Grafting Zeolite Nanoparticles Onto Polyamide Membranes for Enhanced Antifouling Performance in Forward Osmosis Membrane Processes

Forward osmosis (FO) is a promising method for seawater/brackish water desalination, water purification, wastewater reclamation, and energy generation.  However, membrane fouling is still one of the challenges in the advancement of FO membrane technology.  Therefore, there is a pressing need to develop a fouling-resistant membrane for FO applications. This study developed an innovative method to graft zeolite nanoparticles onto polyamide (PA) membrane surfaces to enhance fouling resistance in FO membrane process. Zeolite nanoparticles with composition of 11.25SiO₂/1.8Al₂O₃/6.7 (TMA)₂O/1.2Na₂O/700H₂O was modified with amine functional groups and covalently bonded to the carboxylic functional groups on the PA membrane surface. The properties of the zeolite membranes were characterized by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), water contact angle measurement, and permeation/salt rejection tests, respectively.  Our results showed that the surfaces of zeolite nanoparticles were successfully functionalized by amine groups.  The XPS and SEM results demonstrated that the amine functionalized zeolite nanoparticles were grafted onto the PA membrane by covalent binding between amine and carboxylate functional groups. The zeolite-modified PA membrane is very hydrophilic, with a water contact angle of around 20 degree, which is much lower than that of the unmodified membrane (60 degree).  The antifouling properties of the zeolite-modified membrane were significantly enhanced.  FO fouling experiments showed that both bacterial deposition and organic fouling were inhibited by zeolite modification, most likely due to reduced carboxylic functionality and increased hydrophilicity of the zeolite modified membrane.