Synthesis Of ZIF-8-SPEEK/PES Nanofiltration Membrane And The Effect Of Its Microstructure On Nanofiltration Performance

Polyether ether ketone?PEEK?,which has excellent mechanical strength,thermal stability and chemical corrosion resistance,is an aromatic polyketone.It can be used to prepare solvent-resistant nanofiltration membranes.Sulfonated polyether ether ketone?SPEEK?has good hydrophilicity and excellent ion exchange ability.By changing the degree of sulfonation,the hydrophilicity,ion exchange capacity and proton conductivity of SPEEK can be adjusted,so SPEEK can be prepared into ion exchange membranes and nanofiltration membranes.The SPEEK/PES composite nanofiltration membrane made from SPEEK and polyethersulfone?PES?has low flux and rejection rate.The nanofiltration performance of composite membranes can be improved by adding porous nanomaterials with good compatibility with separation layer.Metal organic frameworks?MOFs?are composed of metal ions and organic ligands through coordination.The existence of organic ligands makes them well compatible with organic polymer membranes.Three parts were studied in this thesis:?1?SPEEKs with different sulfonation degree were synthesized,and ZIF-8 particles were mixed with SPEEK to prepare ZIF-8-SPEEK materials.Ion exchange capacity and water swelling degree of ZIF-8-SPEEK materials were tested,and the influence of ZIF-8 on hydrophilicity of materials was analyzed.The interaction mechanism between ZIF-8 and SPEEK was analyzed by infrared spectroscopy and thermogravimetry.?2?ZIF-8-SPEEK/PES composite membranes were prepared by coating method.The morphological characteristics of the composite membranes were observed and the nanofiltration performance was tested.The effect of ZIF-8 on the nanofiltration performance of ZIF-8-SPEEK/PES composite membranes was analyzed,and the separation mechanism of the composite membranes was studied.?3?Dense SPEEK/PES composite films were prepared by coating method.By testing the pervaporation desalination performance of the composite membranes,the effects of the microstructure,solution composition and temperature of the composite membranes on the pervaporation desalination performance were analyzed.The main conclusions are as follows:?1?The ion exchange capacity and hydrophilicity of SPEEK increase with the increase of sulfonation degree.ZIF-8 improves the thermal stability of SPEEK materials and reduces the ion exchange capacity of SPEEK.With the increase of ZIF-8 loading,the hydrophilicity and swelling degree of ZIF-8-SPEEK composites decrease.It is concluded that the Zn²⁺in ZIF-8 molecule interact with the sulfonic groups of SPEEK.?2?ZIF-8 improves the nanofiltration performance of SPEEK/PES composite membranes.ZIF-8-SPEEK/PES composite membranes prepared by SPEEK with low sulfonation degree had higher rejection rate than those prepared by SPEEK with high sulfonation degree.The retention of composite membranes increased with the increase of ZIF-8 loading.The retentions of Na Cl and Mg SO₄ by composite membranes are low,but those of methyl orange,congo red,methylene blue and polyethylene glycol 1000 are high.It is concluded that the separation mechanism of composite membranes is the result of the combined effect of Donnan effect and sieving effect.The flux and retention of ZIF-8-SPEEK/PES composite membranes remained stable after 100 hours test,which indicated that ZIF-8-SPEEK/PES composite membranes had good stability.?3?SPEEK has good hydrophilicity,and the dense SPEEK/PES composite membrane has the potential of pervaporation desalination.The microstructures of the composite membranes,the composition of the feed solution and the pervaporation temperature have great effects on the desalination performance of the composite membranes.Using 61%sulfonation degree SPEEK as material and with twice coating of 0.5wt%SPEEK methanol solution,the SPEEK/PES composite membrane has the best desalination performance.The retention of Na Cl was 99.99%and the flux was 6.0 L/?m²*h?using 50 g/L Na Cl solution as feed at 70?0.7 bar.In general,ZIF-8 and SPEEK sulfonates interact well.By changing the microstructure of the composite membrane,the composite membrane has different separation properties.ZIF-8-SPEEK/PES composite membrane has high rejection rate and can be used in nanofiltration.Dense SPEEK/PES composite membranes have good pervaporation performance and can be used in desalination.