Microplastics-resistant FO membranes: Zwitterionic MOF nanoparticles for superior fouling control

The increasing contamination of water by microplastics (MPs) underscores the need for efficient tertiary treatments such as forward osmosis (FO). Developing advanced, low-fouling membranes is essential for enhancing FO system effectiveness. This work studies an innovative modification of FO membranes by the incorporation of a synthesized hybrid nanoparticle comprising metal-organic frameworks (MOFs) and sulfobetaine zwitterions into the thin layer of thin-film composite (TFC) membranes. The ZW/MOF (UiO-66-NH₂), nanoparticles were synthesized using a post-synthetic free-radical copolymerization method, resulting in a uniform polymer shell around the MOF nanoparticles. The incorporation of ZW/MOF nanoparticles into the membranes enhanced the hydrophilicity of the membranes by 73 % and imparted a more negatively charged membrane surface. Moreover, the performance tests indicated that the incorporation of ZW/MOF nanoparticles into the TFC membranes significantly enhanced their water flux by 28 % while reducing their reverse salt flux (RSF). Fouling tests employing organic foulants and MPs demonstrated a substantial improvement in the antifouling capabilities of the modified membranes with 17 % flux decline compared to 60 % flux decline for the pure membrane. Notably, the modified membranes showed almost full flux recovery after fouling, indicating a reversible fouling, whereas the control membrane only demonstrated 70 % flux recovery after fouling tests with combined MPs and organic foulants. This highlights the suitability of FO membranes modified with ZW/MOF nanoparticles for treating complex wastewater, particularly in environments with emerging pollutants like MPs. This study provides new insights into the positive contributions of MOFs and their hybrid nanoparticles on the sustainable development of membrane technology dealing with emerging pollutants.