Anti-fouling and thermosensitive ion-imprinted nanocomposite membranes based on grapheme oxide and silicon dioxide for selectively separating europium ions

The increasing amount of europium in aqueous environment from rare earth industry has become a serious environmental challenge. Significant efforts have been focused on ion-imprinting membranes (IIMs) for selective separation of ions from analogues. Based on ion-imprinting technique, we have developed Eu³⁺-imprinted nanocomposite membranes (Eu-IIMs) for selectively separating Eu³⁺ from La³⁺, Gd³⁺ and Sm³⁺. Polydopamine (pDA) was previously synthesized on basal membranes to augment the interfacial adhesion. Grapheme oxide (GO) and modified silicon dioxide (kSiO₂) were synergistically stacked on pDA-modified substrates to form hydrophilic nanocomposite membranes. Ag nanoparticles were modified on the surface to enhance anti-fouling performance. The temperature-controlled selective recognition sites were formed using N-isopropylacrylamide (NIPAm) and acrylamide (Am) as functional monomers as well as europium ions as templates by RAFT (reversible addition-fragmentation chain transfer) method. Large enhanced Eu³⁺-rebinding capacity (101.14 mg g⁻¹), adsorptive selectivity (1.82, 1.57, 1.45 for Eu³⁺/La³⁺, Eu³⁺/Gd³⁺, Eu³⁺/Sm³⁺) and permselectivity (3.82, 3.47, 3.34 for La³⁺/Eu³⁺, Gd³⁺/Eu³⁺, Sm³⁺/Eu³⁺) were achieved on Eu-IIMs with superior regeneration performance. Additionally, the negligible damage of the membranes after buried for 20 d indicated the superior anti-fouling property of the Eu-IIMs. The ion-imprinted nanocomposite membranes synthesized in this work have shown great potentials for selective separation of rare earth ions.