Preparation of Crystallized Mesoporous Ta3N5 Assisted by Chemical Vapor Deposition of Tetramethyl Orthosilicate

Ordered mesoporous Ta3N5 with crystalline thin-wall structures was successfully obtained from an amorphous mesoporous Ta2O5 by nitridation at 1073 K under flowing NH3 (500 mL min(-1)). The silica layer that was deposited on the pore wall by chemical vapor deposition of tetramethyl orthosilicate and later easily removed by alkaline treatment was indispensible for preserving the original mesostructure against phase transition during crystallization and nitridation. Mesoporous Ta3N5 has a mesoporosity and mesoporous structure similar to that of amorphous Ta2O5 and crystallized pore walls composed of orthorhombic Ta3N5. The BET surface area, pore size, and wall thickness of mesoporous Ta3N5 were approximately 100 m(2) g(-1), 4 nm, and 2 nm, respectively. Mesoporous Ta3N5 loaded with Pt nanoparticles was active for photocatalytic H-2 evolution from an aqueous methanol solution under visible light (lambda > 420 nm). The photocatalytic activity of mesoporous Ta3N5 was three times that of conventional bulk Ta3N5 under the same reaction conditions because of the former's thin crystallized pore wall (ca. 2 nm in thickness), which enabled efficient charge transfer of photoexcited electrons and holes to surface active sites.