Six new NiCr layered double hydroxides (LDHs) intercalated with different inter-layer anions, including diphenylamine-4-sulfonate (DPA), dodecyl sulfonate (DS), pentansulfonate (PS), terephthalate (TA), fumarate (FA) and 2-ethylhexyl hydrogenphosphate (EHP), were synthesized and used to removal of Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺ ions from water samples. The maximum adsorption capacities (q_m ) for the mentioned LDHs based on their inter-layer anions were DPA>DS>PS>TA>FA>DEHP. This observation highlights the key role of the structure of the inter-layer anions in the adsorption behavior of LDHs. The sulfonate-based LDHs showed better adsorption efficiency than carboxylate-based LDHs, and phosphonate-based LDHs showed the lowest adsorption efficiency. Also, at both high and low concentrations of the metal ions, the length of R– groups and the type of functional groups of inter-layer anions play a key role in the adsorption process. Subsequently, DPA-LDH, due to having the highest q_m value among intercalated-LDHs, was chosen as an efficient sorbent for the removal of the metal ions from aqueous samples and its selectivity for adsorption of metal ions was investigated. DPA-LDH displayed a selectivity order of Zn²⁺ <Cu²⁺ <<<Cd²⁺ <Pb²⁺ for their adsorption, providing good separation of much more toxic metal ions of Cd²⁺ and Pb²⁺ from Zn²⁺ and Cu²⁺. For the highly toxic Pb²⁺ and Cd²⁺, enormous q_m values as large as 479 and 282mgg⁻¹ can be obtained, respectively; and these are among the highest q_m values reported for Pb²⁺ and Cd²⁺ sorbents. The very high distribution coefficient (K_d ) values for Pb²⁺ (1.99×10⁸ mLg⁻¹) and Cd²⁺ (1.99×10⁷ mLg⁻¹), obtained using a V/m ratio of 2000mLg⁻¹, place the DPA-LDH at the top of materials known for such removal.

中文翻译：

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层状双氢氧化物与二苯胺-4-磺酸盐插层的高选择性高效去除和萃取重金属的比较研究

六种新的NiCr层状双氢氧化物（LDHs）插入不同的层间阴离子中，包括二苯胺-4-磺酸盐（DPA），十二烷基磺酸盐（DS），戊磺酸盐（PS），对苯二甲酸盐（TA），富马酸盐（FA）和2-合成了乙基己基磷酸氢根（EHP），并用于去除水样中的Cd 2 ⁺，Pb 2 ⁺，Cu ²⁺和Zn ²⁺离子。最大吸附量（q _m）基于所述LDH的层间阴离子为DPA＞ DS＞ PS＞ TA＞ FA＞ DEHP。该观察结果突出了层间阴离子结构在LDHs吸附行为中的关键作用。磺酸盐基LDH的吸附效率高于羧酸盐基LDH，而膦酸酯基LDH的吸附效率最低。同样，在高和低浓度的金属离子中，R–基团的长度和层间阴离子的官能团类型在吸附过程中都起着关键作用。随后，由于具有最高的q _m，所以是DPA-LDH选择插层式LDHs的最大吸附值作为从水性样品中去除金属离子的有效吸附剂，并研究了其对金属离子吸附的选择性。DPA-LDH对它们的吸附显示出Zn 2 ⁺＆lt; Cu 2 ⁺＆lt;＆lt; Cd 2 ⁺＆lt; Pb ²⁺的选择性顺序，从而提供了对Cd ²⁺和Pb ^2的毒性更大的金属离子的良好分离。⁺来自Zn ²⁺和Cu ²⁺。对于剧毒的Pb ²⁺和Cd ²⁺，可以获得分别高达479和282mgg ^-1的巨大q _m值；这些是最高的q报告了Pb ²⁺和Cd ²⁺吸附剂的_m值。非常高的分配系数（K _d）为铅值²⁺（1.99×10 ⁸ MLG ^-1）和Cd ²⁺（1.99×10 ⁷ MLG ^-1），使用2000mLg的V /米比获得^-1，地点DPA-LDH位于此类去除材料的顶部。