Hydrothermal preparation of boehmite nanorods by selective adsorption of sulfate

A facile hydrothermal method was developed to synthesize boehmite nanorods with a length of 50-2000 nm, a diameter of 6-20 nm, and a preferential growth along [100] by treating the Al(OH)(3) gel in acidified sulfate solutions at 240 degrees C. Studies on the hydrothermal treatment of AI(OH)3 gel in sulfate solutions showed that the morphology and the composition of the hydrothermal products were connected with the sulfate concentration and the pH of the hydrothermal solution. The aspect ratio of the boehmite nanorods increased to 300 as the initial H2SO4 concentration increased to 0.043 mol.L-1, whereas boehmite nanorods and (H3O)Al-3(SO4)(2)(OH)(6) cubic particles coexisted in the case of the initial H2SO4 concentration >= 0.054 mol.L-1. Sole boehmite nanoflakes with a diameter of about 50 nm were formed under alkaline conditions (pH 10.5) despite the existence of the sulfate. The chemical and Raman analyses indicated that SO42- in acidified solutions adsorbed on the boehmite surface via H-bonds. On the basis of the above results, the growth of boehmite along the [100] direction was attributed to the selective adsorption of SO42- on the (010) and (001) planes of boehmite.