Preparation Of M-phase Nano-Vanadium Oxide By Hydrothermal Method And Application Of Modification In Intelligent Smart Window

Vanadium dioxide（VO₂）nano-powders have a huge research potential in the field of architectural scale curtain walls due to their low phase transition temperature and significant optical and electrical properties before and after the phase transition.When the indoor temperature is low,VO₂ appears as a monoclinic phase.Infrared light can enter the room through the glass to increase the indoor temperature.When the temperature continues to rise to the phase transition temperature,VO₂ appears as a tetragonal rutile phase,blocking infrared light from continuing.Enter,reducing the energy consumption of air-conditioning and refrigeration.VO₂ quickly senses temperature changes and spontaneously responds to phase changes.Without changing the natural lighting of the building glass,it does not change the transmittance of the visible light region,and only responds to the transmission and reflection of infrared light,and dynamically adjusts the indoor infrared light.Variety.However,there are currently three main problems in the practical application of VO₂powder in smart windows:First,it is difficult to industrially prepare high-purity VO₂ ultra-fine powder and it is difficult to prepare;Second,the phase transition temperature of VO₂ nanoparticles is 68℃,and the element doping Impurities can effectively reduce the phase transition temperature of VO₂ to around room temperature,but will cause the weakening of visible light transmittance and sunlight adjustment ability;traditionally,VO₂ film has poor water resistance and cannot meet the requirements of outdoor use of coatings.The research results and conclusions of this paper are as follows:（1）Preparation and performance study of VO₂（M）nano powderThe experiment used a one-step hydrothermal method to prepare VO₂（M）nanopowders.By exploring the reaction ratio of the vanadium source and the reducing agent hydrazine hydrochloride,the hydrothermal reaction temperature,and the hydrothermal reaction conditions,the preparation of the VO₂（M）powder was determined.Preparation process conditions.The results showed that the film prepared by the VO₂ powder prepared by reacting for 24 h under the condition of hydrothermal reaction temperature of 270℃has the best infrared light reflection and heat insulation performance,and the visible light transmittance of the film reaches 60%.11.5%solar control ability,with excellent thermochromic performance.The performance of the powder is analyzed by SEM and DSC.The DSC results show that the heating phase transition temperature of VO₂ powder is 60℃,the cooling phase tran./sition temperature is 37℃,and the average phase transition temperature is 48℃,which is conducive to the practical application of smart windows.To play to the ideal level.（2）Tungsten-doped porous vanadium dioxide powder and performance researchBased on the experimental preparation of VO₂（M）nanoparticles,mesoporous VO₂nanopowders with different tungsten doping contents were prepared and the thermochromic properties of VO₂films were explored.The performance of mesoporous VO₂ with different tungsten doping levels was characterized by XRD,SEM,XPS,BET,DSC and other test methods.The film was prepared using PVP as a cross-linking agent,and the transmittance of the film was expressed by UV-3600,and the thermochromic performance was calculated using related formulas.The two key performance parameters,visible light transmittance and solar light adjustment ability,were calculated.Successfully prepared mesoporous VO₂nanopowders with different doping amounts of tungsten.It was confirmed by XPS and XRD that the W element was successfully doped into the VO₂ lattice.BET data showed that the pore size of the mesoporous VO₂ nanopowders was 5-20.nm.DSC data shows that when the content of doped tungsten is 0.5 at%,the phase transition temperature of VO₂ has dropped by44℃,very close to room temperature.The prepared mesoporous VO₂ nanopowder was dispersed in the ethanol solution of the cross-linking agent PVP to prepare a coating.The transmittance of the film was tested and it was found that with the increase of W doping,the solar regulation ability of the film decreased,but decreased The amplitude is lower than that of the film prepared by VO₂ nanoparticles.When the tungsten doping amount is 0.5 at%,the phase transition temperature of VO₂ is 44℃,the visible light transmittance of the corresponding film is 50%,and the solar light adjustment ability is 7.5%.Possess high thermochromic performance.（3）Preparation and performance study of hydrophobic intelligent temperature control composite coatingBy modifying the surface of VO₂ nanoparticles and grafting organic groups,the modified VO₂ can be effectively dispersed in a hydrophobic polymer to prepare a coating with both thermochromic properties and water-repellent properties.Using VO₂ powder modified with oleic acid,the average particle size distribution of particles was reduced from 157 nm to 56nm.The dispersibility of modified VO₂ powder in organic media was significantly improved compared with that of VO₂ powder before modification.The phase properties of the nanoparticles before and after the modification were detected by XRD tools,and no changes were found in the phase of the modified powder.The powders before and after the modification were added to the PTFE emulsion to prepare the film.It was found that the visible light transmittance of the modified VO₂-PTFE composite film was increased from 37.46%of the film before modification to 54.1%,an increase of 30%,and the solar energy regulation efficiency was increased from 4.5%to 10.1%,which effectively improved the film.The thermochromic properties.The combination of stable thermochromic and hydrophobic properties of VO₂ and PTFE lays the foundation for the practical application of this material in the field of smart windows.