Study of synergetic effect and comparison of novel sulfonated and carboxylated bulky diamine-diol and piperazine in preparation of negative charge NF membrane

Two new sulfonated (SDA) and carboxylated (CDA) aromatic diamine-diol monomers were synthesized and applied to prepare thin-film composite (TFC) nanofiltration (NF) membranes with improved antifouling and performance properties. The interfacial polymerization method was used to make sulfonated and carboxylated TFC-NF membranes with reaction of trimesoyl chloride (TMC) in the organic phase with amine and hydroxyl agents in the aqueous phase. Herein, for the first time, a comparison between carboxylated and sulfonated TFC was carried out. Moreover, the probability of synergetic effect between these two synthetic monomers (CDA and SDA) and piperazine monomer was studied (the sulfonated monomer and piperazine showed a synergetic effect). The outcomes of flux recovery ratio (FRR), flux and contact angle showed that in the presence of newly synthesized monomers, membrane hydrophilicity considerably improved. The salt retention sequence for all membranes was Na2SO4 ≫ NaCl > CaCl2, which means all membranes had a negative charge. Among the five prepared TFC membranes (SDA, CDA, PIP, SDA/PIP, and CDA/PIP), the SDA/PIP showed the best salt rejection (97% Na2SO4) with flux (50 Lm−2 h−1) and 91% FRR, at operating pressure of 10 bars. Although the SDA showed the highest permeability (62 Lm−2 h−1) and FRR of 92%, it presented the lowest Na2SO4 rejection. The results indicated that mixing carboxylated monomers with PIP caused deterioration in properties, while mixing sulfonated monomer with PIP enhanced the performances of the related TFC. Better permeability of the membrane made by newly synthesized monomers is ascribed to the existence of strong hydrophilic sulfonic acid, carboxylic acid and terminal hydroxyls, and amine groups at polyamide top layer producing enhanced membrane antifouling properties.