Enhancing the performance of polyethylenimine modified nanofiltration membrane by coating a layer of sulfonated poly(ether ether ketone) for removing sulfamerazine

In this study, a composite nanofiltration (NF) membrane with tailored pore size and surface charge property for removal of sulfamerazine is developed by coating a layer of negatively charged sulfonated poly(ether ether ketone) (SPEEK) onto a polyethylenimine (PEI) modified positively charged NF membrane surface. Membrane morphologies, pore size, surface charge property as well as separation performance are extensively studied. PEI modified membrane exhibits positive charge at pH below an isoelectric point of 9.8, while SPEEK coated membrane has an isoelectric point of 5.4 and smaller molecular weight cut-off (MWCO). SPEEK coated membrane removes both divalent cations and anions more effectively than monovalent ions. Solution pH significantly influences membrane separation performance. The relationship between separation efficiency, solution pH and membrane surface charge property is being investigated systemically. The results show that the Donnan exclusion mechanism plays a major role in NaCl retention of SPEEK coated membrane under different pH conditions. In the case of sulfamerazine separation, SPEEK coated membrane shows higher removal efficiency than that of PEI modified membrane ascribing to its smaller pore size. In different pH solutions, the electrostatic interaction between sulfamerazine dissociation species and the charged membrane governs the removal efficiency.