Binding TiO2 nanoparticles to forward osmosis membranes via MEMO–PMMA–Br monomer chains for enhanced filtration and antifouling performance

Abstract

Forward osmosis (FO) has attracted increasing interest in various applications for water and wastewater treatment and reuse. However, drawbacks caused by its lower-than-expected flux performance and fouling issues remain bottlenecks that limit the wider applications of FO technology. In this research, titanium dioxide (TiO₂) nanoparticles were grafted onto two commercially available FO membranes, a cellulose triacetate (CTA) membrane and an aquaporin (AqP) membrane, through a specially designed 3-(trimethoxysilyl)propyl methacrylate–polymethyl methacrylate–bromide (MEMO–PMMA–Br) monomer chain, to improve the filtration performance with regard to pure water flux and organic fouling resistance. The success of the surface coating method was verified using FT-IR, SEM-EDX, and AFM. Approximately 30% titanium coverage was obtained for both FO membranes. A reduction of the contact angle on the modified CTA membrane surface indicated enhanced water permeability and antifouling performance. An adverse effect on the surface hydrophilicity of the modified AqP membrane may be attributed to the obstruction of aquaporins from the feed solution due to the coverage of MEMO–PMMA–Br monomers and TiO₂ nanoparticles. The pure water flux of both membranes was significantly improved, with average flux increases of 73.4% and 13.6% identified for the modified CTA and AqP membranes, respectively. In addition, the antifouling performance of the AqP membrane was greatly enhanced after surface modification, attributed to the integrated effects of foulant photodegradation (catalyzed by TiO₂ nanoparticles at the interface) and the prevention of functional water channels being blocked by organic foulants due to TiO₂ coverage.