Instituto de Química

Nanofibras cerâmicas eletrofiadas como nanozymes: síntese, caracterização e aplicação em sensores colorimétricos

2026-04-10T00:00:00Z

Nanofibras cerâmicas eletrofiadas como nanozymes: síntese, caracterização e aplicação em sensores colorimétricos Lima, Jéssica Brito dos Santos Mercante, Luiza Amim The increasing demand for food safety and access to potable water has spurred the development of simple, rapid, and low-cost analytical methods for determining chemical species of interest. However, although highly sensitive, conventional analytical techniques often require expensive instrumentation, extensive laboratory infrastructure, and long analysis times. In this context, nanozyme-based colorimetric sensing has emerged as a promising alternative. Nanozymes are nanomaterials that mimic the catalytic activity of natural enzymes, promoting the oxidation of chromogenic substrates and producing color changes that enable the detection and quantification of analytes. Among the materials investigated for this purpose, metal oxides have attracted significant attention due to their high chemical stability and catalytic activity. However, the use of ceramic nanofibers in nanozyme-based platforms remains limited, despite their structural advantages, such as high surface area and one-dimensional morphology, which can enhance catalytic performance. In this work, precursor nanofiber membranes containing zinc and manganese salts were produced by electrospinning and subsequently calcined to yield ceramic nanofibers (NFII, NFIII, NFIV, and NFV) with compositions controlled by the metal salt ratio. The physicochemical properties of the materials were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, X-ray photoelectron spectrometry, and nitrogen physisorption, enabling correlations between morphology, composition, crystalline structure, and surface area. The oxidase-like activity of the nanofibers was evaluated using the chromogenic substrates tetramethylbenzidine (TMB), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and o-phenylenediamine (OPD), yielding kinetic parameters (Km and Vmax) comparable to or higher than those reported in the literature. Based on this catalytic activity, colorimetric sensors were developed for the determination of nitrite and ascorbic acid. The NFII/TMB system was applied to nitrite detection using ratiometric, spectrophotometric, and smartphone-assisted approaches, with limits of detection (LOD) of 4.0 and 4.8 µmol L-1, respectively. For ascorbic acid determination, the NFIII/ABTS and NFIII/OPD systems showed LODs of 0.7 and 1.5 µmol L-1, respectively. The developed sensors showed good sensitivity, selectivity, and stability, and were successfully applied to the determination of the analytes in drinking water and fruit juice samples, with recoveries ranging from 92.0 to 104.9%. These results demonstrate the potential of electrospun ceramic nanofibers as nanozymes for developing simple, accessible colorimetric platforms for food and water quality monitoring. Universidade Federal da Bahia Tese

Avaliação da composição mineral de material particulado atmosférico coletado na região geográfica intermediária de Salvador e de Amélia Rodrigues, Bahia, Brasil

2025-09-30T00:00:00Z

Avaliação da composição mineral de material particulado atmosférico coletado na região geográfica intermediária de Salvador e de Amélia Rodrigues, Bahia, Brasil Sacramento, Carlos Leandro Cruz Araujo, Rennan Geovanny Oliveira Air pollution has been a major focus of study in the scientific community, aiming to understand its implications for human health, ecosystems, and material heritage, identifying itself as a key element in the pursuit of sustainable development. The accelerated growth of urban areas, driven by industrialization and population increase, has significantly contributed to the current scenario. In this context, the present work aims to investigate, evaluate, and quantify samples of atmospheric particulate matter in the form of total suspended particles (TSP) and respirable particles (PM₂,₅), according to the limits established by Resolution No. 491/2018 of the National Environment Council (CONAMA), in addition to chemically characterizing the mineral composition. Sampling was conducted in the Intermediate Geographic Region of Salvador, encompassing the municipalities of Lauro de Freitas, Madre de Deus, São Sebastião do Passé, São Francisco do Conde, and Amélia Rodrigues, in the Metropolitan Region of Feira de Santana, in August, September, and December 2021, covering both the dry and rainy seasons in the region. Collections occurred during nominal 24-hour periods, using three portable samplers (HANDI-VOL) for PTS and one portable prototype for PM₂,₅, operating simultaneously. The geometric mean concentrations of PTS and PM₂,₅ were below the limits established by Resolution No. 491/2018 of the CONAMA. After the sampling procedures, the particulate matter deposited on the filters was subjected to acid extraction, followed by chemical analysis by inductively coupled plasma optical emission spectrometry (ICP OES) to determine Al, Ba, Cr, Cu, Fe, Ni, Mn, Mo, Pb, Sb, V, and Zn. Based on the results obtained, the trace metals were grouped in ascending order of concentration (Mo < V < Sb < Pb < Ni < Mn < Zn < Ba < Cr < Al < Cu < Fe) for PTS. The concentrations of the chemical elements in the PM2.5 samples were below the quantification limit of the analytical method. With the predominance of Fe concentration in the chemical composition of the atmospheric particulate matter (PTS), the results obtained clearly showed that in the study region, the chemical composition of atmospheric particulate matter is strongly associated with natural sources, but is directly influenced by anthropogenic sources such as the use of fossil fuels, vehicular traffic associated with brake system wear, maritime traffic, industrial, petrochemical and port activities through the presence of Cu, Mn, Pb, Sb and Zn. An investigation of pollution indices was carried out using the enrichment factor (EF) and the geoaccumulation index (Igeo), as geochemical indices, highlighting the need for extra attention to the concentrations of Cu, Cr and Sb. Multivariate data analysis was crucial in determining a possible anthropogenic contribution in the region. Principal component analysis (PCA) showed that Fe was the chemical element with the greatest contribution to the chemical composition of the PTS, mainly associated with natural sources, such as soil resuspension. Meanwhile, the concentration of Cu, Fe, Mn, and Pb indicated anthropogenic influence from traffic and industrial activities. During the dry and rainy seasons, PCA showed variation in the relative weight of the metals, but maintained the distinction between natural and anthropogenic sources. Hierarchical cluster analysis (HCA) consistently grouped the samples, separating sets influenced by industrial/port activities from those of natural origin. This analysis confirmed the correlation between Cu, Mn, and Sb as markers of anthropogenic impact. Together, PCA and HCA reinforced the identification of the main emission sources in the studied region. Finally, this work may assist the corresponding agencies in more effective air quality monitoring in the region. Universidade Federal da Bahia Dissertação

Estratégias baseadas em química verde para microextração em fase líquida e determinação de mercúrio em frutos do mar

2025-12-18T00:00:00Z

Estratégias baseadas em química verde para microextração em fase líquida e determinação de mercúrio em frutos do mar Assis, Rosivan dos Santos de Lemos, Valfredo Azevedo The use of increasingly eco-friendly solvents has been a guiding principle in liquid-phase microextraction (LPME). A solvent can be considered green when it exhibits low toxicity, biodegradability, low cost, and good availability. In this work, two microextraction methods were developed, employing different green solvents for the preconcentration and determination of mercury in seafood samples. In both studies, the reagent ammonium pyrrolidinedithiocarbamate (APDC) was used as a complexing agent, and detection was performed by cold vapor atomic absorption spectrometry (CV AAS). The first study proposes a simple approach based on microextraction with a switchable hydrophilicity solvent (SHS-DLPME). Octanoic acid (C8H16O2) was chosen as the SHS, and sodium carbonate was used as a CO2 source to change the polarity of the extraction solvent. After optimization, the detection limit was 0.010 mg kg-1, and the enrichment factor was 31. The second approach involved a vortex-assisted magnetic deep eutectic solvent dispersive liquid-phase microextraction (VA-MDES-DLPME). The MDES was produced from menthol and octanoic acid, used as proton acceptor and donor, respectively, and incorporated into magnetic iron nanoparticles. For this method, the enrichment factor was 51.4, while the detection limit was 0.009 mg kg-1. Certified reference materials BCR 414 (plankton), BCR 482 (lichen), and ERM-CE 278K (mussel tissue) were used for validation. The methods were applied to determine mercury in fish, mollusk, and crustacean samples, with mercury concentrations ranging from 0.11 to 0.37 mg kg-1 in both methods. The SHS-DLPME and VA-MDES-DLPME methods scored 0.60 and 0.57, respectively, on the AGREE metrics. The results demonstrated that both methodologies align with the principles of green chemistry by providing efficient, selective, and more environmentally friendly alternatives for mercury determination. Overall, the proposed procedures significantly advance sustainable microextraction strategies for contaminant analysis in food. Universidade Federal da Bahia Tese

Estudo teórico-computacional dos mecanismos eletrocatalíticos da oxidação da água por complexos de cobre(II) com ligantes macrocíclicos.

2026-02-11T00:00:00Z

Estudo teórico-computacional dos mecanismos eletrocatalíticos da oxidação da água por complexos de cobre(II) com ligantes macrocíclicos. Neves, João Pedro Costa Sarno Alves, Tiago Vinícius In a contemporary world marked by environmental imbalance, the Energy Transition arises as a solution to mitigate the emission of pollutants from fossil fuels burning. Following this scenario, a promising alternative is, for example, the H2, whose production via water electrolysis faces challenges related to its anodic half reaction, thus evoking the use of catalysts -- e.g. copper(II) complexes bearing macrocyclic ligands -- that remain in constant improvement. For this, it's necessary to elucidate this mechanism, which means to identify the key intermediates and steps for reaction kinetics. Therefore, by means of computational tools, the present work focused on the theoretical study of the water oxidation's electrocatalysis by the coordination complex [Cu(14-TMC)]+2, based on experimental evidence to which the results yielded good correspondence. In this case, the O-O bond formation proceeds through a water nucleophilic attack coupled with a single electron transfer to the metal center or, alternatively, through a crossing point between quartet and doublet potential energy surfaces. Going further, the results of macrocyclic shrinkage were also investigated through [Cu(12-TMC)]2+'s catalysis. Despite of the similar values in terms of energy barrier, this ligand enables the coordination of two water molecules, which impacts the course of reaction. The results, based on electronic and structural fundaments, shed a light on the rational design of ligands aiming better catalytic performance for H2 production. Universidade Federal da Bahia Dissertação