Síntese e aplicação dos óxidos SiO2-ZrO2 e SiO2-ZrO2-BaO pelos métodos de Pechini e complexação meta-quitosana

Abstract

Silica modification has been an alternative to improve some properties of this material, such as the insertion of other metal oxides, providing greater chemical and mechanical resistance. In this work, silica was modified for use in liquid chromatography, as well as the application of oxides in photocatalysis. The oxides were synthesized by the modified Pechini method (MPE) and by the metal-chitosan complexation method (CMQ), to confer better properties to the final material. Thus, the oxides SiO2-ZrO2 (SZ) and SiO2-ZrO2-BaO (SZB) were synthesized by both methods. For use in chromatography, glycerol was added to the surface of the oxides, both those synthesized by MPE and CMQ. To elucidate the structural and textural properties of these materials, they were then characterized by thermogravimetric analysis (TGA), infrared absorption spectroscopy (FTIR), nitrogen physisorption analysis at 77 K (BET) and X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and ultraviolet diffuse reflectance spectroscopy (DRS). The TGA analyses showed that the synthesized materials had an effective calcination, with the absence of organic matter and presented good thermal resistance, without degradation and with mass losses between 4.0 and 8.0%. In the FTIR analyses, the loss of the signal at 800 cm-1 present in pure silica was observed in the spectra, showing that there was modification in the Si-OH groups with the insertion of metals in this bond. In the nitrogen physisorption analyses, by the BET method, a larger surface area was observed for the SZB oxide synthesized by the CMQ method (203 m2 /g), while the SZ oxide presented a larger area when synthesized by the MPE method (335 m2 /g). In the DRS analyses, a lower bandgap value was noted for the oxides synthesized by CMQ, being 2.93 for SZ-CMQ and 3.51 for SZB-CMQ, which were applied in the photodegradation of methylene blue. The materials proved to be active in the degradation of the dye, with the SZB-CMQ oxide being the one that presented the greatest photocatalytic potential, eliminating more than 80% of the dye when activated by simulated sunlight. After the addition of glycerol to the oxides, this addition was confirmed by FTIR through the appearance of bands between 3000-2800 cm-1 referring to the C-H bonds, proving the effectiveness of the synthesis method. At the end of the synthesis, the stationary phases SZCMQ-gly, SZBCMQ-gly and SZMPE-gly were obtained, which were applied in the separation of the compounds 1-methyl imidazole, caffeine, 5-fluorouracil, adenine, benzoic acid and salicylic acid, where it was possible to observe the separation of these 6 compounds in the SZCMQ-gly and SZMPE-gly columns, with a resolution greater than 1.5 for most of the compounds, with the SZMPE-gly column being the most efficient, presenting a minimum theoretical plate height of 0.004.