RESUMEN
In this research, changes in several characteristics of partially reduced titania were studied. The reduction process used made it possible to gradually observe changes in the material depending on the amount of reducing agent used. We used NaBH4 to impregnate commercial TiO2 with isopropyl alcohol. Impregnated TiO2 nanoparticles were dried and thermally treated in a nitrogen flow to obtain blue titania samples. Thorough spectroscopic characterization showed that oxygen atoms from hydroxyl groups, as well as from the surface, and the lattice of TiO2 was consumed. This caused changes in the surface and even in the bulk of TiO2 when the amount of reducing agent used was increased. Structural, optical, superficial, and textural characteristics were studied using XRD, Raman, DRS UV-Vis-NIR, Mid-DRIFT, XPS, and nitrogen adsorption/desorption isotherms. A photocatalytic test of the degradation of methylene blue dye was performed. Among different effects on the mentioned characteristics, we found evidence of changes in the surface properties of the blue titania samples and their probable effect on the photocatalytic properties. The reduction process implied a preponderant decrease in the surface hydrophilicity of the reduced samples, an effect shown for the first time in this type of material.
RESUMEN
The photocatalytic activity of hydrogenated TiO2 was evaluated in the photooxidation of methyl orange (MO). The hydrogenation of TiO2 was carried out by calcination of a mixture of TiO2 P-25 and NaBH4 , at 300 and 350°C for blue TiO2 and black TiO2 , respectively. An experimental design was made for the determination of the best reaction conditions for the oxidation of MO. The influence of catalyst dosage and pH on photocatalytic efficiency was optimized, and the degradation percentage of MO was the response factor. The photocatalytic reaction was performed using a Xenon lamp that simulates the solar light spectrum for the activation of the catalyst. It was determined that both blue and black TiO2 show the greatest activity at pH = 2 and 0.8 g/L of catalyst. Additionally, the positive influence of hydrogen peroxide in the photocatalytic activity of both hydrogenated catalysts was determined. In parallel, COD and TOC were also studied. PRACTITIONER POINTS: The extent of titania reduction by hydrogenation is dependent on the reaction time with sodium borohydride. The extent of titania reduction affects the photocatalytic activity in the oxidation of methyl orange. An excess of catalyst reduction inhibits the oxidation of the dye because of the increase of recombination points. The best reaction conditions were determined by multivariate optimization as pH 2 and 0.8 g L-1 of hydrogenated catalyst. The addition of hydrogen peroxide into the reaction system improves the oxidation yield attributed to their electron accepting capacity.