https://repositorio.ufms.br/handle/123456789/3608 2026-04-12T23:47:08Z 2026-04-12T23:47:08Z https://repositorio.ufms.br/handle/123456789/14326 2026-03-03T21:24:20Z 2025-01-01T00:00:00Z

Título: SÍNTESE DE NANOPARTÍCULAS À BASE DE COBRE PARA APLICAÇÃO COMO ÂNODOS DE CÉLULAS A COMBUSTÍVEL MICROFLUÍDICAS IMPRESSAS EM 3D ALIMENTADAS POR METANOL Abstract: Technological advances have increased the demand for low-power energy converters to supply portable devices such as laptops, smartphones, and smartwatches. This demand arises from growing social automation – communication mediated by electronic devices – and the widespread use of portable systems in healthcare, defense, and entertainment. In this context, miniaturized fuel cells (µFCs) have emerged as promising alternatives. However, their commercial implementation remains limited by: (i) unstable catalysts with low electrocatalytic activity and (ii) architectures that restrict power output. This work aimed to synthesize new materials for application as anodes in microfluidic µFCs. A simple, rapid, small-scale, and surfactant-free route was proposed for the synthesis of Cu nanoparticles (NPs) at room temperature under three distinct conditions: stationary (ST), magnetic stirring (MS), and ultrasonic bath (US). The catalytic activity toward methanol electrooxidation in alkaline medium was evaluated using electrochemical and spectroelectrochemical techniques, revealing higher current densities for the US-synthesized NPs. In situ FTIR analyses confirmed that all materials promote methanol oxidation to carbonate via a formate intermediate, without detectable CO formation. The US sample exhibited superior performance, associated with a higher surface proportion of Cu(OH)2, lower carbon contamination, and greater availability of active sites. At higher potentials, this sample further displayed distinct behavior, involving an additional step of formate formation and its subsequent conversion to carbonate (or CO2 in the thin-layer configuration), suggesting a more efficient reaction mechanism. Finally, a mixed-media µFC was constructed and fed with methanol in alkaline medium and sodium persulfate in acidic medium. The device, comprising a Carbon Paper™ (CP) anode modified with US-synthesized Cu NPs and a metal-free CP cathode, achieved a maximum current density of 0.56 mA cm-2 and a peak power density of 26 µW cm-2 at 100 µL min-1. These results confirm that the membrane-free configuration optimizes the performance of each half-cell and demonstrate the feasibility of µFCs with noble-metal-free anodes and fully metal-free cathodes, representing a promising alternative for sustainable energy conversion technologies. Keywords: fuel cell; microfluidic; methanol electrooxidation; copper anode; metal-free cathode; in situ FTIR; energy conversion. Tipo: Tese

2025-01-01T00:00:00Z https://repositorio.ufms.br/handle/123456789/14197 2026-01-13T16:24:16Z 2025-01-01T00:00:00Z

Título: Correlação entre spins localizados e itinerantes com interações de troca Kondo e magnéticas em um cluster hexagonal (tipo Grafeno) Abstract: The study of magnetic properties in many-body systems remains a fundamental challenge in Condensed Matter Physics, mainly due to the competition between strong electronic correlations, collective quantum effects, and constraints imposed by spatial geometry. Simplified models, particularly finite spin arrangements, are widely used to investigate essential phenomena such as antiferromagnetic interactions, magnetic frustration, singlet formation, and the Kondo coupling between localized and itinerant moments. In this dissertation, we analyze a hexagonal cluster similar to that found in graphene composed of six sites, a structure that preserves relevant symmetries and enables a controlled examination of the influence of itinerant electrons on the behavior of localized spins. Each site hosts a fixed magnetic moment, while itinerant electrons move through the lattice, allowing a direct investigation of the competition between electronic obility and exchange interactions. The theoretical description is based on the Ising–Kondo and Heisenberg–Kondo Hamiltonians, which incorporate kinetic-energy terms, magnetic interactions between localized spins, and local Kondo coupling. The quantum basis of the model is constructed using a binary representation of states, and the numerical solution is obtained through exact diagonalization and the Lanczos method. These matrices are large and grow rapidly with the number of itinerant electrons, which motivates the use of high-performance computational resources such as CENAPAD (the National High-Performance Computing Center) at UNICAMP, allowing the calculation of the relevant magnetic correlations. The analysis focuses on the quantities D, F and S², which characterize, respectively, the correlation between localized spins, the correlation between localized and itinerant spins, and the total spin of the system. The results show that the hexagonal geometry plays a crucial role in shaping the distribution of correlations. Strong Kondo interactions promote the screening of localized spins, while increasing temperature tends to suppress magnetic correlations. Thus, the hexagonal cluster proves to be an effective platform for understanding, in a controlled manner, the competition between different magnetic mechanisms in correlated systems, providing a solid foundation for future studies involving other geometries and interaction regimes. Tipo: Dissertação

2025-01-01T00:00:00Z https://repositorio.ufms.br/handle/123456789/13913 2025-12-06T09:30:26Z 2025-01-01T00:00:00Z

Título: Otimização das propriedades térmicas de telhas de concreto com a incorporação do resíduo de lã de ovinos pantaneiros Abstract: In view of the growing demand for sustainable and energy-efficient construction solutions, this study proposed a new application for Pantaneiro sheep wool in concrete roof tiles, aiming to improve the thermal performance of building coverings. The wool was washed, carded, and manually cut. Its characterization indicated an average fiber diameter of 31.12 µm, coarse texture, yellow coloration, and a washed yield of 71.58%, classifying it as a medium-thickness fiber. Since it does not meet the requirements of the textile industry, this wool shows promise for alternative applications, particularly in construction materials. Concrete roof tiles were produced with 0%, 2%, 5%, and 7% wool incorporation relative to the cement volume, using an industrial process and evaluated according to the standards ABNT NBR 13858-2:2009 and ABNT NBR 15575-5:2021. The 2% mixture exhibited the best physical and mechanical performance, with lower water absorption (4.81%) and higher flexural strength (2.45 MPa), representing a 1.7% increase compared to the reference mixture. The 5% mixture stood out in terms of thermal performance, reducing thermal transmittance to 5.09 W/m²·K and providing an internal temperature reduction of up to 4.2 °C in experimental prototypes. The utilization of this residue proves to be a technically, economically, and environmentally viable alternative, compliant with current standards and market requirements. Tipo: Tese

2025-01-01T00:00:00Z https://repositorio.ufms.br/handle/123456789/13785 2025-12-04T20:37:17Z 2025-01-01T00:00:00Z

Título: Nanobioherbicida responsivo a luz: desenvolvimento, caracterização e avaliação da toxicidade Abstract: This thesis aims to develop environmentally safer and traceable nanobioherbicides (NBHs) by reconciling herbicidal performance, rigorous colloidal control, and multiscale ecotoxicological assessment. To this end, the conjugated polymer CNPPV was employed as a photoactive matrix to encapsulate usnic acid (AU), a bioactive compound with recognized potential but limited by low solubility and intrinsic toxicity. The approach integrates synthesis routes (adapted nanoprecipitation and microfluidics), physicochemical and optical characterizations (DLS, zeta potential, AFM/SEM, FTIR, UV–Vis, and fluorescence), release and photoresponse assays, and biological evaluations in the aquatic plant Lemna minor and in the zebrafish embryo model (ZFET). In Chapter II, a proof of concept was established via nanoprecipitation, yielding two formulations—NBH1 and NBH2 (the latter with 5× higher CNPPV)—that showed >90 days of stability, encapsulation efficiency >80%, spherical morphology, PDI Tipo: Tese

2025-01-01T00:00:00Z