Preparation And Properties Of Carbon Quantum Dots/Silicon Dioxide/Vanadium Dioxide Thermochromic Composites

Vanadium dioxide(VO₂)is one of the phase change materials,not only because of its excellent phase transition characteristics,but more importantly,the metal-insulator phase transition temperature(68?)of VO₂ is the closest to room temperature,and the phase transition temperature can be changed through size control,doping,compounding and other ways,and it has broad application prospects in the field of temperature-controlled packaging and anti-counterfeit packaging.The optical properties of VO₂ can be improved effectively by constructing VO₂ composite structure.Because of its particle size control,versatility and high stability,VO₂/SiO₂ has attracted more and more researchers' attention,and has been used to prepare thermochromic materials with high stability and improved transmittance.However,how to design and prepare VO₂ thermochromic composites with excellent performance still faces great challenges.In this paper,carbon quantum dots(CQDs)were prepared by hydrothermal method,and mesoporous silica(SiO₂)were prepared by sol-gel method,and then the two were assembled to form CQDs/SiO₂ composite materials.Then the CQDs/SiO₂/VO₂ composite system were obtained by in-situ method and self-assembled method respectively.The in-situ method was to mix the VO₂ precursor and CQDs/SiO₂ to form a CQDs/SiO₂/VO₂ composite material through a water bath.The results showed that as the reaction time gradually increases,the amount of VO₂ formed on the surface of CQDs/SiO₂ gradually increases,indicating that prolonging the reaction time has an important role in promoting the conversion of the precursor to VO₂.The UV transmittance of annealed CQDs/SiO₂/VO₂ composites can reach 90%.In addition,the rod-shaped VO₂(B)was prepared by the hydrothermal method,and annealed at 450?,VO₂(B)was transformed into VO₂(M).The phase transition temperature from VO₂(M)to VO₂(R)was about 69.8?.VO₂(M)was combined with CQDs/SiO₂ through self-assembly technology,and its phase transition temperature was about 71.5?.Compared with VO₂(M),CSV-(M)has a higher visible light region high transmittance,showing excellent optical control ability.The new CQDs/SiO₂/VO₂ composites structure were designed and prepared through different paths,and the influences of synthesis route and annealing process on the morphology and structure,phase transition temperature and optical properties of CQDs/SiO₂/VO₂ composites were explored,so as to expand its thermochromic properties.It also provides theoretical basis and experimental basis for the application of high performance VO₂ thermochromic materials in temperature control packaging and anti-counterfeiting packaging.