Preparation, characterization and performance of ZnCl2 incorporated polysulfone (PSF)/polyethylene glycol (PEG) blend low pressure nanofiltration membranes

• Polysulfone based NF membranes were cast using PEG 200 and ZnCl2 as additives.
• Molecular weight cut off of NF membrane was less than 180.
• Membranes were having negative zeta potential.
• About 40% NaCl rejection was obtained at pH 2 and 11 at 690 kPa.
• Rejections of chrysoidine R, crystal violet and congo red were above 95%.

Simultaneous use of organic (PEG 200), and inorganic (ZnCl2) additives to polysulfone for casting of nanofiltration (NF) membrane was reported in this work. Dimethylformamide (DMF) was used as the solvent. The membranes were characterized in terms of surface morphology, permeability, porosity, contact angle, molecular weight cut off and zeta potential. The resultant NF membranes were tested with monovalent and divalent electrolytes sucrose, glucose and three dyes in the range of molecular weight from 263 to 697. Both NF membranes showed rejection of salts, NaCl: 40–43% and Na2SO4: 52–54%, at 690 kPa and pH 11. The corresponding permeate flux were 20 to 22 l/m2·h. Among the dyes crystal violet and congo red are rejected more than 98% and chrysoidine more than 95% over the transmembrane pressure range of 276 to 690 kPa. Electrostatic interaction was found to play a determinant role in rejection of salts, whereas, size exclusion was the major mechanism for rejection of dyes.