Preparation Of Dopamine Carbon Nanotubes Composite Nanofiltration Membrane And Treatment Of Simulated Dyes Wastewater

At present,the preparation of composite membranes by modifying inorganic nanoparticles has attracted much attention.Among all kinds of nanomaterials,carbon nanotubes have become the research hotspot in recent years because of their excellent mechanical,electrical and thermodynamic properties.Applying carbon nanotubes to modified nanofiltration membrane can combine the excellent properties of membrane materials and carbon nanotubes,improve the performance of nanofiltration membrane,and expand its application scope in the field of water treatment.In this paper,carbon nanotubes as the basic research material,dopamine as the auxiliary material,the preparation of modified materials,and then to prepare modified nanofiltration membrane.The proportion of casting solution in ultrafiltration base membrane was optimized,and the optimal deposition time of aqueous and organic phases in nanofiltration membrane was studied.The optimum addition amount of modified material and the influence of experimental pressure and temperature on the performance of nanofiltration membrane were analyzed.In addition,the nanofiltration membrane was characterized by X-ray photoelectron spectroscopy(XPS),scanning electron microscopy(SEM),atomic force microscopy(AFM),Fourier transform infrared spectroscopy(FTIR)and water contact Angle.Finally,the treatment effect of nanofiltration membrane in simulated dye wastewater was investigated.The optimal feed concentration of dye wastewater and the interception performance of nanofiltration membrane for four simulated dye wastewater were further investigated.The experimental results are as follows:(1)Preparation of ultrafiltration base membrane.Two kinds of ultrafiltration membranes were prepared by immersion precipitation phase conversion method.By comparing the permeability of ultrafiltration membrane and scanning electron microscope analysis,it is confirmed that the ultrafiltration membrane prepared under the composition ratio of 17 wt%PSF,8 wt%PVP and 7wt%PEG has better performance.Under the operating conditions of 0.1 MPa,the pure water flux of the ultrafiltration base membrane is 210.24 L/(m~2·h),and the filtration BSA solution flux and rejection rate are 59.28 L/(m~2·h)and 98%,respectively.(2)Preparation of modified carbon nanotubes.Dopamine was inserted into carbon nanotubes to prepare dopamine-carbon nanotubes(DA-CNTs)materials to improve the dispersion of carbon nanotubes in aqueous solution.Through Fourier infrared spectroscopy,transmission electron microscopy and Raman spectroscopy,it was confirmed that dopamine coated carbon nanotubes successfully,and hydrophilic functional groups such as hydroxyl groups increased.By comparing the dispersion of CNTs in aqueous solution before and after modification,it was found that the dispersion of the modified CNTs was obviously better than that of the unmodified CNTs.(3)DA-CNTs modified nanofiltration membranes were prepared by interfacial polymerization.The effect of deposition time of aqueous and organic phases on the properties of nanofiltration membrane was investigated by single factor experiment.The nanofiltration membrane prepared by water deposition time of 120 s and organic deposition time of 80s has the best performance.The modified nanofiltration membrane was prepared under these conditions,and DA-CNTs were introduced into the polypiperazinamide nanofiltration membrane as aqueous phase additive.The effects of different concentrations of DA-CNTs in aqueous phase solution on the structure and performance of the nanofiltration membrane were studied.Through XPS and FTIR analysis,it was proved that DA-CNTs were effectively deposited on the surface of the nanofiltration membrane,and the modified nanofiltration membrane contained significantly more carboxyl groups and hydroxyl groups,and the oxygen content was also significantly higher than that of the unmodified nanofiltration membrane.By SEM,AFM and contact Angle,it was observed that when the concentration of DA-CNTs was0.25wt%,the film surface was smooth,the roughness was low and the hydrophilic effect was the best.According to the membrane selective permeability test,the flux and rejection rate of the 0.25wt%DA-CNTs nanofiltration membrane are the highest.Under the optimal operating pressure of 0.8MPa and operating temperature of 40℃,the rejection rate of 0.25wt%DA-CNTs nanofiltration membrane for monovalent salt is 45%and that for bivalent salt is 89%.(4)Treatment of simulated dye wastewater with modified nanofiltration membrane.Four kinds of simulated dye wastewater were selected as the research object.When the dye feed concentration was 100mg/L,the nanofiltration membrane treatment effect was the best.Under the conditions of 40℃,0.8 MPa and 100mg/L feed concentration,the results of the treatment of four dyes by modified nanofiltration membrane are methyl blue(99.3%)>Congo red(92%)>Crystal violet(71.7%)>Methyl orange(64.5%).Prolonging the time of 0.25wt%DA-CNTs nanofiltration membrane to treat methyl blue solution,the flux and rejection rate of methyl blue dye were stable at30 L/(m~2·h)and 99.7%after 3h.