Research On Surface Wetting Modification And Oil-Water Separation Of Cotton Fibers And Polyacrylonitrile Electrospun Nanofibers

Water is one of the precious non-renewable resources in nature.However,the scale of oil-water mixture produced by industrial production and daily life continues to increase,which poses a great threat to the ecological environment and human health.The effective separation of oil-water mixtures has become an urgent challenge for scientists.The research on separation of oily wastewater(especially for water/oil emulsion)has important scientific significance and social value.Cotton fabrics can provide micro-roughness owing to its ready-made fibers,furthermore,its natural porosity can ensure the free passage of liquid,as well as it can be degraded.Thus,in recent years,it has been widely employed in oil-water separation of free oil with a particle size over 150 ?m.Electrospinning nanofibrous membranes exhibit advantages of high porosity,large specific surface area,continuous intercommunication channels,controllable morphology and wettability,enabling it can be applied in separation of oil/water emulsions with droplet size < 20 ?m.In this dissertation,nanocomposite films which can be used to separate free oil and oil in water emulsion were prepared by chemical impregnation method,based on cotton fabric and electrospinning nanofibrous membranes.And some meaningful conclusions were obtained.The main research contents are as follows:(1)Preparation and characterization of degradable and durable fluorine-free superhydrophobic cotton fabric for oil-water separationA simple and mild low-cost method for fabricating fluoride-free super-hydrophobic cotton fabricsis presented.The two-step method involves the decoration of the cotton fabrics by Zn O nano-rods to construct rough surface and the grafting of low surface energy stearic acid(SA)onto the as-decorated cotton fabrics via an immersion route.The as-prepared Zn O/SA modified cotton fabrics were characterized by X-ray powder diffraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM)and Fourier transform infrared spectroscopy(FTIR).The wetting behavior of coffee,milk,tea,water dyed by methylene blue,strong acid(HCl),strong alkali(Na OH),and saturated salt solution(Na Cl)on the Zn O/SA modified cotton fabrics was evaluated with a contact angle tester,and the durability of the Zn O/SA modified cotton fabrics in corrosive liquids and under ultraviolet(UV)irradiation was tested.In addition,the oil/water separation efficiency of the Zn O/SA modified cotton fabrics towards the oil/water mixed solutions of n-hexane,liquid paraffin,dichloromethane,chloroform and motor oil with different density and viscosity was investigated;and their degradation rate under harsh conditions(e.g.,immersion in acid and alkali or exposure to UV irradiation)was calculated.Results demonstrate that Zn O and SA are chemically bonded onto the surface of cotton fabrics to achieve super-hydrophobicity.The as-prepared Zn O/SA modified cotton fabrics exhibit a water contact angle of over 164°;and they retain the super-hydrophobicity after immersion in acid and alkali solutions or under UV irradiation.Besides,they have an oil/water separation efficiency of over 96.5% for all the tested liquids as well as a biodegradability rate of 59.0% after immersion in phosphate buffer saline solution containing cellulase(p H = 4.8)for 15 days.(2)Preparation of PDA@PAN electrospinning nanofibrous membranes and its application on oil/water emulsion separationThe effective separation of oil/water emulsion,which contain droplets with a mean size smallerthan 20 ?m,has become a focus and challenging task for current studies.It is difficult for cotton fabrics employed herein,due to its relatively large hole sizes.Thus,in this chapter,polyacrylonitrile(PAN)nanofibers was prepared through electrospinning method.Subsequently,poly dopamine(PDA)nanoclusters was in-situ formed and deposited on the surface of PAN nanofibers by controlling the reaction conditions of auto polymerization,and the final product of PDA@PAN electrospinning nanofibrous membranes was obtained.The morphology and structure of the as-prepared PDA@PAN films were characterized by various techniques such as SEM,EDX,XPS,and FTIR.A total organic carbon(TOC)tester was performed to analyses TOC values of emulsion and filtrate for the investigation of separation efficiency.The results demonstrate that the as-fabricated PDA@PAN electrospinning nanofibrous membranes have superhydrophilicity and underwater superoleophobicity,and exhibit good separation ability for several oil/water emulsion including hexane,dodecane,and hexadecane.Furthermore,the flow flux does not decrease obviously,and the TOC of filtrate does not increase significantly,even after 10 separation cycles,indicating that the membranes processes good reusability.(3)Preparation of TA-APTES@PAN electrospinning nanofibrous membranes and its application on oil/water emulsion separationIn order to resolve the problem of low coating density of PDA on PAN nanofibers,in this chapter,tannic acid(TA)was selected to serve as a modification agent.The pyrocatechol in TA can be reacted with the hydrolysate of 3-amino-propyltriethoxysilane(APTES),in the manner of Michael addition and Schiff base reaction.As a result,TA-APTES nanospheres was formed and filled in the surface of PAN nanofibers and holes between fibers.The results confirm that the film has super-hydrophilic-oleophobic properties and excellent separation performance for oil-in-water emulsions.By compared with PDA@PAN membranes,both flow flux and separation efficiency are improved,which may be attributed to the high density of coating deposition.The test of relation curves of flow flux and TOC via separation recycle times also demonstrate that the as-prepared TA-APTES@PAN electrospinning nanofibrous membranes have excellent repeated utility.It's also found that this film also has removing ability for organic dyestuff from its water solution,for example,methylene blue.(4)Preparation of GA-APTES@PAN electrospinning nanofibrous membranes and its application on oil/water emulsion separationDifferent from pyrocatechol in TA,in this chapter,gallic acid(GA)was employed modification agent due to the presence of pyrogallol groups in its molecule,for the aim of improving the membranes' superhydrophilicity and the binding strength of modification agent on the substrate.The experiments of structure characterization,emulsion separation,and removing of organic dyestuff were performed against the as-prepared GA-APTES@PAN electrospinning nanofibrous membranes.The results demonstrate that this film exhibit superior separation activities,repeated utility and removing ability,for oil/water emulsion and organic dyestuff,respectively.