Fe(IV)=O/Fe(V)=O and [FeIVaqO]2+/[FeVaqO]3+ induced high-rate SMX-Cr(VI) simultaneously removal in Fe7S8-PS micro-nano catalytic system

Abstract Conventional persulfate (PS)-based catalytic system devoted to resolving single pollutant sulfamethoxazole (SMX) problems depends on free radicals, which ignores the contribution of non-free radical Fe(IV)/Fe(V) and interaction of co-contamination Cr(VI) and SMX. The production, role, and identification of Fe(IV)/Fe(V) were inefficient, unclear, or not enough. Here, the Fe₇S₈-PS micro-nano catalytic system was independently constructed to quickly stimulate Fe(IV)/Fe(V) species production, which was identified by the Mössbauer spectra. The SMX reaction path and degradation rate were increased by Fe(IV) = O/Fe(V) = O at the Fe₇S₈ interface (providing active chemical bond positions) and the produced [\(\:{Fe}aqIV\)O]²⁺/[\(\:{Fe}aqV\)O]³⁺ in solution (effectively capturing Fe³⁺ and accelerating the transformation to free radical). In the Fe(IV)/Fe(V) species-induced high-rate reaction system, the kSMX (0.0304 min⁻ ¹) raised 152.0 times as against the kSMX (0.0002 min⁻ ¹) in the sole Fe₇S₈ system. SMX had five possible degradation pathways, in which the fractures of S-N and N-C bonds were the two main chain-scission degradation pathways confirmed through density functional theory (DFT) calculation. Furthermore, the Cr(VI) was dominated by a rapid reduction (0.0227 min⁻ ¹) to low toxicity Cr(III) which eventually adsorbed by the dynamically transformed Fe₇S₈ and iron-oxide secondary minerals. Hence, the Fe₇S₈-PS micro-nano catalytic system provides a new strategy for treating SMX-Cr(VI) co-contaminated groundwater.