EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Rare earth elements (REEs) and their compounds are essential for quickly growing advanced technologies. These materials are essential in the area of green/sustainable energy. However, efficient separation and purification of REEs still remain challenging. Additionally, current extraction technologies frequently generate large amounts of wastes. In that perspective, the development of efficient and reusable sorbents is urgently needed. Among several ligands used in the liquid–liquid separation process, the diglycolamide-based (DGA) ligands play a prominent role. Although these ligands show good extraction behaviour in the liquid phase, their extractive behaviour is not broadly studied when these ligands are attached to a solid support. A detailed understanding of the relationship between chemical structure and extraction selectivity at the molecular level is still absent, although it is a main factor for the development of advanced sorbents. To answer this question, we synthetized and tested a series of functionalized mesoporous silica (KIT-6) materials as sorbents for the selective extraction of REEs (Scheme). We performed different spectroscopic studies (solid-state NMR, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy) to better understand the extraction performance of our materials. The obtained results provide valuable insights into the chemical environment and reactivity of the ligand tethered to the silica (KIT-6) support. From our results it can be suggested that depending on the extracted element, structure of the ligand and its attachment to KIT-6, different functional groups (i.e., C═O, N–H, or silanols) act as the main adsorption centres, which in turn can be linked with the different selectivity of the synthesized sorbents. Therefore, different extraction mechanisms or different complexation preferences may occur on the surface. By determining how metals interact with various functionalized silicas, we aim to better understand the solid-phase extraction process of hybrid (organo)silica sorbents and design better extraction materials.