Positively charged nanofiltration membrane formed by interfacial polymerization of 3,3′,5,5′-biphenyl tetraacyl chloride and piperazine on a poly(acrylonitrile) (PAN) support

A novel TFC NF membrane was prepared on a polyacrylonitrile (PAN) supporting film using interfacial polymerization with the 3,3′,5,5′-biphenyl tetraacyl chloride (mm-BTEC) monomer and piperazine (PIP). In the interfacial polymerization process, organic solvents were changed from cyclohexane to toluene, which increased the diffusion rate and solubility of PIP in the organic solvent. The diffusion of PIP and its solubility both influence the structure, morphology and thickness of TFC membranes. The streaming potential of TFC NF membranes was measured at various pHs. The results demonstrate that the surface of the membrane is positive charged. Permeation experiments were employed to evaluate the salt rejection and water flux performance of the membranes. These new NF films exhibited interesting performance properties as compared with commercial nanofiltration membranes in terms of their retention and relative flux for positively charged inorganic compounds. The salt rejection of the mm-BTEC/PIP membranes corresponding to different types of feed solutions are CaCl2 > MgCl2 > NaCl > Na2SO4. The flux and rejection of CaCl2 (500 ppm) were 50.8 L/m2 h and 95.1%, respectively, under 0.4 Mpa. In addition, the NF membranes exhibited enhanced water permeability and salt rejection compared with those prepared from trimesoyl chloride (TMC).