Study on a novel polyamide-urea reverse osmosis composite membrane (ICIC–MPD): I. Preparation and characterization of ICIC–MPD membrane

A novel reverse osmosis (RO) composite membrane-polyamide-urea membrane (ICIC–MPD) was prepared on a polysulphone supporting film through interfacial polymerization with m-phenylenediamine (MPD) and a key functional monomer-5-Isocyanato-isophthaloyl chloride (ICIC), a new crosslinking agent with trifunctional groups including single bondNdouble bond; length as m-dashCdouble bond; length as m-dashO and single bondCOCl. The monomer ICIC was synthesized from 5-amido-isophthalio acid and triphosgene (BTC) as an acyl chlorinating agent in the presence of composite catalysts (pyridine/imidazole), and further identified through elemental analysis, hydrogen nuclear magnetic resonance (1HNMR), carbon nuclear magnetic resonance (13CNMR), gas chromatograph mass spectragraph (GC–MS), infrared spectra (IR), chromatograph (GC), and melting-point measurement. The membrane was characterized for the permeate performance, chemical composition of the near-surface active layer, membrane cross-section structure and membrane surface morphology. Permeation experiment was employed to evaluate the ICIC–MPD membrane performance including salt rejection rate and water flux. X-ray photoelectronic spectroscopy (XPS) was combined with attenuated total reflectance infrared (ATR-IR) to analyze the surface chemical composition of membrane. The results reveal that the active layer of ICIC–MPD membrane is composed of aromatic polyamide with the functional bonds of urea (single bondNHCONHsingle bond) and acylamide (single bondCONHsingle bond), and the functional groups such as amide (single bondNH2) from the hydrolyzed functional isocyanate groups (single bondNCO), carboxyl (single bondCOOH) from the hydrolyzed functional carbonyl choride groups (single bondCOCl). The scanning electronic microscopy images clearly indicate that the thickness of active layer is less than 0.2 μm, and the atomic force microscope (AFM) images further show that the surface morphology is composed entirely of ridges and valleys.