Lincoln Carlos Silva de Oliveira

Synthesis and Characterization of Mesoporous Nb2O5 and Its Application for Photocatalytic Degradation of the Herbicide Methylviologen

This article reports the characterization of mesoporous Nb2O5 synthesized by the sol-gel method for application in photocatalysis. The emerging contaminant methylviologen was employed for photocatalytic tests. Parameters inherent to the synthesis process, such as stirring rate, aging temperature, and calcination temperature, were employed for a range of values to improve the synthetic route. The powders obtained were characterized by thermogravimetric analysis, X-ray diffraction, scanning and transmission electron microscopy, specific surface area, infrared spectroscopy, energy-dispersive spectroscopy, and diffuse reflectance spectroscopy. In samples calcined at 450 °C, a mixture of amorphous and hexagonal phases was observed, with a predominance of the former, while in samples calcined at 650 °C the orthorhombic phase predominated. Samples calcined at 450 °C exhibited larger specific surface areas. Mesoporous structures were confirmed for samples T8035M450 and T8045mi450, which displayed higher photoactivity, with roughly 90% removal of methylviologen.

COMPOSIÇÃO QUÍMICA E TEMPERATURA DE CRISTALIZAÇÃO DE ÉSTERES OBTIDOS DE QUATRO ÓLEOS VEGETAIS EXTRAÍDOS DE SEMENTES DE PLANTAS DO CERRADO

The seed oils from four plants (Scheelea phalerata, Butia capitata, Syagrus romanzoffiana, Terminalia cattapa) found in Mato Grosso do Sul were extracted at good yields. Alkaline transesterification of these seed oils to esters using methanol and ethanol was studied and also produced good yields. Oleic acid (30.5/32.3%), lauric acid (30.7/32.9%) methyl and ethyl esters, were the main components of transesterification of the oils from Scheelea phalerata and Syagrus romanzoffiana. Lauric acid (42.2%), capric acid (15.9%) and caprylic acid (14.6%) methyl and ethyl esters were the main ester components of transesterification of the oil from Butia capitata. Oleic acid (37.8%), palmitic acid (33.5%) and linoleic acid (22.6%) methyl and ethyl esters were the main components of transesterification of oil from Terminalia catappa. Based on differential scanning calorimetry (DSC) studies, the first crystallization peak temperature of esters was observed. Esters derived from oils of the family Arecaceae (Scheelea phalerata, Butia capitata, Syagrus romanzoffiana) showed the lowest points of crystallization, despite having high levels of saturated fat. Esters of Terminalia cattapa oil, rich in unsaturated fat, showed the highest crystallization temperature. This difference in behavior is probably related to the high concentration of esters derived from lauric acid and palmitic acid.

Use of Natural Rubber Membranes as Support for Powder TiO2and Ag/TiO2 Photocatalysts

The purpose of this study was to synthesize TiO2-polymer composites able to act as photocatalyst membranes. TiO2 catalysts were prepared using the sol-gel method to contain 0.0, 0.5, 1.0, and 2.0 wt.% of embedded Ag particles, subsequently incorporated into natural rubber latex at a weight fraction of 15%. Samples of these ceramic powders were suspended in a latex emulsion (natural rubber), cast in Petri dishes and slowly dried in an oven. The resulting materials were evaluated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, diffuse reflectance spectroscopy, differential scanning calorimetry, thermogravimetry, and photocatalytic assaying using methylene blue as an organic pollutant reference. All composite membranes exhibited good photoactivity conferred by TiO2 powder, with 98% dye fading after 300 min of ultraviolet irradiation.

Synthesis of Lamellar Structures of Magnesium (II), Aluminum (III) and Iron (III) Hydroxides Interchanged with Carbonate Ion through Precipitation in pH 11

The synthesis of layered double hydroxides has been investigated aiming innumerous applications, mainly as adsorbent, catalyst and catalyst support materials, due their ability to adsorb anionic species and several aqueous soluble compounds. The carbonated magnesium-aluminium hydrotalcites are known as the main class of the layered double hydroxides and new composition are often characterized under the view point of thermal stability, crystallinity and catalytic performance for many reactions. Few trivalent cations are able to replace the aluminum one due the severe restriction for oxidation state and ionic radii, but the iron (III) one seems to be high potential to improve some of the characteristics required for that materials, such as specificity for built-rebuilt bonds in organic molecules. In this work, we have synthesized carbonated magnesium-aluminum hydrotalcite samples through the coprecipitation at pH 11 and investigate the Fe(III) insertion at 10 and 20 mol%. Thermal analysis, FTIR spectrometry and X-ray diffractometry techniques were used to understand the influence of the Fe(III) co-substitution, keeping the Mg(II) molar fraction invariable among the samples. We show the iron (III) insertion affects the dehydration and dehydroxylation processes due the changes in M-OH bond energies Very homogeneous structures were obtained for all of the samples dried at 100 oC and a consistent lattice volume expansion was observed as a function of iron (III) content, which can be required for catalyst or catalyst matrix applications. DOI: http://dx.doi.org/10.17807/orbital.v10i1.1036

Influence of Chromium (III) Insertion on the Thermal Stability of Carbonated Magnesium and Aluminum Hydrotalcites Synthesized by the Hydroxide Coprecipitation Method

Anionic clays are structures capable of adsorbing large quantities of water and other polar molecules in aqueous medium due to an ordered lamellar arrangement. Generally, the most stable composition contains magnesium and aluminum hydroxides, but other trivalent metal cations with similar ionic radii may also be inserted in co-substitution to the aluminum cation, targeting changes in the specificities of the adsorbed molecules, such as the chromium (III) one. The main objective of this work was to investigate the thermal stability of the carbonated magnesium-aluminum hydrotalcite when different amount of aluminium (III) cation is replaced by chromium (III) one. For that purposes, the hydrotalcite samples were obtained through the coprecipitation method at pH 11, followed by ageing stage at 80 °C, washing and drying at 100 °C for 24 h. The results obtained by thermal analysis, FTIR spectroscopy, and X-ray diffractometry techniques have permitted to conclude that chromium insertion leads to turbostratic disorder along the c-axis, which affects also the thermal stability and crystallinity of the precipitated materials. The chromium-based hydrotalcites showed to be more easily dehydrated at lower temperatures, with dependence predominantly kinetic, which leads to significant volume contraction and the hindering of the subsequent dehydroxylation stage at higher temperatures. DOI: http://dx.doi.org/10.17807/orbital.v10i1.1039

Study of the Zirconium and Silicon Homovalent Dopants Insertion on the Structure and Bandgap Energy of Titanium Dioxide Powders

The reconstructive transformation occurring during the anatase-to-rutile phase transition can be observed through adequate techniques such as Thermal Analyses and Z-ray diffractometry followed by structural refinement. The typical photonic properties of titanium dioxide photocatalysts depend on the anatase structure and how the modifiers can provide their performance enhancement. In the present work, we investigate the structural effects caused by the simultaneous homovalent modification on the anatase structure in order to understand the mechanisms of the anatase-to-rutile phase transition in terms of the atomic coordinates and the lattice parameters. The refined structures along the calcination temperature from 500 to 900 oC suggest the oxygen bonds are strongly affected in unmodified anatase in order to destroy and rebuilt the crystal structure and lead to the rutile phase formation above 700 oC, unless some modifier pairs stabilize them.

Phase Formation in Copper and Calcium Titanate Dielectric Ceramic Obtained by Polymeric Precursor Method

The polycrystalline ceramic named calcium and copper titanate is a dielectric ceramic with very high dielectric constant applicable in several electronic devices. The powder form for that advanced ceramic can be synthesized through chemical route, like the Polymeric Precursor Method at relative lower temperatures the presence of alkaline earth cations harms the structural homogenization during the crystallization process. In this work, the calcium and copper titanate powder was obtained by Polymeric Precursors Method by imposing a slow thermal decomposition of polymeric precursor and several crushing steps before the calcination at 800 °C for 4 hours. The entire process was observed by thermogravimetric analysis and FTIR spectrometry, including the nitrogen adsorption-desorption isotherms and X-ray diffractometry techniques for calcined power samples. It was observed the crystallization of the cubic Im-3 Ca1/4Cu3/4TiO3 phase only starts after organics removal and full calcium carbonate elimination above 700 oC, which is followed by pore elimination and particle sintering. The chemical synthetic route used in this work shows the ability to prepare CCT powders sample with very structural homogeneity, which characteristics are required to manufacturing many electronic devices.

Evaluation of the Structural, Photonic and Morphologic Effects Caused by Zinc Doping in the Titanium Dioxide Powder Samples Obtained by Sol-Gel Method

The anatase phase of titanium dioxide ceramic material plays important rule in heterogeneous photocatalysis, beside the global phase amount and powder morphology. Some of structural parameters are useful to predict several properties, including the crystallization process and mechanism of the irreversible anatase-to-rutile phase transition. The photocatalytic process is based on charge transference from electron-hole pair to material surface, starting some redox reactions in aqueous media. The stable positive defects harm the recombination event and improve the final properties of that material. Modifiers with lower oxidation state than titanium (IV) is applicable for this purpose, what idea becomes the objective of this work. The Sol-Gel method was used to prepare bare and zinc doped-titanium dioxide powder samples reaching good compositional homogeneity for both samples calcined at 500 oC for 4 hours. Rietveld refinement carried out from raw x-ray diffraction patterns was used to demonstrate the formation of solid solution between zinc and titanium oxides. Besides that result, the determination of bandgap energy and SEM images corroborated the structural changes caused by zinc insertion in anatase phase and important difference in powder morphology was observed for zinc doped powder samples in order to reduce the agglomeration degree for better performance for heterogeneous photocatalysis applications.

Thermal Properties of the Blends of Methyl and Ethyl Esters Prepared from Babassu and Soybean Oils

Fatty acid esters (methyl and ethyl) prepared from babassu nut oil were blended with the respective esters from soybean oil. These binary blends (babassu:soybean) were made in proportions of 10:90, 20:80, 30:70, 40:60, and 50:50 (vol%). The ester content of all the blends was higher than 96.5%, which is the minimum value required by the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (Agência Nacional do Petróleo, Gás Natural e Biocombustíveis, ANP). The thermal properties of the babassu, soybean and binary mixtures of esters were investigated by thermogravimetry-differential thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC). The thermal stability of the blended biodiesels decreased as the total contents of the babassu esters increased. From the experiments it was found that babassu methanol biodiesel is stable up to 49.6 °C and the ethanol biodiesel is stable up to 53.7 °C in air. The methyl esters blends were thermally stable up to 83.2 and 56.8 °C, for 90:10 and 50:50 blends (soybean:babassu), respectively. The ethyl ester blends presented values of temperature ranges somewhat higher than the methyl esters, such as 85.2 and 64.5 °C for 90:10 and 50:50 blends, respectively. The esters from babassu oil have satisfactory performance at low temperatures with respect to the point of crystallization, which were below –9.8 °C for ethylic esters and –8.5 °C for methylic esters. A good correlation between the crystallization onset temperature and the increase in the concentration of the babassu oil esters was obtained in the mixtures analyses. In the 50:50 combination (babassu:soybean), the crystallization onset temperature were –6.73 and –9.12 °C for methyl and ethyl esters, respectively.

Data on elemental composition of the medicinal plant Hymenaea martiana Hayne (Jatobá)

This data article provides elemental compositions profile, determined by inductively coupled plasma-optical emission spectrometry (ICP OES), of the medicinal plant Hymeneaea martiana Hayne which belongs of the family Fabaceae (Leguminosae).It is a tree that demonstrates medicinal purposes as antioxidant, immunomodulatory (Boniface et al., 2017) [1], microbial, antiviral, hepatoprotective, gastroprotective (Almeida et al., 2012) [2] and antifungal (Souza et al., 2010) [3].The content of 13 elements (Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, S and Zn) in the barks, leaves, tea leaves and bark tea were detected. Data on the cataloging of the plant can be found in the deposit number 64779 of Federal University of Mato Grosso do Sul herbarium, available in www.splink.org.br/form?lang=pt&collectioncode=CGMS.