Theoretical Investigations of the Relaxation and Reconstruction of the γ-AlO(OH) Boehmite (101) Surface and Boehmite Nanorods

Ab initio molecular dynamics calculations, combined with a simulated annealing approach, were undertaken to study reconstructions in boehmite surfaces and nanorods. Our calculations indicate significant reconstruction for the (101) boehmite surface, leading to dramatic changes on the surface geometry and to higher coordination numbers for Al atoms at the surface (from III for the unreconstructed surface to IV for the reconstructed surface). The energy of the reconstructed boehmite surface decreases by around 23%, and the electronic population is modified accordingly. Due to the recent interest in quasi-unidimensional aluminum oxyhydroxide structures, boehmite nanorods grown in the [100], [010], and [001] directions were also investigated. Whereas calculations suggest a relative stability for [001] and [100] and nanorods, with surface energies of 0.90 and 0.54 J/m(2), respectively, and a majority of Al atoms coordinatively saturated at the surface, [010] nanorods undergo a significant reconstruction in vacuum with partial loss of the interlayer stacked structure. In particular, reconstructed [010] nanorods exhibit a significant amount of tetra- and tricoordinated Al atoms at the surface of the rod and a surface energy of 0.92 J/m(2). At the interface with water, the Al coordination numbers of the Z. Therefore, our [010] rod increase to IV and V, and accordingly, the surface energy decreases to 0.59 J/m(2) calculations allow us to identify the [1.00] and [010] rods as the most stable structures. Most notably, [100] and [010] rods have indeed been observed and characterized experimentally.