Synthesis of alumina aerogels from AlCl3•6H2O with an aid of acetoacetic-grafted polyvinyl alcohol

Alumina aerogels are prepared from the cheap AlCl3 center dot 6H(2)O precursor by the sol-gel method using acetoacetic-grafted polyvinyl alcohol (acac-PVA) as a template and dispersing agent, and propylene oxide as a gelation initiator. The acac-PVA has a high dispersing ability for Al3+ ion through complexation interaction and increases the content of AlCl3 center dot 6H(2)O in sols to as high as 37 wt%, leading to the formation of wet gels without precipitate and crack, and little shrinkage. As-prepared alumina aerogels have high density, high mechanical strength, high mesoporosity, and high-surface area. The shrinkage in supercritical drying processes is greatly reduced. The specific surface area increases and pore size decreases with increasing the content of the acac-PVA in sols. The acac-PVA also acts as a template that provides nucleation sites for boehmite AlOOH particles and inhibits their growth. An excess content of the acac-PVA isolates secondary particles, weakens the interaction between them, and therefore decreases the Young's modulus. Coarsening is not alleviated obviously after removal of the acac-PVA by high-temperature treatment in air, and the fine primary particles grow into nanorods with diameters of 10-20 nm and lengths of 30-70 nm. [GRAPHICS] Acetoacetic group is grafted on polyvinyl alcohol via esterification reaction with a -OH conversion of about 80%. Acetoacetic group on polyvinyl alcohol forms complex with Al3+ and Al-clusters to obtain AlCl3 center dot 6H(2)O sols with a high concentration. The shrinkage of gels in sol-gel and supercritical drying steps are decreased significantly via an aid of the acetoacetic-grafted polyvinyl alcohol. The resulting aluminum aerogels have a high density, high mechanical strength, and high mesoporosity.