Reinforcing the polybenzimidazole membrane surface by an ultrathin co-crosslinked polydopamine layer for organic solvent nanofiltration applications

Here, highly robust and tight PBI-based OSN membranes were developed by reinforcing the active layer with an ultrathin polydopamine (pDA) coating followed by the simultaneous co-crosslinking of the pDA-coated PBI membrane. Although the pDA layer thickness was just under 5 nm, the pDA layer can effectively improve the rejection properties of the pristine PBI membrane by reducing the overall pore size and filling the defects at the membrane surface. The chemical and physical changes clearly showed the effect of the ultrathin pDA layer and co-crosslinking on the membrane properties and separation performance. The modified PBI membranes showed the improved rejection property and excellent stability in various organic solvents, even in polar aprotic solvents. The co-crosslinked pDA-coated PBI membranes showed a very high rejection properties to low molecular weight solutes (97.6% for 236 Da styrene dimer and 99.9% for 308 Da PPG) with stable solvent permeance. Moreover, significantly improved solvent permeances were observed without a notable decrease in the rejection performance after the prefiltration of polar aprotic solvents. The results showed the effective separation performance enhancement of OSN membranes by ultrathin pDA coating and the potential applications of solvent purification, reuse and valuable chemical recovery in various fine chemical industries.