Tannic acid assisted interfacial polymerization based loose thin-film composite NF membrane for dye/salt separation

In this work, a novel tannic acid assisted interfacial polymerization (TAIP) method was developed for preparing loose nanofiltration membranes (LNMs). Piperazine (PIP) and tannic acid (TA), two kinds of common monomer for interfacial polymerization (IP), were employed to deposit on substrate for the TAIP process. The TAIP process resulted in enlarged pores in the skin layer due to the longer monomers, thus achieved considerable permselectivity in separating salts from dye/salt mixture solution. The optimal TAIP membrane (M4) exhibited high permeability (32.57 LMH·bar−1 to Congo Red solution), reasonable rejection to dyes (99.40% and 99.19% for Congo Red and Rose Bengal, respectively) and satisfactory transport to salts (90.59% to Na2SO4 and 97.75% to NaCl). Meanwhile, this membrane retained high performance in dye/salt separation (7.16 LMH·bar−1 of permeability, 97.47% of CR rejection and 2.55% of NaCl retention) under even as high as 6 wt% of salt concentration. Moreover, TAIP LNM showed high stability throughout a 30-hour-long running test to separate salts from dye/salt mixture solution. We anticipated the TAIP methodology, together with the consequential LNM, to provide a potential candidate for dye/salt separation application.