Eco-Friendly OSN Membranes Based on Alginate Salts with Variable Nanofiltration Properties

In this work, membranes for organic solvents nanofiltration (OSN) based on a natural polymer, sodium alginate, were fabricated. They are chemically stable in organic solvents, including aprotic polar solvents. The unique advantage of these membranes is the absence of toxic reagents and solvents during their production. This ensures the safety and environmental friendliness of the production process. It has been shown that an operation as simple as changing the cation in alginate (Cu2+, Fe3+, Cr3+, Al3+, Zn2+, Ca2+) makes it possible to control the transport and separating properties of membranes, depending on the organic solvent being separated. Therefore, to isolate RemazolBrilliant Blue with MM = 626 g·mol−1 from ethanol, membranes based on iron alginate with a rejection R = 97% and a permeability of 1.5 kg·m−2·h−1·bar−1 are the most efficient. For isolation of the same solute from DMF and MP, membranes based on calcium alginate with an R of about 90% and a permeability of 0.1–0.2 kg·m−2·h−1·bar−1 are the most efficient. The resulting membranes based on natural biodegradable sodium alginate are competitive compared to membranes based on synthetic polymers.