Effect Of Morphology And Surface Modification On Trap State Of TiO₂ Nanoparticles

TiO2 nanomaterials have shown great potential in photocatalysis and high-voltage insulation modification due to its excellent physical and chemical properties.It is found that the modification of nano-TiO2 is closely related to its morphology,size and surface state.Therefore,TiO2 nanoparticles,nanorods and nanotubes were prepared by controlling the reaction parameter,and the surface modification was carried out by reflux method and plasma method.The influence of morphology and modification state on the trap state of TiO2 were analyzed.TiO2 nanoparticles,nanorods and nanotubes were prepared by solvothermal method by adjusting the ratio of tetrabutyl titanate to surfactant.The crystal structure and morphology of the products were characterized by X-ray diffraction(XRD)and transmission electron microscopy(TEM).As a result,it was found that the obtained products were all anatase phase TiO2 and crystallized well.The irregularly spherical nanoparticles were obtained with average particle sizes of 5 nm,10 nm and 15 nm,respectively.The nanorods oriented along the[001]direction with the aspect ratio from 3.1-11.5 were achieved and the nanotubes with outer diameter of 7.5 nm and wall thickness of 2 nm were gotten.The surface modification was carried out by reflux method and plasma method using nanoarticles with diameter of 15 nm and without any modification on the surface as object.The surface modification state was characterized by Fourier transform infrared spectroscopy(FTIR)and the amount of surface modification was tested by thermogravimetric analysis(TG).It was found that the carboxylate ions were coordinated with titanium ions by means of double-tooth bridge.The amounts of surface modification is in the range of 4.2-6.0%by reflux method.The absorption peaks of C=C and C=O were not observed at the nanoparticles modified by plasma method.The acrylic acid undergoes breaking bond recombination under the action of plasma,and a polymer coating layer is formed on the surface of TiO2.The amount of surface modification the nanoparticle obtained by the plasma method is 3.5-6.7%.The types and concentrations of surface defects of TiO2 were characterized by X-ray photoelectron spectroscopy(XPS)and cyclic voltammetry(C-V),respectively.As a result,it was found that there were Ti3+ trap state and OH on TiO2.The nanoparticles with diameter of 15 nm unmodified have the highest concentration of Ti3+trap state and OH,the concentration of Ti3+trap state on the nanoparticles of 5 nm is higher than 10 nm modified by oleic acid.The Ti3+trap state on the surface of the nanorods obtained in the hydrolysis system increases with the aspect ratio and is higher than that of anhydrous system.And the content of Ti3+ trap state and OH on surface of the TiO2 nanotubes are 20%and 25.3%,respectively.Further more,the amount of surface Ti3+trap state and OH decrease by the reflow method.And the trap state can be reduced by modification of acrylic acid,while be increased by the plasma treatment.By controlling the morphology,size and surface modification state of titanium dioxide nanoparticles,the regulation of surface trapping properties can be realized,which will provide guidance for the practical application of transformer oil modified by titanium dioxide nanomaterial.