Novel poly(ether sulfone isopropyl sulfide) support layer in thin film composite membrane for desalination

The aim of this research was to design a new polysulfone for the support layer of thin film composite (TFC) membranes and compare it with commercial structures for desalination applications. Accordingly, a novel random terpolymer was synthesized using the polycondensation reaction of bisphenol A and thiodiphenol with dichlorodiphenyl sulfone, comprising both methyl and sulfide groups in the backbone of the polymer. Subsequently, three asymmetric support layers were prepared using: the terpolymer, a polymer blend based on commercial polysulfone and a sulfide-containing polysulfone, and commercial polysulfone. Next, TFCs were prepared through the interfacial polymerization of polyamide on aforementioned support layers. Characterization was performed using ¹H NMR, FTIR, GPC, tensile test, water contact angle, DSC, TGA, SEM, ATR-FTIR, AFM, and zeta potential analyses. M_w, Young's modulus, and contact angle of prepared terpolymer were 88,000 g.mol⁻¹, 3684 MPa, and 59˚ which were predominant properties in respect to commercial polysulfone with 66,000 g.mol⁻¹, 2541 MPa, and 73˚ values, respectively. AFM analysis showed that the mean difference between the highest peaks and lowest valleys increased from 79 nm for commercial polysulfone to 219 nm for synthesized terpolymer. Finally, superior performance was observed for the terpolymer-based TFC with 97% NaCl rejection and excellent 91.8% saline solution flux recovery when tested against NaCl salt and BSA as a natural biofoulant. Long-term stability of water flux and salt rejection were observed as well, reaching ∼ 27 L.m⁻².h⁻¹ and 97.5% values, respectively. The results indicated that this terpolymer could be a promising substitute for commercial polysulfone in water purification membranes.