Covalent Immobilization of Crown Ether on Cellulose Acetate Membranes for Enhanced Heavy Metal Ion Retention

Heavy metal contamination in water remains a major environmental concern due to the persistence, toxicity, and bioaccumulation potential of metal ions such as Ni²⁺ and Cu²⁺. Therefore, the development of sustainable membrane materials with improved permeability and metal ion retention capacity is of significant interest for advanced water purification applications. In this research, crown ether-functionalized cellulose acetate membranes were developed by employing cyanuric chloride as a linker in order to enable advanced heavy metal ion retention capacity. In order to achieve this, the modification process involved a multi-step approach comprising successive hydroxylation, silanization, triazine activation, and crown ether grafting. The successful functionalization was confirmed by FTIR (Fourier Transform Infrared Spectroscopy) and XPS (X-ray Photoelectron Spectroscopy) analyses, while thermal characterization demonstrated improved stability over a wide range of temperatures without compromising the integrity of the cellulose acetate backbone. The crown-ether-functionalized membranes exhibited enhanced performance in terms of heavy metal ion separation, demonstrating significantly higher retention of Ni²⁺ (30%) and Cu²⁺ (27%) as compared to pristine CA membranes (<10%) over repeated filtration cycles. These results demonstrate that crown ether functionalization is a versatile approach for tuning the interfacial features of cellulose acetate membranes in order to achieve increased permeability and selectivity toward heavy metal removal, highlighting their potential for advanced water purification applications.