Understanding the Adsorption of Rare-Earth Elements in Oligo-Grafted Mesoporous Carbon

Abstract

Rare-earth elements (REEs) are 17 elements of the periodic table primarily consisting of lanthanides. In modern society, the usage of REEs is ubiquitous in almost all modern gadgets and therefore efficient recovery and separation of REEs are of high importance. Selective adsorption and chelation of REEs in solid sorbents is a unique and sustainable process for their recovery. In this work, single-stranded oligos with 100 units of thymine were grafted onto carboxylated mesoporous carbon to synthesize a sorbent with phosphorus and oxygen functionalities. The sorbent was characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy-energy-dispersive X-ray spectroscopy. Three different REEs with varying atomic radii and densities, Lu, Dy, and La, were adsorbed onto the carbon from aqueous solutions. It was observed that the adsorbed amounts increased with the increase in the atomic radius or decrease in the atomic density. Calculation of the distribution coefficients for all the equilibrium adsorption amounts suggested that adsorption is more effective in the lower concentration region. The L3-edge X-ray absorption near-edge structure confirmed a 3+ oxidation state of REEs in the adsorbed phase. Extended X-ray absorption fine structure (EXAFS) confirmed the binding of REEs with oxygen functionalities in the adsorbed phase. The radial distribution functions calculated from the EXAFS data suggest a longer RE–O distance for La compared to those for Lu and Dy. The coordination numbers and Debye–Waller factors have typical values of about 8–9 atoms and 0.01–0.02 Å2, respectively.

Direct Ink 3D Printing of Porous Carbon Monoliths for Gas Separations

“…It needs to be noted that the polymer mixture of poly(4-vinylphenol) and Pluronic F127 is the precursor of so-called soft-templated mesoporous carbon, where poly(4-vinylphenol) acts as the carbon precursor and Pluronic F127 acts as porogen or soft-template. In soft-templating strategy, cross-linked phenolic polymer, mostly from phenol, resorcinol, and phloroglucinol serves as the precursor whereas the surfactant (F127) acts as porogen [ 34 , 35 ]. The width and shape of the mesopore depend on the surfactant molecule leading to the formation of micelles that are hydrogen bonded with phenolic polymer, pH of the synthesis medium, and other processing conditions of the polymer mixture before carbonization.…”

On membrane-based approaches for rare earths separation and extraction – Recent developments

“…Owing to chemical inertness and the ability for modification, active and activated carbons are the most popular adsorbents widely applied in the industry [265], thus the attention will focus in this chapter on this adsorbent. Recently Gismondi et al [266] endeavored to address some similarities in the REEs adsorption. Oligo-grafted mesoporous carbons were applied as adsorbents, and Lu 3+ , Dy 3+ , La 3+ adsorption was studied.…”

“…Schematic representation of carboncontaining porous adsorbent, with pores enabling/disabling REEs diffusion (C), schematic representation of carboxylic surface group with possible adsorption -increasing interactions (D) and the DFT -calculated configurations of graphene oxide functional groups -La 3+ (E 1) and Nd 2+ (E 2). Reprinted with permission from[266] Copyright © 2022 Elsevier.…”

Analysis of the Adsorption-Release Isotherms of Pentaethylenehexamine-Modified Sorbents for Rare Earth Elements (Y, Nd, La)

“…Moreover, the possibility to employ suitable materials from natural sources makes solid/liquid adsorption a green answer to the problem of REEs recovery. Clay-based materials [ 13 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ] and carbon-based materials [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ], either in a pristine form or appropriately modified, are typical exponents of the category of natural sorbents, and have been broadly discussed in literature.…”