Preparation And Modification Of Vanadium Dioxide Nanoparticles

As a typical heat-sensitive material,vanadium dioxide showed a semiconductor-metal reversible phase transition(MITD)when it is heated.At the same time,its crystal structure was changed from a monoclinic structure to a tetragonal rutile structure.Its infrared transmittance was also changed from high transmission to low transmission.Therefore,vanadium dioxide can be widely applied as the fields of thermochromic energy-saving windows and solar thermal control.Prepare small-sized VO₂nanoparticles with good crystallization and coat it on the substrate was the most important method to fabrication VO₂(M)film.The preparation of small-sized VO₂nanoparticles with good crystallization and good dispersion was the heart of this method.Hydrothermal method was the main method to prepare VO₂nanoparticles.But it is difficult to produce on a large scale.The precursor pyrolysis method was more suitable for large-scale production of VO₂nanopowders than the hydrothermal method.But a large amount of carbon deposits are generated during the thermal decomposition of CA-V.VO(OH)₂was agglomerated to grow up during the thermal decomposition process.In addition,VO₂was limited to applications due to its low visible light transmittance and poor weather resistanceIn order to prepare VO₂nanoparticles with excellent properties on a large scale,we proposed two schemes.First,the air,CO₂gas,and water vapor are used to remove the carbon deposits generated during the thermal decomposition of CA-V.Second,a VO₂@SiO₂core-shell nanoparticles was prepared to increase the dispersion,optical performance and weather resistance of VO₂nanoparticles.In addition,we prepared a hollow VO₂nanoparticles,it used P(MMA+St)as the template.Specifically,the results can be concluded as follows:(1)First,the thermal decomposition process and thermal decomposition products of CA-V in Ar atmosphere was analyzed.When the CA-V was heat-treated below600?,VO₂particles below 100nm can be prepared,but a large amount of carbon deposits was contained in VO₂.When the temperature is higher than 600?,VO₂ would be reduced to V₂O₃by carbon.Therefore the,the air,CO₂gas,and water vapor was used to remove the carbon deposits in 600?.The influence of gas inlet ratio and reaction time on the product was studied.The reaction between air and carbon deposits was the fastest,but VO₂is also easily oxidized by air,the process was difficult to accurately control.VO₂would be reduced by H₂produced by the reaction of H₂O vapor and carbon when use H₂O vapor to remove carbon deposits.When CO₂was introduced,VO₂would not be oxidized or reduced.But the reaction of carbon and CO₂at 600?was too slow,carbon deposits was completely removed after 24 hours of reaction,VO₂was reunited and grew up in the process.(2)VO(OH)₂without organic ingredients was used to prepare VO₂ nanoparticles.VO(OH)₂@SiO₂core-shell nanoparticles were prepared by coating SiO₂layer on the surface of VO(OH)₂nanoparticles via the surface electric interaction between VO(OH)₂nanoparticles and aminopropyltriethoxylsilane. KH550 has played a decisive role in the coating of SiO₂,it couldn't be successfully coated without KH550.The thickness of SiO₂can be adjusted by adjust the amount of TEOS and NH₃.H₂O.VO₂@SiO₂nanoparticles was prepared by high temperature heat treatment of VO(OH)@SiO₂in Ar.Then the thermochromic film was prepared by dispersing VO₂@SiO₂nanoparticles into the resin and coating on the substrate.The morphology,weather resistance and thermochromism of VO₂@SiO₂ nanoparticles are studied.From TEM images,we find that SiO₂shell prevents the agglomeration of VO(OH)₂during heat treatment.Research on the optical properties of the film shows that the SiO₂and air of low refractive index can improve the optical properties of thermochromic films.The protective effect of the SiO₂shell to the VO₂core obviously improves the oxidation resistance and corrosion resistance of VO₂in damp heating and acidic environment,which makes longer life of VO₂thermochromic film.(3)60nm P(MMA-St)polymer pellets with good dispersibility and negatively charged surface was prepared by dispersion polymerization,it used deionized water as the di spersant,potassium persulfate as the initiator.When styrene(St)monomer was adde d,the dispersibility of the pellets could be significantly improved.Then the precurs or VO(OH)₂was deposited on the PMMA surface used electrostatic self-assembly method.Hollow VO₂nanoparticles was prepared after heat treatment at 500? in Ar atmosphere when PMMA was removed by toluene solvent,Thermochromic film based on hollow VO₂was prepared by disperse hollow VO₂into resin.Researc h on the optical properties of the film shows that the SiO₂and air of low refractive index can improve the optical properties of thermochromic films.