New Chemistry Unit, School of Advanced Materials and International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560064, India.
Inorg Chem. 2021 Jul 5;60(13):10056-10063. doi: 10.1021/acs.inorgchem.1c01479. Epub 2021 Jun 17.
Rapid industrialization has led to the release of hexavalent chromium (Cr(VI)), a "Class A" human carcinogen, mutagen, and teratogen in biological systems. Current adsorbents like anionic exchange resins and metal-organic frameworks can remove harmful heavy metal oxyanions from water but are not stable in a broad pH range, suffer from selectivity, and cannot capture them from trace values below the tolerance limits given by the U.S. EPA (100 ppb) and WHO (50 ppb). Herein, we have synthesized nature-inspired coral-like three-dimensional hierarchical structures of [CoAl(OH)(CO)]·HO (CoAl-LDH) that sets a new benchmark for sequestering oxyanions of Cr(VI). CoAl-LDH shows a broad pH working range (1.93-12.22), high selectivity toward saturated water samples containing monovalent (Cl, F, Br, and NO) and divalent (SO) anions with fast kinetics (reaches equilibrium within a minute), high capacity (93.4 ± 7.8 mg g), and high distribution coefficient of 1.09 × 10 mL g. Unlike other materials, it can decrease Cr(VI) concentration up to 0.012 ppb. This high selectivity for Cr(VI) is linked to the weak bonding interaction between CrO and brucite-like layers, as revealed from thermogravimetric and infrared spectroscopy. With these remarkable features coupled with low cost and an environmentally friendly nature, we have also designed an anion exchange column that can remove >99% Cr(VI) with just 1 wt % of CoAl-LDH and 99 wt % of sand and is a prominent candidate for the elimination of Cr(VI) from industrial effluents.
快速工业化导致六价铬（Cr(VI)）的释放，六价铬在生物系统中是一种“A级”人类致癌物、致突变物和致畸物。目前的吸附剂，如阴离子交换树脂和金属有机骨架，可以去除水中的有害重金属含氧阴离子，但在较宽的 pH 范围内不稳定，具有选择性，并且不能从低于美国环保署（100ppb）和世界卫生组织（50ppb）规定的容忍极限的痕量值中捕获它们。在这里，我们合成了受自然启发的珊瑚状三维分层结构的[CoAl(OH)(CO)]·HO（CoAl-LDH），为捕获 Cr(VI)的含氧阴离子设定了新的基准。CoAl-LDH 显示出宽的 pH 工作范围（1.93-12.22），对含有单价（Cl、F、Br 和 NO）和二价（SO）阴离子的饱和水样具有高选择性，动力学速度快（在一分钟内达到平衡），容量高（93.4±7.8mg/g），分配系数高（1.09×10 mL/g）。与其他材料不同，它可以将 Cr(VI)浓度降低到 0.012ppb 以下。这种对 Cr(VI)的高选择性与 CrO 和水镁石样层之间的弱键合相互作用有关，这从热重和红外光谱中可以看出。由于具有这些显著的特点，再加上成本低和环保的特点，我们还设计了一种阴离子交换柱，只需 1wt%的 CoAl-LDH 和 99wt%的沙子就可以去除超过 99%的 Cr(VI)，是从工业废水中去除 Cr(VI)的突出候选材料。
