Organic aerogel is based on organic matter, including phenolic aerogel, cellulose aerogel, polyimide aerogel, polyurethane (polyurea) aerogel, chitosan aerogel and chitosan-cellulose aerogel. Organic-inorganic hybrid aerogel realizes the special functionalization of aerogel materials by utilizing the advantages of organic matter and inorganic matter respectively.
      In 1931, the American scholar Kistler used supercritical ethanol fluid drying method, sodium silicate as raw material, while maintaining the gel structure, the ethanol liquid in the network structure replaced into a gas, and successfully produced SiO2 aerogel material. Then, inorganic aerogels such as Al2O3, W2O3, Fe2O3, NiO3 and organic aerogels such as cellulose, gelatin and AGAR were prepared successively. Major countries have paid great attention to the research of aerogel materials, developed a variety of new aerogel materials, and expanded the application range of aerogel.

     (1) Major countries have developed a variety of new aerogel materials
     The preparation process of aerogel is mainly divided into two steps: one is to prepare gel through sol-gel process; The second is to use a certain drying method to replace the liquid substance in the gel with gas, so as to produce aerogel. The drying process is divided into supercritical drying, sub-critical drying, freeze drying, atmospheric drying and other methods. Among them, the sol-gel process is the core process of preparing aerogel, which directly determines the various microstructure and properties of aerogel, including hydrolysis and condensation.
     In recent years, researchers from China, the United States and Europe have developed a variety of new aerogel materials such as bio-based aerogel, graphene aerogel and polymer aerogel by improving the preparation process of aerogel. Researchers at the University of Colorado in the United States used waste from the beer brewing industry as a medium, and used bacterial cellulose prepared by aceobacteriae to prepare a bacterial cellulose aerogel material through supercritical drying method, which has the characteristics of low thermal conductivity. Researchers at the French National Center for Scientific Research have prepared tannyl carbon aerogel by hydrothermal treatment, which is different from the traditional preparation process, and has a high specific surface area and specific electrical capacity. Researchers at Shandong University have successfully prepared a high-performance carbaminoxime-modified cyclodextrin/graphene aerogel, which shows strong affinity and selectivity for uranium in seawater, and has excellent uranium extraction capability in natural seawater, with 19.7mg/g uranium adsorption capacity in 21 days. Using bidirectional carbon aerogel composite multi-wall carbon nanotubes, researchers at Sichuan University in China have developed a novel polymer aerogel material capable of remaining functional and hyperelastic at extreme temperatures, which can function in the temperature range of -196 ° C to 500 ° C.
      (2) Biomass-based aerogel materials have become a research hotspot in major countries
       Carbon aerogel (CA) is a new type of nano-porous carbon material obtained by pyrolysis of organic aerogel at high temperature in an inert gas atmosphere. At the same time, it has the characteristics of extremely high porosity, high specific surface area and low density of aerogel, and the characteristics of carbon material such as heat resistance, acid and alkali resistance and high conductivity. However, due to its complex process, long production cycle, small production scale, high cost of raw materials, and easy to cause environmental pollution, the industrial production and application of carbon aerogel are limited. The biomass raw materials have wide sources, low cost and abundant carbon sources, so the use of biomass raw materials to prepare environmentally friendly porous carbon fiber aerogel is an economic and sustainable production method.
       Researchers from China, the United States and Europe have carried out research on the preparation and application of biomass-based aerogel materials and achieved a series of research results. Researchers at the French National Center for Scientific Research dissolved cellulosic materials in a sodium hydroxide solution to prepare a new highly porous pure cellulosic aerogel material with an internal specific surface area of 200-300m2/g and a density of only 0.06-0.3g/cm3. Researchers at the University of Colorado in the United States used waste from the beer brewing industry as a medium to prepare bacterial cellulose using acetobacter, and then prepared bacterial cellulose aerogel materials with low thermal conductivity by supercritical drying method. Researchers from the China-Australia Institute of Advanced Materials and Manufacturing (IAMM) of Jiaxing University, China, have developed an underwater mechanical toughness, high elasticity, and super-hydrophilic cellulose nanofiber Wiki aerogel, which can be used for oil-in-water emulsion separation and solar steam power generation, etc., solving the problems of poor water resistance and low toughness of underwater machinery of cellulose aerogel, breaking the obstacles of its application.
      (3) 3D printing aerogel materials have made a number of technical progress
      Due to the limited mechanical properties of traditional aerogel, it is difficult to form the required complex shape structure through post-processing, so the 3D printing technology of customized preparation of complex shape structural materials is expected to become an advanced manufacturing technology to break through the bottleneck of aerogel material application. In 2015, researchers at the University of California prepared graphene aerogel for the first time through 3D printing technology, and since then 3D printing aerogel has gradually become a research hotspot. At present, the printing methods in the preparation of 3D printing aerogel materials mainly include extrusion, cold field assisted on-demand drip (DOD) method and photocuring method. According to the main components of 3D printing aerogel, it can be divided into 3D printing carbon aerogel, 3D printing inorganic aerogel and 3D printing organic aerogel. Researchers at the University of Akron in the United States first used stereoscopic light curing molding (SLA) technology to make small bricks similar to LEGO bricks, and used the molten deposition manufacturing (FDM) process to make forming molds, and then injected aerogel into the molds and bricks after demudding, curing and other post-processing to achieve the modular production of aerogel bricks. Researchers at the Swiss Federal Laboratory for Materials Science and Technology directly used a slurry of silica aerogel powder for ink direct writing to print miniature silica aerogel objects with high specific surface area and ultra-low thermal conductivity, which can be used as thermal insulators and miniature air pumps and can degrade volatile organic compounds.