Preparation And Compatibility Enhancement Of Chitosan/UiO-66-NH₂ Mixed Matrix Membranes

As an efficient and environmentally friendly separation method,membrane separation technology has a wide range of application prospects in the field of CO₂ separation.Traditional polymer membranes and inorganic membranes have their own limitations,and mixed matrix membranes combine polymers and porous materials to ensure high separation performance while reducing preparation costs,which is one of the effective ways to obtain high-performance membrane materials.Metal organic framework materials（MOFs）have the characteristics of adjustable pore size and easy surface modification,which are beneficial to gas separation,and become excellent fillers for preparing mixed matrix membranes.However,due to the compatibility issue between particles and polymer,non-selective interface defects often appear in mixed matrix membranes,resulting in a decrease in the CO₂ separation performance of the membranes.Therefore,it is a challenge how to obtain a defect-free MOFs mixed matrix membranes with good interface compatibility.For this reason,in this thesis,chitosan（CS）is selected as the membrane material,and UiO-66-NH₂ is selected as the filler to prepare the CS/UiO-66-NH₂ mixed matrix composite membranes,which use hydrogen bonds to strengthen the interface interaction.In order to further improve the interface compatibility,the CS-EPB-UiO-66-NH₂ mixed matrix composite membranes are prepared by chemical cross-linking,which further increases the loadings of UiO-66-NH₂.Firstly,the CS composite membranes are prepared and the preparation conditions are optimized to ensure that the separation layer of the composite membranes is thin and dense without defects.The optimized membrane preparation conditions are determined as follows:CS molecular weight is 100000,coating solution layer thickness is 200μm,coating solution concentration is 2.0 wt%,and CS separation layer thickness is 416 nm.At this time,the CS composite membrane has the best performance:at 0.2 MPa,the CO₂ permeance is 22.6 GPU,the CO₂/N₂ selectivity is 26.5.Secondly,by incorporating UiO-66-NH₂ to regulate the structure and gas transport properties of the CS membrane,CS/UiO-66-NH₂ mixed matrix composite membranes are prepared.The results show that the incorporation of UiO-66-NH₂ disrupts the regular arrangement of CS chain segments and increases the free volume fraction in the membrane.The primary amine groups on the outer wall of the pores can be used as carriers to facilitate the transport of CO₂ at the interface,and the primary amine groups on the inner wall of the pores are conducive to the preferential adsorption of CO₂ in the pores,thus improving the permeability selection performance of the CS membrane.The hydrogen bond interaction between UiO-66-NH₂ and CS also ensures better interface compatibility.When the UiO-66-NH₂ loading is 15 wt%,the CO₂ permeance is 30.1 GPU,the CO₂/N₂ selectivity is34.6,which are 33.2%and 30.6%higher than that of the CS composite membrane.In order to further strengthen the interface interaction between the filler and the polymer,UiO-66-NH₂is modified by post-synthetic modification technology with epibromohydrin,the epoxy group was modified on the surface to obtain EPB-UiO-66-NH₂,and then the epoxy group reacts with the amine group in CS to realize the covalent connection of UiO-66-NH₂and CS.The CS-EPB-UiO-66-NH₂ mixed matrix composite membrane with a loading of 25wt%and no obvious defects is prepared.The CO₂ permeance is increased to 38.9 GPU,and the CO₂/N₂ selectivity is increased to 40.4,which are 29.2%and 16.8%higher than that of the best performance CS/UiO-66-NH₂（15 wt%）composite membrane.