Employing sulfolane as a green solvent in the fabrication of nanofiltration membranes with excellent dye/salt separation performances for textile wastewater treatment

This study explores the potential use of sulfolane, a green and sustainable solvent, as an alternative to toxic solvents in the fabrication of high-performance nanofiltration membranes. A comparison of Hansen solubility parameter (HSP) with N-methyl-2-pyrrolidone (NMP) indicates that sulfolane is a “poor” solvent for the sulfonated polyphenylenesulfone (sPPSU) polymer, which results in a lower critical polymer concentration (CPC) required to produce a macrovoid-free membrane structure. Moreover, the addition of a low molecular weight hyperbranched polyethyleneimine (HPEI) of MW = 800 g/mol as a crosslinker enhances the mechanical rigidity of the membranes without affecting the pore structure required for retaining salts from dye/salt mixtures, enabling practical applications in wastewater treatment. Notably, the membranes demonstrate exceptional dye/salt separation performance with a separation factor SDye/Salt of up to 69.32, even for low molecular weight dyes as low as 268 g/mol (i.e., a Disperse blue 1 and Na2SO4 mixture). To the best of our knowledge, this is the lowest MW dye ever tested for dye/salt separation. The membranes also show good antifouling capability over an extended period of use. Literature comparison shows that the sPPSU/sulfolane membrane crosslinked with HPEI800 for 60 min, referred to as sPSlf-c60, exhibits superior dye/salt separation performance, indicating their potential for the treatment of textile wastewater effluents.