Cr3+-doped macroporous Al2O3 monoliths prepared by the metal-salt-derived sol-gel method

Cr3+-doped alumina (Al2O3) monoliths with well-defined macropores have been synthesized from the aqueous and ethanolic solution of aluminum and chromium salts in the presence of propylene oxide (PO) and poly(ethylene oxide) (PEO) using the sol-gel method accompanied by phase separation. The addition of PEO to the starting solution induces the phase separation, whereas the introduction of PO controls the gelation. The bicontinuous macroporous structures are obtained by inducing the phase separation parallel to the gelation, and the pore size can be controlled by adjusting the composition of starting solutions. The dried gel and that heat-treated at 700 degrees C are amorphous. As the heat-treatment temperature is increased over 700 degrees C, nanocrystalline gamma-Al2O3 is precipitated at 800 degrees C, a mixture of theta- and (alpha-Al2O3 phases appears at 1100 degrees C, and a single of alpha-Al2O3 is obtained at 1200 degrees C, while keeping the bicontinuous macroporous structure. Cr3+-doped alpha-Al2O3 monoliths with well-defined macropores exhibit photoluminescence as observed for ruby, indicating that Cr3+ ions are homogenously dispersed into the skeletons of bicontinuous network and substitute uniformly for the Al3+ sites. (c) 2007 Elsevier B.V. All rights reserved.