Modification of polysulfone ultrafiltration membrane by sequential deposition of cross-linked poly(vinyl alcohol) (PVA) and sodium carboxymethyl cellulose (CMCNa) for nanofiltration

Abstract

This study focused on the modification of flat-sheet polysulfone ultrafiltration membranes for nanofiltration (NF) through sequential deposition of poly(vinyl alcohol) (PVA) and sodium carboxymethyl cellulose (CMCNa) with glutaraldehyde cross-linking after each deposition. The contents of PVA and CMCNa in the coating solutions were varied to optimize the membrane performance and the modified membranes were characterized in terms of surface and permeation properties. It was found that the membrane surface became denser, more hydrophilic, and negatively charged at neutral pH after modification and the modified membrane possessed the NF separation characteristic. Under 5.0 bar, the optimized modified membrane exhibited a high-pure water flux of 89.5 l/m² h and rejections of 37.8 and 93.8% to 500 mg/l NaCl and Na₂SO₄ aqueous solution, respectively. The modified membrane could also efficiently remove anionic dyes from aqueous solution, showing retentions of 99.7 and 99.5% to methyl blue and congo red, respectively, under neutral pH and 5.0 bar. Additionally, the modified membrane possessed good chlorine stability, and acid and alkaline resistances. The technique developed is potentially applicable for the fabrication of high-flux negatively charged NF membranes for partial desalination and anionic dye removal.

Keywords:

• Nanofiltration
• Thin-film composite membrane
• Membrane modification
• Poly(vinyl alcohol) (PVA)
• Sodium carboxymethyl cellulose (CMCNa)
• Dye removal

Acknowledgments

The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China (Grant no. 21476213), the National High-tech R&D Program of China (Grant no. 2012AA03A601), and the 521 personnel training plan of Zhejiang Sci-Tech University.