Functionalized 2D Multilayered MXene for Selective and Continuous Recovery of Rare Earth Elements from Real Wastewater Matrix

Abstract

Rare earth elements (REEs) are the “fuel” for high-tech industry, yet their selective recovery from complex waste matrices is challenging. Herein, we designed a 2D multilayered MXene Ti₃C₂T_x adsorbent for selective extraction of REEs in a broad pH range. By establishing strong Lewis acid-base interactions, extraction capacities of Ti₃C₂T_x to Eu(III) and Ho(III) reached 892.8 and 649.2 mg/g, respectively, even at pH 2.0. Following the Valence Matching Principle, the Ti₃C₂T_x adsorbent also demonstrated high selectivity for recovery of various REEs from real REEs processing wastewater and actual sludge from magnet manufacturing industry. To demonstrate the practical feasibility, a layer-stacked membrane of Ti₃C₂T_x supported on polyethersulfone substrate was fabricated for continuous recovery of REEs and exhibited excellent removal of Eu(III) (99.1% at pH 5.0), showcasing its potential for large-scale applications. DFT calculations and material characterization demonstrated that chemisorption between Lewis acid (REEs cations) and Lewis base (F and O) sites is the main adsorption process involved in the uptake of Eu(III) and Ho(III). Finally, both the Ti₃C₂T_x adsorbent and membrane were successfully regenerated and reused via simple acid wash. Overall, the results demonstrate the Ti₃C₂T_x-based recovery as a promising path for sustainable harvesting of REEs.