Performance enhancement in organic solvent nanofiltration by double crosslinking technique using sulfonated polyphenylsulfone (sPPSU) and polybenzimidazole (PBI)

In this paper, we report a new technique to design highly stable and selective organic solvent nanofiltration (OSN) membranes with enhanced solvent permeance by manipulating the crosslinking reactions. The new technique consists of three steps: (1) membrane fabrication via non-solvent induced phase inversion by blending sulfonated polyphenylsulfone (sPPSU) and polybenzimidazole (PBI) polymers, followed by (2) crosslinking the PBI part using α,α′-dibromo-p-xylene (DBX) to make the membrane chemically stable, and (3) ionically crosslinking the sPPSU part with hyperbranched polyethylenimine (HPEI) to narrow down the membrane pore size without affecting the permeance significantly. Crosslinking reactions have been confirmed by FTIR and XPS analyses. The OSN performance of the double crosslinked membranes was determined by measuring the permeance of various organic solvents and the rejection rates of tetracycline (Mw = 444 g mol⁻¹) as a model pharmaceutical. Depending on the testing solvents, the permeances ranged from 2 to 11.8 L m⁻² h⁻¹ bar⁻¹, while the rejection rates of tetracycline varied from 67% to 97%. Considering the outstanding OSN performance and the great chemical stability in a wide range of solvent polarities, this novel double crosslinking technique represents a step forward in the fabrication of high performance OSN membranes.