The Hydrophobicity Sio <sub> 2 </ Sub> Aerogels With Cu Doping Of Sio <sub> 2 </ Sub> Preparation And Properties Of The Composite Airgel

Silica aerogels are a novel nano-porous, non-crystalline and the lightest solid materials, whose continuous network structures can be controlled and tailored at the nanoscale, due to their special properties such as low density, high specific area, low thermal conductivity and good mechanics characteristics, the best properties in the thermal insulation, the lowest sound velocities and the higher porosity in all solid materials and so on, they have many extensive applied prospect on thermal protection systems of space aircrafts, military thermal battery, heat energy, chemical, metallurgy, lire protection and other fields, especially in the aspects of catalyst carrier, adsorbent, gas filter and insulating material,they have good advantages. In order to make silica aerogels can realize mass production, it is necessary to further improve preparation technique and properties (for example the specific area) of aerogels, and to reduce cost of aerogels.At present, the main problems of the influence of aerogels on commercial application are that preparation technology is harsh, complex, long period, difficult control and high control cost of making. There are so many hydroxyl groups on the surfaces of silica aerogel without hydrophobic modification that make aerogels easy to absorb water in water or moist air to cause materials cracking, it has limited the practical application of aerogels materials. Traditionally the hydrophilic modification of silica aerogel is carried out under supercritical condition or via surface post treatment method under ambient pressure drying, but supercritical drying technique is complex, high cost and has some dangers, silica aerogel prepared by surface post treatment method to hydrophobic modify has lower specific surface area than that modified by in-situ method and the technology is longer.. To prepare hydrophobic silica with high specific surface area and promote practical application on many fields, it is necessary to study hydrophobic silica prepared by ambient drying. We had prepared hydrophobic silica via in-situ method under ambient pressure drying.Using tetraethoxysilare (TEOS) and deionized water as raw material, ethanol (EtOH) as solvent, nitric acid (HNO₃) and ammonia water (NH₃·H₂O) as catalysts, in the sol-gel process of tetraethyl orthosilicate (TEOS) catalyzed by two-step acid-base, added the mixed solution with drying control chemical additive (DCCA) N,N-dimethylformamide (DMF) and trimethylchlorosilane(TMCS) to hydrophobic modification by in-situ method, hydrophobic silica aerogel with a high specific surface area was prepared by ambient pressure drying. Structure and morphology of samples were characterized by N₂ physical adsorption, X-ray diffractometer (XRD), Fourier transform infrared (FT-IR) spectrometer and scanning electron microscope (SEM). Results showed that the specific surface area and hydrophobicity of hydrophobic silica aerogel modified by in-situ method with more hydrophobicity and bigger specific surface area than that modified by surface post treatment method, and the surface area is 979 m²·g^-1, aerogel has a good hydrophobic property linked with hydrophobic group (-CH3) to their surface and has typical continuous network. After heat treatment at 500℃, the surface of aerogel from water-repellent to hydrophilic after lost most of hydrophobic group (-CH₃), after 800℃heat treatment, hydrophobic silica was still amorphous state, it indicated a good thermal stability.Preparation of copper doped silica composite aerogel usually via supercritical drying technology, it has limited the development of composite aerogel materials. Using tetraethyl orthosilicate (TEOS) as silicon precursor and copper nitrate (Cu(NO₃)₂·3H₂O) as copper source, a copper-doped silica nanocomposite aerogel with a high specific surface area was prepared via an in-situ sol-gel process and ambient drying by introduction of a drying control chemical additive (DCCA) N,N-dimethylformamide (DMF) to the composite sol systems. The effect of DMF on gel time, drying process, the morphology and the structure of the composite aerogel is discussed. At the same time, effects of different preparation conditions of various Cu loadings,catalyst concentration and heat treatment on structure of copper doped silica were investigated.Structure and morphology of samples were characterized by N₂ physical adsorption, X-ray diflractometer (XRD), Fourier transform infrared (FT-IR) spectrometer and transmission electron microscope (TEM). Results showed that DMF was effective in preventing gel cracking and inhibiting the formation particle clusters. The diameter of composite aerogel decreased as specific surface area increased and the microstructure became more optimal. Particles of aerogel are uniform distribution; it is good for the formation of CuO crystalline.with the copper content increases, specific surface and pore volume decreased; condensation degree of Si-0 network decreased with the catalyst concentration. CuO crystalline grew and Si hydroxy group reduced gradually with heat treatment temperature increasing. After high temperature treatment, copper components in Cu-SiO₂ were still highly dispersed and had strong interaction with silicon dioxide support, which indicated good thermal stability of the composite aerogel. copper species were still highly dispersed, which indicated good thermal stability of the composite aerogel.