| Nanofiltration membrane separation technology has been widely used in the fields of resource utilization of wastewater,separation and concentration of industrial fluids due to its special separation performance.Nowadays,the most commonly used nanofiltration membranes are the type of thin-film composite membrane with a selective of poly(piperazine amide).However,the major problems that limit the extensive application of polyamide based thin-film composite membrane are its relatively low separation efficiency and membrane fouling due to the physicochemical property of polyamide layer.Therefore,the improvements of water permeability and anti-fouling performance of poly(piperazine amide)thin-film composite membrane are of great significance.In this study,a novel modification method was proposed to incorporate zwitterionic moieties onto the poly(piperazine amide)membrane for simultaneous improvements of water permeability and anti-dye-deposition property.First,an excess of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride(EDC)was used to convert the carboxyl groups in the polyamide separation layer into N-acylurea,whose tertiary amine groups were then adopted to in situ generate zwitterions through the ring-open reaction with of 1,4-butane sultone.The physic-chemical properties of the membranes were characterized by Fourier transform infrared spectroscopy(ATR-FTIR),X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM)and zeta potentiometer.Cross-flow filtration experiments were performed to evaluate the separation performance and anti-dye-deposition property the membranes.The following conclusions were obtained:(1)Tertiary amination of poly(piperazine amide)thin-film composite membrane could be achieved through the treatment of excess EDC.XPS and ATR-FTIR analyses confirmed that excess EDC treatment of the polyamide nanofiltration composite membrane converted the carboxyl groups into N-acylurea containing tertiary amine groups.AFM analysis showed that tertiary amination did not affect the surface morphology of the membrane.Tertiary amination weakened the electro-negativity of membrane surface.After tertiary amination,the isoelectric point of membrane surface shifted from pH 3.5 to 4.3,membrane rejection to calcium chloride increased to 78.4%from 16.2%,while the permeability of the membrane to water remained unchanged.(2)Zwitterionic modification could be implemented through ring-open reaction between tertiary amine and sultone.XPS and ATR-FTIR characterizations confirmed the reaction between 1,4-butane sultone and tertiary amine group of N-acylurea and the generation of zwitterionic units containing quaternary amine and sulfonate.The content of zwitterionic unit could be adjusted by varying the concentration of 1,4-butane sultone.After zwitterionic modification using 0.1 g/mL 1,4-butane sultone,membrane pure water permeability increased from 9.66 L.m-2.h-1.bar-1 of virgin membrane to 13.97 L.m-2.h-1.bar-1,molecular weight cut-off slightly ascended from 300 Da of virgin membrane to 390 Da,and calcium chloride rejection increased from 16.2%of virgin membrane to 38.8%.(3)Zwitterionic modification could significantly improve the anti-dye-deposition property of polyamide nanofiltration membrane.To aqueous Congo red and Victoria blue B solutions,the permeability increased from 7.75 and 6.32 L.m-2.h-1bar-1 of virgin membrane to 12.62 and 12.40 L.m-2.h-1.bar-1 of zwitterionic membrane PA-EDC-BS-2,the flux decline ration decreased from 19.3 and 34.2%of virgin membrane to 10.6 and 12.2%of zwitterionic membrane PA-EDC-BS-2,and the physical flushing flux recovery ratio enhanced from 84.6 and 69.7%of virgin membrane to 91.3 and 94.4%of zwitterionic membrane PA-EDC-BS-2,respectively. |
PDF Full Text Request