Density functional study of the structure and water adsorption activity of anAl30O30star-shaped alumina nanocage

Abstract

Molecular and electronic structures of a novel Al30O30star-shaped alumina nanocage (SANC) were studiedusing the recently developed CAM-B3LYP density functional method. Comparison of the stretching vibrational modesof this compound with the corresponding modes related to an Al20O30perfect cage and Al50O75tubular aluminananomaterials showed a shift to lower frequencies, while the bending modes moved to higher frequencies. The highestoccupied molecular orbital (HOMO) of the SANC had 65% nonbonding character, whereas the lowest unoccupiedmolecular orbital (LUMO) was 72% antibonding. The HOMO and LUMO of the SANC arose mostly from Al3sand2patomic orbitals. The theoretically estimated energy gap for this compound was 4.4 eV, which is lower than thosefor the alumina nanocage (ANC) and nanotube (ANT). The SANC with internal and external diameters of 5.7 and 6.2 A had potential to interact with water molecule from sites Al(I) in the openings of the cage, Al(II) in the internal pore,and Al(III) in the external arms. The relative water adsorption activity of these sites was Al(I)>Al(III)>>>Al(II).The SANC can be introduced as a novel alumina nanostructure with lower stability and higher activity than well-knownalumina materials.