Tuning the structure of alumina
Using aluminum nitrate as aluminum source, mesoporous alumina was respectively synthesized via cation-anion double hydrolysis method, sol-gel method and hydrothermal method. The pore structure, acidic property and microstructure etc. can be controlled by different methods and synthesis conditions. Different formation mechanisms induce different average crystallite sizes. The samples obtained from sol-gel and cation-anion double hydrolysis method have mono-modal mesopores with pore size in the range of 3.5-20.6 nm, while samples derived from hydrothermal method show bimodal mesoporous structure. There are more Lewis acid sites on the surface of the samples synthesized by sol-gel method. Nanorod morphology was observed in all the samples. Of note is that samples prepared with hydrothermal method show some irregular nanoparticles among the rods and samples synthesized by other methods bear pure nanorod structure. Moreover, there is more six-coordination aluminum (AlO6) in the framework of alumina prepared with hydrothermal method compared to that of samples synthesized by other methods.