Hydrothermal Synthesis of FeS₂ as a High-Efficiency Fenton Reagent to Degrade Alachlor via Superoxide-Mediated Fe(II)/Fe(III) Cycle

Abstract

In this study, we demonstrate that hydrothermally synthesized FeS2 (syn-FeS2) is highly efficient at catalyzing the H2O2 decomposition for alachlor degradation at a wide range of initial pH (3.2-9.2). The alachlor degradation rate of syn-FeS2 heterogeneous Fenton system was almost 55 times that of its commercial pyrite (com-FeS2) counterpart at an initial pH of 6.2. Experimental results revealed that the alachlor oxidation enhancement in the syn-FeS2 Fenton system was attributed to the molecular oxygen activation induced by more surface-bound ferrous ions on syn-FeS2. The molecular oxygen activation process could generate superoxide anions to accelerate the Fe(II)/Fe(III) cycle on the syn-FeS2 surface, which favored the H2O2 decomposition to generate more hydroxyl radicals for the alachlor oxidation. It was found that the hydroxyl radicals generation rate constant of syn-FeS2 Fenton system was 71 times that of its com-FeS2 counterpart, and even 1-3 orders of magnitude larger than those of commonly used Fe-bearing heterogeneous catalysts. We detected the alachlor degradation intermediates with gas chromatography-mass spectrometry to propose tentatively a possible alachlor degradation pathway. These interesting findings could provide some new insights on the molecular oxygen activation induced by FeS2 minerals and the subsequent heterogeneous Fenton degradation of organic pollutants in the environment.

Biochar-Supported FeS/Fe3O4 Composite for Catalyzed Fenton-Type Degradation of Ciprofloxacin

“…In this study, the degradation reaction of ciprofloxacin was dramatically suppressed when methanol (40 mmol/L) was added in the systems catalyzed by FeS/Fe3O4 and FeS/Fe3O4@BC500, according to the results shown in Figure 6a. The results confirm that • OH is the reactive species that has made the major contribution for the oxidation of ciprofloxacin, which is consistent with previous reports about the Fenton-type reactions catalyzed by iron minerals [27,29,31,32,39,47,48]. For further investigating the role of biochar, the cumulative production of • OH in the two Fenton-type systems was measured using benzoic acid (BA) as the probe.…”

Alachlor dechlorination prior to an electro-Fenton process: Influence on the biodegradability of the treated solution

“…was formed by direct scission of the C-Cl bond of alachlor, and was further oxidized to compounds 8 and 7, as reported in other AOPs[18,45,46]. The cleavage of the C-N bond occurring by α/β scission of the bond and hydroxylation generate compound which could be oxidized via the further cleavage of the C-Cl bond and hydrogen abstraction to form 8, as also reported in BDD(•OH) oxidation[21].…”

“…On the basis of these intermediates and the related literatures [16,18,20,21,[45][46][47], we proposed that alachlor degradation mechanism involved alkylic oxidation, cleavage of C-N, C-Cl, C-O, and/or C-C bonds, cyclization, and dealkylation ( Figure 4). First, compound A c c e p t e d m a n u s c r i p t 11 2 was generated by dealkylation of alachlor upon the attack by •OH and then further oxidized to compounds 6 and 5 by scission of the R-N bond and hydroxylation, as it has been previously observed in photo-Fenton oxidation [16].…”

Ultra-sustainable Fe78Si9B13 metallic glass as a catalyst for activation of persulfate on methylene blue degradation under UV-Vis light

“…The improved performance of the Fe 78 Si 9 B 13 reusability is owing to the following reasons. (1) The pH value plays a significant role in the Fenton/Fenton-like reaction5960, as hydroxyl radicals (∙OH) can be rapidly activated under pH 2 by using Fe 78 Si 9 B 13 and H 2 O 2 13 whereas the pH of MB dye solution after adding Fe 78 Si 9 B 13 and persulfate in this work is only 3.39. The acidic conditions can enhance the corrosive speed of the SiO 2 layer on the Fe 78 Si 9 B 13 surface leading to fast surface decay behaviour.…”