HKUST-1 bridged calcium alginate gel nanofiltration membrane for separating drugs from organic solvents

Organic solvent nanofiltration (OSN) membranes are suitable for separating drugs from solvents, especially heat-sensitive drugs. However, the trade-off effect between permeance and rejection limits the effective utilization of OSN membranes. In this study, a gel OSN membrane with high permeability-selectivity was prepared by bridging sodium alginate (SA) with HKUST-1 and then cross-linking with Ca²⁺ ions. The interspersed distribution of HKUST-1 among the flexible polymer chains results in three-dimensional pores of the gel membrane, which enriches the solvent transport channels. Meanwhile, SA is cross-linked by Cu²⁺ from HKUST-1 and Ca²⁺, which densifies the pore structure and enhances the solute rejection of the gel membrane. When the concentrations of HKUST-1, SA, and Ca²⁺ are 2.5 wt%, the gel membrane (HKUST-1_2.5%-CaSA) has strong hydrophilicity (11.1°), a small pore size (0.59 nm), and a relatively high porosity (56.89 %). The ethanol permeance of the HKUST-1_2.5%-CaSA gel membrane reaches 43.8 L·m⁻²·h⁻¹·bar⁻¹, with a tracycline (TC) rejection as high as 97 %. Moreover, the HKUST-1_2.5%-CaSA gel membrane is capable of achieving high rejection of TC in other organic solvents (acetone, ethyl acetate, and isopropanol). Even after being immersed in non-polar (n-hexane) and polar solvents (N,N-dimethylformamide, isopropanol, ethanol) for a period of 20 days, the separation performance of the gel OSN membrane remains consistent, confirming the excellent solvent resistance and potential in drug separation and solvent recovery.