Preparation of high-permeance tannic acid/copper ion-calcium alginate gel membranes for organic solvent nanofiltration

A gel organic solvent nanofiltration (OSN) membrane with high permeance was prepared using calcium alginate (CaAlg) as the substrate membrane and tannic acid/copper ion (TA/Cu 2+ ) complexes as the selective layer. The gel OSN membrane was characterized with respect to the chemical properties, microstructure and tensile properties. The preparation conditions and separation factors affecting dye/ethanol separation were investigated. In addition, the long-term solvent resistance was evaluated. The results demonstrate that the TA/Cu 2+ selective layer causes the pore size of the gel membrane to decrease significantly from 2.85 nm of the substrate membrane to 0.79 nm. Consequently, the rejection of anionic dyes (congo red, reactive red 2, and acid chrome blue K) exceeds 95.0 %, and the ethanol permeance is greater than 19 L·m −2 ·h −1 ·bar −1 . Furthermore, the separation performance of the gel OSN membrane is hardly affected by the dye concentration (25–100 mg/L) and transmembrane pressure (1–5 bar). Even following a 60-day immersion in the aprotic polar solvent N, N-dimethylformamide (DMF), the gel OSN membrane can still ensure a 96.0 % rejection for congo red, demonstrating its stable separation performance in organic solvents.