Synthesis of ordered porous graphitic-C₃N₄ and regularly arranged Ta₃N₅ nanoparticles by using self-assembled silica nanospheres as a primary template

Uniform-sized silica nanospheres (SNSs) assembled into close-packed structures were used as a primary template for ordered porous graphitic carbon nitride (g-C₃N₄), which was subsequently used as a hard template to generate regularly arranged Ta₃N₅ nanoparticles of well-controlled size. Inverse opal g-C₃N₄ structures with the uniform pore size of 20-80nm were synthesized by polymerization of cyanamide and subsequent dissolution of the SNSs with an aqueous HF solution. Back-filling of the C₃N₄ pores with tantalum precursors, followed by nitridation in an NH₃ flow gave regularly arranged, crystalline Ta₃N₅ nanoparticles that are connected with each other. The surface areas of the Ta₃N ₅ samples were as high as 60m²g^-1, and their particle size was tunable from 20 to 80nm, which reflects the pore size of g-C₃N₄. Polycrystalline hollow nanoparticles of Ta ₃N₅ were also obtained by infiltration of a reduced amount of the tantalum source into the g-C₃N₄ template. An improved photocatalytic activity for H₂ evolution on the assembly of the Ta₃N₅ nanoparticles under visible-light irradiation was attained as compared with that on a conventional Ta₃N₅ bulk material with low surface area. Following an order: Silica nanospheres were used as a template to form ordered porous graphitic carbon nitride (g-C₃N₄), which were used in the synthesis of crystalline Ta₃N₅ nanoparticles. These showed improved photocatalytic activity for H₂ evolution under visible-light irradiation.