The Preparation Of Carbon Nanofiber Membrane And The Study Of Water Treatment And Separation Performance

Water is the most necessary resource for life,and its safety and availability are tightly linked to public health,economic development,and global sustainability.Although water and wastewater treatment experienced transformative improvement in the 21^thcentury,with the growing quantity and number of contaminants released to the environment and the rising demand for high quality water,the need of new water treatment technologies is becoming increasingly urgent.Catalytic membrane has been demonstrated to be effective in remove water contaminants,bearing multiple benefits including low energy cost,high catalytic efficiency,easy operation,and no secondary pollution.Electrospinning is a commonly used method for membrane fabrication.The electrospun polymeric nanofiber membranes have high porosity and large surface-to-volume ratio,and therefore can effectively retain or catalytically convert contaminants and enable gravity-driven membrane filtration that requires significantly less energy.Owing to these advantages,nanofiber membranes have been extensively explored in treating wastewater in recent years.However,in spite of their great performance in water systems,the application of nanofiber membranes in acidic,alkaline solutions or organic solvents remains an issue because of their poor stability under those harsh conditions.Recently,nitrogen-doped carbon nanomaterials were found to be resistant to organic solvents and solutions with extreme p H values,along with other valuable properties such as easy preparation,fast electron transfer rate,high adsorption capacity,and good catalytic capability,thus offering a promising platform to solve the stability issue of polymeric nanofiber membranes and expand their applications in liquid purification.In this study,we fabricated a nitrogen-doped carbon nanofiber（cPAN）membrane through carbonizing a polyacrylonitrile（PAN）nanofiber membrane at high temperature.Taking advantage of the reducing power of carbon,MnO₂nanoparticles（MnO₂）that are capable of catalyzing the decomposition of hydrogen peroxide（H₂O₂）,were subsequently in situ loaded on the cPAN membrane,which the pores size of the cPAN is about 1.7μm and the flux of the cPAN is about 5.7×10⁴L m^-2h^-1bar^-1.Due to the high porosity of cPAN and the catalytic property of MnO₂,we achieved efficient removal of organic contaminants and separation of oil and water emulsion in both water and organic solvent systems,the flux can keep about4.3×10⁴L m^-2h^-1bar^-1.Our study opens new avenues for cPAN membranes in water treatment and liquid purification.（1）Through Fenton-like reactions,MnO₂catalyzed the decomposition of H₂O₂to reactive oxygen radicals,which mediated the degradation and mineralization of water-based dyes[methylene blue（MB）and rhodamine B（Rh B）].In addition,owing to the excellent stability of MnO₂loaded cPAN membrane,it was able to catalyze the reversible oxidation and reduction reactions of MB and Rh B in dimethyl sulfoxide（DMSO）.Hydroxyl radicals generated from H₂O₂decomposition exhibited strong oxidation power and high efficiency in the above reactions.The cPAN membrane prepared in this study were resistant to extreme p H and organic solvents,which stands as a new application of catalytic membranes.（2）Even though cPAN membrane displays numerous oxygen-containing functional groups on the surface and has high hydrophilicity,it still experienced serious fouling during oil/water separation and showed sharp decrease in permeability after 10-minute operation.In this study,we demonstrated that the MnO₂doped membrane actively removed fouling agents through the hydrophobic interaction between the surface-retained oil and bubbles in situ generated from MnO₂-mediated H₂O₂decomposition.The results showed that,with in situ bubble generation,the cPAN membrane exhibited negligible permeability decrease in 60minutes,suggesting excellent fouling resistance of this new nanofiber membrane.