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

Ordered mesoporous Ta 3 N 5 with crystalline thin-wall structures was successfully obtained from an amorphous mesoporous Ta 2 O 5 by nitridation at 1073 K under flowing NH 3 (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 Ta 3 N 5 has a mesoporosity and mesoporous structure similar to that of amorphous Ta 2 O 5 and crystallized pore walls composed of orthorhombic Ta 3 N 5 . The BET surface area, pore size, and wall thickness of mesoporous Ta 3 N 5 were approximately 100 m 2 g −1, 4 nm, and 2 nm, respectively. Mesoporous Ta 3 N 5 loaded with Pt nanoparticles was active for photocatalytic H 2 evolution from an aqueous methanol solution under visible light (λ > 420 nm). The photocatalytic activity of mesoporous Ta 3 N 5 was three times that of conventional bulk Ta 3 N 5 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.