Effect of carboxylic acid crosslinking of cellulose membranes on nanofiltration performance in ethanol and dimethylsulfoxide

Cellulose membranes were fabricated via phase inversion using 1-ethyl-3-methylimidazolium acetate as solvent and acetone as volatile cosolvent. 1,2,3,4-butanetetracarboxylic acid was used to partially crosslink the hydroxyl groups of cellulose, thereby changing mechanical properties of the membranes and the interactions with solvents, ethanol and dimethyl sulfoxide, and solutes. Rejection of dyes of similar size, Bromothymol Blue, Rose Bengal and Crystal Violet were shown to correlate inversely with sorption in the membranes, with the higher the sorption coefficient, the lower the rejection observed. This shows that the solute-membrane affinity is the determining factor in solute rejection in cellulose membranes. Upon crosslinking, the rejection of positively charged Crystal Violet decreased, that of negatively charged Rose Bengal increased and 93% rejection of Rose Bengal in DMSO was obtained with the crosslinked membrane. This change upon crosslinking was attributed to altered electrostatic interactions between the dyes and the membrane surface, as free carboxylic acid groups of the crosslinker leaves the membrane with a net the negative charge. Overall, it was shown that cellulose membranes can perform stably in a harsh aprotic solvent and that the rejection, which is determined by membrane-solute affinity can be tuned with carboxylic acid crosslinking.