Structural Design And Performance Research Of Composite Forward Osmosis Membrane Based On 3D Printing Support Layer

In recent years,the forward osmosis separation technology has received a lot of attention from domestic and international researchers because of its advantages of driving force from the osmotic pressure difference inside the system and no additional operating pressure from outside.However,in practical commercial application,the forward osmosis separation technology is limited by many factors,among which the internal concentration polarization phenomenon in the support layer of heterogeneous membrane is the main reason to limit the performance of forward osmosis membrane.As one of the emerging technologies developed in recent years,3D printing technology is promoting the innovation of many industries and academic research,including the field of membrane separation,it brings more possibilities for the optimization and development of membrane materials and membrane structures.Using 3D printing technology to prepare the forward osmosis membrane support layer with micro-through hole structure can achieve ideal structural parameters,thus greatly alleviating the phenomenon of internal concentration polarization.Therefore,breaking through the structural design of traditional forward osmosis membrane and developing a new generation of 3D printed support layer composite forward osmosis membrane will make the development of forward osmosis membrane separation technology step up to a new level.In this study,on the basis of a series of high-performance forward osmosis membrane materials with carboxyl groups developed by our research group,the ultra-thin homogeneous forward osmosis active layer was obtained by solution casting.Then,the ultra-thin homogeneous forward osmosis active layer with excellent performance was combined with a series of supporting layers with micro-through hole structure prepared by cutting-edge 3D printing technology to develop a new generation of high-performance composite forward osmosis membrane technology with subversive significance.The main research contents are as follows:（1）Preparation and performance research of 3D printing materials for supporting layer of water treatment membraneIn response to that problem that there is no 3D printing material dedicated to the support layer of the composite forward osmosis membrane has been developed,this study based on Suzhou Boli Technology Co.,Ltd.,we firstly selected ten photosensitive resin formulations and analyzed the properties of various materials by testing the properties of photosensitive resin 3D printing materials such as tensile strength,shrinkage of molding line and hardness,and then selected A2 photosensitive resin with excellent comprehensive performance for composite forward osmosis membrane support layer 3D printing materials.（2）Preparation and properties of POD-COOH/3D printing support layer composite forward osmosis membrane.In order to overcome the inherent defects of self-supporting homogeneous forward osmosis membrane,such as poor integrity and easy membrane breakage,based on the POD-COOH forward osmosis membrane material previously developed by our research group,firstly,the ultra-thin forward osmosis active layer was obtained by solution casting,and then the ultra-thin forward osmosis active layer was combined with a series of 3D printing support layers with micro-porous structure by interfacial electrostatic force and hydrogen bonding,and the series of POD-COOH/3D printing support layer composite forward osmosis membrane were prepared.Furthermore,the permeability of the prepared series of composite forward osmosis membranes were characterized and tested in detail,and the effects of carboxyl groups of active layer,porosity of 3D printing support layer and thickness of ultra-thin active layer on the comprehensive properties of composite forward osmosis membranes such as hydrophilicity,electronegativity,permeability,internal concentration polarization and key performance parameters were systematically studied.The results show that due to the introduction of carboxyl groups,the surface microphase separation and the ideal through-hole structure of the support layer,the maximum reverse flux selectivity of POD-COOH/3D printing support layer composite forward osmosis membrane with the thinnest active layer thickness（2μm）reaches335.7±35.8 L·mol^-1.Moreover,there is almost no concentration polarization phenomenon in the forward osmosis process of this kind of 3D printing support layer composite forward osmosis membrane,and the osmotic pressure difference produced by the membrane in the actual forward osmosis process is close to the ideal osmotic pressure difference.（3）Preparation and properties of PES-COOH/3D printing support layer composite forward osmosis membrane.In order to further control the ultra-thin active layer of composite forward osmosis membrane to a thinner level,effectively improve the permeation separation performance of the composite membrane,and make it have high mechanical strength and less prone to breakage.In this study,the PES-COOH material with high carboxyl content and excellent mechanical properties was used to obtain the ultra-thin forward osmosis active layer by solution casting method,and the active layer was combined with the prepared 3D printed support layer to prepare a series of PES-COOH/3D printed support layer composite forward osmosis membrane,and the prepared series of composite forward osmosis membrane were systematically characterized and tested.The results showed that the microphase separation structure formed on the surface of the thinner PES-COOH active layer was more pronounced compared to the POD-COOH/3D printed support layer composite forward osmosis membrane.The composite forward osmosis membrane with the thinnest active layer thickness（1μm）shows an unusually low Js value,and the maximum reverse flux selectivity of the composite forward osmosis membrane reaches 1523.8±132.6 L·mol^-1.