Study on Thin Film Nanocomposite Polyamide Membrane via an In-situ Polymerization of Chlorosilane

Author:Shen Hong Mei

Supervisor:gao cong zhou yong


Degree Year:2019





Nanocomposite polyamide reverse osmosis membrane is a new type of thin film composite(TFC)prepared by the interfacial polymerization process.Nanoparticles embedded into the polyamide thin film can greatly improve the performance o f reverse osmosis membranes.However,the poor dispersion and easy aggregation of nanoparticles in the solution are still challenging.The weak attachment between the polymers and nanoparticles would lead to the formation of non-selective voids at the interface.Even now,most of the thin film nanocomposite(TFN)membranes are made by a complex procedure where nanoparticles are synthesized or modified via chemical reactions.This paper is designed to develop a simple in-situ polymerization strategy with few chemicals.Three chlorosilane precursors are selected.They can react with hydroxyl and amine groups.The precursors were put in the organic solution.Water and amine monomers diffusing from the aqueous solution will react with them.The in-situ generated silicon-oxygen nanocomposites interact strongly with the polyamide polymers.Silicon tetrachloride,methyl trichloride,and benzene trichloride precursors were systematically studied.The performance of the thin film nanocomposite reverse osmosis membrane was improved.Firstly,an in-situ preparation of nanocomposite polyamide reverse osmosis membrane of silicon tetrachloride(SiCl4)was established.A highly hydrophilic nanocomposite polyamide reverse osmosis membrane was prepared by the in-situ polymerization of silicon tetrachloride with hydroxyl and amine groups.The influence of silicon tetrachloride on the structures,morphologies,compositions,and properties of the polyamide membranes were systematically studied.The in-situ generated nanoparticles of SiCl4 are highly hydrophilic.They are effectively embedded into the polyamide matrix.Covalent and hydrogen bonds are formed between the polyamide polymers and nanoparticles.Abundant hydroxyl groups are produced in the polyamide membranes.Silicon tetrachloride greatly increases the pores of the back surface and the voids of the depth profile of the polyamide film.An increasingly loose protuberance is produced on the front surface.The water permeability of the TFN membrane was increased to 171%,while the water/salt selectivity was kept constant.It is an in-situ polymerization precursor with excellent properties.The water permeability,hydrophilicity,mechanical properties,and chemical resistance of the film are significantly improved.The polyamide/SiCl4 nanocomposite membranes outperform many other TFN membranes.However,the more hydrophilic the polyamide membrane is,the less water/salt selective the membrane is.The high hydrophilicity of silicon tetrachloride can only maintain the water/salt selectivity.A nanocomposite polyamide reverse osmosis membrane with high permeability and selectivity was prepared by hydrophobic methyl trichlorosilane(MeSiCl3).The in-situ polymerized methyl trichlorosilane is integrated into the thin polyamide film.Covalent and hydrogen bonds between the polyamide polymers and MeSiCl3 are formed.The in-situ polymerized methyl trichloride not only produced abundant hydroxyl and amide groups,but also created functional groups,such as methyl,silica-oxygen,and silica-nitrogen groups.Methyl trichloride greatly increases the pores of the back surfaces and voids of the depth profile of the polyamide.The larger leaf-like protuberance is produced on the top surface.The distance between the ridges and valleys of the polyamide membranes become larger.The water permeability and anti-fouling performance of the polyamide nanocomposite film are greatly improved.When the loading of methyl trichloride was increased from 0 to 0.1mM,the pure water permeability of the polyamide film increased up to 196%,while the water/salt selectivity was enhanced.In the anti-fouling experiment,the MeSiCl3modified polyamide film with 0.1 mM loading showed a permeance increase of 200%,elevated rejection,and enhanced flux recovery ratio in the BSA solution.Finally,to obtain the nanocomposite reverse osmosis membrane with more permeability and selectivity,we adopted benzene trichloride(PhSiCl3)precursor.It has a greater volume and better chemical stability.The effect of benzene trichloride on the polyamide membrane was studied systematically.The in-situ polymerized benzyl trichloride was effectively introduced into the polyamide film.Covalent and hydrogen bonds are formed between the polyamide polymers and PhSiCl3.When the water/salt selectivity of the membrane is maintained,the loading of benzene trichloride can be increased to 0.2 mM.Meanwhile,the water permeability of the membrane is increased to 300%.The nanocomposite membrane with the greatly enhanced permeability is suitable for the ultra-low RO membranes.Nanoparticles of PhSiCl3 are embedded into the polyamide membrane.They are evenly distributed.PhSiCl3 effectively solves the agglomeration of nanoparticles in the in-situ polymerization.