UV-induced grafting of quaternary ammonium salts onto PVDF membranes: a dual-functional strategy for enhanced antibacterial and antifouling performance

Multifaceted bio-contamination, including natural organic matter (NOM) and microbial colonization, challenges the application of hydrophobic polyvinylidene fluoride (PVDF) membranes in water purification. To address organic and biofouling, a UV irradiation grafting strategy is developed to fabricate dual-functional PVDF membranes with integrated antibacterial and anti-fouling capabilities. Two quaternary ammonium salts (QAS)—short-chain allyltrimethylammonium chloride (ATMAC, C6) and long-chain methacryloxyethyltrimethylammonium chloride (DMC, C9)—are grafted onto PVDF membranes. Herein, C6 and C9 denote quaternary ammonium salts bearing hexyl and nonyl alkyl substituents, respectively. The best surface modification induced a 43.4% reduction in water contact angle (88.5° to 45.1°), demonstrating significantly enhanced hydrophilic characteristics of the modified membranes, surfaces with enhanced positive character (zeta potential shifted from − 30.22 mV to − 20.15 mV), and dual antifouling mechanisms via pore-clogging mitigation and hydration layer formation. The PVDF membrane grafted with 7.5 wt% DMC demonstrates optimal performance, achieving a 98.5% flux recovery ratio during sodium alginate filtration and > 99% bactericidal efficiency against E. coli and S. aureus. By grafting QAS(e.g., DMC/ATMAC) onto PVDF membranes, this approach mitigates irreversible fouling while sustaining long-term antimicrobial activity, providing a robust solution for biofouling-resistant membranes in sustainable water treatment.