https://ri.ufs.br/jspui/handle/riufs/2148 2026-04-07T16:02:21Z https://ri.ufs.br/jspui/handle/riufs/24753 Título: Materiais adsorventes obtidos da biomassa de Ingá-cipó (Inga edulis): remoção de metais pesados e avaliação ecotoxicológica Autor(es): Lima, Lucas dos Santos Abstract: Water contamination by toxic metals, especially hexavalent chromium Cr(VI) and divalent lead Pb(II), represents a significant environmental challenge due to their persistence and harmful effects on aquatic organisms. In this study, two adsorbent materials derived from the biomass of Inga edulis bark were developed and evaluated: raw biomass (BMIG) and sulfuric acid–activated biomass (BMIGA). The materials were characterized using physicochemical techniques, which confirmed structural modifications and the presence of functional groups capable of interacting with the studied metals. Batch adsorption experiments enabled the identification of favorable operational conditions and showed that BMIGA exhibited maximum adsorption capacities of 356.6 and 222.1 mg g-1 for Cr(VI) and Pb(II) ions, respectively, compared to BMIG, which presented an adsorption capacity of 46.0 mg g-1 for Cr(VI) and showed no removal of Pb(II) ions. Chemical activation resulted in an increase in surface area and the introduction of oxygenated functional groups, which enhanced the adsorption of both metal ions. Kinetic models indicated that Cr(VI) adsorption by BMIG and BMIGA followed the Elovich model, characterizing a chemisorption process on a heterogeneous surface. For BMIGA and Pb(II), the best fit was obtained with the pseudo-second-order model, suggesting interaction with oxygenated functional groups. In isotherm studies, Cr(VI) adsorption fitted both the Langmuir and Freundlich models, whereas Pb(II) showed a better fit to the Freundlich model. Thermodynamic analyses demonstrated that Cr(VI) adsorption by BMIG was non-spontaneous, while BMIGA promoted spontaneous adsorption for both metals. Under continuous-flow conditions, fixed-bed columns exhibited stable performance, with breakthrough times of 200.0 min and 281.7 min for Cr(VI) adsorption and 554.8 min for Pb(II) adsorption at low concentrations, which were compatible with practical applications and showed good agreement with the Thomas, Yoon–Nelson, and Clark models. The ecotoxicological assessment performed with Daphnia similis confirmed the high toxicity of solutions containing Cr(VI) and Pb(II) ions prior to treatment. After adsorption, no acute effects were observed on the organisms, demonstrating that the materials were able to significantly reduce toxicity. Finally, the saturated adsorbents were applied in electrochemical tests for green hydrogen and oxygen production, revealing potential for reuse and value addition after environmental application. Overall, the results demonstrate that Inga edulis bark is a promising biomass for the production of sustainable and efficient adsorbents with multifunctional potential, contributing to pollution mitigation strategies and technologies associated with the circular economy. 2026-01-27T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/24695 Título: Prescrição de curvaturas gaussiana e geodésica em superfícies compactas com característica de Euler não positiva Autor(es): Santana, Junior Tavares de Abstract: This dissertation, based on the article [30], addresses the problem of prescribing Gaussian and geodesic curvatures on a compact Riemannian surface with boundary (Σ, g). The main goal of this work is to prove, in broad terms, the existence of a conformal metric g = e u g such that the Gaussian and geodesic curvatures with respect to g are prescribed. The problem is reduced to finding a solution for a second-order elliptic partial differential equation with boundary conditions. Furthermore, the work explores the energy functional associated with this problem and its variational properties, addressing issues of coercivity and the existence of minimizers. The study focuses on different scenarios, including cases where the Euler characteristic of Σ is negative or zero. Additionally, there exists a function defined on ∂Σ, denoted by D, which plays a fundamental role in the study. When D(q) > 1 for some point q E ∂Σ, the analysis becomes more delicate. The work employs concepts from Riemannian Geometry, Functional Analysis, and Partial Differential Equations to develop the proofs of the main theorems. Moreover, advanced methods such as blow-up analysis and the Morse index of solutions are used to handle more refined situations. 2025-03-07T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/24449 Título: Estudo Ab-Initio das propriedades estruturais, eletrônicas, ópticas e fotovoltaicas dos compostos NaBiS2 e NaBiSe2 Autor(es): Maia, Luciano Paulo de Araújo Abstract: Ferroelectric semiconductor compounds with photovoltaic properties (photoferroics) represent promising alternatives to conventional semiconductors used in solar cells, as they are not subject to the energy conversion efficiency limitation imposed by the ShockleyQueisser limit. In this context, this thesis investigates the potential of the compounds NaBiS2 and NaBiSe2, both with orthorhombic and ferroelectric structures, for applications in photoferroic devices. Density Functional Theory (DFT)-based calculations were conducted to explore their structural, electronic, and optical properties, employing the modified Becke-Johnson exchange potential for a more accurate description of the electronic structure and optical properties. Additionally, energy conversion efficiencies were estimated using the spectroscopic limited maximum efficiency method to assess the potential performance of these materials in photovoltaic cells. The results indicate that the direct band gap energies of NaBiS2 and NaBiSe2 are approximately 1.2 eV and 0.75 eV, respectively. NaBiS2 exhibits a band gap value considered ideal for photovoltaic applications under solar illumination, while NaBiSe2 shows a lower-than-expected value from a theoretical standpoint, yet still relevant for absorption in the near-infrared region. Both compounds display absorption coefficients in the visible spectrum range with intensities on the order of 105 cm−1, a favorable optical characteristic that allows the use of relatively thin lms to efficiently absorb sunlightan essential factor for high-performance devices. A pronounced optical anisotropy was also observed, associated with the electronic structure of both compounds. Visible light absorption mainly arises from transitions between the 3px,y states of S to the 6x,y states of Bi, and from the 4x,y states of Se to the 6x,y states of Bi. Thus, the local BiS(Se)6 structure of the studied compounds is crucial for their optical properties. The spectroscopic limited maximum efficiencies obtained were 32.2% for NaBiS2 and 23.3% for NaBiSe2. The value for NaBiS2 surpasses that of the perovskite MAPbI2 (29.5%), which is currently one of the most efficient photoferroics, with an experimental efficiency around 20.3%. Combining these results with previously published estimates for ferroelectric polarization and carrier mobility, this thesis reveals the unexplored potential of the orthorhombic compounds NaBiS2 and NaBiSe2 for application in photoferroic devices and next-generation solar cells. 2025-10-23T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/24224 Título: Eletrocatalisador bifuncional baseado em material carbonáceo para geração de hidrogênio e oxigênio de baixo carbono Autor(es): Santos, Marcos Vinícius Quirino dos Abstract: The high cost, scarcity, and limited durability of noble-metal-based electrocatalysts, such as platinum, iridium, and rhodium, have driven the search for alternative materials that are abundant, sustainable, and economically viable for use as catalysts in water electrolysis. In this context, biochar derived from plant residues has emerged as a promising carbon-based material for the development of efficient and environmentally friendly electrocatalysts. This dissertation reports the development of an electrocatalyst based on biochar derived from the aquatic plant Marsilea minuta (BMQ), applied to the hydrogen evolution reaction (HER) in acidic medium and to the oxygen evolution reaction (OER) in alkaline medium. The biochar was prepared by pyrolysis at 500 °C under an inert nitrogen atmosphere and characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results revealed an amorphous structure with a porous surface and the presence of oxygen- and nitrogen-containing functional groups, which act as active sites for electrocatalytic reactions. Electrochemical tests using a glassy carbon electrode modified with the material demonstrated significant activity for both HER and OER, exhibiting low overpotentials required to reach a current density of 10 mA cm⁻² and Tafel slopes consistent with favorable reaction kinetics. Electrochemical stability was confirmed by chronopotentiometry, highlighting the potential of BMQ as a bifunctional electrocatalyst with low carbon emissions. These results indicate that biochar derived from Marsilea minuta is a promising and sustainable alternative for application in water electrolysis systems, contributing to the advancement of low carbon hydrogen and oxygen production technologies. 2025-08-14T00:00:00Z