Preparation And Characterization Of Vanadium Dioxide Based Nanoparticles With Composite Structure

Vanadium dioxide?VO₂?is a typical thermochromic material,which has a pronounced metal-insulator transition?MIT?behavior at the critical temperature?T_c?near 68°C.Attributed to the MIT,VO₂ exhibits a dramatic change on near-infrared radiation?NIR?transmittance,being transparent to NIR at the temperatures below T_cand translucent to NIR above T_c.Therefore,VO₂ has shown a significant application in“smart window”for energy-efficient building.Currently,in the research of VO₂-based smart windows,two preparation methods are used widely.One is coating VO₂ directly on glass,such as physical vapor deposition?PVD?.The other one is preparing VO₂nanoparticles,and then combining with polymer to form composited coating materials.Compare with them,the method based on VO₂ nanoparticles has gained great attention due to its relatively simple equipment and process,excellent optical properties,and large range of color change with VO_2-based films.However,the VO₂-based smart window still has some problems such as the poor luminous transmittance(T_lum)and the low solar regulation efficiency(?T_sol).Besides,because of the instability of V⁴⁺,the chemical state of VO₂ will be changed easily and lost thermochromic property in complex environment.Therefore,there remains another important challenge in practical application of VO₂-based smart window:its environmental durability,which is also a great challenge in the application.Finally,realizing the multifunction of VO₂-based smart window can improve the value and market competitiveness of the products.Therefore,the research and development of multifunctional thin films has become a research hotspot in the field of smart window.In order to solve these issues,in this paper,we used core-shell structure to modify and protect VO₂ nanoparticles in order to enhanced the optical property and environmental durability of VO₂ films.After that,the VO₂ films were composited with hydrophilic and hydrophobic materials to get multifunctional VO₂-based films.The main works and results can be concluded as follows:?1?VO₂ nanoparticles were synthesized by hydrothermal method,with uniform morphology,small size and well dispersibility.Then prepare the VO₂@Si O₂nanoparticles using TEOS?Tetraethyl Orthosilicate?-NH₃·H₂O system and Na₂Si O₃-H₂SO₄system,respectively.Compare with the VO₂ nanoparticles,the VO₂@Si O₂nanoparticles have enhanced environmental durability:The VO₂@Si O₂ nanoparticles-based film keeps 25.3%of thermochromic property after 72 hours in 60°C and 90%relative humidity environment,while relevant property of uncoated VO₂ nanoparticles-based film badly deteriorates after the same time.?2?Using ascorbic acid?AA?pretreated the VO₂ nanoparticles and synthesized the AA-VO₂ nanoparticles successfully.The VO₂ nanoparticles were coordinated with AA molecules by a new connecting bond of C-O-V after AA treated,which could be protected by an AA^-chelated H_xVO₂ layer with enhanced anti-acid and anti-oxidation properties.Compare with pure VO₂,the AA-VO₂ nanoparticles exhibit enhanced stability in 1 mol/L H₂O₂ and 0.5 mol/L H₂SO₄solution.Besides,the enthalpy of AA-VO₂ nanoparticles only decrease 0.9 J/g after 3 days in 60°C and 90%relative humidity environment and remain 56.3%phase transition properties after 10 days accelerated experiment.?3?The core-shell structure of VO₂@Zn O nanoparticles have been prepared using zinc oxide?Zn O?as the coating material.Compare with the VO₂ films,the VO₂@Zn O films have enhanced optical property and excellent environmental durability:?T_solincrease from 17.2%to 19.1%?increased by 11.0%?and T_lum increase from 38.9%to51.0%?increased by 31.1%?.Besides,The VO₂@Zn O film exhibits a robust durability that the?T_sol keeps 77%?from 19.1%to 14.7%?after 10³ hours accelerated experiment in 60°C and 90%relative humidity environment.?4?The Si O₂-based hydrophilic and F-Si O₂ hydrophobic materials have been prepared by using tetraethyl orthosilicate?TEOS?and heptadecafluoro-1,1,2,2-tetradecyl trimethoxysiloxane?PFDTES?and composited with VO₂ films.The composited films have excellent anti-fogging and hydrophobic property.Besides,the hydrophobic coating can enhance the environmental durability of VO₂ films.In 60°C and 90%relative humidity environment,the?T_sol decrease from 16.0%to 11.9%after240 h and keep at 8.3%after 480 h?remain 51%thermochromic property?.Compare with pure VO₂ films,the environmental durability of composited VO₂ films have been enhanced for 4?5 times.