Síntese de catalisadores a partir do pentóxido de nióbio e do dióxido de titânio para uso em processos fotocatalíticos

Abstract

The textile industry stands out not only for its economic importance, but also for its polluting potential, generating liquid effluents that impact the environment. The main characteristic of these effluents is the color, resulting from the incomplete fixation of the dyes during the dyeing of the fabrics. Since 1972, photocatalysis has attracted attention to its applicability in the treatment of effluents and titanium dioxide is the most studied photocatalyst, including degradation of textile effluents. However, other semiconductor oxides are also potentially attractive for this use. Brazil holds more than 90% of the world's exploitable reserves of niobium, making the development of technology associated with the use of this raw material interesting for the country. In this work, four catalysts containing 1%wt. Nb2O5 in TiO2 were synthesized for use in the photocatalytic discoloration of textile dyes using visible light. Three catalysts were synthesized by wet impregnation of titania using ammonium oxalate solutions of niobium and ammonium diperoxo dioxalonium and one by sol-gel method from niobium ethoxide and titanium isopropoxide, followed by calcination at 500 °C. The catalysts were characterized by XRD, textural analysis, DRS and FTIR. The doped titanias obtained by impregnation have similar physicochemical properties in relation to the original P25 titania, with anatase and rutile phases. The material obtained by the sol-gel method presents high crystallinity, with predominance of the brookite structure, which is a difficult titania phase, according to the literature. Increases in specific areas and in the mean pore diameters were also observed, with percentages above 34 and 17%, respectively, relative to pure titania. Photocatalytic tests using aqueous solutions of the Reactron 4GL Yellow or Marine Intracron VS-B Ultra dyes were conducted for 2 hours under visible radiation lamp. The color removal was measured by UV/VIS spectrophotometry. In the photocatalytic tests using the Yellow dye, the catalysts had excellent performances, presenting a very significant discoloration, with percentages above 93%. Significant results were also obtained in the photocatalytic tests using the Marine dye, with percentages above 71% being discolored. The methodologies for the synthesis of titania doped with niobia are original and the results have proved the efficient materials for the photocatalytic process aiming at the removal of color from textile effluents.