Preparation Of Electrospun Composite Nanofibrous Membrane Based On Layer-By-Layer Self-Assembly And Its Water Purification Performance

In recent years,with the development of the world economy and the increase of population,the number of cities is also increasing and expanding.The issue of water resources has become one of the most concerned issues in the world at present.The shortage of water resources restricts the economic development and social activities of all countries in the world.Recycling of water resources is a significant measure of economic efficiency.Among them,the application of membrane technology in life and production is also increasingly prominent.Nanofiltration has the advantages of low operating pressure,low operating temperature,physical and chemical stability,and has been widely used in food industry,pharmaceutical,wastewater treatment and desalination.In this paper,natural graphite powder as raw material,graphite oxide prepared by the improved Hummers method.After centrifugation and purification,the graphene oxide（GO）was prepared by using an ultrasonic stripping dispersion in water.By SEM,XRD,Raman spectra,XPS,FT-IR and UV-vis characterization showed that the prepared GO surface was pleated.The d-spacing increased from 0.34 nm of natural graphite to 0.71 nm.The main functional groups were C-OH,C-O-C and C-COOH.The molar ratio of C to O was 2.64:1,which was consistent with the previously reported literature,which proved that GO was successfully prepared.The prepared GO has a good dispersibility in water and has an excellent linear relationship between absorbance and concentration at low concentrations.Polyamide 6（PA6）nanofibrous membrane were prepared by electrospinning as porou s support.PA6 nanofiber composite membrane were prepared by the Layer-by-Layer（LbL）method using chitosan（CTS）and GO as polyelectrolytes.The prepared PA6 nanofiber s have an average diameter of 122 nm.Through the optimization of the preparation proc ess,the rejection of Na⁺was 25.68%,the rejection of Mg²⁺was 33.07%and the flux was 2.74 L·h^-1·m^-2·bar^-1.The order of rejection for different inorganic salts was:K₂SO₄（37.39%）>MgCl₂（27.99%）>MgSO₄（23.75%）>NaCl（20.80%）>KCl（17.63%）.At different values of pH,the rejection of Mg²⁺by the composite membrane decreased with the increase of pH value.The retention of Mg²⁺is optimal at pH=3.The best using time of composite membrane was 20 h.The rejection effect of heavy metals is Co²⁺>Cu²⁺,and the rejectio n rates of Co²⁺and Cu²⁺were increased after regeneration.As the number of layers incr eased,the porosity of the composite film also increased.In the third layer,the porosity was 51.97%and the average pore size was 5.31 nm,all at higher levels in different lay ers.The composite membrane showed good anti-fouling ability in the anti-fouling test.