The well-ordered two-dimensional hexagonal (2D-hex) structure of mesoporous Ta2O5 was maintained after crystallization with the aid of SiO2 reinforcement, which was removed after crystallization. The photocatalytic activity of the mesoporous Ta2O5 for overall water splitting under ultraviolet (UV) irradiation was improved by changing the solid phase structure from amorphous to crystalline by nearly 1 order of magnitude. The resulting photocatalytic activity of NiO
x
(3.0 wt %)-loaded crystalline mesoporous Ta2O5 for water decomposition (3360 μmol·h−1 of H2 and 1630 μmol·h−1 of O2 evolution at the initial 1 h) was found to show one of the highest activities among so far reported photocatalysts under similar conditions. The high activity is attributable to the efficient transfer of the excited electrons and holes from inside to the surface of the catalyst through thin-walled crystalline phase.
Three-dimensionally ordered mesoporous niobium oxide was prepared by a neutral templating route with the addition of a trace amount of cations, which have 5- and 2-nm pore diameter and wall thickness, respectively.
Single-crystal particles of mesoporous niobium-tantalum mixed oxide with a wormholelike 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(CH 2 CH 2 O) 20 (CH 2 CH(CH 3 )O) 70 (CH 2 CH 2 O) 20 H, 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. N 2 -gas adsorption-desorption analysis indicated that the pore volume of the crystallized sample remained the same as that of the amorphous precursor. The fabricated niobiumtantalum mixed oxide exhibits high thermal, hydrothermal, and mechanical stability.
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