Self-assembly of hierarchically mesoporous-macroporous phosphated nanocrystalline aluminum (oxyhydr)oxide materials

A hierarchical structure of mesoporous-macroporous phosphated aluminum (oxyhydr)oxide (PAI) materials was prepared via a simple self-assembly process with the use of precursor aluminum sec-butoxide in a mixed solution of H3PO4 and Na-2HPO4. Direct phosphation resulted in the incorporation of phosphorus into the inorganic framework of aluminum (oxyhydr)oxides by the Al-O-P bonds. The X-ray diffraction (XRD) patterns revealed that, despite slight phosphorus incorporation or phosphation, the frameworks of the as-synthesized autoclaved PAI samples remained in a crystalline phase of boehmite A1OOH-type, and their calcined products had a phase of gamma-Al2O3-type. The macroporous structures are uniform, with sizes of 500-1800 nm, and the macropore walls are composed of accessible inesopores of a scaffold-like nanoparticle assembly. It is shown that the direct incorporation of phosphorus from a phosphate solution of the synthesis system can stabilize the framework of mesoporous-macroporous aluminum oxides with high surface areas and acidic properties. The present study also demonstrated that the surfactant (Brij 56) did not seem to have a direct role in the formation of macroporous structures, but significantly influenced the textural properties of the resultant PAI materials. The surface areas of surfactant-synthesized PAI exceeded 700 m(2)/g, which is almost two times of that of surfactant less-synthesized samples. The synthesized hierarchical PAI exhibited high thermal stability (at least 800 degrees C), possessing surface hydroxyl groups and acid sites, which may attract much interest for practical applications, including catalysis.