Sol-Gel Synthesis of Alumina Using Inorganic Salt Precursor

Abstract A simple procedure based on gelatification, promoted by the ring-opening reaction of propylene oxide, was proposed for the synthesis of alumina, in which hydrated aluminium nitrate (Al(NO 3 ) 3 ·9H 2 O) was mixed with propylene oxide and gelated in ethanol solvent. After being dried and calcined under air atmosphere, a kind of amorphous alumina with a well-defined mesoporous structure was obtained. The samples were characterized by BET, SEM, FT-IR, and DTA. The results of liquid nitrogen adsorption indicated that two clear peaks appeared in the pore size distribution of each sample, whereas the larger pores were inkbottle-like. The average pore size of the alumina could be controlled by tuning the molar ratio of propylene oxide to aluminium nitrate over a range of pore diameters from 2.8 to 6.0 nm. The mechanism of the gelatification was finally proposed according to the characterizations. Both pH detection and FT-IR results demonstrated that propylene oxide indeed acted as an irreversible proton scavenger that induced inorganic aluminium ions to undergo hydrolysis and condensation to form the aluminium oxide framework.