Design of an MXene-based ion-imprinted membrane for lithium ion recognition

Abstract

Recovery of lithium from battery-related waste streams has attracted increasing attention, yet selective separation of Li⁺ from coexisting ions remains challenging. In particular, the similar physicochemical characteristics of Li⁺ and Mg²⁺ complicate their discrimination in aqueous systems. In this work, an MXene-based ion-imprinted membrane (MXIM) was prepared as a porous membrane with bulk modification and surface functionalization for lithium ion recognition and selective separation. Compared with the pristine PVDF membrane, MXIM exhibited improved hydrophilicity, higher Li⁺ adsorption capacity, and a measurable preferential response toward Li⁺ in a binary Li⁺/Mg²⁺ system. The adsorption behavior of Li⁺ on MXIM was well described by the Langmuir model, with a maximum adsorption capacity of 35.45 mg g⁻¹ under the investigated conditions. In addition to the binary system, competitive adsorption experiments in ternary systems containing Li⁺/Mg²⁺/Ca²⁺ and Li⁺/Mg²⁺/Al³⁺, together with a competitive permeation experiment in the Li⁺/Mg²⁺/Al³⁺ system, were further carried out. The results showed that MXIM maintained a preferential adsorption and transport response toward Li⁺ even under more complex ionic conditions, although the overall selectivity remained moderate. Therefore, rather than demonstrating immediate practical deployment, the present study provides a proof-of-concept basis for further optimization of MXene-containing ion-imprinted membranes for lithium-selective separation under competitive conditions.