Synergistic scavenging of sulfamethoxazole and hexavalent chromium in groundwater sample induced by iron-char composites activated persulfate triggering dominant electron transfer process

Abstract

Effectively scavenging combined pollutants in complex water matrix via dominant electron transfer pathway using modified zero-valent iron (ZVI) remains challenging. Herein, novel iron-based catalysts were synthesized using ball milling and pre-oxidation modified biochar (MOBC), which featured abundant pore structure and oxygen-rich functional moieties to support nZVI in activating persulfate (PS). The most suitable catalytic system achieved ultrafast simultaneous removal of 89.0 % of sulfamethoxazole (SMX) and nearly 100 % of hexavalent chromium (Cr(VI)) within 5 min (with nearly complete removal of SMZ and Cr(VI) in 60 min). By serving as an electron shuttle, MOBC700 could accelerate electron transfer from SMX to PS adsorbed on the nZVI1.0@MOBC700 for SMX decomposition, with reactive oxygen species (ROSs) also contributing. Moreover, nZVI facilitated the reduction of Cr(VI) adsorbed on nZVI1.0@MOBC700 through electron transfer. The dissolved Fe(II) generated via PS activation and Cr(VI) reduction further facilitated Cr(VI) removal from the solution, while the gradual consumption of excess Fe(II) ensured continued ROSs-mediated degradation of SMX. Additionally, the system also demonstrated resistance to interference from NO3-, CO32-, and humic acid, and was effective in remediating four different water samples. Overall, this study presents a promising method for designing iron-char composites to address combined antibiotic and heavy metal contamination in groundwater samples via dominant electron transfer process.