https://repositorio.ufu.br/handle/123456789/5136 Sat, 22 Aug 2026 03:07:23 GMT 2026-08-22T03:07:23Z https://repositorio.ufu.br/handle/123456789/49580 Title: Desenvolvimento de monolitos compósitos hierarquicamente porosos de acetato de celulose funcionalizados com TiO₂ para remoção de corantes em soluções aquosas por adsorção e fotocatálise Abstract: The contamination of aquatic systems by organic dyes constitutes an important environmental problem due to the high chemical stability and low biodegradability of these compounds. In this work, hierarchically porous cellulose acetate monoliths (CAM), both pure and functionalized with TiO₂, were developed aiming at the removal of methylene blue and Rhodamine B dyes through combined adsorption and photocatalysis processes. The materials were obtained by non-solvent-induced phase separation, using DMF and 1-octanol, with the incorporation of different TiO₂ contents. The characterizations confirmed the formation of porous monolithic structures and the incorporation of the inorganic phase into the polymeric matrix. The presence of TiO₂ promoted morphological changes and a significant increase in the specific surface area, with the composites containing 2% and 11% TiO₂ standing out, presenting areas of 54.61 and 57.82 m² g⁻¹, respectively, compared to 23.17 m² g⁻¹ for the pure monolith. In the methylene blue adsorption assays, the materials showed a removal capacity influenced by the composition and porous structure of the monoliths. The kinetic data showed the best fit to the pseudo-second-order model, indicating that the adsorption process is mainly associated with interactions between the dye and the active sites present in the matrix, with contributions from surface area, porosity, and TiO₂ incorporation. In the cyclic adsorption/photocatalysis assays with methylene blue and Rhodamine B, the TiO₂-containing composites showed greater stability in removal capacity over four cycles, evidencing the contribution of photocatalysis to the partial regeneration of the adsorbent sites. Despite the observed diffusional limitations and structural heterogeneity, the results demonstrate that TiO₂-functionalized monoliths have potential for application in wastewater treatment processes, combining a renewable polymeric support, a hierarchically porous structure, and integrated photocatalytic activity. Thu, 14 May 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/49580 2026-05-14T00:00:00Z https://repositorio.ufu.br/handle/123456789/49392 Title: Determinação de amônia volatilizada de solos fertilizados com fotômetro uv-vis portátil e de baixo custo Abstract: The continuous growth of the world population has increased the demand for more efficient food production systems. In Brazil, the agricultural sector faces significant challenges in meeting both domestic and international markets, especially due to the limitation of available land for cultivation. In this context, the use of nitrogen fertilizers stands out as a widely adopted strategy to increase productivity, as it provides essential nutrients for plant development. Among these inputs, urea (CH₄N₂O) is one of the main sources of nitrogen used in agriculture. After its application to the soil, urea is rapidly hydrolyzed by the action of the enzyme urease, resulting in the formation of gaseous ammonia and bicarbonate. This process reduces fertilizer efficiency, increases production costs, and may cause negative environmental impacts, mainly due to ammonia volatilization. Given this scenario, the present work proposes the development of a portable analytical method capable of quantifying volatilized ammonia in fertilized soils through active sampling and measurements carried out directly in the field. The experimental procedure consisted of collecting air containing NH₃ by bubbling it through a sulfuric acid solution with methyl orange, using a flow rate of 50 mL·min⁻¹. Absorbance readings were performed using a portable photometer produced by 3D printing, equipped with a 490 nm wavelength LED, a digital optical sensor, and an air pump, all integrated into an Arduino microcontroller. The method showed linear behavior in the range of 0 to 3.0 × 10⁻⁶ mol of NH₃, considering a collection time of 20 minutes. In addition, its application allowed the quantification of volatilized ammonia over four days, with collections carried out every 24 hours after fertilizer incorporation into the soil. As a form of validation of the sampling procedure, a parallel test was conducted in the Technical Assistance laboratory of Adfert. In this test, the quantification of ammonia resulting from urea volatilization in the soil was performed by titration of the solution obtained from filter papers used to capture the analyte. Fri, 31 Jul 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/49392 2026-07-31T00:00:00Z https://repositorio.ufu.br/handle/123456789/49375 Title: Desenvolvimento de um método eletroanalítico para a determinação de sibutramina em amostras biológicas e forenses utilizando folha de grafite como eletrodo de trabalho Abstract: The detection of sibutramine in different matrices is of significant importance due to its irregular use in dietary supplements and illicit weight-loss products, posing risks to public health and implications for forensic and antidoping analyses. In this context, electrochemical methods stand out as attractive alternatives to conventional techniques, offering low cost, rapid analysis, high sensitivity, and potential for in situ applications. This study aimed to develop an electroanalytical method for the determination of sibutramine (SIB) using a graphite sheet as the working electrode. Different surface modification strategies were evaluated, and electrochemical treatment was selected due to its superior analytical performance. The treated electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), demonstrating an increase in electroactive area and improved charge transfer kinetics. The electrochemical behavior of SIB was investigated, indicating a predominantly adsorption-controlled oxidation process. Differential pulse voltammetry (DPV) and square wave voltammetry (SWV) were evaluated, with SWV selected due to its higher analytical sensitivity. After optimization, two linear response ranges were obtained: 0.1–5.0 μmol L⁻¹ (R² = 0.993) and 7.5–45.0 μmol L⁻¹ (R² = 0.994). The limits of detection (LOD) were 0.01 μmol L⁻¹ for the first range and 1.89 μmol L⁻¹ for the second, while the limits of quantification (LOQ) were 0.03 μmol L⁻¹ and 6.32 μmol L⁻¹, respectively. The developed method was successfully applied to the determination of SIB in synthetic urine, multivitamin samples, and seized materials, showing satisfactory recovery results. Validation was performed through comparison with an HPLC-UV/Vis reference method, demonstrating good agreement between the results. The findings indicate that the electrochemically treated graphite sheet electrode is a promising, low-cost, and easy-to-prepare alternative for the determination of SIB in different matrices, with potential applications in forensic analysis, sanitary control, and antidoping. Tue, 19 May 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/49375 2026-05-19T00:00:00Z https://repositorio.ufu.br/handle/123456789/49124 Title: Estudo químico de lúpulos cultivados em diferentes localidades por RMN e CLAE - EM/EM e desenvolvimento de um método eletroanalítico para quantificação de iso-α-ácidos em cervejas Abstract: Hops (Humulus lupulus) are a key raw material in beer production, responsible for important sensory characteristics such as aroma and, notably, bitterness. During wort boiling, the α-acids present in hops undergo thermal isomerization to form iso-α-acids compounds directly linked to the beverage's bitterness intensity. In this study, commercial hop varieties were characterized using Nuclear Magnetic Resonance (NMR) and High-Performance Liquid Chromatography coupled with Mass Spectrometry. NMR analysis provided structural information via fingerprints, enabling the identification of major metabolites in the hop extracts, while HPLC-ESI-MS/MS analysis allowed for the annotation of the primary metabolites present in the samples. Specifically, for the Sabro hop variety, the α-acid mixture was separated yielding 31% of the hop extract and subsequently isomerized, resulting in a 42.5% yield of the iso-α-acid mixture. Structural confirmation was achieved through ¹³C NMR spectroscopy; α-acids exhibited a characteristic signal at δ 79.2 ppm, whereas the cis and trans isomers of the iso-α-acids showed signals in the δ 205.1–207.3 ppm range. Subsequently, an electrochemical study using a graphite sheet as the working electrode was conducted to investigate the behavior of iso-α-acids and their relationship to beer bitterness. The voltammetrics profiles obtained for α-acids and iso-α-acids displayed distinct potential regions; consequently, the analysis focused on iso-α-acids, as they are the primary contributors to the beverage's bitterness. Direct analysis of commercial beers revealed the presence of interfering compounds, such as sodium metabisulfite, necessitating sample pre-treatment via isooctane extraction. The efficiency of this procedure was monitored using HPLC-ESI-MS/MS, confirming the presence of iso-α-acids following the extraction step. Finally, bitterness values expressed in IBU were determined using Square Wave Voltammetry; the measured values (BS1 = 48.1; BS2 = 41.6; BS3 = 17.6) were close to those declared by the manufacturers (BS1 = 46; BS2 = 40; BS3 = 18). The results demonstrated that the developed electroanalytical method offers a higher-performance alternative for determining iso-α-acids and for future applications in beer quality control. Fri, 17 Jul 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/49124 2026-07-17T00:00:00Z