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Avaliação do teor inorgânico e bioacessível de arsênio em amostras de macroalgas do litoral do Ceará-Brasil

Wed, 01 Jan 2025 00:00:00 GMT

Título: Avaliação do teor inorgânico e bioacessível de arsênio em amostras de macroalgas do litoral do Ceará-Brasil Autor(es): Nobre, Iago Gabriel Medeiros Abstract: Brazil has an extensive coastline where a wide variety of macroalgae species can be found, especially in the northeast region. The global production of macroalgae has increased significantly in recent years due to its growing use in the cosmetics, pharmaceutical, and food industries. Macroalgae are capable of bioaccumulating inorganic elements, including potentially toxic ones such as arsenic (As). For this element, toxicity depends on its chemical form, with its inorganic species, As (III) and As (V), considered carcinogenic, while arsenobetaine is non-toxic. Consequently, speciation analysis of As in macroalgae, the study of the bioaccessibility of this element and physicochemical analyses are crucial to ensure the safety of consumers. In this study, the levels of As in four species of macroalgae from the Ceará coast (Sargassum vulgare, Ulva lactuca, Gracilaria birdiae, and Solieria filiformis) were determined by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) after sample digestion in an acidic medium with microwave-assisted heating. The macroalgae samples showed As contents ranging from 2.5 to 34.6 mg kg-1. The water-soluble species of As, including iAs, were extracted in water and analyzed by ICP-OES, representing 34-52% of the total As content. The iAs levels were measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) after magnetic solid-phase extraction and ranged from 0.15 to 2.59 mg kg-1. The species Sargassum vulgare stood out for having higher levels of As and iAs. Arsenic in a certified reference material sample ERM-CD200 (Bladderwrack - Fucus vesiculosus) was determined with statistically similar values at a 95% confidence level. The macroalgae samples showed high moisture content (67.9% to 86.7%), ash (13.43% to 34.44%), carbohydrates (62.09% to 79.98%), and proteins (3.47% to 6.59%), and low lipid content (<1%). The bioaccessibility analysis of As in the samples yielded results ranging from 0.98 to 11.54 mg kg, with percentages of bioaccessible arsenic relative to the total ranging from 33.31% to 58.13%. For a more conclusive assessment regarding the absorption of As by the body, in vivo bioavailability studies are necessary due to the involvement of more complex metabolic activities. Tipo: Dissertação

Computational study of water adsorption on iron surfaces and metallic alloys

Wed, 01 Jan 2025 00:00:00 GMT

Título: Computational study of water adsorption on iron surfaces and metallic alloys Autor(es): Castro, Gizele do Nascimento de Abstract: Uma das alternativas para reduzir a concentração de gases de efeito estufa (GEE) na atmosfera consiste na substituição dos combustíveis fósseis por fontes de energia limpas e renováveis, como o hidrogênio verde. Entretanto, o método empregado para sua produção, a eletrólise da água, ainda não é amplamente utilizado no mercado devido ao seu elevado custo, uma vez que esse processo requer eletrocatalisadores baseados em metais nobres, escassos na natureza, como irídio e platina. O presente estudo adota uma abordagem computacional para investigar a etapa de adsorção da água em ligas de ferro, ferro-cobalto e ferro-níquel. Foram realizadas otimização geométrica, dinâmica molecular e cálculos de propriedades eletrônicas com base na Teoria do Funcional da Densidade (DFT). Os resultados computacionais indicam que a energia de Gibbs de adsorção da água é mais espontânea na seguinte ordem dos planos cristalográficos: (110) > (100) > (111). A adição de um átomo de níquel à superfície metálica aumentou a densidade parcial de estados dos átomos de ferro adjacentes, favorecendo a adsorção da molécula de água, uma vez que foi na posição entre o átomo de ferro e o átomo de níquel que se observou maior disponibilidade de estados eletrônicos para a interação. Adicionalmente, a adsorção da molécula de água na superfície metálica promoveu a diminuição da densidade parcial de estados do átomo de ferro. Esse comportamento foi observado tanto para o ferro puro quanto para as ligas metálicas, quando a água interage com o sítio ativo mais favorável na superfície, indicando que o átomo de ferro doa densidade de estados à molécula de água durante o processo de adsorção. Tipo: Dissertação

Insights acerca da deposição e da dinâmica molecular de microplásticos em ambientes estuarinos: um comparativo entre o teórico e o experimental

Wed, 01 Jan 2025 00:00:00 GMT

Título: Insights acerca da deposição e da dinâmica molecular de microplásticos em ambientes estuarinos: um comparativo entre o teórico e o experimental Autor(es): Parente, Guilherme de Sandes Abstract: Microplastics (MPs) are persistent and ubiquitous contaminants capable of interacting with various environmental components, particularly natural organic matter, such as humic acid (HA) present in sediments. In estuarine environments, this interaction is particularly critical, as estuaries are known to be areas of MP deposition, ant the presence of HA is frequently reported in extraction procedures. Thus, understanding the interaction between MPs and HA, and the mechanisms involved is highly relevant from an environmental perspective. In this study, experimental and computational approaches were employed to investigate the tendency of interaction between MPs of the types polyethylene (PE), polypropylene (PP), and polystyrene (PS) and HA. The experimental approach, associated with Principal Component Analysis (PCA), was applied to evaluate the correlation between MPs, HA, and different studied estuarine environmental parameters, such as granulometry (sand, gravel and silt), organic matter (OM), and organic carbon (OC). The PCA revealed a positive correlation between MPs and HA, evidencing their affinity and ability of HA to influence the distribution of MPs in estuarine sediments To further investigate these interactions, the Molecular Dynamics (MD) computational technique was applied. This method provided a important details about the interaction, such as the predominance of van der Waals interactions in the stabilization of the systems (HA-PE, HA-PP, and HA-PS), with a higher affinity between HA and PS compared to the others, due to the more negative IPE value. In addition, a more significant reduction in the number of hydrogen bonds involving HA-H2O was observed for the system containing PS, suggesting a more favorable HA-PS interaction. Through the Independent Gradient Model (IGM), it was possible to visualize the interactions and confirm the presence of van der Waals interactions in all systems, as well as to verify strong interactions between HA and PS, mainly near the oxygen atoms of HA. Therefore, the high affinity directly impacts the environmental dynamics of these contaminants in estuarine environments, favoring their retention and deposition in sediments. These results highlight the strong affinity between HA and MPs, especially PS, emphasizing the need to further environmental studies further environmental studies on MPs to better understand their impacts on estuarine environments. Tipo: Dissertação

Avaliação da adsorção de cátions metálicos de efluente simulado de galvanoplastia por compósito derivado de cinzas volantes e zeólita A

Wed, 01 Jan 2025 00:00:00 GMT

Título: Avaliação da adsorção de cátions metálicos de efluente simulado de galvanoplastia por compósito derivado de cinzas volantes e zeólita A Autor(es): Nascimento, Ricardo Jadson da Silva Abstract: The growing generation of metal-containing effluents by the electroplating industry poses environmental challenges due to the toxicity and persistence of these contaminants. This study evaluated an adsorbent composite of geopolymer and zeolite A, synthesized from steel furnace fly ash, for the removal of Cu²⁺, Ni²⁺, and Zn²⁺ ions from aqueous solutions. The proposal aims to valorize solid waste and develop alternative materials to conventional adsorbents. The synthesis resulted in a material with structural and morphological features of both components, confirmed by physicochemical characterization techniques. Batch adsorption tests were conducted using a synthetic solution representative of electroplating effluents. In kinetic studies, Cu²⁺ exhibited the highest initial adsorption rate, Zn²⁺ stood out for its higher equilibrium capacity, and Ni²⁺ showed the lowest performance in both aspects. Among the isotherm models evaluated, the Sips model provided the best fit to the experimental data, reflecting the heterogeneity of the adsorptive surface. Site saturation was observed at approximately 150 mg·L⁻¹, with maximum adsorption capacities of 162.393 mg·g⁻¹ (Zn²⁺), 99.801 mg·g⁻¹ (Cu²⁺), and 63.266 mg·g⁻¹ (Ni²⁺). The initial concentration influenced both the adsorption rate and removal efficiency, particularly for copper, which was more sensitive to ion availability. The highest removal percentages were observed at the lowest initial concentration (0.8 mmol·L⁻¹): 34.7% (Cu²⁺), 32.67% (Zn²⁺), and 17.12% (Ni²⁺). Ion exchange was identified as one of the main mechanisms, supported by the increase in Na⁺ concentration in solution from 800 mg·L⁻¹ to 1,112 mg·L⁻¹, indicating the release of this cation from the adsorbent matrix in exchange for the metal ions. The results indicate that the developed composite is a promising and sustainable alternative for the treatment of metal-laden effluents. Tipo: Dissertação