Preparation ofPolysulfone/Zeolitic Imidazolate Framework-8@PotassiumCopper Hexacyanoferrate Composite Membranes for Selective Extractionof Rubidium

The development of extraction methods for rare and valuable rubidium (Rb) from the aqueous phase remains a challenge today. In this work, based on the promising physicochemical properties of polysulfone (PSF), the strong binding ability of zeolitic imidazolate framework-8 (ZIF-8) to Cu²⁺, as well as the excellent adsorption ability of potassium copper hexacyanoferrate (KCuFC) toward Rb⁺, a novel PSF/ZIF-8@KCuFC composite membrane was developed. The prepared composite membrane was applicable for efficient separation of Rb⁺ from the aqueous solution. The theoretical maximum adsorption capacity of Rb⁺ could reach 204.45 mg/g at 45 °C. The composite membrane possessed remarkable desorption and regeneration properties, which were demonstrated by a 0.5 mol/L NH₄Cl/HCl solution and six adsorption/desorption cycles, respectively. Furthermore, the PSF/ZIF-8@KCuFC composite membrane could still uptake Rb⁺ with good effect from actual salt lake brine, and the recovery efficiency was maintained at about 38% during ten adsorption/desorption processes.