https://repositorio.ufu.br/handle/123456789/5136 2026-04-21T03:06:21Z https://repositorio.ufu.br/handle/123456789/48352 Title: Influência do tamanho da cadeia carbônica no processo de fotoreforma de álcoois para obtenção de H2 de baixo carbono Abstract: Alcohol photoreforming constitutes a promising route for the simultaneous production of low-carbon hydrogen and higher value-added products. In this work, the influence of carbon chain length (C1–C5) on the photocatalytic activity of TiO2 P25 was investigated by evaluating individual alcohols (methanol, ethanol, propanol, butanol and isoamyl alcohol), as well as binary, ternary and quaternary mixtures, aiming to represent multicomponent systems closer to real matrices. Additionally, the performance of TiO2 samples obtained under supercritical conditions (TiO2 - SC) was studied and compared to TiO2 P25, using methanol as the reference system. The materials were subjected to different thermal treatments and characterized morphologically and spectroscopically. Photocatalytic tests were carried out under aerobic conditions, in which oxidation products were identified and quantified, as well as under anaerobic conditions in the presence of Pt as a co-catalyst for monitoring H₂ evolution. The results showed that, for TiO2 SC, rapid thermal treatments (30 min) at high temperatures (700 ºC) favor photocatalytic activity. For the photoreforming of different alcohols, it was observed that, for individual alcohols, H2 production decreases with increasing carbon chain length, following the trend: Methanol ~ Ethanol > Propanol > Butanol ~ Isoamyl alcohol. Regarding the products, predominant formation of the corresponding aldehydes (methanal, acetaldehyde, propionaldehyde and butyraldehyde) was observed, accompanied by carboxylic acids as minor products. In multicomponent mixtures, ethanol exhibited dominant behavior, maintaining acetaldehyde as the major product and influencing the overall selectivity of the system, while the complexity of the reaction medium intensified competition effects for active sites, impacting the overall efficiency of photooxidation and hydrogen production. Thus, the overall results demonstrate that carbon chain length and the simultaneous presence of multiple alcohols are determining factors for the kinetics, selectivity and H2 evolution in TiO2 - based photocatalytic systems, contributing to a more integrated understanding of multicomponent conditions applicable to the valorization of complex organic streams. 2026-02-10T00:00:00Z https://repositorio.ufu.br/handle/123456789/48302 Title: Síntese de derivados de di(2-piridil)piperazinas como potenciais agentes antimaláricos Abstract: This work describes the planning, synthesis, and biological evaluation of a new series of di(2-pyridyl)piperazine derivatives, aiming to obtain effective agents against resistant strains of Plasmodium falciparum. The synthetic strategy adopted was based on the convergent construction of the heteroaromatic skeleton through Nucleophilic Aromatic Substitution (SNAr) reactions, employing sodium carbonate in DMF or propanol under heating (60 – 100°C). This step proved robust, providing nitrated intermediates with high yields, mainly ranging from 65 to 100%. For subsequent functionalization, the reduction of nitro groups was optimized using tin(II) chloride dihydrate (SnCl2.2H2O) in ethanol, a method that proved superior to classical catalytic hydrogenation in terms of cost-effectiveness and selectivity, achieving yields in the range of 61 to 84%. The final diversification of the compounds was carried out via amidation reactions, largely using EDC and HOBt coupling reagents (with yields ranging from 17 to 93%), the synthesis of the most promising analog (13b) required prior activation of the carboxylic acid to its corresponding acid chloride, isolated in 31% yield. Structure-Activity Relationship (SAR) analysis demonstrated that bioisosteric substitution of the original thiophene ring with furan or oxazole preserved antiparasitic activity, while the introduction of more polar heterocycles was important. The most significant advance, however, lay in the modification of the central ligand: the expansion of the six-membered piperazine ring to a seven-membered diazepam homopiperazine core resulted in the optimized candidate of the study. The 13b derivative, obtained via the acid chloride route, showed submicromolar potency (IC50 = 0,60 ± 0,05 µM) and an extremely high selectivity index (SI > 166), validating the hypothesis that the greater conformational flexibility conferred by the seven-membered ring favors antiparasitic activity. 2026-02-12T00:00:00Z https://repositorio.ufu.br/handle/123456789/48300 Title: Aplicação de técnicas eletroquímicas para a quantificação de amônia Abstract: This study presents the development of an electrochemical device fabricated using platinum wires, modified with electrodeposited Pt microparticles, for the voltammetric determination of NH3 in natural and drinking waters. Ammonia plays a relevant role in the nitrogen cycle and has a negative environmental impact when present at high concentrations due to its ability to cause eutrophication in aquatic environments. The method proposed in this study employs differential pulse voltammetry in an alkaline medium, aiming to combine instrumental simplicity, low reagent consumption, and high analytical sensitivity. Initially, three miniaturized devices were fabricated and characterized using a Pt wire (⌀ = 0.5 mm) as the working electrode. Subsequently, optimization studies of experimental conditions were carried out, including the type of abrasive used for working electrode polishing, the concentration of the supporting electrolyte, and the presence of dissolved oxygen. It was found that the use of alumina as an abrasive and the presence of dissolved oxygen in solution provided improved voltammetric responses and greater repeatability, with RSD for ammonia oxidation peak currents lower than 10%. The modification of the working electrode surface with electrodeposited Pt microparticles increased sensitivity by approximately threefold, and lowered limits of detection (LOD = 0.57 µmol L-1) and quantification (LOQ = 1.92 µmol L-1) compared to the unmodified Pt electrode (LOD = 0.9 µmol L-1 e LOQ = 3.0 µmol L-1). The linear range obtained with the modified electrode was from 0.5 to 50 µmol L-1 (0.007 to 0.7 ppm N), which meets the Brazilian drinking-water regulatory limits (Resolution 357 of 2005). The applicability of the miniaturized device was assessed through the analysis of four water samples, showing satisfactory accuracy and precision for all samples in accordance with AOAC International criteria. NH3 recoveries ranged from 92 to 103%, meeting validation requirements according to the AOAC guide. It is concluded that the proposed miniaturized system is a promising tool for the determination of NH3 in aquatic environments, offering advantages such as high sensitivity, low sample and reagent consumption, reduced waste generation, and minimal sample preparation requirements. 2026-02-10T00:00:00Z https://repositorio.ufu.br/handle/123456789/47985 Title: Caneta de plasma de ar atmosférico para modificação de eletrodos serigrafados: análise de paracetamol e codeína em saliva e fármacos Abstract: Screen-printed electrodes (SPEs) are widely employed as electrochemical sensors. These three-electrode systems (working, reference, and counter electrodes) involve the preparation of a substrate and the deposition of a composite consisting of an organic binder and a conductive material, typically graphite powder or, more recently, boron-doped diamond (BDD) films. Although the use of SPEs as sensors has shown promising results, they often require surface treatment to enhance electrochemical performance. In this context, plasma stands out as a promising, reagent-free approach compatible with a wide range of electrode materials. In this work, we propose the use of a handheld atmospheric air plasma pen to efficiently (2 min) treat different carbonaceous surfaces, specifically graphite-based electrodes (G-SPE, sp²) and BDD-based electrodes (BDD-SPE, sp³). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed surface changes after plasma treatment. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) demonstrated an increase in the sp² carbon content on both types of SPE surfaces. Furthermore, electrochemical impedance spectroscopy (EIS) measurements showed a decrease in charge transfer resistance (Rct) and an increase in the heterogeneous electron transfer rate constant (k0) for plasma-treated SPEs. Electrochemical performance was evaluated by cyclic voltammetry in 0.50 mmol L⁻¹ solutions of different electroactive species. To assess the feasibility of the proposed method, plasma-treated G-SPE was employed for the simultaneous determination of paracetamol (PAR) and codeine (COD) in pharmaceutical formulations and synthetic saliva. Using treated electrodes, linear response ranges of 1.00–9.00 µmol L⁻¹ (LOD = 0.15 µmol L⁻¹) for PAR and 1.00–80.00 µmol L⁻¹ (LOD = 0.71 µmol L⁻¹) for COD were obtained. Recovery studies yielded values ranging from 81–116% for saliva and 90–107% for pharmaceutical samples, indicating that the method is accurate and suitable for the analysis of these matrices. Additionally, treatment with the plasma pen also enabled the regeneration of aged G-SPE and BDD-SPE electrodes. 2025-12-19T00:00:00Z