Covalent bonding of silver phosphate nanoparticles in fully aromatic active layer of reverse osmosis membrane with improved desalination and fouling resistance

The current study was focused on developing a completely aromatic polyamide selective layer of a thin film nanocomposite (TFN) reverse osmosis membrane having silver phosphate nanoparticles bonded to active layer. This was achieved by ultrasonication-assisted synthesis of silver phosphate nanoparticles (AgP) followed by the reaction of these nanoparticles with the amine-terminated silane, namely 3-aminopropyltriethoxy silane (APTES). The presence of amino groups on the silver phosphate was confirmed by FE-TEM, XRD, etc. The decoration of amino groups on the silver phosphate nanoparticles assisted in the nucleophilic substitution reaction between the nanoparticles and acid chloride groups on trimesoyl chloride during interfacial polymerization (IP) between NH₂-AgP, which resulted in variations in the structural and functional properties of the NH₂-AgP/MPD-TMC membrane. Among the most noticeable variations in the features of the newly fabricated membrane were the increase in hydrophilicity and reduced charge with no isoelectric point (IEP). Owing to these characteristics, the NH₂-AgP/MPD-TMC (NH₂-AgP-PA) membrane showed an enhanced permeate flux of 37.1 L m⁻² h⁻¹ compared to 28.6 L m⁻² h⁻¹ for the control MPD-TMC (C-PA) membrane at a pressure of 30 bar. The NH₂-AgP-PA membrane showed a rejection of 95.6 % for Na₂SO₄ at a concentration of 2000 ppm, which was nearly the same as that of the C-PA membrane with a rejection of 96.0 %. In the case of monovalent salt-containing feed, the NH₂-AgP-PA membrane showed a rejection of 94.1 % for NaCl, whereas the C-PA showed a rejection of 95.9 % at a NaCl concentration of 2000 ppm. Moreover, the NH₂-AgP-PA membrane showed performance stability over 480 min of testing with antifouling behavior compared to the control membranes, where the NH₂-AgP-PA was able to maintain its normalized flux at 0.90 compared to 0.70 for the C-PA membranes. The NH₂-AgP-PA also possessed biofouling resistance by inhibiting the growth of bacterial strains like E. faecalis ATCC 29212 and E. coli ATCC 25922.