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

Alumina aerogels are prepared from the cheap AlCl3·6H2O 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 AlCl3·6H2O 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.