Synthesis of Ordered Porous Graphitic‐C 3 N 4 and Regularly Arranged Ta 3 N 5 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‐C 3 N 4 ), which was subsequently used as a hard template to generate regularly arranged Ta 3 N 5 nanoparticles of well‐controlled size. Inverse opal g‐C 3 N 4 structures 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 C 3 N 4 pores with tantalum precursors, followed by nitridation in an NH 3 flow gave regularly arranged, crystalline Ta 3 N 5 nanoparticles that are connected with each other. The surface areas of the Ta 3 N 5 samples were as high as 60 m 2 g −1 , and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g‐C 3 N 4 . Polycrystalline hollow nanoparticles of Ta 3 N 5 were also obtained by infiltration of a reduced amount of the tantalum source into the g‐C 3 N 4 template. An improved photocatalytic activity for H 2 evolution on the assembly of the Ta 3 N 5 nanoparticles under visible‐light irradiation was attained as compared with that on a conventional Ta 3 N 5 bulk material with low surface area.