Synergistic Removal of Cr(VI) and Acid Red 73 by Biochar-Supported Sulfidated nZVI: Performance, Mechanisms, and Environmental Compatibility

Nano zerovalent iron (nZVI) faces challenges of agglomeration, oxidation, and biotoxicity in environmental remediation. To address these issues, we synthesized biochar-supported sulfur-functionalized nZVI (BC-S-nZVI) and evaluated its performance in the simultaneous removal of Cr(VI) and acid red 73 (AR73), with exploration of the mechanisms and assessment of the ecotoxicity. The FeSx layer on BC-S-nZVI not only alleviated nZVI agglomeration and oxidation but also provided extra active sites, thus boosting the reactivity. BC-S-nZVI achieved high removal efficiencies of 99.9% for Cr(VI) and 96.9% for AR73 within 300 min with maximum adsorption capacities of 87.3 and 63.7 mg/g, respectively. The adsorption process followed Langmuir and pseudo-second-order models, indicative of monolayer chemisorption. Furthermore, BC-S-nZVI exhibited robust practicality, effectively decontaminating diverse natural water samples and maintaining high efficiency during continuous column operation for 432 h. Ecotoxicity assessments revealed that the BC-S-nZVI composite significantly reduced biotoxicity toward aquatic organisms (e.g., Hyriopsis cumingii) and relieved the inhibitory impact of Cr(VI) and AR73 on soil microorganisms. These findings highlight BC-S-nZVI as a promising, ecofriendly adsorbent for simultaneous remediation of heavy metals and organic pollutants from wastewater and groundwater.