Photocatalytic hydrogen production using visible-light-responsive Ta3N5 photocatalyst supported on monodisperse spherical SiO2 particulates

• Fine nanoparticles of Ta3N5 were immobilized on the surfaces of SiO2 giving SiO2@Ta3N5 core–shell spheres successfully produced H2 from methanol solution under visible light.
• The presence of support (SiO2) ensures the dispersion of the particulate in solution maintaining high photocatalytic activity of Ta3N5.
• The obtained supported photocatalyst gives uniform size distribution and control the degree of dispersibility in the solution, which may control nature of light absorption and reflection of the photoreactor.

Fine nanoparticles of Ta3N5 (10–20 nm) were synthesized on the surfaces of SiO2 spheres with a diameter of ∼550 nm. A sol–gel method was used to modify the surface of SiO2 with Ta2O5 from TaCl5 dissolved in ethanol in the presence of citric acid and polyethylene glycol. The resulting oxide composites were treated in an NH3 flow at 1123 K to form core–shell structured Ta3N5/SiO2 sub-microspheres. The obtained samples were characterized using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectra (EDX), transmission electron microscopy (TEM), and photocatalytic activity measurements for H2 evolution from an aqueous methanol solution. The XRD results demonstrate the expected sequential formation of Ta2O5 layers, followed by Ta3N5 after nitridation on the Ta2O5/SiO2 composite. SEM and TEM observations indicate that the obtained Ta3N5/SiO2 sub-microspheres have a uniform size distribution with high crystallinity and an obvious core–shell structure. The presence of support maintained the intrinsic photocatalytic activity of Ta3N5 nanoparticles, but it did drastically improve the dispersion of the photocatalysts in the solution. This study proposes the use of an inert support in photocatalytic reactors to improve ease of handling the powder photocatalyst for gas-phase photocatalysis and the suspension of the solution, controlling nature of light harvesting and degree of scattering of the photoreactor.

A simple and effective sol–gel process followed by nitridation in an NH3 flow has been developed to deposit Ta3N5 semiconductor photocatalyst layers onto monodisperse spherical SiO2 particles. The obtained Ta3N5/SiO2 particles maintain an original spherical morphology of SiO2 and a sub-micrometer size with a narrow size distribution and without aggregation. The presence of SiO2 support shows at least no detrimental effects on photocatalytic activity, but tunes the secondary particle size to control dispersibility of the photocatalyst in the solution.Figure optionsDownload as PowerPoint slide