DSpace Collection:

Influência da co-dopagem com íons La3+ em sistemas binários de óxidos de SiO2-TiO2:Eu3+ obtidos pelo método sol-gel

2025-12-17T00:00:00Z

Title: Influência da co-dopagem com íons La3+ em sistemas binários de óxidos de SiO2-TiO2:Eu3+ obtidos pelo método sol-gel Abstract: This study investigates the synthesis and characterization of photoluminescent materials based on SiO2-TiO2 matrices co-doped with Eu3+ and La3+. Prepared via the sol-gel method and calcined at 750 °C, the matrices were analyzed by X-ray Diffraction (XRD), Raman spectroscopy, Fourier-Transform Infrared spectroscopy (FTIR), Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM), and Photoluminescence (PL). Structural results confirmed the stabilization of the anatase phase, where the incorporation of La3+ acted as a crystal growth inhibitor, except at concentrations of 0.3 and 1.0 mol%, which exhibited a singular bulk-like behavior regime. Diffuse reflectance analysis (DRS) revealed an adjustable direct band gap between 2.75 and 3.02 eV, correlated with the structural disorder monitored by the Urbach energy. Thermal treatment proved crucial, promoting the removal of hydroxyl suppressors and resulting in an average 6.5-fold (547%) jump in luminescence lifetimes (τ), which reached values exceeding 1000 µs. Spectroscopic analysis indicated that La3+ co-doping induces a symmetry breaking at the Eu3+ local site (site symmetries Cs, Cn ou Cnv), evidenced by the splitting of the 5D0→7F1 transition into three singlets and a 120% increase in the emission intensity of the 5D0→7F2 hypersensitive band. In situ PL monitoring as a function of temperature confirmed the reversibility and thermal robustness of the system, mitigating quenching effects. These findings demonstrate the high potential of SiO2-TiO2:Eu3+,La3+ composites for the development of advanced photonic devices, such as WLEDs and high-sensitivity sensors for optical thermometry.

Development of conductive and printable filaments for electrochemical sensors applied to environmental, pharmaceutical, food and biological analyses

2026-05-08T00:00:00Z

Title: Development of conductive and printable filaments for electrochemical sensors applied to environmental, pharmaceutical, food and biological analyses Abstract: Chemical sensors have been widely developed in response to the growing demand for the monitoring of analytes in environmental, biological, forensic and food samples. Among them, electrochemical sensors stand out for translating chemical information into measurable electrical signals and for offering advantages such as good selectivity, sensitivity, low limit of detection, ease of miniaturisation and versatility for both materials and designs. In this context, these devices have grown together with advances in new manufacturing technologies, especially additive manufacturing, which has emerged as a promising approach for the production of electrochemical sensors. In parallel, new conductive filaments have been developed to improve electrochemical responses, expand possibilities for new applications and incorporate sustainability perspective. However, as this is still a relatively recent field, challenges remain in regard to the achievement of improved electrochemical responses, better printability and the use of new polymers to broaden applications. Thus, this Thesis aimed to explore the fabrication and application of new alternative filaments produced in the laboratory for the monitoring of paracetamol, ascorbic acid, dopamine, uric acid, nitrite and carbendazim, demonstrating the versatility of these devices in environmental, biological and food samples. Divided into six chapters, the work presents: general introduction, filaments modified with carbon nanodiamonds and functionalised nanodiamonds, demonstrating the possibility of modifying and improving electrochemical responses; filaments with the addition of edible oils as plasticisers, with a focus on sustainability and demonstrating, for the first time, the influence of specific plasticisers on sensor responses; alternative thermoplastic polyurethane (TPU)-based filaments, used both as sensors obtained from the direct use of the filament itself and as printed electrodes which, compared with polylactic acid (PLA), show greater flexibility without loss of analytical performance, in addition to biocompatibility, thereby expanding the potential for application in wearable sensors; and, finally, more sustainable filaments produced from high-density polyethylene recycled (rHDPE) from cleaning-product packaging, with emphasis on greater chemical resistance and durability when compared with other polymers. All materials were extensively characterised, and the electroanalytical devices were evaluated against the proposed applications. The results expand the possibilities for the development and optimisation of electrochemical sensors, highlighting efficient, versatile, low-cost materials with low waste generation.

Determinação do teor de biodiesel metílico de palmiste (BMPALM) e pinhão manso (BMPM) usando espectroscopia no infravermelho médio e calibração multivariada por resolução multivariada de curvas com mínimos quadrados alternados (MCR-ALS) e regressão por vetor de suporte (SVR)

2025-07-03T00:00:00Z

Title: Determinação do teor de biodiesel metílico de palmiste (BMPALM) e pinhão manso (BMPM) usando espectroscopia no infravermelho médio e calibração multivariada por resolução multivariada de curvas com mínimos quadrados alternados (MCR-ALS) e regressão por vetor de suporte (SVR) Abstract: The growing demand for biodiesel has increased the risk of marketing fuels that do not meet the standards established by the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP), with the concentration of biodiesel in diesel blends being one of the main parameters of non-compliance. In response to this analytical demand, this study developed methods for quantifying the content of palm kernel methyl biodiesel (BMPALM) and jatropha methyl biodiesel (BMPM) in diesel blends, using mid-infrared (MIR) spectroscopy combined with multivariate calibration techniques: multivariate curve resolution with alternating least squares (MCR-ALS), support vector regression (SVR), and partial least squares (PLS) as the reference method. Samples were prepared in different concentrations (1.00 to 30.00% v/v), submitted to spectral acquisition, and then modeled using chemometric approaches. The models built for each type of biodiesel showed good accuracy, with low root mean square errors (RMSEs < 1%) in all stages (calibration, cross-validation, and prediction), and good linearity, as evidenced by determination coefficients (R²) very close to 1. Statistical tests (F-test) indicated similar variances between most models, with few exceptions in specific comparisons between techniques. The results confirm that the combination of FT-MIR spectroscopy with advanced multivariate calibration methods, especially SVR and MCR-ALS, enables reliable quantification of BMPALM and BMPM in diesel blends. Moreover, these two methods offer advantages over PLS, such as lower sample requirements for model construction and reduced operational costs, representing promising alternatives for quality control in the fuel industry and for regulatory monitoring.

Plataformas eletroquímicas de baixo custo produzidas em laboratório para a determinação de antibióticos em matrizes farmacêuticas, alimentares e ambientais

2025-12-09T00:00:00Z

Title: Plataformas eletroquímicas de baixo custo produzidas em laboratório para a determinação de antibióticos em matrizes farmacêuticas, alimentares e ambientais Abstract: The development and application of simple, rapid, and low-cost electroanalytical platforms are essential for the determination of antibiotics in various sample matrices. In this study, three distinct approaches were proposed and evaluated for the quantification of antibiotics in pharmaceutical, food, and environmental samples, focusing on strategies that combine selectivity, sensitivity, and operational feasibility. In pharmaceutical analysis, the batch injection analysis with amperometric detection (BIA-AD) technique was employed using a boron-doped diamond (BDD) electrode for the sequential determination of amoxicillin (AMX) and potassium clavulanate (CLA). The analytical strategy involved the application of two sequential potential pulses (+1.3 V and +1.8 V), enabling selective quantification of AMX at +1.3 V and oxidation of both (AMX + CLA) at +1.8 V. The oxidation current of CLA was obtained by subtraction, using a correction factor. The method showed high analytical throughput (>200 injections/hour), excellent precision (RSD < 1.3%), and detection limits of 0.31 μmol·L⁻¹ for AMX and 1.99 μmol·L⁻¹ for CLA. In food analysis, a disposable electrode composed of graphite, glass varnish, and acetone was developed for the detection of sulfamethoxazole (SMX) in milk. Selectivity and stability were enhanced by using two detection potential pulses (+1.0 V and +1.3 V) and two cleaning potential pulses (+1.5 V and −1.5 V). The method showed good linearity (1.0–50.0 μmol·L⁻¹), a detection limit of 0.31 μmol·L⁻¹, and recoveries of 68 ± 7%, 103 ± 7%, and 115 ± 7% for milk samples fortified with 5.0, 10.0, and 20.0 μmol·L⁻¹ of SMX, respectively. For environmental monitoring, a voltammetric approach was developed for the indirect detection of AMX in water using disposable sensors fabricated by additive manufacturing (3D printing). The strategy involved three sequential steps: (i) chemical and electrochemical activation of the 3D electrode in alkaline medium, (ii) preconcentration of AMX by adsorption onto the electrode surface, and (iii) detection via oxidation of adsorbed AMX, followed by reduction and reoxidation of the oxidized product (quinone). The differential pulse voltammetry (DPV) technique enabled a detection limit of 0.01 μmol·L⁻¹, with high selectivity against evaluated interferents and recoveries ranging from 82 to 106% in different water types. All three approaches demonstrated robust analytical performance, operational simplicity, low cost, and strong potential for portability, highlighting the effectiveness of electrochemical platforms as tools for routine applications in quality control, food safety, and environmental surveillance.