Síntese de espumas vítreas decoradas com partículas de óxido de nióbio para aplicação fotocatalítica

Abstract

The inadequate disposal of synthetic dyes in water is a constant concern of public health agencies. These colored effluents if not treated correctly can cause several environmental damages. An attractive alternative for the treatment of this type of effluent is one that uses powdered semiconductors to photodegrade such organic compounds. However, the recovery of these powders is complex and requires expensive separation processes. Therefore, the use of glass foams, a material with a high surface area and porous, as a support material for the deposition of catalysts can be an interesting option to reduce the costs of the purification process. Consequently, the present work aimed to obtain glass foams using the fluorescent lamp waste glass and eggshell as a foaming agent, decorated with niobium oxides, aiming at the application in photocatalysis systems for degradation of the synthetic tartrazine yellow dye from aqueous solutions. The glass foams were synthesized using 5% foaming agent at 700 °C. The impregnation with particles of the niobium oxide catalyst was carried out in a microwave oven, under different temperatures, of 130, 145, and 160 ºC, controlled pressure of 5 kgf cm-2, and synthesis times of 5, 10, and 15 min. The influence of the synthesis parameters on the foam covering was evaluated. Vitreous foams, as well as foams decorated with niobium oxide, were characterized by X-ray diffraction techniques, X-ray fluorescence, Raman and infrared spectroscopies, and optical and scanning electron microscopies. Also, the glass foams covered with Nb2O5 have their optical band gaps elucidated through the diffuse reflectance technique. The synthesized systems presented an optical band gap in the range of 2.8 to 3.2 eV. Through scanning electron microscopy, it is possible to confirm the covering of the glass foams with Nb2O5, presenting different growth morphologies. Furthermore, it was possible to verify that the synthesis temperature has a strong influence on the shape of the deposited niobium oxide particles on the glassy foams. Systems synthesized at 160 oC for 15 min show particles shaped like micro rods, which are organized giving rise to a “forest of rods”. The photocatalysis tests of the Tartrazine Yellow synthetic dye were performed using a reactor with six 15 W mercury lamps. Tests using glass foams decorated with niobium oxide, glass foams, and only the light source were performed. Through the results obtained, it was possible to verify that all foam compositions recovered with Nb2O5 showed photoactive properties and were efficient in the degradation of the synthetic dye, with the system produced at 160 ºC and 15 min the most photoactive. The use of glass foams as a support material for catalyst materials presents itself as a viable alternative and with significant results for photocatalysis, eliminating the step of separating the suspended catalyst.