Preparation and characterization of PDA/PIP mixtures polyamide composite nanofiltration membranes

Polyamide thin-film composite NF membrane was prepared by interfacial polymerization of 1,3-phenylenediamine(PDA), piperazine(PIP) and trimesoyl chloride(TMC) on polysulfone(PSF) ultrafiltration membrane. The separation properties, contact angle, structure of the active layer polymer and the surface morphology of the composite membranes which prepared with different mass ratio of PDA/PIP, were systematically investigated. And the effect of interfacial polymerization conditions on the performance of composite membrane were carried out. The results showed that the shape of active layer has changed gradually from partially crystalline to amorphous state with the decrease of PDA in the PDA/PIP mixtures, which resulted in decreasing the roughness and contact angle of membrane surface. Moreover, the decrease of PDA led to the improvement of the pure water flux, accompanied by a decreased salt rejection of composite membrane. The optimum PDA/PIP mass ratio is 25/75 when the optimum polymerization conditions are as follows: the concentration of PDA and PIP is 0.5 wt % and 1.5 wt %, respectively, while the concentration of TMC is 0.1 wt %; reaction time is 60 s, curing temperature and curing time is 80 ℃ and 3 min, respectively. The rejection order of composite membrane prepared in the optimized condition to four salt solution was Mg SO4Na2SO4Mg Cl2Na Cl, while the flux order was Na ClMg Cl2Na2SO4Mg SO4.