The Preparation And Application Of Tungsten Oxide

Windows are the most important functional parts of the buildings,providing natural lighting,ventilation,indoor and outdoor interaction and solar heat gain,and improving the building's aesthetic appeal.However,compared with other building envelopment structures,windows have poor thermal insulation performance,and the energy loss generated by windows accounts for 40%of the total energy consumption of the buildings.At the same time,in modern buildings,in order to pursue architectura aesthetic feeling and comfortable indoor environment,windows occupy an increasing proportion of the area,so the energy-saving renovation of Windows has important practical significance.The most important point of energy-saving renovation of Windows is to make Windows have solar spectral selectivity,so as to ensure basic lighting and reduce energy loss caused by solar thermal radiation as far as possible.Tungsten oxide material has rich stoichiometric ratios and special pore structures,which is an ideal host material for ion intercalation.The ion embedding and releasing in the lattice of tungsten oxide can change its optical properties and generate selective absorption to the solar spectrum.Based on this,tungsten oxide material is widely used in the field of solar radiation control,such as electrochromic smart windows,photochromic and transparent thermal insulation fields.Our work mainly uses tungsten oxide as the solar radiation control material,and achieves static,active and intelligent regulation of solar radiation by preparing cesium tungsten bronze transparent thermal insulation film,tungsten oxide quantum dots electrochromic films and photochromic composite films.The specific research contents are as follows:(1)The size morphology and Cs/W doping ratio have important influence on the transparent thermal insulation performance of cesium tungsten bronze.We developed a simple two-step method to prepare cesium tungsten bronze nanoparticles.The first step was to prepare the precursor by adding cesium into the tungsten oxide sol,so that the raw materials could be mixed at the molecular level,which was conducive to the doping of cesium ions,reduced the reaction temperature and shortened the reaction time.In the second step,the precursor is subjected to solvent thermal reaction in oleic acid.During the reaction,oleic acid can be adsorbed on the surface of nanoparticles,which limits the growth and agglomeration of particles.At the same time,oleic acid has certain reducing property,which is conducive to the formation of oxygen vacancy.Finally,nano-cesium tungsten bronze with small particle size(20 nm),light agglomeration and high Cs/W(0.32)doping ratio was obtained after 4 hours reaction at 260 ^oC.The cesium tungsten bronze film has excellent transparent thermal insulation performance,visible light transmittance up to 70%,and can shield over90%near infrared light.The results of temperature test in the simulated room show that cesium tungsten bronze film coating on ordinary glass can greatly improve the thermal insulation performance,and it is better than ITO glass.(2)As a transparent thermal insulation material,the main construction method of cesium tungsten bronze is to form a film on the glass surface.However,since cesium tungsten bronze mainly absorbs the near-infrared light and inorganic glass has high thermal conductivity,obvious secondary heat radiation will be generated.Some studies have shown that cesium tungsten bronze release cesium ions in high temperature and humidity environment,resulting in the attenuation of near-infrared absorption performance.To solve the above problems,cesium tungsten bronze nanoparticles were successfully embedded into PMMA matrix by in-situ polymerization,and nanocomposites with high visible light transmittance,low haze and excellent near infrared absorption were prepared.The insertion of nanoparticles improved the stability of the material,and the low thermal conductivity of PMMA reduced the secondary heat radiation.At the same time,PMMA has lower density and higher safety compared to inorganic glass.The visible light transmittance of the nanocomposite is over 70%,the haze is less than 1%,and absorb more than 90%near-infrared light.(3)Tungsten oxide quantum dots were used as the electrochromic materials,WO₃quantum dots electrochromic films were successfully achieved by gas spraying,the small size effect of the quantum dots brought excellent electrochromic performance in conventional lithium ion electrolyte,including large optical modulation(97.8%),fast response time(4.5 s for colouring,4 s for bleaching)and excellent cycle performance(10000).By replacing lithium ion electrolyte with aluminum ion electrolyte,the cycling performance was further greatly improved,with no attenuation after 20,000 cycles.Therefore,we solved the problem of poor cycle stability of electrochromic films prepared by liquid phase method,which promoted the development of low cost electrochromic devices.(4)We studied the photochromic properties of tungsten oxide quantum dots and prepared polyvinyl alcohol PVA composite films of quantum dots.The small size effect of quantum dots greatly promotes the process of photoexcited redox reaction and makes the composite film have excellent photochromic properties,including large optical modulation and fast optical response speed.WO₃quantum dots glycol solution can be directly used as a photochromic ink,in which words can be displayed and faded under ultraviolet light and light-proof treatment.