www.afm-journal.de FULL PAPER © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 2668 www.MaterialsViews.com wileyonlinelibrary.com 1. Introduction Since the beginning of this millennium, the rare-earth elements (REEs) global consumption rate has increased significantly while supplies have drastically diminished, mainly as the result of restrictions on exportations from China. According to the latest market analyses, carried out by the USA and Chinese govern- ments, the exploitation of REEs over the past few years remains constant, although the demand for rare-earth compounds has been growing rapidly worldwide. [1] High purity REEs have found applications in numerous advanced technologies, such as for the production of magnets, chemical sensors or lasers. [2,3] In domestic electronics, REEs are used in computers, plasma and LCD screens, cell phones or cameras. Among roughly 250 REE minerals that can be found, only 10–20 are considered as useful, while only 5 are practically applicable. [4] Therefore, the main objective of the present work is the development of effi- cient solid sorbents for the extraction and valorization of REEs, especially from alternative sources, e.g., industrial or mining wastes. Mining residues contain a number of elements, including some radioactive elements, transition metal oxides, as well as REEs, which often are present at eco- nomically interesting concentrations. [5] However, selective lanthanide separation and pre-concentration is one of the most difficult tasks, as these elements have only subtle differences in their proper- ties. [6] Industrially, extraction and purifica- tion of REEs require multiple sequential extraction steps, which are mostly based on liquid-liquid or liquid-solid extrac- tion procedures. Liquid–liquid extraction (LLE) strategies are commonly used for industrial separation and purification in hydrometallurgy as they provide acceptable enrichment needed for many extrac- tion applications. However, separation and purification of REEs by such technique requires the treatment of a large volume of solvents over continuous, repeated steps, which lead to signifi- cant amounts of undesired and radioactive wastes. In compar- ison, liquid-solid extraction is a simpler and greener alternative. Chromatographic-based resins (ion-exchange, IEC, or extraction resins, EXC) have been used with respect to REEs separation and purification. As early as 1947, Spedding [7] has demonstrated that ammonium citrate / citric acid could selectively elute REEs loaded onto a Amberlite IR-100 (strong cationic ion-exchanger). Similarly to extraction performed by LLE, shifting stability of coordinated REEs, owing to change in ionic radius resulting from the lanthanide contraction, enables elemental separation. Other studies using anion-exchange resins where REEs are com- plexed with negatively charged ligands have also been reported. [8] More recently, liquid-liquid extraction on a solid support (also referred as EXC) has been applied to the separation and purifica- tion of REEs. [9] In most EXC resins, a selective ligand is dissolved in an hydrophobic organic phase which is impregnated on a solid support. Among the selective ligands reported, diglycolyla- mide (DGA) derivatives have demonstrated interesting extractive properties for REEs. Recently, researchers attempted to replace the organic phase, in which the extractant was dissolved, by an ionic liquid which was entrapped into a silica sol–gel composite for the extraction of La(III). Unfortunately, the impregnation strategies employed resulted in EXC materials that demon- strated pronounced leaching of the stationary liquid phase which translated into cross-contamination and lack of reusability, [10–13] thus hampering their applicability. To overcome such issues, it has been proposed to chemically anchor the extracting agent to the solid support. To do so, Zhang suggested first a polymeric Nanostructured Hybrid Materials for the Selective Recovery and Enrichment of Rare Earth Elements Justyna Florek, François Chalifour, François Bilodeau, Dominic Larivière,* and Freddy Kleitz* The importance of rare-earth elements (REEs) in the global economy is booming as they are used in numerous advanced technologies. Industri- ally, the extraction and purification of REEs involve multiple liquid–liquid extraction (LLE) steps as they exhibit very similar complexation properties with most common ligands. In order to substantially improve this process and provide a greener alternative to LLE, functional porous hybrid materials, demonstrating enhanced selectivity towards heavier REEs compared to commercially-available products, are proposed. In addition, because of the grafting procedure used in the synthesis, the proposed materials demonstrate a higher degree of reusability, increasing their marketable potential. DOI: 10.1002/adfm.201303602 Dr. J. Florek, F. Chalifour, Prof. D. Larivière, Prof. F. Kleitz Department of Chemistry Centre de Recherche sur les Matériaux Avancés (CERMA) and Centre en Catalyse et Chimie Verte (C3V) Université Laval Quebec, G1V 0A6, QC, Canada E-mail: dominic.lariviere@chm.ulaval.ca; freddy.kleitz@chm.ulaval.ca F. Bilodeau Hydro-Quebec Production Gentilly-2 Nuclear Power Plant Gentilly, G9H 3X3, QC, Canada Adv. Funct. Mater. 2014, 24, 2668–2676