Ultrasonic Preparation And Physical Characterization Of Doped Binary Metal Oxides Nanoparticles

A great number of types of nano binary oxides have outstangding physical properties and extensive application prospects,e.g.,Nd-doped TiO₂ nanoparticles have been considerd to be used as a new type photocatalyst in the reaction of deep oxidation of organic pollutants;application of Cd-doped ZnO nano-materials in the fabrication of optoelectronic devices（laser devices,photodiodes,and so on）;in the short wavelength（400-500 nm）region,Co-doped Fe3O₄ nana-material has strong magneto-optical Kerr effect,which means it is a excellent material to fabricate high density memory,such as computer hard disk device.In this paper,the preparation method to prepare these nano-materials is sonochemical method.The extremely high temperature and high pressure of the cavitation effect is helpful to make some difficult reaction easier to react.In our work,we have prepared some high doping concentration samples which are hard to dope by using traditional method.For these materials,control of the preparation conditions and changes in doping concentrations will strongly affect the physical properties.For example,in Nd-doped TiO₂,different annealing temperatures will lead to a shrink or expansion of the crystal lattice,which influence the optical properties of TiO₂.High concentration of Cd doping will greatly narrow the band gap of ZnO nanoparticles,and significantly enhanced its intrinsic defect luminescence.So studying how the control of the preparation conditions and changes in doping concentrations affect the physical properties of nano binary oxides,has an important meaning for optimizing performance of nano-materials and expanding its application fields.This thesis mainly discusses preparing above mentioned nano binary oxides by using sonochemical method,and analyzing the crystal structure and physical properties by means of transmission electron microscope（TEM）,X-ray diffraction（XRD）,UV-Vis absorption spectroscopy,Raman spectroscopy and photoluminescence spectra.Based on these,this thesis contains three parts:Part Ⅰ:Nd-doped TiO₂ nanoparticles are prepared by sonochemical method.The lattice distortion in samples with various grain sizes D in the range 5-68nm are investigated by means of x-ray diffraction（XRD）and Raman spectroscopy.The anatase phase is found to dominate all the samples below 54nm.With decreasing D,a significant lattice distortion takes place,which changes with the grain size,that is,lattice parameter c firstly shrinks and then expands while a shows a continuous shrink.We ascribe the change of the lattice distortion to the different depositions of Nd ions on the TiO₂ surface.Part Ⅱ:For the first time,a sonochemical method has been used to synthesize CdxZn1-xO（x = 0,0.05,0.15 and 0.40）nanoparticles.By XRD investigation,we have found that CdxZn1-xO nanoparticles can keep the wurtzite structure with increasing x up to 0.40,which indicates the stability of the CdxZn1-xO nanoparticles synthesized by the sonochemical method.In the wurtzite structure,the lattice parameters gradually increase with increasing x.The findings of the Raman investigation are consistent with the XRD results.We also observed Cd-doping induced red-shifts of the band gap and a near band-edge（NBE）emission band for CdxZn1-xO nanoparticles.In addition,we observed broad photoluminescence（PL）around 590 nm,which increases with increasing x up to 0.15 and decreases when the x-value further increases to 0.40.Simultaneously,a weak PL band seems to appear around 450 nm.The variation of the PL bands has been ascribed to the change of the defect states induced by Cd-doping and the nonradiative energy transfers.Part Ⅲ:Trough ultrasonic generator and probe ultrasound generator were used to prepare lanthanides（Eu,Nd and La）-doped ZnO.In sonochemistry,because the trough ultrasonic generator is significantly worse than the probe ultrasonic generator,doping ions were adsorbed on the surface of the particles and did not cause significant changes in the physical properties of ZnO.In samples prepared by ultrasonic probe:（1）in UV-Vis absorption spectroscopy,it is found that lanthanide doping can reduce the band gap of ZnO,the band gap is smaller with the doping ions with larger radius,which is due to different tensile stress caused by the different radius of ions;（2）Raman spectra indicates lanthanide doping make the move of the E2 mode to lower wavenumber.Larger ion mass will make more moving wave number.Ion mass affects the molecular rotation and vibration influential;（3）in photoluminescence spectrum,wavelength of defect emission of ZnO show red shift as a result of lanthanide doping,and Eu3+ ions doping can effectively extend the 620 nm luminescence decay time,which has a significant role to strengthen the potential applications of lanthanide ions doped ZnO materials.Part Ⅳ:Co-doped ferrite（CoxFe3-xO₄）nanoparticles are investigated.In absorption spectra,as the x increases,transfer from O₂-ions to Fe²⁺ ions decreases and the transfer between O₂-ions and Co²⁺ ions increases.Raman spectra shows hardening of two peaks,which is a result of Fe²⁺-O₂-bond is longer than Co²⁺-O₂-bond.Finally we analyze theoretically the relationship between occupying tendency of doping Co ions and magnetic property of Co-doped ferrite.