Study On Controllable Preparations And Properties Of The Nanostructured Cerium Oxide And Zinc Oxide

In order to improve the performance of the single metal oxide,a variety of methods are used to prepare nanostructured metal oxide and this purpose is achieved by the means of doping,composite and surface modification.The author has improved the performance of single metal oxide ZnO or CeO₂,because these nanostructures including ZnO nanoparticles-CeO₂nanorods heterostructure,CeO₂/ZnO shell-core nanostructure,Ce doped ZnO nanoparticles-rods mixed structure of and ZnWO₄ nanorods-nanosheets hybrid structure are synthesized by simple one-pot hydrothermal method with easy operation,low cost and mild synthetic conditions and without any template and surfactant.The nanostructures are characterizated by these modern material research methods of XRD,SEM,EDS,TEM,XPS,BET and so on.The research works are mainly carried out in the several aspects of dumbbelled ZnO-CeO₂nano heterostructure for charge storage,humidity sensitive mechanism of Ce doped ZnO nanoparticles-rods hybrid structure,optical properties of CeO₂/ZnO shell-core nanostructure,and nano-structured Zn WO₄,the main conclusions are drawn in the following:（1）The dumbbell ZnO-CeO₂ heterostructure is designed and fabricated,the formation mechanism of the heterostructure is illuminated.The heterostructure is made up of ZnO particles（ZnONPs）and CeO₂ nanorods（CeO₂NRs）single crystal,and ZnO grain dispersed evenly on the surface of the dumbbell clusters composed of CeO₂ grains.ZnONPs-CeO₂NRs nanoheterostructure has a larger BET specific surface area which with a specific surface area of 28.455m²g^-1 is larger than CeO₂NRs specific surface area of 21.567m²g^-1.The super capacitor built by Zn ONPs-CeO₂NRs nanoheterostructure as electrode material shows higher the specific capacitance of 162.08mFg^-1 than 151.43mFg^-1 of CeO₂NRs precursor in the course of constant current charge/discharge.The charge storage of ZnONPs-CeO₂NRs heterostructured super capacitor is 581.39Fg^-1,which is 12 times higher than 46.63Fg^-1 of CeO₂NRs.The improved property of the charge storage is due to the fact that the increased conductivity of CeO₂NRs and the change in their surface morphology and structure when ZnONPs are deposited on the surface of the CeO₂NRs.ZnONPs-CeO₂NRs electrode capacitance retained 87.1%of the initial capacity 581.39Fg^-1,and CeO₂NRs electrode capacitance retain 70.0%of the initial capacity 46.63Fg^-1,ZnONPs-CeO₂ NRs electrode has better cycle stability than CeO₂NRs electrode.The super capacitor assembled by ZnONPs-CeO₂NRs nanoheterostructure exists simultaneously the reversible Faraday effect and irreversible electrostatic effect of non-Faraday effect,which contributes synchronously to the charge storage of the assembled super capacitor to improve the charge storage capacity.（2）Precursors of CeCO₃OH and Zn₅（CO₃）₂（OH）₆ are synthesized directly in a pot of mixed aqueous solution of cerium nitrate and zinc acetate and urea without additional surface active agent when the Ce/Zn mole ratio is changed.The synthesized precursors of formed are converted into the corresponding metal oxides by pyrolysis forming two phases CeO₂/Zn O shell-core heterostructure where CeO₂ grains wrap well the surface of the ZnO grains.The formation mechanism of CeO₂/ZnO heterostructure is proposed.Different Ce/Zn mole ratios affect the heterostructure performances of fluorescence emission and ultraviolet absorption.With the increase of Ce/Zn mole ratio,Ce O₂/ZnO shows the intense fluorescence emission and visible light transmittance,the weaker ultraviolet absorption.These results are due to the fact that CeO₂/ZnO optical band gap is reduced from 3.25eV to 3.08eV when the Ce/Zn mole ratio is increased from 0 to 0.08.On the base of the comprehensive analysis of the optical properties for CeO₂/Zn O heteronanostructure with different Ce/Zn mole ratios,ZnO/CeO₂-0.04 heteronanostructure has the double properties of high ultraviolet absorption and visible light transmittance.ZnO/CeO₂-0.04 heteronanostructured composite powder is adapted to become a skin care cosmetic.（3）The humidity sensor is set up by the ZnO particles-rods hybrid structure as sensitive material,which is prepared at low temperature by free-template one-pot hydrothermal method without any surfactant.Ce doping content affects the morphology and crystallinity of ZnO hybrid nanostructure,which provides important information for the manufacture of the humidity sensor.The humidity sensitive mechanism is studied via electrochemical impedance spectroscopy.5%Ce doped ZnO nanostructure is composed of the average length of 125nm ZnO nanorods and a large number of tiny particles,there are many hole clearance in the hybrid structure.The impedance changes of Ce doped ZnO nanostructure depends on adsorption of moisture on its activated surface,the more positions of surface adsorption,the better humidity sensitivity of the sensor.The optimal operating frequency is 100Hz for Ce doped ZnO particles-rods hybrid nanostructures.5%Ce doped ZnO nanostructure shows the average sensitivity of 44030.80 and its rapid response time and recovery time are 25s and 19s respectively in the entire range of 11-95%RH.Enhanced chemical adsorption causes the enhancement of electron conduction ability,enhanced physical adsorption results in the enhancement of H₃O⁺and ionic conductive ability.The humidity sensing mechanism of Ce doped ZnO nanostructure owns both transmission mechanisms,which are decomposition water electronic conductance at low humidity adsorption and ionic polarization conductance at high humidity.The wide detection range and high sensitivity of Ce doped Zn O nanostructured resistance-type humidity sensor shows that Ce doped ZnO is a kind of promising humidity sensing material.（4）ZnWO₄ nanorods and nanosheets can be synthesized by controlling the solution pH value and being Zn（CH₃COO）₂·2H₂O and Na₂WO₄·2H₂O as tungsten and zinc sources,respectively.With the increase of solution pH,ZnWO₄ nanorods have evolved into ZnWO₄ nanosheets.Compared with ZnWO₄ nanosheets,ZnWO₄ nanorods own good crystallinity and less oxygen vacancy defects.It is illustrated for the nanostructured ZnWO₄ that the correlations between their structural characteristics and optical properties as well as the correlations between the spectra.The fluorescence spectrum has an intimate connection with ultraviolet visible light spectrum for ZnWO₄ nanorods.The fluorescence emission and UV-Vis transmission spectra of ZnWO₄ nanorods are enhanced while the fluorescence excitation and ultraviolet absorption are reduced in the wavelength range of 250-325nm.The inverse results are obtained in the wavelength scope of 325-400nm.With the increase of pH value,the intensity of fluorescence emission is raised,the intensity of fluorescence excitation is abated and the recombination probability of electron-hole become low.Absorption spectra complement transmission ones each other while absorption spectra are closely related to the transport of light induced electron-hole pairs.Zn WO₄ nanorods absorbs selectively ultraviolet light in the wavelength range of 325-400nm and own low recombination probability of light induced electron-hole pairs,which imply they are suitable for photo-catalytic materials for their good photo-catalytic activity.At the same time,there exists intrinsic relevance between the fluorescence spectra and absorption spectra.