Navegando por Autor "Machado, Alan Rodrigues Teixeira"
Agora exibindo 1 - 3 de 3
Resultados por página
Opções de Ordenação
Item Catalytic growth of carbon nanofibers on Cr nanoparticles on a carbon substrate : adsorbents for organic dyes in water.(2013) Oliveira, Luiz Carlos Alves de; Silva, Adilson Cândido da; Machado, Alan Rodrigues Teixeira; Diniz, Renata; Pereira, Márcio CésarWe have produced carbon nanofibers (CNFs) using leather waste that had been tanned with a chromium bath, and when dried contained Cr2O3. Suitable reduction processing produced a carbon substrate with supported nanoparticles of chromium metal. Powder X-ray diffraction showed that the Cr2O3 is reduced on the carbon surface to produce CrC and metal Cr, which is the effective catalyst for the CNFs growth. The CNF arrays were confirmed by TEM images. Raman data revealed that the synthesized CNFs have a poor-quality graphite structure which favors their use in adsorption processes. These CNFs presented higher affinity to adsorb anionic dyes, whereas the cationic dyes are better adsorbed on the carbon substrate. The low-cost and availability of the carbon precursor makes their potential use to produce CNFs of interest.Item Enhanced photocatalytic activity of TiO2/γ-Fe2O3 by using H2O2 as an electron acceptor under visible light radiation.(2020) Oliveira, Victor L.; Lima, André Luiz Dias; Gabriel Filho, José Balena; Pereira, Márcio César; Souza, Thainá Stefanie Ferreira; Ardisson, José Domingos; Machado, Alan Rodrigues Teixeira; Silva, Adilson Cândido daTiO2 is a photocatalyst widely used for the degradation of organic compounds in aqueous media; however, it presents some difficulties for application on larger scales. The biggest limitations are its bandgap value of 3.2 eV which corresponds to the UV range of the spectrum and its difficult removal from the reaction medium after the reaction. An alternative to enhance the photocatalytic activity of TiO2 consists in design heterojunctions with semiconductors that are active under visible light irradiation. Some reports have described the magnetic property and synthesis procedures based on inexpensive and abundant raw material. In this work, we synthesized photocatalysts based on γ−Fe2O3impregnated with different levels of TiO2. This may contribute to improving the wide application of TiO2 in water, since γ-Fe2O3 has magnetic features that facilitate the removal of the catalyst after the reaction run. The materials were characterized by X-ray diffraction, analysis of adsorption/desorption of N2, reflectance diffuse, and 57Fe Mössbauer spectroscopy. The photocatalytic activity of the materials was tested for removing rhodamine under visible or visible light in the presence of H2O2. From the X-ray diffraction and 57Fe Mössbauer spectroscopy data, it was observed the formation of γ-Fe2O3 phase with small particle. Without visible light, only 45% of RhB was adsorbed, and with the light on, there is no increase in removal after 60 min. However, after adding H2O2, the photocatalytic activity of material was significantly improved, reaching 80% of dye removal. Tests using scavengers of reactive species revealed that − O2 and OH are the main species in this system. Moreover, the H2O2 retards the electron−hole recombination, thus increasing its photocatalytic activity. The ESI-MS analysis revealed that in 15 min of reaction, deethylation (m/z = 415, 388), deamination (m/z = 301 and 279), and rhodamine B severe oxidation products (m/z < 250) were present in solution, and TOC analysis confirms the mineralization of the rhodamine.Item Improved photocatalytic activity of d-FeOOH by using H2O2 as an electron acceptor.(2017) Silva, Adilson Cândido da; Almeida, Monique Rocha; Rodriguez, Mariandry del Valle Rodriguez; Machado, Alan Rodrigues Teixeira; Oliveira, Luiz Carlos Alves de; Pereira, Márcio CésarIn this work, d-FeOOH nanoparticles were synthesized by a simple co-precipitation method and used as a photocatalyst in the presence of H2O2 for the oxidation of Rhodamine B (RhB) dye under artificial light. The d-FeOOH was characterized by powder X-ray diffraction, 57Fe Mössbauer spectroscopy, N2 adsorption/desorption and UV–vis diffuse reflectance measurements. The d-FeOOH nanoparticles have high specific surface area (101 m2 g 1) and optical bandgap energy of 2.02 eV. Under artificial light, only 59% of RhB (100 mL; 20 mg L 1) was photocatalytically degraded by d-FeOOH in 60 min reaction. However, after adding H2O2, the photocatalytic activity of d-FeOOH was significantly improved, reaching 87% of dye removal. Tests using scavengers of reactive species and EPR analysis revealed that h+ and OH are the main species in this system. Based on the experimental results, the mechanism of RhB photodegradation in the presence of d-FeOOH and H2O2 was proposed. By this mechanism, the OH can be formed by direct water oxidation or by H2O2 reduction, as the electron transfer from the conduction band of d-FeOOH to H2O2 is thermodynamically favorable. Moreover, the H2O2 retards the electron-hole recombination in d-FeOOH, thus increasing its photocatalytic activity. Given its high efficiency for degrading RhB in water, d-FeOOH revealed to be a promising photocatalyst to be tested in the oxidation of emerging pollutants for the environmental decontamination.