+ leaching from Heat-FeS2 was 0.23 mmol•L −1 , much higher than that (< 0.02 mmol•L −1 ) for Fresh-FeS2. The change in the surface Fe and S species in the Heat-FeS2 system during the Fenton-like reaction was monitored by XPS to elucidate the enhanced Fenton oxidation mechanism. The characterization results