Research On The Performance Of PVDF Ultrafiltration And Nanofiltration Membranes Modified By MOF

In recent years,membrane technology has gradually become a popular separation technology due to its advantages such as simple operation and high effluent water quality.PVDF is one of the commonly used polymer organic membrane materials,which has the characteristics of good chemical resistance,high thermal stability,high mechanical strength,and good film forming properties,so it is widely used in the field of water treatment.However,due to the low surface energy and hydrophobicity of the PVDF membrane,there are two prominent problems in the use of the membrane,namely the membrane is easy to scale and the wettability is poor.Therefore,PVDF membranes still have limitations in the applications of ultrafiltration and nanofiltration.In the field of ultrafiltration,the hydrophobicity of PVDF membranes causes the membrane to easily adsorb organic pollutants such as proteins during the filtration process,which causes problems such as increased driving force required for the membrane and decreased water flux;in the field of nanofiltration,the hydrophobicity of the membrane causes interfacial polymerization process is difficult to perform on a PVDF support layer.Therefore,the emergence of metal-organic frameworks(MOFs)has attracted researchers' attention and applied it to PVDF membrane modification studies.Because,MOFs have excellent properties such as high porosity,regular pore channels,and many adsorption sites.The research content of this subject is to introduce MOFs into PVDF membranes through specific modification methods to make up for the defects of PVDF membranes and make them exhibit excellent membrane performance in the fields of ultrafiltration and nanofiltration.The specific research contents are as follows:(1)PVDF composite ultrafiltration membrane based on MOF-5Firstly,the MOF-5 crystal porous material with regular cube structure was synthesized by stirring at room temperature under mild conditions.Subsequently,MOF-5 was doped into PVDF casting solution by means of blending modification,and the casting solution was cast into a new type of MOF-5 /PVDF ultrafiltration membrane by means of immersed-precipitation phase transformation.The results of characterization test showed that the porosity of the MOF-5 /PVDF membrane increased significantly,with a maximum increase of about 20%,and the roughness value also decreased.In addition,the maximum pure water flux of the MOF-5 /PVDF membrane increased by 86.43%,the retention effect of the composition membrane on bovine serum protein(BSA)was also increased by 38.10%,and the anti-pollution performance evaluation of the composition membrane was also effectively improved,among which the recovery water flux increased by 38.36%.(2)PVDF composite nanofiltration membrane based on IRMOF-3IRMOF-3 crystalline porous material was synthesized by stirring at room temperature,and then the material was reacted with the cross-linking agent polyacrylic acid(PAA)under ultrasonic to dissolve and disperse it better in aqueous solution.Then,an aqueous solution of irmuf-3 /PAA was extracted from the PVDF supporting membrane,and the interlayer was present to form a more hydrophilic membrane surface.Finally,the composite nanofiltration membrane was successfully prepared by interfacial polymerization of m-phenylenediamine(MPD)and tribenzoyl chloride(TMC)on the membrane surface.The existence of IRMOF-3 /PAA interlayer directly affects the growth integrity of polyamide(PA)layer through the observation of SEM.