Single-Crystal Particles of Mesoporous Niobium−Tantalum Mixed Oxide

Single-crystal particles of mesoporous niobium−tantalum mixed oxide with a wormhole-like structure were successfully prepared and characterized. The mixed oxide was prepared by a neutral templating method, and the samples provided have thick walls and an unordered pore structure. Neutral block copolymer, HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H, and metal chlorides were used as the template and inorganic source in propanol. The crystallized mesoporous single-crystal structures were obtained by a two-step calcination process; the first calcination process removes the template, forming a mesoporous structure with amorphous wall material, and the second calcination process crystallizes the pore walls while maintaining the mesoporosity. The submicrometer mesoporous particles forming the walls were confirmed by transmission electron microscopy to be single crystals. The pore diameter was found to increase upon crystallization, while retaining the open-pore system. N2-gas adsorption−desorption analysis indicated that the pore volume of the crystallized sample remained the same as that of the amorphous precursor. The fabricated niobium−tantalum mixed oxide exhibits high thermal, hydrothermal, and mechanical stability.