Modification of poly(amide-urethane-imide) (PAUI) thin film composite reverse osmosis membrane with nano-silver particles

A novel reverse osmosis (RO) composite membrane, poly(amide-urethane-imide@Ag) (PAUI@Ag), was prepared on a polysulfone supporting film through two-step interfacial polymerization. First, in the 1st interfacial polymerization procedure, a new tri-functional crosslinking agent with –OCOCl and –COCl groups, 5-choroformyloxyisophaloyl chloride (CFIC), was reacted with 4-methyl-phenylenediamine (MMPD) without curing treatment to obtain the poly(amide-urethane) base membrane with a CFIC–MMPD precursor separation layer. And then N,N′-dimethyl-m-phenylenediamine (DMMPD) with nano-Ag particle dispersion was introduced onto the base membrane to further construct a CFIC–DMMPD modified ultrathin separation layer via the 2nd interfacial polymerization. Thus, the PAUI@Ag RO membrane with poly(amide-urethane-imide) bi-layer skin was obtained. The membrane was characterized for the chemical composition of separation layer, the membrane cross-section structure and the membrane surface morphology. Permeation experiment was employed to evaluate the PAUI@Ag membrane performance including salt rejection rate and water flux. The results revealed that the PAUI@Ag membrane composed the highly cross-linked separation layer with entire ridges and valleys, small surface roughness, and well dispersed nano-Ag particles. Upon exposure of the membranes to high concentration of free chlorine solutions, the PAUI@Ag RO membrane showed a slightly less chlorine-resistant property compared with the nascent PAUI RO membrane, but was still superior to the conventional polyamide MPD-TMC RO membrane, meanwhile it processed higher anti-biofouling property.