Preparation, structural and morphological studies of Ni doped titania nanoparticles

Ni-doped and Ni/Cr co-doped TiO2 nanotubes for enhancement of photocatalytic degradation of methylene blue

Ni-doped and Ni/Cr co-doped TiO₂ nanotubes were successfully synthesized using a novel hydrothermal method. The surface and bulk properties of as-synthesized nanopowders were characterized using various microstructural and optical techniques. The photocatalytic ability of these nanopowders was investigated systematically for the decomposition of methylene blue dye (MB) under visible light illumination. The morphological results revealed the structural transformation of TiO₂ nanotubes to nanosheets, and further to a mixture of nanosheet/nanotube on doping with Ni and co-doping of Ni/Cr, respectively. Moreover, the Ni doping causes an optical absorption edge shifts towards lower wavelengths, while doping by Ni/Cr results to an optical absorption edge shifts towards higher wavelength in comparison to TiO₂-nanotubes. Also, Ni-doping and Ni/Cr co-doping strongly affects the Raman vibrational modes owing to the changes in interplanar distance, crystallite size, dislocation density, and crystal microstrains. Among the undoped, doped and co-doped TiO₂ nanoparticles, the 6Ni/4Cr co-doped TiO₂ exhibited a higher efficiency of 95.6% and excellent stability towards the photocatalytic degradation of MB. It is attributed to the availability of many carriers for the efficient photo-oxidation within the UV-Vis optical absorption range. Also, the photocatalytic reaction kinetics and degradation mechanism of MB were discussed.

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

Ilmenite-rich black sands from an alluvial deposit of Barbacoas (Nariño, 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°) 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 μm, 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.