Zwitterionic polysiloxane-polyamide hybrid active layer for high performance and chlorine resistant TFC desalination membranes

Hybrid polysiloxane-polyamide thin-film composite (TFC) reverse osmosis (RO) membranes were produced in the presence of a zwitterionic silane compound during polyamide active layer preparation by interfacial polymerization for an enhanced desalination performance and chlorine resistance. The zwitterionic functional silane monomer, (3-sulfopropylbetaine-propyl)-trimethoxysilane (SPPT), was added to an aqueous m-phenylenediamine (MPD) monomer solution at different concentrations; 0.05, 0.1, 0.25, 0.5 and 1.0 SPPT/MPD ratios. The aqueous monomer solutions adsorbed on a polysulfone support layer were contacted with an organic trimesoyl chloride (TMC) monomer solution to create a polysiloxane-polyamide hybrid active layer by interfacial polymerization. Hybrid active layers were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA), and zeta potential measurements. Membranes produced with a SPPT/MPD ratio of 0.1 exhibited an increase in permeate flux from 25 L m⁻² h⁻¹ to 33 L m⁻² h⁻¹ (55 bar operating pressure; 3.2% NaCl feed) while the salt rejection was not compromised, but slightly increased from 98.8% to 98.9%, when compared to the control membrane prepared without SPPT. The highest resistance against chlorine was observed for the membranes produced with a SPPT/MPD ratio of 1.0, for which, a significant membrane damage and consequent loss of salt rejection were observed after six hours of exposure to chlorine solution, while the control membrane was prone to chlorine damage after two hours.