Formation mechanism of mesoporous aluminum hydroxide film by alkali surface modification

Abstract

In this study, a new, relatively simple fabrication method for forming a mesoporous Al(OH)3 film on Al substrates was demonstrated. This method, i.e., alkali surface modification, was simply comprised of dipping the substrate in a 5 × 10-3 M NaOH solution at 80°C for one minute and then immersing it in boiling water for 30 minutes. After alkali surface modification, a mesoporous Al(OH)3 film was formed on the Al substrate, and its chemical state and crystal structure were confirmed by XPS and TEM. According to the results of the XPS analysis, the flake-like morphology after the alkali surface modification was mainly composed of Al(OH)3, with a small amount of Al2O3. The mesoporous Al(OH)3 layer was composed of three regions: an amorphous-rich region, a region of mixed amorphous and crystal domains, and a crystalline-rich region near the Al(OH)3 layer surface. It was confirmed that the stabilization process in the alkali surface modification strongly influenced the crystallization of the mesoporous Al(OH)3 layer.