Dissertação (PPGQUIM)

Avaliação da composição mineral de material particulado atmosférico coletado na região geográfica intermediária de Salvador e de Amélia Rodrigues, Bahia, Brasil

2026-03-19T18:19:16Z

Avaliação da composição mineral de material particulado atmosférico coletado na região geográfica intermediária de Salvador e de Amélia Rodrigues, Bahia, Brasil Sacramento, Carlos Leandro Cruz Araujo, Rennan Geovanny Oliveira Air pollution has been a major focus of study in the scientific community, aiming to understand its implications for human health, ecosystems, and material heritage, identifying itself as a key element in the pursuit of sustainable development. The accelerated growth of urban areas, driven by industrialization and population increase, has significantly contributed to the current scenario. In this context, the present work aims to investigate, evaluate, and quantify samples of atmospheric particulate matter in the form of total suspended particles (TSP) and respirable particles (PM₂,₅), according to the limits established by Resolution No. 491/2018 of the National Environment Council (CONAMA), in addition to chemically characterizing the mineral composition. Sampling was conducted in the Intermediate Geographic Region of Salvador, encompassing the municipalities of Lauro de Freitas, Madre de Deus, São Sebastião do Passé, São Francisco do Conde, and Amélia Rodrigues, in the Metropolitan Region of Feira de Santana, in August, September, and December 2021, covering both the dry and rainy seasons in the region. Collections occurred during nominal 24-hour periods, using three portable samplers (HANDI-VOL) for PTS and one portable prototype for PM₂,₅, operating simultaneously. The geometric mean concentrations of PTS and PM₂,₅ were below the limits established by Resolution No. 491/2018 of the CONAMA. After the sampling procedures, the particulate matter deposited on the filters was subjected to acid extraction, followed by chemical analysis by inductively coupled plasma optical emission spectrometry (ICP OES) to determine Al, Ba, Cr, Cu, Fe, Ni, Mn, Mo, Pb, Sb, V, and Zn. Based on the results obtained, the trace metals were grouped in ascending order of concentration (Mo < V < Sb < Pb < Ni < Mn < Zn < Ba < Cr < Al < Cu < Fe) for PTS. The concentrations of the chemical elements in the PM2.5 samples were below the quantification limit of the analytical method. With the predominance of Fe concentration in the chemical composition of the atmospheric particulate matter (PTS), the results obtained clearly showed that in the study region, the chemical composition of atmospheric particulate matter is strongly associated with natural sources, but is directly influenced by anthropogenic sources such as the use of fossil fuels, vehicular traffic associated with brake system wear, maritime traffic, industrial, petrochemical and port activities through the presence of Cu, Mn, Pb, Sb and Zn. An investigation of pollution indices was carried out using the enrichment factor (EF) and the geoaccumulation index (Igeo), as geochemical indices, highlighting the need for extra attention to the concentrations of Cu, Cr and Sb. Multivariate data analysis was crucial in determining a possible anthropogenic contribution in the region. Principal component analysis (PCA) showed that Fe was the chemical element with the greatest contribution to the chemical composition of the PTS, mainly associated with natural sources, such as soil resuspension. Meanwhile, the concentration of Cu, Fe, Mn, and Pb indicated anthropogenic influence from traffic and industrial activities. During the dry and rainy seasons, PCA showed variation in the relative weight of the metals, but maintained the distinction between natural and anthropogenic sources. Hierarchical cluster analysis (HCA) consistently grouped the samples, separating sets influenced by industrial/port activities from those of natural origin. This analysis confirmed the correlation between Cu, Mn, and Sb as markers of anthropogenic impact. Together, PCA and HCA reinforced the identification of the main emission sources in the studied region. Finally, this work may assist the corresponding agencies in more effective air quality monitoring in the region. Universidade Federal da Bahia Dissertação

Estudo teórico-computacional dos mecanismos eletrocatalíticos da oxidação da água por complexos de cobre(II) com ligantes macrocíclicos.

2026-02-26T10:54:41Z

Estudo teórico-computacional dos mecanismos eletrocatalíticos da oxidação da água por complexos de cobre(II) com ligantes macrocíclicos. Neves, João Pedro Costa Sarno Alves, Tiago Vinícius In a contemporary world marked by environmental imbalance, the Energy Transition arises as a solution to mitigate the emission of pollutants from fossil fuels burning. Following this scenario, a promising alternative is, for example, the H2, whose production via water electrolysis faces challenges related to its anodic half reaction, thus evoking the use of catalysts -- e.g. copper(II) complexes bearing macrocyclic ligands -- that remain in constant improvement. For this, it's necessary to elucidate this mechanism, which means to identify the key intermediates and steps for reaction kinetics. Therefore, by means of computational tools, the present work focused on the theoretical study of the water oxidation's electrocatalysis by the coordination complex [Cu(14-TMC)]+2, based on experimental evidence to which the results yielded good correspondence. In this case, the O-O bond formation proceeds through a water nucleophilic attack coupled with a single electron transfer to the metal center or, alternatively, through a crossing point between quartet and doublet potential energy surfaces. Going further, the results of macrocyclic shrinkage were also investigated through [Cu(12-TMC)]2+'s catalysis. Despite of the similar values in terms of energy barrier, this ligand enables the coordination of two water molecules, which impacts the course of reaction. The results, based on electronic and structural fundaments, shed a light on the rational design of ligands aiming better catalytic performance for H2 production. Universidade Federal da Bahia Dissertação

Determinação multielementar em amostras de açúcar empregando a espectrometria de fluorescência de raios-X por dispersão de energia após procedimento de diluição

2026-02-20T11:19:36Z

Determinação multielementar em amostras de açúcar empregando a espectrometria de fluorescência de raios-X por dispersão de energia após procedimento de diluição Matos, Eloá Veiga Alves Teixeira, Leonardo Sena Gomes Sugar is widely consumed and can represent a route of exposure to potentially toxic metals, making it essential to monitor its contamination to ensure food safety and public health. This study evaluated samples of white, demerara, and refined sugars for the presence of Co, Cr, Cu, Ni, and Zn using energy-dispersive X-ray fluorescence spectrometry (EDXRF). The samples were diluted in nitric acid solution and applied directly to the instrument’s sample holders for measurement of analytical signals. Calibration was performed using analyte standards prepared in sucrose, ensuring matrix matching and external calibration. The calibration curves showed good linearity, with limits of detection of 0.30, 0.40, 0.40, 0.30, and 0.60 mg kg⁻¹ for Co, Cr, Cu, Ni, and Zn, respectively. The addition and recovery tests yielded results between 82% and 108%, and the relative standard deviation (RSD) was below 7% in both intraday and interday evaluations. Concentrations obtained by EDXRF were compared with those determined by inductively coupled plasma optical emission spectrometry (ICP OES) after microwave-assisted acid digestion, with no statistically significant differences observed between the methods. The average concentrations for Co, Cr, Cu, Ni, and Zn ranged from 0.89 to 1.63 mg kg⁻¹, 2.10 to 3.66 mg kg⁻¹, 1.02 to 1.93 mg kg⁻¹, 1.23 to 1.85 mg kg⁻¹, and 2.66 to 4.04 mg kg⁻¹, respectively. The risk assessment indicated that the detected levels do not pose toxicological, carcinogenic, or non-carcinogenic hazards, suggesting that sugar consumption does not pose long-term health risks associated with the evaluated elements. Universidade Federal da Bahia Dissertação

Síntese mecanoquímica solvent-free de La2NiO4 para aplicação na reforma a seco do metano: análise termodinâmica e contribuições na instrumentação de medidas de vazão gasosa.

2026-02-20T11:10:03Z

Síntese mecanoquímica solvent-free de La2NiO4 para aplicação na reforma a seco do metano: análise termodinâmica e contribuições na instrumentação de medidas de vazão gasosa. Neves, Igor Rodrigues Brandão, Soraia Teixeira Dry reforming of methane enables the production of synthesis gas (syngas) with an H₂:CO ratio of approximately 1:1 from CH₄ and CO₂, both greenhouse gases, using nickel-based catalysts. In this work, a perovskite route was employed, with La₂NiO₄ reduced in situ to Ni/La₂O₃, aiming to propose a synthesis route that is more economical and sustainable than the conventional one through the milling of reactants without water. To comprehensively understand the system and the materials, thermodynamic calculations based on equilibrium constants and Gibbs free energy were performed and were found to be in agreement with experimental and literature data, allowing the inference of kinetic characteristics. During the study, the gas flow rate measurements were also automated in order to ensure reproducible tests, resulting in the development of an instrument that was incorporated into the laboratory and shows potential for patenting. The materials were synthesized via the citrate method (reference material) and by ball milling, varying the nickel precursors (oxide or nitrate) and the use of a milling aid (citric acid). To differentiate the materials, characterization techniques such as X-ray diffraction (XRD), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), temperature-programmed surface reaction (TPSR), nitrogen adsorption, and post-test temperature-programmed oxidation were employed, in addition to evaluating their performance in a continuous-flow reaction for 20 h. The influence of the nickel precursor and synthesis method on catalytic performance was evidenced through characteristics such as nanoparticle diameter and crystallite size. The reference materials and those obtained from nitrate precursors proved to be promising, as they were active and stable for 20 h. The best material obtained exhibited H2/CO ratio closer to 1, higher H₂ and CO yield, and up to 70% water savings during synthesis. Universidade Federal da Bahia Dissertação