Synthesis Of Metal Organic Frameworks And The Application Of Mixed Matrix Membrane In Water Treatment

Metal-organic frameworks（MOFs）have unique properties of adjustable pore structure,high specific surface area,good stability and compatibility.The mixed matrix membranes prepared using MOFs particles as fillers can effectively solve the problem of membrane defects caused by poor compatibility of inorganic particles as fillers with polymer substrates,and thus becomes a research hotspot in the field of membrane separation.In this paper,high-performance MOF mixed matrix membranes were prepared for water desalination processes.Firstly,three typical metal organic frameworks,ZIF-8,Ui O-66 and MIL-101（Cr）were successfully prepared through solvothermal（hydrothermal）synthesis methods and microwave-assisted synthesis.Especially,a novel hydrangea-like morphology ZIF-8 crystal was obtained using solvothermal synthesis for the first time.The appearance of this morphology is possibly caused by the particle self-assembly growth and Oswald ripening process.The rhombohedral polyhedron ZIF-8 crystals prepared with microwave method have high crystallinity,regular shape and good thermal stability.The microwave-assisted synthesis method successfully shortened the reaction time of preparing Ui O-66 and MIL-101（Cr）to 5 min and 30 min,which greatly improved the reaction efficiency.The obtained products all possess regular octahedral structures.The specific surface areas of Ui O-66 and MIL-101（Cr）can reach 1500 m²·g^-1 and 2667 m²·g^-1,and the pore volumes are 0.65 cm³·g^-1 and 1.37cm³·g^-1,respectively.Their highly ordered pore structures have good molecular sieving properties.Subsequently,the MOFs particles synthesized with microwave-assisted synthesis method were as fillers to prepare MOF mixed matrix membranes through phase inversion method.The effects of PVDF concentration,the MOF type and MOF doping amount on the morphology,water swellability and mechanical properties of mixed matrix membranes were investigated.The performance of MOF mixed matrix membranes in water desalination process were tested.The results show that when the MOF doping amount is 10 wt%and 20 wt%at PVDF concentration between 10 wt%and 20 wt%,the obtained mixed matrix membranes are uniform and dense.The water uptake and swelling degree increase with the increase of hydrophilic MOF doping in a certain range.Compared with the pure PVDF membrane,the introduction of hydrophilic MIL-101（Cr）and Ui O-66 crystals significantly increases the water flux of the mixed matrix membranes,wherein the water flux of membrane U-20%-30%is725.7 L·m^-2·h^-1·MPa^-1.However,the incorporation of hydrophobic ZIF-8 has no significant effect on the water flux of the mixed matrix membrane.The ordered pore structures of different MOFs have selective permeability to salt ions,which can improve the desalination rate of the mixed matrix membranes.The desalination rate for Na Cl,Mg SO₄ and Al Cl₃ of membrane U-20%-30%and Z-20%-20%are above96%,97%and 98%,while the desalination rate of membrane M-20%-20%is less than90%.Comprehensive evaluation shows that the salt rejection of membrane U-20%-30%is between commercial membrane NF90-4040 and SWC6-4040（91%and 99%）and the water flux of membrane U-20%-30%is 3.5 times and 3.8 times that of commercial membranes NF90-4040 and SWC6-4040 respectively.Meanwhile,membrane U-20%-30%has good cycle stability as well as good commercial prospects.