Cross-linked cellulose acetate membrane with mixed-charge feature: A new approach to antifouling ultrafiltration membrane for drinking water

Ultrafiltration (UF) membranes made from cellulose acetate (CA) have garnered significant interest in drinking water purification due to their sustainability and biodegradability. However, their widespread application is hindered by weak mechanical properties and insufficient resistance to fouling. This study addresses these challenges by introducing an anionic isocyanate cross-linker (MDI-DMPA) with carboxyl groups to cross-link CA with cationic quaternized cellulose nanocrystals (QCNC), resulting in a mixed-charge cross-linked cellulose acetate-based membrane (CMQ) with zwitterionic characteristics. The high Young's modulus of QCNC, combined with the effective cross-linking capabilities of MDI-DMPA, enhances the tensile strength of the CMQ membrane to 5.9 MPa, approximately 2.2 times that of the pure CA membrane. Additionally, the CMQ membrane with the hydrophilic zwitterionic interface exhibits superior water permeance of 268 L m⁻ 2  h⁻ 1  bar⁻ 1 and a low irreversible resistance, outperforming the commercial RC 030 cellulose membrane. Notably, a large-scale CMQ membrane (0.4 × 0.6 m) effectively treats complex surface water, achieving a filtration rate of 1405 L·day⁻ 1 and producing water that complies with the drinking water standards set by the World Health Organization (WHO). These findings underscore the potential of CMQ membrane for engineering applications in drinking water purification.