This study utilized waste mango kernels as a green reducing agent with the residue serving as the biochar precursor in a one-pot, two-step process to prepare mango kernel biochar supported polysulfide-green synthesized-nanoscale zero valent iron (FeS@Fe⁰-MKB) for Cr(VI) removal from water. The oxidation resistance and electron transfer capacity of Fe⁰ were significantly enhanced by the introduction of calcium polysulfide (CaS_x) as a sulfide reagent. The composite with S/Fe molar ratio of 2/1 (FeS@Fe⁰-MKB2) exhibited the greatest efficacy for Cr(VI) treatment, with a removal efficiency of 99.9 % in 30 min. The pseudo-second-order kinetic model and intra particle diffusion model provided better explanations for Cr(VI) removal kinetics by FeS@Fe⁰-MKB2. Sulfur species (S_n^2–, S^2– and S₂^2–), iron species (Fe⁰, Fe²⁺) and biochar functional groups served as pivotal electron donors in the FeS@Fe⁰-MKB system. FeS@Fe⁰-MKB2 was a composite with satisfactory stability and cyclability.

中文翻译：

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芒果仁生物炭负载的多硫化物-绿色合成纳米级零价铁对水性 Cr（VI） 的增强去除：性能与机理


本研究利用废弃芒果仁作为绿色还原剂，残留物作为生物炭前体，采用一锅两步法制备芒果仁生物炭负载的多硫化物绿色合成纳米级零价铁 （FeS@Fe ⁰ -MKB），用于从水中去除 Cr（VI）。引入多硫化钙 （CaS _x ） 作为硫化物试剂，显著提高了 Fe ⁰ 的抗氧化性和电子转移能力。S/Fe 摩尔比为 2/1 （FeS@Fe ⁰ -MKB2） 的复合材料对 Cr（VI） 处理效果最好，30 min 去除效率为 99.9 %。准二级动力学模型和粒子内扩散模型为FeS@Fe ⁰ -MKB2 对 Cr（VI） 去除动力学提供了更好的解释。硫物质 （S _n ^2– ， S ^2– 和 S ₂ ^2– ）、铁物质 （Fe ⁰ ， Fe ²⁺ ） 和生物炭官能团是 FeS@Fe ⁰ -MKB 系统中的关键电子供体。FeS@Fe ⁰ -MKB2 是一种具有令人满意的稳定性和循环性的复合材料。