A novel monoamine modification strategy toward high-performance organic solvent nanofiltration (OSN) membrane for sustainable molecular separations

The main drawback of polyimide (PI) based OSN membrane capable to separate molecules is the declined solvent permeance after crosslinking. In this study, the hydrophilic monoamine named as Tris(hydroxymethyl) aminomethane (Tris) was first utilized to modify polyimide OSN membranes by adding Tris into the dope solution before phase inversion and diamino crosslinking for improving membrane-solvent mutual affinity so as to obtain high-performance OSN membranes. Such Tris modified membranes were proved by chemical characterizations, and the further contact angles and surface energy measurements revealed that the hydrophilicity and surface energy of the novel membranes increased with the Tris loading. Interestingly, the morphological observation demonstrated that the macrovoids shown in the pristine membranes can be completely displaced by sponge-like pores in Tris modified membranes. Surprisingly, the isopropanol (IPA) permeance of 10% Tris modified crosslinked membranes increased to 270% of the original value with only slight decline in dyes rejections. Besides, the fundamental study on the relationship between IPA or N,N-dimethylformamide (DMF) permeance and the membrane-solvent solubility parameter distance were performed. Our novel monoamine modification strategy can provide a new incentive to develop advanced membranes applicable to aqueous solution separation, gas separation and pervaporation for future sustainable usages.