http://repositorio.ufc.br/handle/riufc/310 2026-04-08T15:18:09Z http://repositorio.ufc.br/handle/riufc/85345 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 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/85068 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 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/84290 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 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/83283 Título: Sonda baseada em nanopartículas fluorescentes para detecção seletiva de íons dicromato em amostra de solo Autor(es): Rodrigues, Vivian Stephanie Ferreira Abstract: Hexavalent chromium [Cr(VI)] is widely recognized for its high toxicity, environmental persistence, and carcinogenic potential. In this context, fluorescent nanomaterials such as Carbon Quantum Dots (CQDs) stand out as promising platforms for the development of sensitive, selective, and economically viable sensors aimed at monitoring this contaminant. Accordingly, this study aims to develop a sensing strategy based on CQDs with high quantum yield, capable of detecting Cr(VI), in the form of dichromate ions, in soil samples. The CQDs were synthesized using a hydrothermal method, subsequently purified, and characterized by spectroscopic, structural, and microscopic techniques. The nanoparticles exhibited an average size of approximately 1.5 nm, and their surfaces were found to contain functional groups such as carbonyl, carboxyl, and amine, which facilitated interaction with the target analyte. Additionally, the fluorescence quantum yield achieved was 40.6%. After optimizing the experimental conditions, a chemical sensor for the detection and quantification of Cr(VI) was developed, employing a turn-off sensing mechanism predominantly based on Inner Filter Effect (IFE) and dynamic quenching phenomena. The developed probe demonstrated high selectivity for the dichromate oxyanion, even in the presence of potential interfering species. Finally, the sensor’s sensitivity was validated through detection and quantification limits, estimated at 2.8 and 8.6 mg kg-1, respectively. Recovery experiments conducted with real soil samples corroborated the potential of the proposed methodology, underscoring the efficacy of the probe for environmental monitoring of dichromate ions, a naturally occurring species of Cr(VI). Tipo: Dissertação 2025-01-01T00:00:00Z