Interfacially\nCross-Linked Polydopamine/Polybenzimidazole\nComposite Membranes for Organic Solvent Nanofiltration

Interfacial cross-linking was used\nto prepare composite organic\nsolvent nanofiltration (OSN) membranes comprising a polydopamine (PDA)\nactive layer formed on a polybenzimidazole (PBI) substrate. Dibromo-<i>p</i>-xylene (DBX) was employed as a cross-linking agent to\nmake the composite membranes chemically stable against harsh polar\naprotic solvents. The interfacial cross-linking of PDA/PBI allowed\nfor finely tuning the molecular weight cutoff (MWCO) of the membrane,\nresulting in a membrane with precise molecular separation capabilities\nfor OSN. The morphology and surface properties of the membranes were\ncharacterized, and a membrane with a MWCO of 286 Da was investigated\nfor OSN of a series of solvents. The membrane permeance was in the\norder of acetonitrile (MeCN) > methanol (MeOH) > acetone >\ntoluene\n> dimethylformamide (DMF) > heptane > ethanol (EtOH) >\nisopropanol\n(IPA) > tetrahydrofuran (THF). The membranes displayed a sharp\npore\nsize distribution, yielding a rejection rate of over 99% for Rose\nBengal (RB, MW 1020 g/mol) and Remazol brilliant blue (RBB, MW 626.5\ng/mol) from DMF and EtOH solutions. When it came to methyl orange\n(MO, MW 327.3 g/mol) that had a molecular weight closer to the MWCO\nof the membrane, the membrane still displayed a high rejection rate\nof 95% and 99% in nanofiltrating solvents DMF and EtOH, respectively.\nIn addition, it was demonstrated that the membrane was able to effectively\nfractionate mixed solutes having molecular weights appropriate for\nthe MWCO rating of the membrane during OSN.