Mixed matrix membranes for rubidium-dependent recognition and separation: A synergistic recombination design based on electrostatic interactions

Exposure and distribution of recognition sites are critical for membrane separation materials to enhance adsorption and separation efficiency toward rubidium ion. Herein, we prepared the rubidium (Rb) ion separation membranes (Rb-ISMs) through a delayed phase inversion method taking advantage of the different polarities between ethanol and water. Fabrication process was conducted through immersion of a poly (vinylidene fluoride)/graphene oxide (PVDF/GO) casting solution into coagulating bath containing 18-crown-6 (18C6) grafted mesoporous silica, ethanol and water. After phase inversion process, the as-prepared adsorbent materials were immobilized on membrane surface by strong electrostatic interaction force. The method could effectively avoid the embedding and aggregation recognition sites, and the coagulating bath only required the ethanol and water that was relatively healthy and environmental. The Rb-ISMs prepared at optimal conditions showed enhanced rebinding capacity (49.344 mg g⁻¹) towards Rb^±, with a superior rebinding selectivity (11.8, 6.82, 9.08 for Rb^±/Ca²⁺, Rb^±/Cs^±, Rb^±/Mg²⁺, respectively). Importantly, Rb-ISMs showed remarkable perm-selectivity and regeneration performance, which further demonstrated its potentials in the rapid and effective separation field of Rb ions.