Sensitive electrochemical detection of methimazole based on a unique copper and exfoliated graphene oxide nanocomposite.

Herein, we report the creation of a novel sensitive electrochemical sensing platform based on a copper and exfoliated graphene oxide (Cu-eGO) nanocomposite using a facile synthesis technique, which simultaneously removes the sodium ions that result from the exfoliation process to generate eGO from graphite. This novel Cu-eGO nanocomposite was characterized via SEM, EDX, Raman and XPS. The Cu-eGO/GCE exhibited much greater activity for the electrochemical oxidation of methimazole than the eGO/GCE or bare GCE. The electrochemical properties and kinetics involved in the oxidation of methimazole at the Cu-eGO were examined using voltammetry and electrochemical impedance spectroscopy (EIS). This Cu-eGO based sensing platform demonstrated high sensitivity at 1.32 µAµM-1cm-2, a low limit of detection at 0.06 µM, robust stability, and strong anti-interference against potential interferents that may exist in biological systems for the detection of methimazole. The developed electrochemical sensor was successfully employed in blood serum samples that mimicked real biological environments, showing its high applicability.

Estimating hydroxyl/epoxy ratio in graphene oxide through adsorption experiment and semiempirical GFN2-xTB quantum method.

CONTEXT: The reactivity of graphene oxide (GO) with amines is related to the ring-opening of the epoxy groups in its basal surface, as addressed experimentally. Therefore, discussing the hydroxyl/epoxy ratio for GO is relevant to improve the characterization of such material. As the adsorption of Methylene Blue into GO is related to a graphene derivative's oxidation degree (OD), we combined adsorption experimental information and theoretical data to estimate the hydroxyl/epoxy ratio. The theoretical data were compared to the experimental adsorption of Methylene Blue and Indigo Carmine into GO synthesized in our department. Our results show GO systems with hydroxyl/epoxy ratios equal to 0.7, 0.8, and 0.9 are the most representative in which the most coherent model corresponds to OH/EP=0.8 for our GO previously synthesized. METHODS: The GO-MODEL software was developed in the present work to obtain cartesian coordinates of GO systems. We investigated 204 systems comprising models with 486 carbon atoms with the GFN2-xTB semiempirical quantum method. The supramolecular arrangements were constructed with the recently developed UD-APARM program.

Characterization of Brazilian green propolis throughout the seasons by headspace GC/MS and ESI-MS.

BACKGROUND: A screening of the chemical composition of eight commercial classes of raw Brazilian green propolis throughout the seasons was carried out. A multivariate exploratory analysis of chemical composition obtained by gas chromatography associated with mass spectrometry with headspace extraction (HS-GC/MS), and by mass spectrometry with electrospray ionization (ESI-MS) was carried out using principal component analysis (PCA). RESULTS: Differences in the volatile and polyphenolic profiles of propolis samples were verified during the seasons. Within each season, the high quality commercial classes of propolis presented similar characteristics, while the low quality classes presented distinct compositions. In spring and summer, propolis of the trimming class, commonly considered of low quality by beekeepers, presented a composition similar to the superior quality propolis. CONCLUSION: Seasonality influences the chemical composition of the commercial classes of raw Brazilian green propolis. Headspace-GC/MS and ESI-MS assisted by PCA are effective to characterize volatile and non-volatile compounds of the propolis samples, and to correlate it to the seasons.

Phenol adsorption by activated carbon produced from spent coffee grounds.

The present work highlights the preparation of activated carbons (ACs) using spent coffee grounds, an agricultural residue, as carbon precursor and two different activating agents: water vapor (ACW) and K(2)CO(3) (ACK). These ACs presented the microporous nature and high surface area (620-950 m(2) g(-1)). The carbons, as well as a commercial activated carbon (CAC) used as reference, were evaluated as phenol adsorbent showing high adsorption capacity (≈150 mg g(-1)). The investigation of the pH solution in the phenol adsorption was also performed. The different activating agents led to AC with distinct morphological properties, surface area and chemical composition, although similar phenol adsorption capacity was verified for both prepared carbons. The production of activated carbons from spent coffee grounds resulted in promising adsorbents for phenol removal while giving a noble destination to the residue.

Solid waste from leather industry as adsorbent of organic dyes in aqueous-medium.

The industrial tanning of leather usually produces considerable amounts of chromium-containing solid waste and liquid effluents and raises many concerns on its environmental effect as well as on escalating landfill costs. Actually, these shortcomings are becoming increasingly a limiting factor to this industrial activity that claims for alternative methods of residue disposals. In this work, it is proposed a novel alternative destination of the solid waste, based on the removal of organic contaminants from the out coming aqueous-residue. The adsorption isotherm pattern for the wet blue leather from the Aurea tanning industry in Erechim-RS (Brazil) showed that these materials present high activity on adsorbing the reactive red textile dye as well as other compounds. The adsorbent materials were characterized by IR spectroscopy and SEM and tested for the dye adsorption (reactive textile and methylene blue dyes). The concentrations of dyes were measured by UV-vis spectrophotometry and the chromium extraction from leather waste was realized by basic hydrolysis and determined by atomic absorption. As a low cost abundant adsorbent material with high adsorption ability on removing dye methylene blue (80mgg(-1)) and textile dye reactive red (163mgg(-1)), the leather waste is revealed to be a interesting alternative relatively to more costly adsorbent materials.

In-situ monitoring of the structure of a goethite-based catalyst during methane oxidation by X-ray absorption near-edge structure (XANES) spectroscopy assisted by chemometric methods.

A goethite-based catalyst was evaluated using in-situ X-ray absorption near-edge structure (XANES) spectroscopy during methane oxidation under increasing reaction temperature. Determination of rank by median absolute deviation (DRMAD), evolving factor analysis (EFA), and multivariate curve resolution (MCR) were used to detect the species present in the catalyst during the reaction and determine their concentration profiles and their pure spectra. The reactants and reaction products were monitored on-line by mass spectrometer. The goethite-based catalyst was active for methane oxidation, with CO(2) and H(2)O as the main products. DRMAD and EFA were useful to determine the number of chemical species present in the catalyst structure during reactions. The catalyst presented phase transition during the reaction from goethite to maghemite according to XANES spectra determined by MCR. On the other hand, it was verified that the catalyst presented phase transition from goethite to wüstite in the process in the absence of the oxidant (O(2)).

Experimental and theoretical investigation of epoxide quebrachitol derivatives through spectroscopic analysis.

Two synthetic epoxide derivatives, important intermediates in organic synthesis, were obtained from L-quebrachitol, and their conformations were proposed based on spectroscopic analysis. Density functional theory (DFT) calculations of infrared and NMR spectra were shown to be reliable enough for organic chemistry applications. The observed structures were determined with the aid of the DFT spectroscopic data, stressing the relevance and utility of combined experimental/theoretical studies and also the usefulness of the (13)C NMR B3LYP/6-31G(d,p) calculations.

Activated carbon/iron oxide composites for the removal of atrazine from aqueous medium.

The adsorption features of activated carbon and the oxidation properties of iron oxides were combined in a composite to produce new materials for atrazine removal from aqueous medium. Activated carbon/iron oxide composites were prepared at 1/1 and 5/1 mass ratios and characterized with powder X-ray diffractometry (XRD), infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and nitrogen adsorption measurements. The adsorption and oxidation processes were evaluated in batch experiments, in order to monitor the atrazine removal capacity of these composites. The main iron oxide actually present in the composites was goethite (alpha-FeOOH). Impregnation with iron oxide reduced the surface area by its deposition in the activated carbon pores. However, a higher iron concentration promoted a higher oxidation rate, indicating that the efficiency of the oxidation reaction is related with the iron content and not with the pre-concentration of the contaminant on the carbon surface through adsorption process.

PRODUCCIÓN Y CARACTERIZACIÓN DE CARBONES ACTIVADOS A PARTIR DE RESIDUOS DE CANDEIA (Eremanthus erythropappus) Y SU APLICACIÓN EN LA ADSORCIÓN DE COMPUESTOS ORGÁNICOS / PRODUCTION AND CHARACTERIZATION OF ACTIVATED CARBONS FROM WASTE CANDEIA (Eremanthus erythropappus) AND THEIR APLICATION ON ORGANIC COMPOUNDS ADSORPTION / PRODUÇÃO E CARACTERIZAÇÃO DE CARVÕES ATIVADOS A PARTIR DE RESIDUOS DE CANDEIA (Eremanthus erythropappus) E TESTES DE ADSORÇÃO DE compostos orgânicos

En este trabajo se prepararon dos carbones activados (CA), utilizando como agentes activantes ZnCl2 yK2CO3, denominados CA/ZnCl2,CA/K2CO3, respectivamente, a partir de residuos generados en el proceso de extracción del aceite esencial de candeia, árbol nativo de Brasil. Estos carbones se caracterizaron por microscopía electrónica de barrido, análisis termogravimétrico, análisis elemental, superficie específica por el método BET e índice de iodo. Estos materiales se probaron en la adsorción de dos moléculas modelos: el fenol y el azul de metileno, y se comparó su capacidad de adsorción con un carbón activado comercial (Merck), denominado CA/Com. Las isotermas de adsorción para CA/ZnCl2, CA/K2CO3 y CA/Com mostraron capacidades de adsorción máxima de 297, 228 y 271 mg g-1, para azul de metileno y de 109, 195 y 161 mg g-1, para el fenol, respectivamente. Los resultados evidenciaron que los carbones son eficientes en el proceso de adsorción de las moléculas modelo ensayadas. Las isotermas fueron ajustadas a las ecuaciones de Langmuir y de Freundlich. El modelo de Langmuir entregó un ajuste mejor, mostrando que los adsorbentes presentan superficies energéticamente más uniformes. Los carbones activados producidos se presentan como potenciales adsorbentes para compuestos orgánicos, agregando un valor adicional al residuo.

In this work, two activated carbons were prepared, using as activating agents ZnCl2 and K2CO3, denominated CA/ZnCl2,CA/ K2CO3, respectively, from waste generated in the process of extraction of essential oil of Candeia, a tree native of Brazil. These carbons were characterized by scanning electron microscopy, thermal analysis, elemental analysis, BET surface area and iodine index. These materials were tested in the adsorption of model molecules: Phenol and Methylene Blue, and a commercial activated carbon (Merck) was used for comparison purposes. Adsorption isotherms for CA/ZnCl2,CA/K2CO3 and CA/Com showed maximum sorption capacities of 297, 228 and 271 mg g-1 for Methylene Blue and 109,195 and 161 mg g-1 for phenol respectively. The results showed that the carbons are efficient in the adsorption process of molecules tested. The isotherms were fitted to equations of Langmuir and Freundlich. The Langmuir model provided better fit, showing that the adsorbents have energetically uniform surfaces. The materials produced were characterized as potential adsorbents for organic compounds that can be used as an alternative for obtaining activated carbons adding value to the residue.

Neste trabalho, foram preparados dois carvões ativados, utilizando como agentes ativantes o ZnCl² eoK2CO3, a partir de resíduos gerados no processo de extração de óleo essencial de Candeia, árvore nativa no Brasil. Estes carvões foram caracterizados por microscopia eletrônica de varredura, análise termo-gravimétrica, análise elementar, área superficial BET e índice de iodo. E testados na Adsorção das moléculas modelo: Fenol e Azul de Metileno, foi utilizado um carvão comercial (Merck) para fins de comparação. As isotermas de Adsorção para o CA/ZnCl2, CA/K2CO3 e CA/Com apresentaram capacidades máximas de adsorção de 297, 228 e 271 mg g-1 para Azul Metileno e de 109, 195 e 161 mg g-1 para fenol respectivamente. Os resultados evidenciaram que os carvões são eficientes no processo de adsorção das moléculas testadas. As isotermas foram ajustadas as equações de Langmuir e Freundlich, o modelo de Langmuir forneceu melhor ajuste, mostrando que os ad-sorventes apresentam superfícies energeticamente uniformes. Os materiais produzidos se caracterizaram como potenciais adsorventes para compostos orgânicos podendo ser utilizados como alternativa para obtenção de carvões ativados, além de agregar valor ao resíduo.