Effect of monovalent and divalent ions in non-solvent coagulation bath-induced phase inversion on the characterization of a porous polysulfone membrane

Abstract

Variations in the conditions of a non-solvent coagulation bath-induced phase inversion have a wide potential for the modification of porous membranes besides preventing leaching of additives in the membranes in an actual operation. In this study, a porous asymmetric polysulfone (PSf) membrane was prepared by the phase inversion method in different non-solvent coagulation baths containing monovalent (sodium chloride, potassium chloride) and divalent salts (sodium sulphate) at different concentrations (1, 3 and 5%). The PSf membranes were prepared using N-methyl-2-pyrrolidone as a solvent and polyethylene glycol (PEG 400 MW) as an additive. The viscosity of the non-solvent coagulation bath and the gelation time were the main factors that affected the morphology of the PSf membranes in particular. The optimum characteristics were displayed in the porous PSf membrane that was immersed in 1% sodium sulphate. A low viscosity (1.00 CP) and gelation time (72.33 s) produced a dense top and more continuous finger-like pore structures extending from the top to the bottom layers of the membranes with good physical characteristics. The penetrating effect of the divalent ions (Na2+) in sodium sulphate speeded up the diffusional exchange rate between the NMP solvent and the Na2SO4 non-solvent coagulation bath during the phase inversion process. This membrane achieved a high permeation of water flux (208.75 L m−2 h−1) and the highest rejection of humic acid (99.54%). This proved that the presence of divalent ions (Na2+) in the non-solvent coagulation bath of inorganic salts improved the properties and performance of the membrane.