Electrochemical sensor based on carbon nanotube decorated with manganese oxide nanoparticles for naphthalene determination.

In this work, an electrochemical sensor was developed for the determination of naphthalene (NaP) in well water samples, based on a glass carbon electrode (GCE) modified as a nanocomposite of manganese oxides (MnOx) and COOH-functionalized multi-walled carbon nanotubes (MWCNT). The synthesis of MnOx nanoparticles was performed by the sol-gel method. The nanocomposite was obtained by mixing MnOx and MWCNT with the aid of ultrasound, followed by stirring for 24 h. Surface modification facilitated the electron transfer process through the MnOx/MWCNT/GCE composite, which was used as an electrochemical sensor. The sensor and its material were characterized by cyclic voltammetry (CV), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Important parameters influencing electrochemical sensor performance (pH, composite ratios) were investigated and optimized. The MnOx/MWCNT/GCE sensor showed a wide linear range of 2.0-16.0 µM, a detection limit of 0.5 µM and a quantification limit of 1.8 µM, in addition to satisfactory repeatability (RSD of 7.8%) and stability (900 s) in the determination of NaP. The determination of NaP in a sample of water from a gas station well using the proposed sensor showed results with recovery between 98.1 and 103.3%. The results obtained suggest that the MnOx/MWCNT/GCE electrode has great potential for application in the detection of NaP in well water.

Bibliometric analysis of global research progress on electrochemical degradation of organic pollutants.

As a result of anthropogenic action, an increasing amount of toxic organic compounds has been released into the environment. These pollutants have adverse effects on human health and wildlife, which has motivated the development of different types of technologies for the treatment of effluents and contaminated environments. The electrochemical degradation of organic pollutants has attracted the interest of research centers around the world for its environmental compatibility, high efficiency, and affordable cost. In the present study, a bibliometric analysis was performed using the Web of Science database in order to assess the progress of publications related to electrochemical degradation of organic pollutants between the years 2001 and 2021. The data retrieved showed a significant increase in publications related to the topic in the last 20 years. Electrochimica Acta was the magazine responsible for the largest number of publications (291, 6.52%). The studies mainly included the areas of engineering, chemistry, and environmental science ecology. China with a total of 1472 (32.96%) publications dominated research in this area, followed by Spain (436, 9.76%) and Brazil (345, 7.72%). The institutions with the highest number of contributions were the University of Barcelona and the Chinese Academy of Sciences, and the most productive authors were Brillas E. and Oturan M. A. The results of this study provide important references and information on possible research directions for future investigations on electrochemical degradation of organic pollutants.

Quantum chemical DFT study of the interaction between molecular oxygen and FeN4 complexes, and effect of the macrocyclic ligand.

Density functional theory (DFT) was used to examine the interaction between molecular oxygen (O2) and macrocyclic iron complexes of the type FeN4 during the formation of FeN4--O2 adducts. In order to understand how this interaction is affected by different macrocyclic ligands, O2 was bonded to iron-tetraaza[14]annulene (FeTAA), iron-tetramethyl-tetraaza[14]annulene (FeTMTAA), iron-hexamethyl-tetraaza[14]annulene (FeHMTAA), iron dibenzotetraaza[14]annulene (FeDBTAA), and two iron-tetramethyl-dibenzotetraaza[14]annulene complexes (FeTMDBTAA1, FeTMDBTAA2). The ground state for FeN4-O2 adducts was the open-shell singlet. Analysis of the factors influencing the O2 bonding process showed that different macrocyclic ligands yielded adducts with differences in O--O and Fe--O2 bond lengths, total charge over the O2 fragment, O--O vibrational frequency, and spin density in the O2 fragment. A smaller energy gap between the α-HOMO of the FeN4 complexes and the ß-LUMO of O2 increased the interaction between the complex and the O2 molecule. The order of activity was FeDBTAA < FeTMDBTAA2 < FeTMDBTAA1 < FeTAA < FeTMTAA < FeHMTAA.

Análises físico-químicas de polpas de frutas congeladas / Physico-chemical analysis of frozen fruit pulp

Alguns tipos de frutas tropicais tidas diferentes, como bacuri, cupuaçu, acerola, buriti, açaí, murici, sapoti e graviola, comumente encontradas no norte e nordeste do Brasil, também estão presentes na flora do Estado do maranhão. Ricas em sais minerais e vitaminas, são consumidas in natura ou na forma de doces, refrescos e sucos, muitos dos quais preparados da polpa processada industrialmente. O presente trabalho apresenta a análise físico-química de polpas de frutas (acerola, Malpighia glabra L.; bacuri, Platonia insignis, Mart. e cupuaçu, Theobroma grandiflorum) produzidas e comercializadas no município de Barra do Corda, Maranhão, com a finalidade de verificar a sua adequação às normas e padrões vigentes no país. Realizou-se as análises de pH, sólidos solúveis (grau Brix), acidez em ácido cítrico, ácido ascórbico e açúcares totais. Os resultados obtidos revelaram que a maior parte das polpas analisadas está de acordo com o padrão de qualidade vigente na legislação brasileira (Instrução Normativa n. 01, de 7 de janeiro de 2000). Contudo, a polpa de acerola apresentou alguns valores de açúcares totais naturais que podem ter sido advindos de adulteração atribuída à adição de água, o que corrobora o baixo teor de ácido ascórbico encontrado para essa polpa.