Study of the Formation Mechanism of Boehmite with Different Morphology upon Surface Hydroxyls and Adsorption of Chloride Ions

Abstract

Identification of the key factors of morphology control in nanomaterial synthesis is important for mechanism understanding of the reactivity–structure relationship and rational design of crystals with desired morphology. Among others, the inorganic ions in solution were found to be a key factor in controlling the final morphology. To reveal the effect of inorganic ions, the boehmite with different morphologies influenced by chloride ions is studied by a combined experimental and computational approach. The quantum mechanical calculations reveal that the chloride ions interact with crystal planes through surface hydroxyls and act as morphology-directing agent. The growth directions and exposed planes of the boehmite determined from HR-TEM images indicate an oriented-aggregation process which is consistent with the DFT calculations. It is envisaged that the defects caused by excessive hydrochloric acid are due to its dissolving property combined with the reduction of adsorption energies. Overall, all the morphologies of boehmite suggested by the calculations are confirmed by experimental results.