Preparation and Characterization of Polypiperazine-amide Composite Nanofiltration Membrane

A polypiperazine-amide composite nanofiltration membrane was fabricated by interfacial polymerization (IP) of piperazine and the mixture of isophthaloyl (IPC) and trimesoyl chloride(TMC) onto the polysulfone (PS) support membrane. The effeet of the characteristics of PS membrane, the concentrations of monomers, surfactant (SDS) and alkaline, and the reaction time of IP on the character of the composite nanofiltration membrane were carefully studied for preparing the best NF membrane. The feasible concentration of IPC and TMC mixture for IP is approximately 0.08~0.1mol-1, the concentration of piperazine is 0.08~0.12molL-1 and the reaction time of IP is 3~5min. The composite nanofiltration membranes were characterized through flux/retention tests of different inorganic salts and organic dyes at 0.4 MPa and 25℃. The experimental results show that the retention of the composite nanofiltration membrane to NaCl (0.01molL-1) is about 30%~40%, to Na2SO4 (0.005molL-1), nearly 80%~90%, and to organics of molecular weight greater than 300g穖oL-1, more than 95%. These separation performances are similar to those of the commercial nanofiltration membranes. The experimental results indicate that the composite nanofiltration membrane bears the slightly negative charges, and that the steric (sieving) and Donnan effects are main mechanisms of the electrolyte permeation across the membranes.