Surface Modification of Reverse Osmosis Desalination Membranes with Zwitterionic Silane Compounds for Enhanced Organic Fouling Resistance

Three different zwitterionic functional trimethoxysilane compounds, 4-(diethyl(3-(trimethoxysilyl)propyl)ammonia)butane-1-sulfonate (EPBS), 4-(dimethyl(3-(trimethoxysilyl)propyl)ammonia)butane-1-sulfonate (MPBS), and 3-(dimethyl(3-(trimethoxysilyl)propyl)ammonia)propane-1-sulfonate (MPPS), were synthesized and used for the surface modification of commercial polyamide thin-film composite reverse osmosis membranes to enhance their salt rejection and antifouling performance. Commercial membrane surfaces were spray-coated using three different aqueous solution concentrations (1.0, 1.5, and 2.0%) of each zwitterionic silane compound. Surface characterization of coated membranes performed via X-ray photoelectron spectroscopy and water contact angle measurements confirmed the successful, permanent attachment of zwitterionic groups to membrane surfaces. Organic fouling studies accomplished through dead-end stirred cell filtration experiments using xanthan gum and bovine serum albumin revealed that all coated membranes had higher flux recovery rates upon cleaning with water and NaOH, demonstrating the easier cleanability provided by zwitterionic groups on the membrane surface. For example, in the case of xanthan gum fouling experiments, membranes coated with 2.0 wt % MPPS solution regained 100% of its initial flux after cleaning with deionized water, whereas the control membrane had 69% flux recovery.