Magnetic removal and recovery of precious metals from wastewater and complex biological media pose significant challenges mostly due to the need for efficient, selective, and stable materials. This work reports a methodology that allows these challenges to be addressed by synthesizing iron oxide nanoparticles (IONPs) coated with a covalent layer of calix[4]arene-tetracarboxylate (X4C4) capable of binding polyethylenimine (PEI) functionalities via electrostatic interactions. In contrast to citrate coating, which was previously utilized as an attachment layer for PEI, the reductive grafting of X4C4-tetra-diazonium salts onto IONPs results in a considerably more stable coating that proves to be an excellent substrate for the adsorption of PEI. This efficiently results in a synergistic interaction that significantly improves the durability of the PEI coating and maintains the particles in a dispersed state. The stability of the resulting IONPs@X4C4@PEI particles is demonstrated by their ability to withstand both acidic and alkaline conditions without significant particle aggregation or loss of magnetic properties. Moreover, these particles exhibit exceptional magnetic reusability, retaining their selectivity and recovery efficiency over multiple separation cycles. The selective affinity of IONPs@X4C4@PEI particles for gold (Au) and platinum (Pt) stems from the specific binding interactions between the complexes formed by these metals in solution and the PEI coating, enabling efficient recovery of these precious metals. This work places these IONPs at the forefront in terms of stability, reusability, and selectivity, which will undoubtedly open new avenues for environmental remediation and purification applications.

中文翻译：

---

稳定的 calix[4]芳烃-聚乙烯亚胺包被的氧化铁纳米颗粒，用于提高金和铂氯化物络合物的回收率


从废水和复杂生物介质中磁性去除和回收贵金属带来了重大挑战，这主要是由于需要高效、选择性和稳定的材料。这项工作报告了一种方法，该方法通过合成涂有 calix[4]芳烃-四羧酸盐 （X4C4） 共价层的氧化铁纳米颗粒 （IOMP） 来解决这些挑战，该共价层能够通过静电相互作用结合聚乙烯亚胺 （PEI） 官能团。与以前用作 PEI 连接层的柠檬酸盐涂层相比，X4C4-四重氮盐的还原接枝到 IONP 上会产生相当稳定的涂层，这被证明是 PEI 吸附的优秀基材。这有效地产生了协同作用，显著提高了 PEI 涂层的耐久性，并使颗粒保持分散状态。所得IONPs@X4C4@PEI颗粒的稳定性表现为它们能够承受酸性和碱性条件，而不会出现明显的颗粒聚集或磁性损失。此外，这些颗粒表现出优异的磁性可重用性，在多个分离循环中保持其选择性和回收效率。IONPs@X4C4@PEI 颗粒对金 （Au） 和铂 （Pt） 的选择性亲和力源于这些金属在溶液中形成的络合物与 PEI 涂层之间的特异性结合相互作用，从而能够高效回收这些贵金属。这项工作使这些 IONP 在稳定性、可重用性和选择性方面处于领先地位，这无疑将为环境修复和净化应用开辟新的途径。