Hexavalent chromium, a potentially toxic micropollutant in industrial effluents due to anthropogenic activities, contaminates the water and poses severe health hazards. The present work demonstrates a scalable approach to synthesize nitrogen-doped activated carbon from agroforestry waste biomass for simultaneous adsorption and reduction of hexavalent chromium into remarkably less toxic Cr(III) species. Bhimal fiber (agroforestry waste biomass)-derived nitrogen-doped activated carbon (BFNAC) enriched with graphitic domains exhibits high surface area (1527 m²·g^–1) and plentiful nitrogen functionalities (12.6 at % nitrogen). The chemical characterization based on XPS analysis revealed the amine, pyrrolic, pyridinic, protonated nitrogen, hydroxyl, and carboxylic functionalities on the surface of BFNAC. These functionalities facilitated the adsorption of chromium oxyanions via electrostatic interactions under acidic pH. The BFNAC showed significantly higher adsorption of chromium oxyanions (255 mg·g^–1) compared to the corresponding activated carbon without nitrogen doping (BFAC; 168 mg·g^–1), revealing the role of nitrogen-based functionalities to aid the adsorption of chromium oxyanions. XPS analysis revealed the reduction of highly toxic hexavalent chromium oxyanions into notably less toxic trivalent species during the adsorption, mitigating the hazardous effect of Cr(VI) contaminants. The BFNAC exhibited pH swing-driven excellent recyclability and maintained >99% removal of chromium oxyanions even after 7 adsorption–desorption cycles. These findings promise lignocellulosic biomass-based nitrogen-doped carbons as potential adsorbents to remove the toxic and hazardous micropollutants from wastewater.

中文翻译：

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农林业生物质衍生的富氮活性炭吸附分离并同步还原剧毒铬氧阴离子


六价铬是人为活动导致工业废水中具有潜在毒性的微污染物，会污染水并对健康造成严重危害。这项工作展示了一种从农林业废弃生物质中合成氮掺杂活性炭的可扩展方法，用于同时吸附和还原六价铬成毒性显着降低的 Cr（III） 物种。富含石墨结构域的 Bhimal 纤维（农林业废弃物生物质）衍生的氮掺杂活性炭 （BFNAC） 表现出高表面积 （1527 m²·g^–1） 和丰富的氮官能团 （12.6% 氮）。基于 XPS 分析的化学表征揭示了 BFNAC 表面的胺、吡咯、吡啶、质子化氮、羟基和羧基官能团。这些功能有助于在酸性 pH 值下通过静电相互作用吸附铬氧阴离子。与未掺氮的相应活性炭 （BFAC;168 mg·g^–1） 相比，BFNAC 对铬氧阴离子的吸附率 （255 mg·g^–1） 显著提高，揭示了氮基官能团在帮助吸附铬氧阴离子方面的作用。XPS 分析显示，在吸附过程中，剧毒的六价铬氧阴离子被还原成毒性明显较低的三价物质，减轻了 Cr（VI） 污染物的有害影响。BFNAC 表现出 pH 波动驱动的出色可回收性，即使在 7 次吸附-解吸循环后仍能保持 >99% 的铬氧离子去除率。这些发现有望将木质纤维素生物质基氮掺杂碳作为潜在的吸附剂，以去除废水中的有毒和有害微污染物。