Fabrication Of Polyamide Nanofibrous Membranes For Filtration And Adsorption Applications

Currently,the discharge of wastewater containing organic components,dyes and other pollutants is one of the urgent problems need to be solved.The nanofibrous membranes prepared by electrostatic spinning technology have been widely used in the field of wastewater treatment.The pollutants such as nanoparticles,dyes and bisphenol A(BPA)can be removed by nanofibrous membrane with filtration and adsorption.However,low mechanical properties and large pore size of nanofibrous membranes limited the application in filtration of wastewater,while the adsorption efficiency is directly affected by the number of adsorption sites.Therefore,to obtain a kind of self-supporting membrane with good filtration-adsorption performance and high mechanical properties,the preparation,filtration performance,adsorption performance and separation mechanism of ultrafine polyamide-66(PA-66)nanofibrous membrane were carried out in this thesis.Ultrafine PA-66 nanofibrous membrane with a diameter of 79 ± 10 nm was prepared by a four-nozzle approach,through optimizing the concentration of PA-66 solution.The problems in mechanical properties,filtration properties and adsorption efficiency of the nanofibrous membrane are solved.The results from scanning electron microscopy(SEM)observation and capillary flow porometer measurements showed that the surface morphology and pore size distribution of the nanofibrous membrane were mainly affected by the concentration of PA-66 solution.The membranes exhibited remarkable mechanical properties,verified by tensile experiments,which could be used as a self-supporting membrane.Meanwhile,the water contact angle experiment shows that the electrospun nanofibrous membranes exhibit reasonable hydrophobic properties which will be benefit to water purification application.The filtration performance of the ultrafine PA-66 nanofibrous membrane against polystyrene nanoparticles and the adsorption performance of BPA were demonstrated.The adsorption kinetics,isotherm and thermodynamics against BPA were explored and the results showed that the maximum adsorption capacity of BPA on ultrafine PA-66 nanofibrous membrane was127.6 mg/g.Meanwhile,the membrane could be employed to remove both fine particulates and BPA from water,verified separately by filtration and dynamic adsorption performance.The results show that the membrane has high efficiency and selectivity,evidenced by the retentions against 200-and100-nm-particles were 99.8% and 21.1%,respectively.Moreover,dynamic experiments show that the separation efficiency of the membrane can be improved by decreasing the flow rate and increasing the thickness of nanofiber layers.Based on XPS,Fourier Transform Infrared Spectroscopy(ATR-FTIR),water contact angle experiment and adsorption results of different phenols,the adsorption mechanism of PA-66 nanofibrous membrane with BPA was proposed which mainly depended on hydrogen-bonding and hydrophobic interaction.The regeneration efficiency of the nanofibrous membrane reached87% after 14 cycles of static adsorption-desorption,indicating that the membrane can be continuously used for wastewater treatment.Ultrafine PA-66 nanofibrous membrane can also remove anion(metanil yellow)and cationic dye(chrysoidine)from wastewater.Again,kinetics,isotherm,and thermodynamics of the nanofibrous membrane against metanil yellow and chrysoidine were investigated,while high adsorption capacities of133.3 mg/g and 204.5 mg/g,respectively,were achieved.Meanwhile,the membrane also exhibited remarkable dynamic adsorption capability against metanil yellow,with the regeneration efficiency still reached 95% after 8cycles of dynamic adsorption-desorption,implying the reproducibility and robustness of the membrane in wastewater treatment.A multiple separation mechanism including both filtration and adsorption was proposed based on XPS,FTIR,SEM,and surface wettability measurement,where size exclusion and depth filtration mechanism are involved in the filtration of nanoparticles,and electrostatic interaction,hydrogen bonding,as well as hydrophobic interaction plays an important role for dye adsorption.The results show that the nanofibrous membrane is a good candidate membrane for multi-component wastewater treatment.A spiral wound filtration cartridge based on the membrane was fabricated,and a multicomponent wastewater containing dye mixture and nanoparticles were employed to challenge the membrane cartridge,which resulted in substantially high permeability and separation efficiency.