Understanding Selectivity of Mesoporous Silica-Grafted Diglycolamide-Type Ligands in the Solid-Phase Extraction of Rare Earths

Abstract

Rare earth elements (REEs) and their compounds are essential for rapidly developing modern technologies. These materials are especially critical in the area of green/sustainable energy; however, only very high-purity fractions are appropriate for these applications. Yet, achieving efficient REE separation and purification in an economically and environmentally effective way remains a challenge. Moreover, current extraction technologies often generate large amounts of undesirable wastes. In that perspective, the development of selective, reusable, and extremely efficient sorbents is needed. Among numerous ligands used in the liquid–liquid extraction (LLE) process, the diglycolamide-based (DGA) ligands play a leading role. Although these ligands display notable extraction performance in the liquid phase, their extractive chemistry is not widely studied when such ligands are tethered to a solid support. A detailed understanding of the relationship between chemical structure and function (i.e., extraction selectivity) at the molecular level is still missing although it is a key factor for the development of advanced sorbents with tailored selectivity. Herein, a series of functionalized mesoporous silica (KIT-6) solid phases were investigated as sorbents for the selective extraction of REEs. To better understand the extraction behavior of these sorbents, different spectroscopic techniques (solid-state NMR, X-ray photoelectron spectroscopy, XPS, and Fourier transform infrared spectroscopy, FT-IR) were implemented. The obtained spectroscopic results provide useful insights into the chemical environment and reactivity of the chelating ligand anchored on the KIT-6 support. Furthermore, it can be suggested that depending on the extracted metal and/or 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 centers and preferentially capture targeted elements, which in turn may be associated with the different selectivity of the synthesized sorbents. Thus, by determining how metals interact with different supports, we aim to better understand the solid-phase extraction process of hybrid (organo)silica sorbents and design better extraction materials.

Synthesis and Enhanced Capture Properties of a New BioMOF@SWCNT‐BP: Recovery of the Endangered Rare‐Earth Elements from Aqueous Systems

“…In that perspective, the development of extremely efficient, reusable, and selective sorbents is needed. [ 46 ]…”

Porous organic–inorganic hybrid materials for catalysis, energy and environmental applications

“…In the same year, Florek and co-workers fabricated several tailor-made 3D-porous, functionalized KIT-6 materials with different chelating ligands such as diglycol-2,4-diamido-propyltriethoxysilane (DGA-N), 3,6dioxaoctanediamido-propyltriethoxysilane (DOODA-N), and furan-2,4-diamido-propyltriethoxysilane (FDGA-N) for the solid-phase extraction of rare earth metals. 42 The metal adsorption selectivity was reflected by the metal and specific surface functional group (N-donor, O-donor, and silanol groups) interactions, highlighting the importance of precise design and grafting of the chelating ligand on the inorganic silica matrix. Recently, in 2021, Marjani et al synthesized multi-organofunctionalized fibrous silica (MF-KCC-1) containing amine (-NH 2 ), thiol (-SH), and tetrasulfide (-S-S-S-S-) groups via the post-modified technique, which was proven to be a potential adsorbent for the removal of acid fuchsin (AF) and acid orange II (AO) synthetic dyes from water.…”

A perspective on developing solid-phase extraction technologies for industrial-scale critical materials recovery

“…There is tremendous variability amongst SPE systems, and each different extractant has advantages and disadvantages for metal recovery and purification purposes. Modern experimental sorbents range from prawn carapace 19 to bacteria, 20,21 clay minerals, 22,23 mesoporous silica, 12,24 carbon nanotubes, 25,26 and many others. The ideal adsorbent would exhibit both a high capacity and a high selectivity for the desired metal or metals and would be inexpensive, readily available/scalable, mechanically and chemically stable, and environmentally-friendly.…”

“…, triblock copolymers and cationic surfactants). 12,24,32,34,45–47 After the template is removed, the powders that remain exhibit an ordered array of well-calibrated mesopores (2–50 nm in diameter), providing exceptionally high surface area and high pore volume for adsorption (Fig. 3).…”