http://tede.unicentro.br:8080/jspui/handle/tede/573 Programa de Pós-Graduação em Química (Doutorado) Mon, 13 Apr 2026 09:32:08 GMT 2026-04-13T09:32:08Z http://tede.unicentro.br:8080/jspui/handle/jspui/2375 Título: Modificação da argila montmorilonita sódica utilizando diferentes solventes orgânicos: uma nova metodologia Autor: Stoski, Adriana Primeiro orientador: Almeida, Carlos Alberto Policiano Abstract: Polar organic solvents have the ability to interact with and modify the structure of Montmorillonite (MMT), through solvation or complexation in the clay mineral gallery and/or on the MMT surface, involving certain atomic groups. In this paper, the interaction between MMT and four polar organic solvents - dimethylsulfoxide (DMSO), dimethylformamide (DMF), acetic acid (AA) and acetonitrile – was studied. A mixture of ethyl alcohol, MMT and organic solvent was kept under magnetic stirring in a reflux condenser for 1h. Statical analysis has been applied to evaluate the effects of the amount of DMSO, temperature and sonication time on the modified clay (DMSO-MSAT) basal plane (d001) distance trough a 23 factorial desing. An average increase of 0.57 nm for d001 distance has been found after swelling with DMSO interaction, as confirmed by FTIR analysis with the appearance of bands at 3017, 2931, 706, 1329, 1402 and 1432 cm-1 characteristics of DMSO molecules vibration. BET analysis revealed a decrease in the surface area (from 41.8933 m²/g to 2.1572 m²/g) for SMAT and DMSO-MSAT, respectively. The porosity increases from 1.74 to 1.87 nm for SMAT and DMSO-MSAT, respectively. Statistical analysis showed that only the effect of the amount of DMSO is significant for increasing the interlamellar distance. In addition, at room temperature, the drying time of the sample was only 30 minutes using this methodology. Afterwards, this study proceeded by testing the methodology and interactions that occurs between MMT with the other three solvents, and through XRD analyses revealed that reaction time of 4 hours and 5 mL of an organic solvent were necessary to achieve modifications, such as larger lamellar spacing, reduced delamination, improved structural organization, and interaction with the inner surface of MMT. The TG/DTG diagrams confirmed that the interaction of MMT with DMF occurs trough two different mechanism: free electron pair of the nitrogen or the carbonyl group. This is supported by two endothermic events observed at 202 and 303°C, indicating the release of DMF molecule. Additionally, FTIR spectra demonstrated the interaction between organic solvents and MMT, as the band at 3627cm-1 exhibited a significant decrease, with the MSAT+DMF sample showing the lowest intensity in this band. Notably, the FTIR spectra also suggested that the MMT’s structural decomposition was limited, as the reflected band for the octahedral cations showed a minimal displacement. Furthermore, it can be concluded that when following the methodology proposed in this paper, there is only a low degree of evaporation of the organic solvent molecules insert into the MMT gallery during the material’s drying stage. Consequently, this leads to an increase in the interlamellar space, with values of 0.11 nm for acetonitrile, 0.27 nm for AA and 0.85 nm for DMF. Instituição: Universidade Estadual do Centro-Oeste Tipo do documento: Tese Fri, 23 Aug 2024 00:00:00 GMT http://tede.unicentro.br:8080/jspui/handle/jspui/2375 2024-08-23T00:00:00Z http://tede.unicentro.br:8080/jspui/handle/jspui/2293 Título: A ESPECTROMETRIA DE RAIOS GAMA NA CARACTERIZAÇÃO DE FÓSSEIS E ARTEFATOS ETNOARQUEOLÓGICOS Autor: Rodriguez, Duvan Gil Primeiro orientador: Bastos, Rodrigo Oliveira Abstract: Gamma-ray spectrometry (GRS) is a widely utilized nuclear physics technique across various sectors, including nuclear industry, geology, and astrophysics. It enables the measurement of concentrations of radionuclides from the 238U and 232Th series, as well as the radionuclide 40K, providing valuable insights into mineralogy, geological processes, and formation environment. However, its applicability in studies involving samples where crushing and homogenization are not feasible is limited due to geometric adequacy issues. Nevertheless, GRS technique, when employed without strict control of measurement geometry, can unveil intriguing sample characteristics, particularly when analyzing concentration ratios among different radionuclides of the 238U and 232Th series and the radionuclide 40K, a procedure that mitigates geometry's influence on results. This paper presents three studies examining the potentials and limitations of gamma-ray spectrometry technique applied to the investigation of objects with diverse geometries. To explore the influence of geometry on measurements conducted by GRS technique and assess the possibility of determining concentration ratios of natural radionuclides (Th/U, Th/K, and K/U) in samples with different geometries, measurements were carried out on a sample enriched with higher than natural content of thorium, uranium, and potassium. The sample was packed into nine cylinders, each weighing 30 grams. Measurements were taken both on the top and the side of the detector, reproducing and varying distinct geometric shapes in each measurement. The spectral analysis methodology followed the International Atomic Energy Agency (IAEA) recommendations for U, Th, and K analysis in rocks, soils, and sediments, followed by simple calculation of concentration ratios. The results demonstrated that gamma-ray spectrometry technique is a viable alternative for analyzing samples with different geometries, provided it is performed with equivalent elemental ratios of eTh and eU, determined by the nuclides 212Pb (238.63 keV), 214Pb (351.93 keV), 214Bi (1764.49 keV), 208Tl (2614.51 keV), and 40K (1460.82 keV). Following the same methodology, 32 fossil samples from the Museum of Natural Sciences of Guarapuava were also analyzed, along with 11 ceramic samples and 4 clay samples from three Quilombola communities in three municipalities in the state of Maranhão. In the case of fossils, the interpreted GRS data provided insights into diagenetic processes (mineralization) and the redox conditions of the sedimentary environment in which they were formed. Thus, the feasibility of characterizing fossil samples with irregular geometries and varied densities using gamma-ray spectrometry was demonstrated. For ceramic and clay samples, an experimental archaeology study was conducted, testing the hypothesis of the technique's efficiency in separating previously known distinct samples. In addition to the GRS technique, energy-dispersive X-ray fluorescence (EDXRF) technique was also tested, both coupled with multivariate statistical tools. The results of both techniques revealed the existence of three sample groups, as expected. Furthermore, additional sample information was indicated, such as the type of clay mineral and redox potential. These findings suggest that the GRS technique can be utilized in research related to archaeological and paleontological samples, as well as other cultural heritage samples, where preservation of their integrity is of vital importance. Instituição: Universidade Estadual do Centro-Oeste Tipo do documento: Tese Fri, 21 Jun 2024 00:00:00 GMT http://tede.unicentro.br:8080/jspui/handle/jspui/2293 2024-06-21T00:00:00Z http://tede.unicentro.br:8080/jspui/handle/jspui/2215 Título: Análise do comportamento eletroquímico de 2-Mercaptobenzotiazol em Célula Solar Sensibilizada por corante Autor: Larsson, Letícia Fernanda Gonçalves Primeiro orientador: Rodrigues, Paulo Rogério Pinto Abstract: Dye-sensitized solar cells (DSSCs) are third-generation devices that have shown a steady increase in energy conversion efficiency. However, one of the problems encountered for these devices is electronic recombination reactions, which can be understood as processes between the electron from the conduction band of TiO2 and the electrolyte, hindering electron transport in the electrical circuit, consequently reducing the cell's efficiency. Materials capable of anchoring to the surface of the semiconductor oxide, known as coadsorbents, have been employed in DSSCs with the aim of promoting blocking between oxide and electrolyte. 2-Mercaptobenzothiazole (2-MBT), used as a corrosion inhibitor, has sulfur atoms in its structure capable of coordinating to form hydrophobic complexes, thus enabling the formation of a protective film in the cell. The main objective of this work was to employ 2-MBT and evaluate its performance as a coadsorbent in DSSCs. Variations such as the concentration of 2-MBT, type of insertion, and impregnation time were carried out to determine the best cell operating parameters. Cells composed of working electrode (FTO/TiO2/2-MBT) were analyzed by j-E curves, photocurrent chronopotentiometry, chronoamperometry, electrochemical impedance spectroscopy (EIS), photocurrent spectroscopy (IMPS), and modulated intensity photo-voltage (IMVS). Charge extraction and the dye and coadsorbent solution were evaluated by UV/Visible spectroscopy. The results showed that the addition of 2-MBT at a concentration of 2 mg mL-1 increased the cell current density from 9.7 mA cm-2 to 11.4 mA cm-2, promoting a 20.5% increase in cell efficiency compared to the conventional cell. Electrochemical tests showed that the addition of 2-MBT in small amounts caused a decrease in the electrical resistance of the cell, indicating adsorption in TiO2 regions not filled by the dye, promoting disorganization of the electrical double layer that aids in electron injection from the cell, resulting in higher current densities, and indicating that the injection and transport of electrons in the device were facilitated. Instituição: Universidade Estadual do Centro-Oeste Tipo do documento: Tese Tue, 27 Feb 2024 00:00:00 GMT http://tede.unicentro.br:8080/jspui/handle/jspui/2215 2024-02-27T00:00:00Z http://tede.unicentro.br:8080/jspui/handle/jspui/2214 Título: SÍNTESE E CARACTERIZAÇÃO DE MEMBRANAS HÍBRIDAS MULTIFUNCIONAIS CONTENDO HIDRÓXIDOS DUPLOS LAMELARES INTERCALADOS COM NIMESULIDA PARA APLICAÇÃO ODONTOLÓGICA Autor: Machado, Monielly Viomar Primeiro orientador: Marangoni, Rafael Abstract: Considering the increase in life expectancy of the world population, the study of new materials that can act as alloplastic grafts and also have the characteristic of releasing drugs directly at the site of pain is considered of great importance. Thus, this work presents a study on the synthesis and characterization of hybrid membranes composed of biopolymers (alginate, chitosan and collagen) added with layered double hydroxides of zinc and aluminum interspersed with nimesulide, a non-steroidal anti-inflammatory. Such membranes have the potential to be used as resorbable grafts that release the drug in question more slowly. Presenting different synthesis methodologies for LDH Zn/Al and Mg/Al intercalated with Nimesulide and dispersed in the membrane produces a multifunctional composite, so that the variation of the synthesis method for LDH produced different morphologies for the final composite (granulated, three-dimensional porous and membrane). For the synthesis of the hybrid membrane, an experimental study was carried out with six variables to define the best composition for the synthesis of the membranes. The best condition presented was characterized by XRD, and subsequently a study on the release of nimesulide using UV-Vis spectroscopy was carried out. Release studies as a function of pH showed that LDH releases around 20% of the intercalated nimesulide at pHs above 2, while the membranes contribute to maintaining the nimesulide in its protonated form, not making it available to the environment, which contributes significantly, since this membrane, when used as a graft, will fulfill its structural function, and as it is absorbed by the body, it will release nimesulide into the focus of the patient's pain. Instituição: Universidade Estadual do Centro-Oeste Tipo do documento: Tese Wed, 28 Feb 2024 00:00:00 GMT http://tede.unicentro.br:8080/jspui/handle/jspui/2214 2024-02-28T00:00:00Z