Development of antifouling nanofiltration membranes for separation of dye/salt mixture through incorporation of novel polyelectrolyte-decorated silica

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Various physical and chemical methods can improve hydrophilicity and prevent fouling in polyethersulfone (PES)-based nanofiltration membranes. Here, two additives containing hydrophilic polymer brushes were used to modify the hydrophilicity of PES membranes. First, the surface of mesoporous silica (MS) was modified with poly(2,3-epoxypropyl methacrylate) (P(EPMA)) and poly[2-(acryloyloxy)ethyl]trimethylammonium chloride (P(AEtMAC)) brushes using the surface-initiated atom transfer radical polymerization (SI-ATRP) method to prepare MS-g-P(EPMA-SO3) and MS-g-P(AEtMAC) as additive. Various weight percentages of the additives from 0.05 to 0.2 wt% were used to fabricate PES-based membranes and by adding the polymer brushes, the hydrophilicity of PES-based membranes increased. The membrane containing 0.075 wt% of MS-g-P(AEtMAC) additive exhibited a higher water flux of 18.6 (L/m2.h) at 5 bars. The separation of Coomassie Brilliant Blue G-250 (CBB) and Congo Red (CR) dyes (100 mg/L) was investigated; all membranes rejected more than 99 % of both dyes. However, the PES/MS-g-P(EPMA-SO3) membrane, M2, showed a rejection rate of 11.5, 6.1, and 5.1 % for Na2SO4, MgCl2, and NaCl, respectively. PES/MS-g-P(AEtMAC) membrane, M6, rejected Na2SO4, MgCl2, and NaCl at 6.2, 11.9, and 6.8 %, respectively. Finally, the constructed membranes demonstrated remarkable selectivity for dye/salt mixtures, indicating great potential for treating dye-containing wastewater.