Nanopartículas de óxido de manganês e alumínio aplicadas como catalisadores na ozonização de ácidos húmicos

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Química, Florianópolis, 2017A ozonização associada ao uso de catalisadores é proposta como uma tecnologia promissora aplicada ao tratamento de águas e efluentes, na qual há a formação de espécies radicalares altamente reativas e não seletivas, que conduzem a um aumento da razão de mineralização dos poluentes orgânicos. Vários óxidos metálicos têm sido propostos como catalisadores, mas ainda existem diversos aspectos relativos a este processo que precisam ser estudados para que se torne uma alternativa tecnológica para aplicação em larga escala. O objetivo deste trabalho é investigar a eficiência dos óxidos de manganês e de alumínio na ozonização catalítica dos ácidos húmicos, avaliando os efeitos das condições operacionais na taxa relativa de mineralização e oxidação parcial. Os catalisadores foram caracterizados através de análise do ponto de carga zero, área superficial específica (BET), espectroscopia de infravermelho (FTIR), microscopia eletrônica de varredura (MEV), espectrometria por energia dispersiva (EDS), difração de raios X (DRX) e espectroscopia de fotoelétrons de raios X (XPS). A cinética de adsorção dos ácidos húmicos revelou que somente o óxido de alumínio é capaz de adsorver os ácidos húmicos, enquanto que a adsorção em óxido de manganês é muito pequena. Na ozonização não catalítica foi avaliada a influência do pH na reação de mineralização dos ácidos húmicos visando a redução de UV254 e VIS400. A taxa da ozonização não catalítica aumenta com o aumento do pH e, em pH 5,5, atingiu-se, respectivamente, 81,4% e 89,3% de remoção da matéria orgânica em 1 h em UV254 e VIS400. Os catalisadores foram avaliados quanto à atividade catalítica e o emprego do catalisador de óxido de alumínio resultou na maior mineralização dos ácidos húmicos com 98,8% e 97,1% de mineralização em UV254 e VIS400, respectivamente. A taxa da ozonização catalítica dos ácidos húmicos aumenta com o aumento da dosagem dos catalisadores na seguinte ordem: 0,5 g/L Al2O3 > 0,1 g/L Al2O3 > 0,5 g/L Mn2O3 0,1 g/L Mn2O3. Foi observado que o processo de ozonização catalítica utilizando óxido de alumínio apresentou uma taxa de degradação dos ácidos húmicos 2,3 vezes maior do que a da ozonização não catalítica.Abstract: The ozonation associated with the use of catalysts is proposed as a promising technology applied to the treatment of water and effluents, in which there is a formation of species radically highly reactive and non- selective, which has an increase in the mineralization ratio of organic pollutants. Several metal oxides have been proposed as catalysts, but there are still several aspects related to this process that need to be studied to become a technological alternative for large scale application. The goal of this work is to investigate the efficiency of manganese and aluminum oxides in the catalytic ozonation of humic acids, evaluating the effects of operational conditions on relative rate and mineralization and partial oxidation. The catalysts were characterized by point of zero charge analysis, BET surface area, infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X- ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The adsorption kinetics of humic acids revealed that only aluminum oxide is capable of adsorbing humic acids, whereas the adsorption on manganese oxide is very small. In non-catalytic ozonation the influence of pH on the humic acid mineralization reaction was evaluated aiming at the reduction of UV254 and VIS400. The rate of non-catalytic ozonation increases with increasing pH and, at pH 5.5, 81.4% and 89.3% removal of the organic matter were achieved in 1 h in UV254 and VIS400, respectively. The catalysts were evaluated for catalytic activity and the use of the aluminum oxide catalyst resulted in the higher mineralization of humic acids with 98.8% and 97.1% of mineralization in UV254 and VIS400, respectively. The rate of catalytic ozonation of humic acids increases by increasing catalyst dosage in the following order: 0,5 g/L Al2O3 > 0,1 g/L Al2O3 > 0,5 g/L Mn2O3 0,1 g/L Mn2O3. It was observed that the catalytic ozonation process using aluminum oxide achieved a mineralization rate of humic acids 2.3 times greater than non-catalytic ozonation

Synthesis of citrate–modified cufes2 catalyst with significant effect on the photo–fenton degradation efficiency of bisphenol a under visible light and near–neutral PH

In this study, for the first time, citric acid was employed as a chelating agent in CuFeS2 synthesis in order to accelerate the regeneration of Fe2+ during the photo–Fenton reaction, promoting a faster production of •OH radicals. The novel CuFeS2 material showed remarkable catalytic efficiency for bisphenol A (BPA) degradation during the photo–Fenton process under visible light and near–natural pH, with a rate 10 times faster than that of CuFeS2 prepared without citrate. Furthermore, CuFeS2 promoted rapid generation of •OH radicals and showed efficient H2O2 consumption, sustaining the catalytic efficiency and stability even after 4 consecutive cycles of use. CuFeS2 was also efficient for BPA degradation from a municipal wastewater treatment plant effluent. BPA by–products were identified and a mechanism for BPA degradation was proposed. After the photo–Fenton process, no Fe3+ species were identified on the catalyst surface by X–ray photoelectron spectroscopy (XPS), indicating that citric acid accelerated the conversion of Fe3+/Fe2+, thus increasing the generation of •OH and the process efficiency

Investigation of the reaction pathway for degradation of emerging contaminant in water by photo-Fenton oxidation using fly ash as low-cost raw catalyst

In this work, fly ash from a Brazilian thermal power plant was employed as a low-cost raw catalyst for Procion red degradation by photo-Fenton process. The ash was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms (BET), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDX). The material had an iron content of 4.10 wt%, distributed homogeneously on the solid surface. The ash particles showed mainly spherical morphology between 0.5 and 20 µm. The catalyst presented promising activity, reaching 93% of dye decolorization at 60 min of reaction, and 85% of organic load removal at 240 min. The predominant oxidizing species involved on the degradation of dye molecules during the photo-Fenton reaction were the hydroxyl radicals (HO·). The material showed remarkable stability and reusability after five successive cycles of reuse. The reaction intermediates were identified by LC/MS analysis and a reaction pathway was proposed

Photo-assisted degradation of organic pollutant by CuFeS2 powder in RGB-LED reactors: A comprehensive study of band gap values and the relation between wavelength and electron-hole recombination

This work investigated the relation between direct band-gap conversion and excitation wavelength towards catalysis efficiency in red, green, and blue (RGB) light-emitting diode (LED) reactors. An integrating sphere and spectroradiometer system obtained the emission wavelengths of the operating modes spectra of the RGB-LED reactors. The effects of pH, catalyst, and H2O2 dosage were investigated, and the optimal photocatalysis conditions were found to be at pH 3, catalyst loading of 0.25 g L 1, 0.25 mmol L 1 of H2O2(aq) (30% v/v) for an initial model pollutant concentration of 75 mg L 1 and reaction time of 60 min. Under the higher intensity red mode (R1), the highest color removal rate was reached (88.1%), while in the conventional white light mode (WL), the decolorization efficiency remained 64.3%. Furthermore, the R1 mode showed a superior TOC removal than the WL mode, reaching the final removal efficiencies of 91.86% and 61.06%, respectively. Contrary to what has been reported, as the dominant wavelength of the irradiation source decreased, the efficiency also tended to decrease. The electronhole recombination increased as the irradiation mode decreased, and a work function (u) representing this phenomenon was obtained by the deduction of the relation between energy (E) and frequency (f) of the photons involved. Therefore, the insights presented in this work are valuable tools in increasing LED photocatalysis efficienc