Microspheres based on black sand mineral as a photocatalyst for photocatalytic hydrogen production under UV light

Abstract

Frequently, black sand from coastal deposits is a magnetic ore with a complex structure that is composed principally by iron, titanium and silica oxides, and metals such as vanadium, chromium, nickel, strontium, etc. This material could be used in oxidation/reduction processes as a photocatalyst that is naturally doped. However, its low surface area and the mass transfer constraints caused by the cluster formation in bulk reaction due to its magnetic character, also limits the photocatalytic performance. Microspheres of black sand as starting material were prepared by a simple associating method with alginate-Na, and then calcined under oxidizing atmosphere at 1100°C. After, they were characterized by XRF spectroscopy, SEM/EDX, XRD diffraction, N₂ adsorption/desorption measurements, FT-IR spectroscopy, differential thermal thermogravimetric analysis, and UV-Visible spectrophotometry. The photocatalytic activity of the microspheres was evaluated for hydrogen production from EDTA solutions under UV light irradiation using the Response Surface Methodology (RSM), in order to determine the optimum conditions of the process. At calcination temperature, rounded microspheres with rough surface were prepared, and had an apparent different density from the raw material. Due to their buoyancy in the suspension, the contact between photons that entered into suspension and the as-prepared microspheres favors hydrogen production. Although the BET specific surface decreased owing to the sintering surface, the chemical composition was similar compared with the starting material. Finally, the RSM can be used to readily determine the optimal conditions for photocatalytic hydrogen production by as-prepared microspheres used as photocatalyst under UV light irradiation, based on black sand mineral.