Preparation And Application Of WO₃/SiO₂ Composite Aerogel

Silicon dioxide（SiO₂）aerogel is a kind of gel material with gas as dispersion medium,which is a kind of lightweight nanoporous solid material with controllable structure formed by colloidal particles aggregating with each other,with a continuous three-dimensional network structure,its solid particles and the porosity in the middle are nanometers,and the porosity is very high,up to 99.8%,which is the world’s smallest density and the best solid material with the best isolation temperature effect,and has shown excellent performance in many aspects.Among the existing researches,silica aerogel is undoubtedly one of the most in-depth and thorough aerogel materials in the aerogel family.Therefore,its preparation process is mature,the synthesis route is clear,the production sample property is stable,the performance is superior,and it is a good particle carrier and skeleton support body.In previous studies,sol-gel method is the most commonly used and most mature aerogel preparation process,researchers continue to optimize the synthesis route,from raw material selection to preparation route and even drying methods have carried out a lot of exploration,but also in order to find an energy saving,simple,fast synthesis method.In these processes,the drying of aerogel is undoubtedly an important part.The commonly used drying methods include supercritical drying,freeze-drying and atmospheric drying.The self-combustion method is a new drying method of aerogel recently explored,which is not only convenient to operate,but also takes less time.WO₃ is a transition metal oxide and a classic N-type semiconductor material,so it has many outstanding physico-chemical properties,including photochromism,gas chromism,photocatalysis,high gas sensitivity and many other outstanding physico-chemical properties.WO₃ itself has the disadvantages of small specific surface area and few catalytic sites,so it is worth considering to find a suitable skeleton to provide sufficient specific surface area,so as to improve the catalytic properties of tungsten oxide.This paper mainly studied the use of silica aerogel as the basic skeleton,composite with tungsten oxide,tungsten oxide ions evenly distributed in the silica aerogel,using different drying methods,so as to prepare a new and efficient tungsten oxide composite material,and explore the preparation process on the performance of the aerogel.The main conclusions are as follows:（1）WO₃/SiO₂ composite gel was prepared by sol-gel method with ethyl orthosilicate and tungstic acid peroxide as precursors,and lightweight WO₃/SiO₂ aerogel with high specific surface area was prepared by atmospheric drying method,and its properties were studied.The experimental results show that:The aerogel prepared by atmospheric drying method has low density（0.148 g/cm³）,high porosity（94.28%）,high specific surface area（676 m²/g）,high pore volume（2.08 cm³/g）,high hydrophobicity（135℃）and high thermal stability（407.8℃）.With the increase of W ratio,the specific surface area and density of aerogel and other related properties decreased,but the thermal stability increased by 43℃,which was much higher than the thermal decomposition temperature of pure silica at 340℃.（2）On the basis of the previous part,WO₃/SiO₂ composite gel was prepared by sol-gel method after reflux of the two precursors,and WO₃/SiO₂composite aerogel with molar ratio of tungsten-silicon at 1:6,1:4 and 1:2 was prepared by combustion drying method.The results show that:1)with the increase of W content,XRD of the composite aerogel has a relatively obvious crystallization peak;2)With the increase of tungstan-silicon molar ratio from 1:6 to1:2,the density of composite aerogel prepared by combustion drying method increased from0.074g/cm3 to 0.150 g/cm3,and the specific surface area,pore diameter and hydrophobic Angle showed a downward trend.However,compared with atmospheric drying method,the performance of composite aerogel prepared by atmospheric drying method was better than that of samples prepared by atmospheric drying method,especially the thermal stability.Increase to 590.8℃.3)It can be completely dried in five minutes,greatly improving the drying efficiency and saving the cost.（3）Taking methylene blue as the target material and WO₃/SiO₂ composite aerogel prepared by combustion method as the photocatalyst,the photocatalytic performance of aerogel with different proportions of tungsten-silica ratio under the condition of visible light was explored.The results showed that the photocatalytic degradation efficiency of the sample with W:Si=1:2 could reach 98%,and that of the other two samples could reach 90%.Therefore,the band gap of the three samples was determined by ultraviolet absorption spectrum,which was2.27～2.45 e V,much lower than that of the ordinary photocatalysts.Therefore,WO₃/SiO₂composite aerogel samples have good photocatalytic performance.