PART.1
Classification of Carbon Aerogels
Based on their source materials, carbon aerogels can be broadly categorized into three types: graphite-based carbon aerogels, organic carbon aerogels, and hybrid carbon aerogels.
Graphite-based carbon aerogels, such as graphene aerogels and carbon nanotube aerogels, are formed by directly assembling graphite carbon materials into three-dimensional aerogel structures through appropriate assembly processes. Due to their high electrical conductivity, these materials are widely used in various electronic devices and sensors.
Organic carbon aerogels are derived from organic precursors that undergo high-temperature carbonization to convert into carbon materials, which are then assembled into three-dimensional porous structures. This category is primarily divided into two groups: biomass-based carbon aerogels and polymer-based carbon aerogels. They exhibit excellent adsorption properties and unique structural characteristics, making them promising for applications in environmental protection and energy fields.
Hybrid carbon aerogels represent a major development trend in recent years. By incorporating organic functional groups or polymer components, the ratio between different constituents can be precisely controlled, thereby overcoming issues such as brittleness, hygroscopicity, and poor flexibility commonly found in single-component carbon aerogels. Hybrid carbon aerogels not only maintain superior performance but also achieve functional complementarity among different materials, significantly expanding the application potential of carbon aerogels.
PART.2
Carbon Aerogel Preparation Methods
Sol-gel, hydrothermal, chemical vapor deposition (CVD), and ice-templating methods are currently the most commonly used approaches for preparing carbon aerogels. Each method has distinct characteristics and applicable ranges.
The sol-gel process is a widely used fabrication technique known for its mild reaction conditions, simple operation, and high product purity. Carbon aerogels prepared by this method typically exhibit narrow pore size distributions and relatively ordered pore structures. The sol-gel process generally involves five steps: sol preparation, gel aging, solvent exchange, drying, and carbonization. Among these, the drying step—such as supercritical drying, freeze-drying, or ambient-pressure drying—plays a crucial role in determining the final structure and properties of the aerogel.
The hydrothermal method is usually carried out in a high-temperature, high-pressure reactor using deionized water as the solvent. A crosslinking agent is added to induce a chemical reaction between carbon-containing precursors and the liquid solvent, leading to self-assembly and formation of three-dimensional porous carbon aerogel materials. This method is currently the most widely used for producing reduced graphene oxide aerogels.
Chemical vapor deposition (CVD) is a technique in which reactants undergo chemical reactions in the gaseous phase, resulting in solid deposits on a substrate or catalyst surface. It is also one of the common methods for fabricating carbon aerogels.
The ice-templating method, also known as "freeze-casting," utilizes ice crystals formed during freezing as templates to create porous materials.
These methods offer diverse options for carbon aerogel synthesis, allowing researchers to select the most suitable approach based on specific requirements.
PART.3
Carbon Aerogel Applications
Oil Absorbent Materials: Compared to traditional adsorbents, carbon aerogels offer advantages such as low density, high specific surface area, high adsorption capacity, easy desorption, and excellent cycling stability. As a result, they show great potential in wastewater treatment applications.
Supercapacitors: Carbon aerogels retain the high electrical conductivity of carbon materials, making them widely used as electrode materials in supercapacitors. Moreover, their rich porosity, large surface area, and three-dimensional cross-linked porous structure effectively shorten electron/ion transport pathways, thereby delivering superior electrochemical performance.
Thermal Insulation Materials: Carbon aerogels exhibit excellent thermal stability, maintaining their three-dimensional porous structure even at 2800°C under inert atmospheres. Their abundant pore structures also endow them with ultra-low thermal conductivity. Therefore, carbon aerogels are considered highly promising next-generation high-performance thermal insulation materials.
Catalyst Supports or Catalysts: Due to their large specific surface area, stable electrochemical properties, and excellent electrical conductivity, carbon aerogels are commonly used as catalyst supports or direct catalyst materials in fuel cells.
Microwave Absorbing Materials: High-performance microwave absorbing materials require good impedance matching to allow electromagnetic waves to penetrate deeply into the material for effective attenuation. The high porosity of carbon aerogels means most of their interior consists of air, providing favorable impedance matching. Additionally, their unique porous structure enables multiple reflections of electromagnetic waves, effectively extending the wave propagation path and enhancing electromagnetic wave dissipation.
Photothermal Conversion: With excellent thermal and electrical conductivity, broad light absorption range, and high specific surface area, carbon aerogels hold great promise in photothermal conversion applications.
Flexible Sensors: As sensing materials, carbon aerogels provide numerous functionalizable active sites due to their high surface area and interconnected pore structures, accelerating electron transfer and offering suitable channels for analyte adsorption and transport, thus enabling high sensitivity and rapid response. Furthermore, carbon aerogels with outstanding flexibility and compression stability are widely employed as functional materials in flexible sensors and various smart wearable devices.
PART.4
In summary, carbon aerogels, as a new type of solid material, are continuously expanding and innovating in both their preparation methods and application fields. We believe that with ongoing advances in science and technology, carbon aerogels will further demonstrate their unique advantages and play an increasingly significant role across various domains, making greater contributions to the development and progress of human society.