Study On Preparation And Properties Of Mesoporous NaYF₄ And SnO₂-Based Micro/Nanomaterials

Mesoporous nanomaterials have been widely used in sensors,catalysts,biomedicine and even environmental applications due to their unique properties such as high specific surface area,easy surface modification,high porosity and high biocompatibility.The mesoporous material Na YF₄ has attracted much attention due to its unique upconversion luminescence properties.However,the liquid phase preparation method of mesoporous upconversion submicrospheres reported at present is difficult to achieve massive preparation,and the preparation process will produce a large amount of waste liquid,resulting in environmental pollution.We intend to develop a novel method that uses almost no solvent to induce the self-assembly of nanocrystalline nuclei in a microreactor with multi-tooth-shaped polymers,and establish a controllable synthesis system with ultra-high concentration to synthesize mesoporous upconversion submicrospheres in green large-scale.According to the"multidentate polymer microreactor"method,Na YF₄ nanoclusters were synthesized,and the morphologies and properties of the products were explored by changing the reaction conditions.Binary mesoporous Sn O₂ materials were selected to study the universality of the method,and the effects of reaction parameters and doping on crystal growth were explored.In addition,the influence of co-doping on the luminescence properties of ternary Sn O₂-based materials（Mg₂Sn O₄）was investigated.The main research results are as follows:1.A method of preparing nanoclusters by multidentate polymer microreactor is proposed.Taking Na YF₄:Yb³⁺,Er³⁺as examples,it was proved that sodium polyacrylate（PAAS）,acting as a"multidentate polymer microreactor",induced the controlled growth of primary nanocrystals and induced the crystals to aggregate into mesoporous microspheres.The sizes of Na YF₄ submicrospheres and primary particles can be regulated by the types of fluorine sources and polydentate polymers.The morphology of microspheres can be adjusted by changing the ratio of F^-/RE,and the microspheres can grow into mesoporous rods of different lengths.Compared with the reported method,the single batch yield of this experiment was also increased by 15 times.2.SnO₂ was selected as the research object.On the one hand,the universality of the"multidentate polymer microreactor"method was verified,on the other hand,the influence of reaction parameters on the morphology and size of Sn O₂ was studied.It was found that the reaction time had little effect on particle size.When PAAS was 10 mmol,microspheres with uniform morphology and size could be formed.It is found that PEI and PAAS have similar induction effect and can be used as a member of the"multidentate polymer microreactor".By regulating the concentration of Zn²⁺,the morphology and size of the products were regulated,which changed from cauliflower microspheres to sea urchin microspheres.The growth mechanism of hollow microsphere formation is proposed.The R_hollow:T_shell of these hollow microspheres is positively correlated with the doping amount of Zn²⁺.Compared with undoped Sn O₂,Zn²⁺doping has larger particle size,pore size and specific surface area,and has a higher photocatalytic degradation rate for MB.3.A new afterglow material Mg_1.96Sn_1-xO₄:0.04Eu³⁺,x Gd³⁺was prepared by high temperature solid-state method.Compared with single doped Eu³⁺,the duration of afterglow is increased by 175 times,and the maximum sustained luminescence intensity of the sample is about 14 times higher than that of single doped Eu³⁺.The ratio of red to orange can be changed by adjusting the content of Gd³⁺,and Gd³⁺co-doping is conducive to the enhancement of afterglow.Gd³⁺can promote the ⁵D₁→⁷F₄ energy level transition of Eu³⁺and trigger the emission peak at 628 nm.It was found that when the concentration of co-doped Gd³⁺was 0.04,the color purity of the sample was up to 99.9%,which could be used as a promising orange afterglow phosphor in lighting applications.Three types of defect clusters produced by Mg₂Sn O₄:Eu³⁺,Gd³⁺were inferred as[Gd*_Mg-V’’_Mg-Gd*_Mg],[Eu*_Mg-V’’_Mg-Gd*_Mg]and[Gd*_Mg-Eu’_Sn],respectively.The afterglow luminescence mechanism of Mg₂Sn O₄:Eu³⁺,Gd³⁺was analyzed and summarized.