Synthesis of silicon dioxide, silicon, and silicon carbide mesoporous spheres from polystyrene sphere templates

Abstract

Amberlite XAD 16N mesoporous polystyrene spheres were used as a template to create silicon dioxide (SiO2), silicon, and silicon carbide (SiC) mesoporous spheres. Polystyrene spheres, infiltrated with either hydrochloric acid catalyzed tetraethyl orthosilicate or dimethylethylamine catalyzed tetramethyl orthosilicate, were heated to 550 °C to induce oxidation and/or decomposition of the polystyrene template and yielded SiO2 spheres. To create Si and SiC spheres, SiO2 and SiO2-infiltrated spherical polystyrene templates, respectively, were distributed in finely grated magnesium before heating to 675 and 700 °C each in an argon atmosphere. Mg by-products in the form of magnesium silicates and residual SiO2 were removed by washing the spheres with hydrochloric acid and hydrofluoric acid, respectively. X-ray diffraction, Brunauer–Emmet–Teller model specific surface area analysis, Barrett–Joyner–Halenda model pore diameter analysis, transmission electron microscopy and scanning electron microscopy were employed to investigate the microstructure and porosity during and after synthesis of the spheres. All three types of spheres maintained high porosity and their spherical shape throughout the synthesis. SiO2 spheres had a surface area of 700 m2 g−1, Si spheres a surface area of 160 m2 g−1, and SiC spheres a surface area of 215 m2 g−1. SiO2 spheres with dispersed Ag nanoparticles were also successfully created by adding AgNO3 to the precursor solution; they had a surface area of 220 m2 g−1. To prove the versatility of this infiltration method, Dy2O3 spheres were also fabricated, though they were not porous. This infiltration method is not only versatile, as it is suitable for the preparation of numerous types of mesoporous spheres, but it is also a simple synthesis method that guarantees a well-defined spherical shape and narrow particle size distribution, primarily while maintaining a high surface area.