Contamination of arsenic in the form of arsenite (As³⁺) and arsenate (As⁵⁺) in potable water causes serious illness in the human body even at a very low concentration (10 µg/L). As³⁺ is comparatively 60 times more toxic than As⁵⁺ species. This work is focused on the preparation of adsorbents for efficient removal of As³⁺ with higher adsorption affinity at trace level (≤ 50 µg/L). The iron-doped hydroxyapatite (Fe-HAp) synthesized by hydrothermal technique is employed as an efficient adsorbent. A significantly less quantity of Fe²⁺ ion (0.5 wt%) is incorporated in the tetrahedral and octahedral sites of the HAp lattice along the c-axis, which leads to a drastic reduction in particle size (400% in length and 225% in width) and enhances the specific surface area (105%), colloidal stability, and adsorption affinity. The maximum adsorption capacity of As³⁺ is 139 ± 2 µg/g and 183 ± 2 µg/g for HAp and Fe-HAp, respectively. The adsorption rate of Fe-HAp is very rapid, which is 538% higher than HAp. Also, the As³⁺ adsorption affinity or sensitivity (0.71 µg/L) significantly improved 83–99% when compared to the adsorbents reported in the previous literature. The adsorption capacity of As³⁺ ion was unaffected by other competing ions and obtained 97% recycling efficiency up to 7 cycles using Fe-HAp. The monolayer adsorption of As³⁺ is purely strong chemisorption as confirmed by the Langmuir and Dubinin–Radushkevich (DKR) isotherm. The structure and morphology of HAp and Fe-HAp remain unchanged after the adsorption of As³⁺ ions and also no secondary toxic products were observed. Hence, the above results reveal Fe-HAp as an efficient and low-cost adsorbent for the removal of highly toxic As³⁺ ions at the trace level.

Graphic Abstract

中文翻译：

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使用水热合成的掺铁羟基磷灰石纳米棒增强 As3+ 离子的痕量级吸附亲和力

饮用水中以亚砷酸盐 (As ³⁺ ) 和砷酸盐 (As ⁵⁺ )形式存在的砷污染即使浓度非常低 (10 µg/L) 也会导致人体严重疾病。As ^{3+ 的}毒性是 As ⁵⁺物种的60 倍。这项工作的重点是制备吸附剂，以在痕量水平（≤ 50 µg/L）具有更高的吸附亲和力，以有效去除 As ³⁺。通过水热技术合成的掺铁羟基磷灰石（Fe-HAp）被用作一种高效的吸附剂。Fe ^{2+ 的}量显着减少离子 (0.5 wt%) 沿 c 轴掺入 HAp 晶格的四面体和八面体位点，这导致粒度急剧减小（长度减少 400%，宽度减少 225%）并提高比表面积(105%)、胶体稳定性和吸附亲和力。对于 HAp 和 Fe-HAp，As ³⁺的最大吸附容量分别为 139 ± 2 µg/g 和 183 ± 2 µg/g。Fe-HAp的吸附速度非常快，比HAp高538%。此外，与之前文献中报道的吸附剂相比，As ³⁺吸附亲和力或灵敏度 (0.71 µg/L) 显着提高了 83-99%。As ³⁺的吸附能力离子不受其他竞争离子的影响，使用 Fe-HAp 最多可循环 7 次，回收效率高达 97%。正如朗缪尔和杜比宁-拉杜什克维奇 (DKR) 等温线所证实的，As ³⁺的单层吸附是纯粹的强化学吸附。吸附As ³⁺离子后HAp和Fe-HAp的结构和形态保持不变，也没有观察到二次毒性产物。因此，上述结果表明 Fe-HAp 是一种高效且低成本的吸附剂，可用于去除痕量水平的剧毒 As ³⁺离子。

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