Crystalline ZrO2 monoliths with well-defined macropores and mesostructured skeletons prepared by combining the alkoxy-derived sol-gel process accompanied by phase separation and the solvothermal process

We have successfully prepared multiscale porous crystalline zirconia (ZrO2) monoliths by combining alkoxy-derived sol-gel process accompanied by phase-separation and the solvothermal process. The gelation can be controlled by the addition of N-methylformamide to the starting solution, while the phase separation is induced by the incorporation of poly(ethylene oxide). Amorphous ZrO2 monolithic gels with well-defined bicontinuous macropores and microstructured skeletons are obtained when the transient. structure of polymerization-induced phase separation is fixed by the gelation. The size of the macropores is controlled in the range of 300 nm to 2 mu m by adjusting the amount of poly(ethylene oxide). The solvent exchange of the mother liquor in the as-gelled wet specimens with absolute ethanol, followed by the solvothermal treatment at temperatures above 210 degrees C, brings about the formation of mesopores and stabilizes tetragonal ZrO2 nanocrystals without disturbing the macroporous morphology. The resultant macro-mesoporous crystalline ZrO2 gels possess the surface area over 200 m(2) g(-1).