Constructing An Organic Interlayer Based On Catechol Polymerization To Control Performance Of Polyamide Composite Membrane

With the rapid development of industrialization in China,more and more attention has been paid to the field of water treatment.Membrane separation technology dominated by nanofiltration and reverse osmosis has been widely used with its unique advantages.In order to meet the increasing demand of modern economic system for energy saving and consumption reduction,the development of energy-saving membrane materials is of great value and significance in promoting the development of membrane technology innovation.Therefore,polyamide composite membranes with enhanced performance were studied here to meet the above needs.The existing polyamide composite membrane has the“trade-off”phenomenon of selectivity and permeability.In order to break this phenomenon and prepare high-throughput and high rejection composite membrane,its performance can be optimized by adjusting the physical and chemical properties of different layers.From the point of the view of constructing multi effect interlayer to control the interfacial polymerization process,the high performance polyamide composite membrane was prepared by introducing interlayer to control the structure and properties of polyamide active layer.In this paper,a simple and universal method to construct an interlayer was proposed.The hydrophilic interlayer rich in carboxyl groups was prepared by self-polymerization of catechol with low cost and simple,and then the composite membrane with high performance was prepared by interfacial polymerization.The hydrophilicity of the modified bottom film is improved and more piperazine（PIP）can be stored,which provides a smooth reaction platform with uniform PIP distribution.At the same time,there are unreacted quinones on the modified surface,which can covalently combine with PIP molecules through Michael addition reaction.On one side,the diffusion of PIP is inhibited and the interfacial polymerization process is affected,resulting in the formation of a smooth,dense and thin polyamide layer.On the other hand,the existence of covalent bonds makes the combination of the separation layer and the modified base membrane more stable.The flux of the composite membrane was increased by1.7 times,and the retention was maintained at more than 98%.Secondly,the morphology and separation performance of the composite membrane can be controlled by changing the modification process of the intermediate layer.By the layer by layer modification method,firstly,it is to reduce the reaction time of single CA-SP and regulate the carboxyl content on the surface of the bottom membrane to affect the formation process of PA separation layer.Second,the polymerization reaction takes place on the membrane surface,which makes the interlayer more stable and not easy to fall off.The results show that the composite membrane is thin and the surface becomes rough with the increase of the number of layers,so the flux increases by nearly two times,and the retention remains above 98.5%.MOFs are porous materials composed of metal nodes and organic ligands through coordination bonds.As porous materials,MOFs can provide more transport paths for water molecules,so they are also widely used in membrane materials.The ZIF-8 is one of MOFs materials used in membrane separation.Due to its hydrophobicity,the ZIF-8 has been widely studied in the preparation of reverse osmosis membrane.In this paper,the modified polysulfone substrate was co-deposited with CA-SP,and the surface of the substrate was rich in carboxyl groups,which were used to complexing Zn²⁺,providing sites for in-situ growth of ZIF-8.Compared with the traditional reverse osmosis membrane,the flux is increased by 2.8 times,and the retention is kept at about 97%.