The ever-increasing demand for Rare Earth Elements (REEs) due to their increased use in various high-tech and futuristic applications has stimulated the development of new sustainable approaches for efficient REE separation and recovery. Herein, we report on the development of polyethylenimine (PEI) cross-linked cellulose nanocrystal (CNC) materials for use as high performance sustainable adsorbents for REEs. This cross-linking reaction occurs in aqueous solution and traditional toxic cross-linkers are not involved. Importantly, PEI acts not only as an emerging cross-linker but also as coordination sites for REE binding. The adsorbents were qualitatively and quantitatively characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis, zeta-potential, thermogravimetric analysis (TGA), and conductometric–potentiometric titration. In a single-component system, the adsorption behavior showed heterogeneous adsorption capacities of 0.611, 0.670, and 0.719 mmol g⁻¹ for La(III), Eu(III), and Er(III), respectively. The similarity of chemical properties makes REEs difficult to separate from each other, but the materials displayed preferential adsorption for Er(III) compared to La(III) and Eu(III) in a ternary REE solution. The FT-IR, XPS and EDS mapping results revealed the importance of the primary and secondary amino functional groups as the principal REE binding sites. Overall, this study demonstrates a facile route for separation, recovery, and enrichment of REEs from aqueous solution.

中文翻译：

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聚乙烯亚胺交联纤维素纳米晶体从水中高效回收稀土元素的机理研究

由于稀土元素（REE）在各种高科技和未来应用中的越来越多的使用，对稀土元素的需求与日俱增，从而刺激了开发新的可持续方法以进行有效的REE分离和回收的需求。在这里，我们报告了聚乙烯亚胺（PEI）交联的纤维素纳米晶体（CNC）材料的开发，这些材料可用作REE的高性能可持续吸附剂。该交联反应在水溶液中发生，并且不涉及传统的有毒交联剂。重要的是，PEI不仅充当新兴的交联剂，而且充当REE结合的协调位点。吸附剂通过透射电子显微镜（TEM），傅立叶变换红外（FT-IR）光谱，X射线光电子能谱（XPS），元素分析，定性和定量表征，ζ电位，热重分析（TGA）和电导-电位滴定法。在单组分系统中，吸附行为显示出0.611、0.670和0.719 mmol g的非均相吸附容量^分别对于La（ III），Eu（ III）和Er（ III）为^-1。化学性质的相似性使得REE难以彼此分离，但是与三元REE溶液中的La（ III）和Eu（ III）相比，该材料表现出对Er（ III）的优先吸附。FT-IR，XPS和EDS作图结果揭示了伯氨基和仲氨基官能团作为主要的REE结合位点的重要性。总体而言，这项研究表明从水溶液中分离，回收和富集REE的简便途径。