Investigation On The Preparation And Performance Of Several Metal Oxide Fibers

One dimensional nanomaterials have obvious advantages over other nanomaterials,such as large aspect ratio,anisotropy,large specific surface area,electronically oriented transport and so on.One dimensional nanomaterials have been widely used in many fields,such as catalyst,electrode,supercapacitor,superhard composite material,sensor and so on.Therefore,it is a very important work to investigate the preparation,morphology,structure,composition and property of one-dimensional nanomaterials.Metal oxide fiber is a compound fiber formed by the combination of a metal element and oxygen element.In addition to several inactive noble metals,other metals can form the corresponding oxides,such as NiO,TiO2,ZrO2,Co3O4 and so on.The metal oxides have been extensively studied because of their excellent electrical,optical,thermal,mechanical,magnetic and acoustic properties.Each kind of oxide structure is different,leading to their own unique property,so that the application is also very different.The methods for preparing one dimensional nanomaterials are usually hydrothermal,template,solvothermal,electrospinning,centrifugal spinning and the like.The electrospinning method is an emerging method for preparing a fibrous material in recent years.Nanofibers with different morphologies and diameters can be obtained by adjusting sol properties,process parameters and environmental conditions.The centrifugal spinning is simple,high-yield and easy to achieve mass preparation of fibers.The property of a material is related to not only its structure,but also the composition,crystallization state and other factors.Ti02 is a common photocatalytic material.Its photocatalytic activity is limited by the wide bandgap and fast recombination rate of photogenerated carriers.Zr02 is a very important ultra-high temperature insulation material and is required a high mechanical strength and a low thermal conductivity,which is in connection with the crystal form,crystallinity,grain size and so on.There is little report on the investigation of NiO and Co3O4 fibers,even less about mass preparation of both the fibers.In this paper,several kinds of oxide fibers were prepared by electrospinning or centrifugal spinning.The problems of each fiber were further optimized respectively.The study is of great significance for the theoretical significance and application value of oxide fibers.The main contents of the thesis are as follows:1.Preparation and photocatalytic performance of the TiO2 composite fibersThe nanofibers with uniform diameter were obtained by electrospinning.The diameter of the fibers was about 500 nm.The gold nanospheres with diameter of 16 nm were obtained by Turkevich method,and were deposited on the TiO2 fibers by ligand exchange.The results of SEM and TEM show that the gold nanoparticles in the Au/TiO2 composite fibers are uniformly distributed on the surface.The composite fibers with different sizes of gold nanoparticles(6 nm and 30 nm)can be prepared by the same method.The photocatalytic activity of Au1/TiO2 composite fibers was higher than that of P25 and pure TiO2 fibers.The degradation rate of Au1/TiO2 composite fibers was up to 90%after 40 minutes under ultraviolet and visible light irradiation.The photocatalytic activities of Au/Ti02 composite fibers with different gold contents were compared,indicating that the photocatalytic activities increased with the increase of the Au content,while descended when the content exceeded 1%.Under the irradiation of ultraviolet light and visible light,the photocatalytic effect of composite fibers was the best when the content of gold was 1%.The photocatalytic mechanism was studied by ultraviolet and visible diffuse reflectance spectroscopy,photoluminescence spectroscopy and photocurrent spectra of Au/TiO2 composite fibers with different gold contents.The results show that under the irradiation of UV light,the photogenerated electrons are effectively separated by transferring from the conduction band of TiO2 to the energy band of Au nanoparticles.Under the visible light irradiation,gold nanoparticles can absorb visible light due to the surface plasmon resonance effect.The excited hot electron transfer to the Ti02 conduction band to participate in the photocatalytic reaction,utilizing the visible light effectively.When the Au content is excessive,it may be act as a composite center,and covers the TiO2 surface,so the photocatalytic effect of composite fibers decreased.In addition,g-C3N4 nanosheets were prepared and the lamellar structure and composition were confirmed by SEM,TEM,FT-IR and XRD.G-C3N4/TiO2 composite fibers were prepared by deposition method.The photocatalytic degradation of methyl orange was carried out.The results showed that the composite fibers had a good photocatalytic activity under visible light.Moreover,the mechanism of photocatalysis is also discussed.Photogenerated electrons excited on g-C3N4 can be transferred to the TiO2 conduction band,which are effectively separated and more efficiently participate in the photocatalytic reaction.2.Preparation,high pressure water vapor treatment and high temperature structure of ZrO2 fibersThe ZrO2 precursor fibers were obtained by sol-gel and electrospinning,and then were subjected to a high pressure water vapor treatment.After the treatment,the internal organic matter of fibers can be almost completely removed,and the fibers can be crystallized to form polycrystalline fibers composed of small grains at a lower temperature.The effect of directly high pressure water vapor treatment of precursor fibers is not good,because the solvent content is too much in the precursor.It is the best when the precursor fibers pretreated at 300 ℃ for 2 h and then treated with high pressure water vapor.The effects of temperature,water and holding time on the treatment of high pressure water vapor were studied.When the temperature is low,the effect is not obvious.When the temperature is 300 ℃ or 400 ℃,organic matter can be removed more fully.The difference in holding time(2 h,5 h and 10 h)has no significant effect on the effect of high pressure water vapor treatment.Water plays an important role in the treatment of high pressure water vapor,which can provide vapor pressure in the closed system and promote the crystallization of the precursor.The optimal condition is 400 ℃,holding 2 h incubation,and 30%water.In addition,we also studied the properties of the fibers after sintering at high temperatures.The grains of high pressure water vapor treated fibers after sintering at 1000 ℃ were significantly reduced compared to that of untreated samples.With the sintering temperature increases,the grain grows.When the temperature rises above 1400 ℃,the grain grows abnormally.3.Preparation and performance of NiO and Co3O4 fibersNiO and Co3O4 micrometer fibers were prepared by sol-gel method and centrifugal spinning.The fibers diameters were about 10 μm.Citric acid was used as a ligand to prepare the corresponding precursor sol.It was found that the ratio of nickel salt or cobalt salt to citric acid has an important effect on the spinnability of the precursor sol.When the ratio was 1.5,the spinnability is the best.The evolutions of the precursor fibers at different heat treatment temperatures were analyzed by TG-DSC,FT-IR and XRD.It was found that the precursors had been subjected to removal of absorbed water,decomposition of organic matter and crystallization of the oxides.TEM and Raman analyses confirmed the compositions of the fibers.According to the SEM,the compositions and microstructures of the fibers were confirmed.The results show that the final NiO fibers are solid,and CO3O4 fibers are hollow.The hysteresis loops of the two fibers were measured.Both the NiO and CO3O4 fibers have weak ferromagnetism,which are different from antiferromagnetic bulk materials.As the heat treatment temperature increases,both the magnetic saturation and the coercivity reduced.NiO fibers also exhibit a excellent photocatalytic activity for Congo red.In addition,porous NiO/Co3O4 composite fibers were prepared by a similar method,also proved to have certain ferromagnetism.In this paper,TiO2 and ZrO2 fibers were prepared by electrospinning.NiO and Co3O4 fibers were prepared by centrifugal spinning.On this basis,the performances of the fibers were further optimized.The photocatalytic performance of the TiO2 fibers was enhanced by the uniformly loading Au nanoparticles on the surface.The effect of Au dosages on the photocatalytic activity of composite fibers was discussed.G-C3N4/TiO2 composite fibers were prepared and their photocatalytic properties were investigated under visible light.The ZrO2 precursor fibers are subjected to high pressure water vapor treatment.The internal organic matter of fibers can be almost completely removed,and the fibers can be crystallized to form polycrystalline fibers composed of small grains at a lower temperatures.The NiO and Co3O4 fibers were prepared by centrifugal spinning using citric acid as ligand.The magnetic and photocatalytic properties of NiO and Co3O4 were discussed.