The Fabrication And Performance Of Nanofiltration Membrane Based On PET Ion Track Membrane

Nanofiltration,as an important membrane separation process,can achieve precise rejection and sieving in nanoscale.It is of great significance in many aspects such as advanced water treatment.Ion track membrane（ITM）has been widely applied in water treatment such as microfiltration and ultrafiltration due to uniform pore,free-defect and hydrophilic surface.In nanofiltration,separation membranes must have nano-scale pore.At present,there are still difficulties in using ion track membrane directly for nanofiltration due to the limitations of controlled preparation of nano-scale pore and thickness of ion track membrane.Different from the membrane with symmetric structure,the membrane with asymmetric structure consists of a porous support layer and a dense,ultra-thin selective layer,which allows the membrane to have both good permeation and retention properties.In this thesis,nanofiltration membranes were prepared based on nuclear pore membranes by constructing asymmetric structure composite membranes.Firstly,the organic-inorganic composite membrane was prepared by co-deposition of polydopamine（PDA）and polyethyleneimine（PEI）to grow a sense selective layer of zirconia on the surface of the PET ion track membrane.The water flux of composite membrane is 5.7 L m^-2 h^-1.The rejection rates of Na₂SO₄,Mg SO₄,Mg Cl₂ and Na Cl are53.0%,45.0%,31.6%and 20.3%,respectively.Comparing with the current commercial nanofiltration membrane,the nanofiltration performance of the composite membrane is relatively poor,which is manifested by low water flux and rejection rate.However,the preparation method of the organic-inorganic composite membrane based on ion track membrane has certain reference value for the modification of ion track membrane and the preparation of composite membrane based on ion track membrane.In addition,the PA-PET composite nanofiltration membrane,with the ion track membrane as support and polyamide（PA）as selective layer,was prepared by combining ion track membrane with interfacial polymerization.The ion track membranes with pore density of 5×10⁹ and 1×10⁹ cm^-2,corresponding pore size of 65nm and 95 nm respectively,were used to research substrate to filtration performance of composite membrane.The results show the PA-PET exhibits excellent nanofiltration performance.Its water flux is 38 L m^-2 h^-1.The rejection rate for sulfate is above 90%,for Mg Cl₂is 86%,and for Na Cl is only 32%,which show good selectivity for monovalent salts and divalent salts.The PA-PET composite membrane exhibits good water flux while maintain excellent rejection rate.The combination of ion track membrane and interfacial polymerization is a successful practice in the preparation of high-performance nanofiltration membranes.