Sponge-based FeSx triggers enhanced and durable water decontamination from Cr(VI): Accelerated electron transfer and slow-releasing property.

Developing strategies for efficient and durable reduction of Cr(VI) in wastewater is still a desirable and challenging task. Herein, we successfully load the iron-sulfur composite (FeSx) uniformly on the melamine sponge (MS) through in-situ deposition to form a three-dimensional composite FeSx/MS. Compared with typical iron minerals (e.g., FeS2), FeSx/MS was significantly better at removing Cr(VI) in water, with the removal rate increased from 14.78 % to 99.44 %. The reaction kinetics of FeSx/MS (0.1011 min-1) was 37 times that of FeS2 (0.0027 min-1). SEM-EDS results showed that FeSx was uniformly loaded on the sponge, forming a high density of active sites. XPS analysis displayed that the proportion of SO42- was increased from 39.22 % to 61.18 %, implying the involvement of FeSx/MS in the reduction of Cr(VI). Tafel scanning and cyclic voltammetry (CV) results confirmed that the enhanced reduction performance was attributed to the accelerated electron transfer and sufficient electron supply capability. Additionally, the deposition of Cr(OH)3 on FeSx/MS is evidenced to be responsible for eliminating total Cr from water. The influence of water chemistry, i.e., pH, Cr(VI) concentration, and co-existed substances, on Cr(VI) removal during FeSx/MS treatment was systematically examined. The removal capacity of Cr(VI) in tap water, natural water, and industrial wastewater, is more than 90 %, suggesting a strong anti-interference ability of FeSx/MS. The rapid flow dynamic simulation experiment demonstrates that FeSx/MS can achieve efficient removal of Cr(VI) and slow-releasing of Fe. The removal rate of Cr(VI) reached 100 % in the first 10 cycles, whereas the final effluent concentration was only 0.14 mg/L. This study provides a rational design of corresponding approaches to deal with Cr(VI) pollution.