Synthesis,Structure And Properties Of TiO₂ And SiO₂/TiO₂ Based Rare Earth Bifunctional Composites

As the most promising photocatalyst,TiO₂ materials have been widely used in the field of photocatalytic degradation of organic pollutants to solve environmental pollution problems.In addition,due to its relatively wide band gap,high refractive index,high chemical stability and low phonon energy,TiO₂ can be used as the host matrix of RE-doped luminescent materials,which can be applied in the field of phosphors,X-ray imaging,scintillators,lasers and display monitors.However,little research has been reported on the relationship between luminescence and photocatalysis of TiO₂.In addition,SiO₂ modified TiO₂ composites exhibited the higher luminescence intensity and photocatalytic activity than those of pure TiO₂materials.SiO₂@TiO₂ composites with different morphology and crystal phase SiO₂can be controlled by the etching process of SiO₂,and the physicochemical properties of materials are often closely related to the crystal phase and morphology.Therefore,it is necessary to control the synthesis of TiO₂-based luminescence and photocatalytic materials,and to discuss the luminescence intensity,photocatalytic activity and the correlation between luminescence and photocatalytic properties in detail.In this paper,a variety of rare earth doped TiO₂ and rare earth doped SiO₂@TiO₂nanomaterials with different morphologies,sizes and crystal phases were prepared.The growth mechanism,luminescent properties and photocatalytic activity of the products were studied in detail.Correlation between luminescence intensity and photocatalytic efficiency has been discussed.The research work mainly includes the following parts:1.TiO₂:Eu³⁺nanorods,straw bundles,micro-flowers and nanofibers were synthesized by hydrothermal and electrospinning methods.The materials exhibited red emission of Eu³⁺under excitation by ultraviolet light.The formation mechanism of the materials was inferred.The relationship between morphology and luminescence properties was discussed.The effects of calcination temperature on the anatase-rutile phase ratios and morphology were studied.It was found that the introduction of an appropriate amount of Eu³⁺not only imparts luminescence properties to TiO₂,but also improves the photodegradation efficiency of methyl orange.It is inferred that the Eu³⁺ions mainly occupy the C_2v,C₂ and C_s sites in TiO₂ by calculating the Judd-Ofelt parameters.2.Using SiO₂ spheres as templates,SiO₂@TiO₂:Eu³⁺/Sm³⁺core-shell,yolk-shell and hollow structures were successfully synthesized by solvothermal coating method and subsequent etching process.The effects of morphology on luminescence intensity and photocatalytic performance were investigated.The effects of light utilization,crystallinity,Ti-O-Si bond and specific surface area on the photocatalytic and luminescence properties of the products were investigated.Under the excitation of ultraviolet light,all materials exhibited characteristic red emission of Eu³⁺and red-orange emission of Sm³⁺.Core-shell composites have the highest degradation efficiency for methyl orange under simulated solar light irradiation.3.SiO₂@TiO₂:Sm³⁺core-shell structures composites were successfully prepared by sol-gel and solvothermal coating method.The effect of coating methods on the luminescence and photocatalytic properties of core-shell structure,the effect of doping concentration of Sm³⁺ions on the phase transition of TiO₂,and the effect of crystal phase ratios on photocatalytic activity were studied.Then,the yolk-shell and hollow structures composites were prepared by etching process.The luminescence and photocatalytic properties of different morphological materials were studied,and the correlation between luminescence and photocatalytic properties was discussed systematically by factors such as crystallinity,specific surface area and light utilization.When the sol-gel coating method is used,the core-shell structure has the maximum orange-red light emission intensity and photo-degradation efficiency.When the solvothermal coating method is used,the core-shell structure has a slightly lower luminescence intensity than the yolk-shell structure.4.Based on SiO₂@TiO₂:Eu³⁺core-shell materials,SiO₂@SiO₂:Eu³⁺@SiO₂ core double-shell materials were obtained by sol-gel coating method.The SiO₂ coating improved the luminescence intensity of core-shell material effectively.The effect of SiO₂ coating thickness on the luminescence intensity was studied in detail,and the luminescence improvement mechanism was proposed.In addition,the yolk-shell and hollow structures can be obtained by changing the order of etching and calcination treatment of the core-shell and the dual-core shell structure.The performance test results show that the hollow structure has the maximum red-emission intensity,and the core-shell structure has the best photodegradation efficiency of methyl orange.5.Based on SiO₂@TiO₂:Eu³⁺core-shell materials,SiO₂@TiO₂:Eu³⁺@TiO₂ core double-shell structure materials were obtained by sol-gel method and solvothermal coating method.The effect of the difference in coating method on the luminescence intensity of the materials was studied.The results showed that the sol-gel coating method improved the luminescence intensity of core-shell materials,the solvothermal coating method reduced the luminescence intensity.In addition,the effects of calcination treatment on the luminescence and photodegradation of polyacrylamide were investigated,and the correlation between photocatalysis and luminescence properties of the materials was analyzed.The polyacrylamide photodegradation activity of core double-shell structure with anatase inner shell and anatase-rutile mixed-phase shell is higher than that of core-shell materials and P25.