Photo-oxidative and photo-reductive capabilities of ilmenite-rich black sand concentrates using methyl orange as a probe molecule

摘要

Ilmenite-rich black sands from an alluvial deposit of Barbacoas (Narino, Colombia) were used as a natural source aiming to obtain a low-cost and highly available photocatalyst. Mineral concentrates were obtained by gravimetric concentration in a Wilfley table (deck tilt angle: 11-14 degrees) followed by dry magnetic or wet electromagnetic separation. Afterwards, the particle size was manually reduced down to -325 mesh. Rietveld refinements using X-ray diffraction data showed that the highest purity achieved was 93.46 of ilmenite (FeTiO3). Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy revealed a polyhedral morphology with an average grain size of 1.33-2.27 mu m, granular inclusions of aluminosilicates and appreciable quantities of manganese. The band-gap values determined by UV-Vis diffuse reflectance spectroscopy were underestimated compared to those reported in the literature, given the impurities in the samples and their optical behavior. Photoluminescence experiments provided a band-gap of 2.68 eV. The photo-oxidative and photo-reductive capabilities of the concentrates were evaluated in the degradation of methyl orange in aqueous solution under UV irradiation. 99 of discoloration was achieved after 50 min for oxidation and after 20 min for reduction, showing the potential of ilmenite-rich concentrates as photocatalysts.