https://tedebc.ufma.br/jspui/handle/tede/5115 2026-05-15T03:18:36Z https://tedebc.ufma.br/jspui/handle/tede/6947 Título: Hidróxidos duplos lamelares e derivados como materiais multifuncionais para processos de adsorção, fotocatálise e energia limpa Autor: CAMPOS, Vanessa Niely Soares Primeiro orientador: ALCÂNTARA, Ana Clécia Santos de Abstract: This thesis investigates the development and application of layered double hydroxides (LDHs) and their derivatives, mixed metal oxides (MMOs), as multifunctional materials aimed at environmental remediation and clean energy production. The research was structured in interconnected chapters, ranging from a systematic literature review to the experimental evaluation of the synthesized materials. The systematic review revealed a growing interest in LDHs and MMOs for adsorption, photocatalysis, and photocatalytic hydrogen production processes, highlighting limitations related to efficiency, stability, and action mechanisms. Based on these challenges, bimetallic (CoAl and NiAl) and trimetallic (NiCoAl) systems were synthesized, along with their calcined derivatives, which were extensively characterized in terms of their structural, morphological, textural, and electronic properties. The results demonstrated that CoAl-LDH exhibited a high adsorption capacity for naproxen, with rapid kinetics influenced by parameters such as pH, initial concentration, and temperature. The process was well described by kinetic and isothermal models, indicating a predominance of chemical and electrostatic interactions. In the energy context, NiAl-LDH and CoAl-LDH showed photocatalytic activity for hydrogen production via water splitting, highlighting the influence of metallic composition on charge separation and process efficiency. Furthermore, mixed metal oxides, particularly the trimetallic NiCoAl-MMO system, exhibited high performance in the photodegradation of ciprofloxacin, with effective removal under different operating conditions and evidence of mechanisms mediated by reactive species. Overall, the results reveal a direct relationship between composition, structure, and functional performance, demonstrating that modulation between lamellar phases and derived oxides is a promising strategy for the development of multifunctional materials. Thus, this thesis contributes significantly to scientific advancement in the area of materials applied to environmental remediation and clean energy generation, offering perspectives for sustainable applications in the real world. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese 2026-03-13T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6939 Título: Nanoplataformas híbridas a base de pontos quânticos de carbono e suportes inorgânicos naturais e sintéticos Autor: CUTRIM, Elaine Sá Menezes Primeiro orientador: ALCÂNTARA, Ana Clécia Santos de Abstract: Clays are widely combined with other nanomaterials to improve their properties and to obtain multifunctional hybrid systems. These materials offer advantages such as enhanced mechanical and rheological performance, reduced toxicity, and compatibility with green chemistry principles, making them suitable platforms for incorporating functional nanostructured materials. In this work, hybrid nanomaterials based on carbon quantum dots (CQDs) and inorganic supports with different morphologies were developed, including fibrous sepiolite (SEP), layered montmorillonite (MMT), and ZIF-8. CQDs were synthesized by a solvothermal route using citric acid and urea in dimethylformamide and subsequently associated with the supports either using preformed CQDs or through in situ synthesis. Spectroscopic analyses indicate that CQDs interact with SEP mainly through surface silanol groups and hydroxyl groups associated with zeolitic water, as evidenced by FT-IR spectroscopy. Photoluminescence (PL) spectroscopy demonstrates that the association between CQDs and clay minerals does not compromise the PL properties of the CQDs. The hybrid nanomaterials exhibit shifts in the maximum emission wavelength, indicating modification of the emissive states induced by the clay environment. In addition, most hybrid systems display dual-emission behavior. Raman analysis shows an increase in the sp² carbon network for sepiolite–CQD hybrids synthesized in situ, accompanied by a decrease in the ID/IG ratio, indicating higher structural ordering as a function of synthesis time. For the MMT-based hybrid nanomaterials, X-ray diffraction (XRD) analysis reveals both the presence of diffraction features associated with CQDs and an increase in the basal spacing of MMT. Drug intercalation studies demonstrate that 5-fluorouracil is incorporated into MMT as a monolayer with planar orientation, producing an increase in basal spacing from approximately 1.21 nm to values close to 1.27 nm, depending on drug loading. The resulting clay–CQD–drug systems exhibit stable structural organization without collapse of the layered framework. The ZIF-8/CQD hybrid nanomaterial preserves the crystalline structure and porosity of ZIF-8, as confirmed by XRD and nitrogen adsorption–desorption analyses, although a reduction in specific surface area is observed due to the incorporation of CQDs. Hemolysis assays performed over a concentration range from 5000 to 36 µg mL⁻¹ show hemolysis percentages below 5%, indicating good hemocompatibility. Overall, the results demonstrate that the association of CQDs with clays and metal–organic frameworks leads to structurally stable hybrid nanoplatforms with tunable optical properties, preserved porosity, and low toxicity. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese 2026-03-06T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6810 Título: Avaliação eletrocatalítica de nanomateriais com diferentes composições: estudo teórico-experimental Autor: RODRIGUES, Marta Venancia França Primeiro orientador: GARCIA, Marco Aurélio Suller Abstract: This thesis is organized into four chapters, which address advanced strategies in the study of metallic nanoparticles (NPs) applied to the oxygen reduction reaction (ORR) and the electrooxidation of glycerol, with emphasis on the controlled synthesis of nanomaterials. Chapter 1 presents a detailed literature review on the theoretical aspects of the ORR, synthesis strategies for metallic NPs, and the use of these NPs in fuel cells. The reaction mechanisms, as well as the influence of NP composition and morphology on electrocatalytic activity, are discussed, along with the current challenges in developing more efficient and durable catalysts. This review provides the conceptual foundation necessary for the subsequent experimental studies. Chapter 2 describes the experimental methodology employed throughout this work, divided into three parts: bimetallic platinum–molybdenum NPs applied to the ORR; trimetallic NPs composed of platinum, rhodium, and tin applied to the same reaction; and the physicochemical characterization of materials, along with electrochemical and theoretical analyses. The synthesis procedures were optimized to achieve precise control over NP composition, size, and dispersion, enabling the investigation of how these parameters influence catalytic efficiency. Chapter 3 comprises complementary studies involving platinum and rhodium NPs applied to electrooxidation and the controlled synthesis of platinum. The results demonstrate how subtle variations in NP composition and morphology can significantly affect electrocatalytic activity, providing valuable insights for the development of new catalysts. Finally, Chapter 4 presents the general conclusions of the thesis, highlighting the benefits of using metallic NPs in the ORR, including enhanced electron-transfer efficiency and improved stability under operational conditions. The findings indicate that precise control over NP composition and morphology is essential to optimize their electrocatalytic performance, opening promising perspectives for the development of clean and sustainable energy-generation technologies. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese 2025-10-17T00:00:00Z https://tedebc.ufma.br/jspui/handle/tede/6705 Título: Perfil químico e potencial biotecnológico antioxidante e anticancerígeno de nanoemulsões (o/a) dos óleos essenciais de Citrus limon (L.) Burn, Cymbopogon citratus (DC) Stapf e Citrus sinensis (L.) Osbeck Autor: EVERTON, Gustavo Oliveira Primeiro orientador: MONTEIRO, Odair dos Santos Abstract: This study characterizes the chemical profile, antioxidant activity, and in vitro anticancer properties of essential oils (EOs) from Cymbopogon citratus, Citrus sinensis, and Citrus limon, along with their nanoemulsions. Leaves of C. citratus and C. sinensis, along with C. limon peels, were collected in Maranhão state, Brazil, with EOs extracted by hydrodistillation. Nanoemulsions (NEOs) were prepared using phase inversion methodology. Chemical composition of EOs and NEOs was determined by GC-MS-FID analysis. Antioxidant activity was evaluated through radical scavenging assays (ABTS, DPPH, hydroxyl, superoxide, and hydrogen peroxide). In vitro anticancer activity was assessed against human cancer cell lines from colon, lung, liver, cervical, prostate, oral, and neuroblastoma tissues. Extraction yields were 0.92% for C. citratus, 1.55% for C. sinensis, and 1.01% for C. limon EOs. GC-MS analysis identified geranial and neral as major components in C. citratus, while limonene predominated in C. sinensis (85.28%) and C. limon (75.12%). The NEOs exhibited droplet sizes of 57.00 71.66 nm, zeta potentials ranging from -21.15 to -20.11 mV, polydispersity indices of 0.21 0.28, and pH values between 4.12-4.77. Both EOs and NEOs demonstrated potent antioxidant activity (IC50: 6.23-84.58 μg/mL). Significant cytotoxicity was observed against all tested cell lines, with particularly strong effects against 502713 (colon; IC50=1.00 μg/mL), IMR-32 (neuroblastoma; 1.10 μg/mL), Hep-2 (liver; 1.20 μg/mL), and SiHa (cervical; 1.60 μg/mL). These findings suggest that EOs and NEOs from C. citratus, C. sinensis, and C. limon show promise as potential candidates for innovative therapeutic applications. Keywords: Instituição: Universidade Federal do Maranhão Tipo do documento: Tese 2025-04-25T00:00:00Z