pH stable thin film composite poly(amine-urea) nanofiltration membranes with excellent rejection performance

pH stable nanofiltration membranes are highly desirable in treating acidic and alkali effluents and recovering the valuable byproducts. Efforts have been devoted to preparing nanofiltration membranes with good acid/alkali resistance but the separation performance is still to be improved. Poly(amine-urea) nanofiltration membranes with excellent rejection performances were prepared by the interfacial polymerization between polyethyleneimine with the mixed organic monomer of cyanuric chloride and 1, 4-phenylene diisocyanate. In comparison with pure polyamine and polyurea membranes, the optimal poly(amine-urea) membranes exhibit simultaneously improved membrane permeability and salt rejection, > 99% for MgSO4. The membrane morphology, pore structure and chemical properties of the membranes were thoroughly characterized, demonstrating that the poly(amine-urea) selective layer is thinner and denser compared with the polyamine/polyurea prepared with a single organic monomer. The underlying mechanisms for the synergistic effect between cyanuric chloride and 1, 4-phenylene diisocyanate were revealed. In addition, the poly(amine-urea) nanofiltration membranes maintain a high rejection for MgSO4, >96%, after exposure to 20 wt% HCl and 20 wt% NaOH aqueous solutions for 150 days, demonstrating excellent acid/alkali stability.