Synthesis of Ordered Porous Graphitic-C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self-Assembled Silica Nanospheres As a Primary Template

Uniform-sized silica nano- spheres (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-C₃N₄structures with the uniform pore size of 20–80 nm 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 Ta₃N₅ samples were as high as 60 m² g^-1,and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g-C₃N₄. Polycrystalline hollow nanoparticles of Ta₃N₅ 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.