Fe(IV)═O/Fe(V)═O and [Fe<sub>aq</sub><sup>IV</sup>O]<sup>2+</sup>/[Fe<sub>aq</sub><sup>V</sup>O]<sup>3+</sup> Cooperating with Free Radicals Induced High-Rate Sulfamethoxazole-Cr(VI) Simultaneous Removal in a Fe<sub>7</sub>S<sub>8</sub>-Persulfate Micro/Nanocatalytic System
Chunyang Li, Wenbing Wang, Qifeng Fan, Yunhui Zhang, Meng Zhang, Qianling Dong, Ghebretensae Aron Kifle, Hui Li
Abstract
Conventional persulfate-based (PS-based) catalytic systems that resolve single-pollutant sulfamethoxazole (SMX) problems depend on free radicals. However, research on the contribution or cooperative effect of nonfree radical Fe(IV)/Fe(V) species and the interaction of cocontamination Cr(VI)-SMX has not been sufficiently elucidated. The production source of the Fe(IV)/Fe(V) species requires further exploration and expansion. Here, a pyrrhotite-PS (Fe 7 S 8 -PS) micro/nanocatalytic system was independently constructed to stimulate the production of Fe(IV)/Fe(V) species, which were identified by Mössbauer spectroscopy. In the Fe(IV)/Fe(V) species cooperating with the free-radical-induced high-rate reaction system, k SMX (0.0304 min –1 ) raised 152.0 times to k SMX (0.0002 min –1 ) in the sole Fe 7 S 8 system. SMX has five possible degradation pathways in which the fractures of the S–N and N–C bonds are the two main chain scission degradation pathways confirmed through density functional theory (DFT) calculations. Furthermore, Cr(VI) was dominated by rapid reduction (0.0227 min –1 ) to low-toxicity Cr(III), which was eventually adsorbed by the dynamically transformed Fe 7 S 8 and secondary iron-oxide minerals. The SMX reaction path and degradation rate were increased by [Fe aq IV O] 2+ /[Fe aq V O] 3+ in the solution (reacting with SMX and accelerating the transformation of free radicals). Hence, the Fe 7 S 8 -PS micro/nanocatalytic system provides a new strategy for treating high-concentration SMX-Cr(VI) cocontaminated wastewater and groundwater.