Author Identifier (ORCID)
Mohadeseh Najafi’s ORCID record 
Javad Farahbakhsh’s ORCID record
Abstract
Nanoplastic (NP) fouling is an emerging barrier to the reliable application of ultrafiltration (UF) membranes, particularly in chemically complex waters where NP surface functionality governs deposition, cake formation, and cleaning performance. Herein, pH-responsive mixed-charge UF membranes were fabricated by plasma-induced graft copolymerisation of mono-2-(methacryloyloxy) ethyl succinate (MMES) and N-[3-(dimethylamino)propyl] methacrylamide (DMAPMA) onto poly(ethersulfone) (PES) to simultaneously regulate surface charge, hydration, and fouling reversibility. Unlike conventional single-charge or zwitterionic modifications, this approach enabled independent tuning of anionic and cationic moieties, generating composition-dependent and pH-switchable interfacial properties. ATR-FTIR, XPS, FESEM/EDX, AFM, WCA, streaming zeta potential, and MWCO analyses confirmed successful grafting, modified surface morphology, improved hydrophilicity, and pronounced charge switching from positive under acidic conditions to negative at neutral and alkaline conditions for the mixed-charge membranes. Among the fabricated membranes, the equimolar mixed-charge membrane (M1D1) provided the most favourable overall performance, combining a pure water flux of 138 LMH with NP rejection above 95 %. Fouling behaviour depended strongly on both membrane chemistry and NP functionality, with mixed-NP suspensions imposing the most severe fouling challenge. Under mixed-NP filtration, the neat PES membrane exhibited a first-cycle flux decline ratio of 36 %, whereas M2D1, M1D1, and M1D2 reduced this value to 15 %, 15 %, and 20 %, respectively, with hydraulic cleaning flux recovery ratios of 85–92 %. The M1D1 membrane also showed superior pH-responsive cleaning efficiency during sequential acid-alkali treatment, sustaining greater flux recovery than the neat PES membrane over repeated fouling-cleaning cycles. These findings position mixed-charge surface engineering as a promising route for next-generation UF membranes with improved resistance to NP fouling and enhanced operational cleaning efficiency.
Keywords
mixed-charge surface, nanoplastic fouling, pH-responsive cleaning, plasma-induced graft copolymerisation, ultrafiltration membranes
Document Type
Journal Article
Date of Publication
10-1-2026
Article Number
110416
ISSN
24680230
Volume
98
Publication Title
Surfaces and Interfaces
Publisher
Elsevier
School
School of Engineering / Nutrition and Health Innovation Research Institute / School of Medical and Health Sciences
Funding Information
The authors express their gratitude for the financial support provided by the Australian Research Council (ARC DECRA DE220101043) and the generous support from the AMP Foundation for Dr. Masoumeh Zargar and the ARC PhD Scholarship for Mohadeseh Najafi.
Funding received from the Australian Research Council (ARC)
DE220101043
Administering Institution
Edith Cowan University
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Najafi, M., Farahbakhsh, J., Ghanbari, R., Mahmoudi, E., Johns, M., & Zargar, M. (2026). pH-responsive mixed-charge ultrafiltration membranes for adaptive control of single and mixed nanoplastic fouling. Surfaces and Interfaces, 98, Article 110416. https://doi.org/10.1016/j.surfin.2026.110416