A Simple Synthetic Approach to Al2O3–TiO2 and ZnO–TiO2 Mesoporous Hollow Composite Assemblies Consisting of Homogeneously Mixed Primary Particles at the Nano Level

A simple synthetic approach to Al2O3–TiO2 and ZnO–TiO2 mesoporous hollow composite assemblies consisting of homogeneously mixed primary particles at the nano scale was demonstrated. The composites, Al2O3–TiO2 and ZnO–TiO2, have a large specific surface area (250–600 m2 g–1) and were synthesized by high-temperature and high-pressure treatment of precursor solutions containing Al(OiPr)3 or Zn(OAc)2, Ti(OiPr)4, and phthalic acid in methanol. Aggregated, fused spherical, and individual spherical morphologies of the hollow assemblies with amorphous Al2O3 and anatase TiO2 were obtained, depending on the Al/Ti ratio of the precursor solutions. Hollow spherical composite assemblies with amorphous ZnO and anatase TiO2 phases were obtained by treating precursor solutions with lower Zn contents (5–25 %). A phase transition from anatase to rutile was not observed for the Al2O3–TiO2 composite assemblies (50 % Al) even at 1000 °C. The band gap energies of the ZnO–TiO2 hollow assemblies were tuned (3.12–3.21 eV) by changing their Zn content.