Scielo RSS <![CDATA[Química Nova]]> vol. 41 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[ADSORPTION OF BIODIESEL CONTAMINANTS BY SURFACE-MODIFIED BAGASSE FIBERS]]> Sugarcane bagasse fibers chemically modified on its surface were used to adsorb contaminants from biodiesel. Two biodiesel samples were used as adsorbates: crude and washed biodiesel. The contaminants were mainly glycerol and water, but also ions, and methanol. The biodiesel is usually washed, in order to remove most of the contaminants, but the procedure introduces large amounts of water, which are further difficult to remove, because the biodiesel acting as an acceptor of hydrogen bond. The adsorbent used in this work was proved to be very efficient to remove the contaminants and also to remove water from the washing the crude biodiesel. The contaminants adsorbed from biodiesel were identified by thermal analyses (DSC and DTA) of the fibers (adsorbent) and of the biodiesel (adsorbate) by comparing the results with the pure biodiesel. The proportion of free glycerol showed high adsorption efficiency for the crude biodiesel. A total amount of 1.34 g of fibers was estimated as being needed for its complete removal. The mass of bagasse fibers added (up to 1g) in a fixed volume of biodiesel was a relevant condition, as the saturation in fibers started at around 0.70 g cleaning up to about 98% removal of the impurities. <![CDATA[OPTOELECTRONIC PROPERTIES OF TRIPHENYLAMINE BASED DYES FOR SOLAR CELL APPLICATIONS. A DFT STUDY]]> Abstract: Dye-sensitized solar cells (DSSCs) based on triphenylamine (TPA) as a donor group linked with the acceptor cyanoacrylic acid electron acceptor by 2,2’-bithiophene as π-bridged (D-π-A) has been investigated by Density Functional Theory (DFT) at the B3LYP/6-311G(d,p) level of theory, to establish the conformational orientation of cyanoacrylic acid group as well as evaluate the effect of planarizing the 2,2’-bithiophene unit in position 3 and 3’ by electron withdrawing or donor groups on the electronic structure properties of ground and doping(n,p) states. Also, the Time Dependent Density Functional Theory (TD-DFT) at the CPCM-TD-CAM-B3LYP//CAM-B3LYP/6-311G(d,p) level of theory were selected to modulate the electronic absorption spectra and charge-transfer capabilities of the molecules analyzed in the present work. The results indicate that adding an auxiliary donor or withdrawing group to the 2,2’-bithiophene in the (D-π-A) arrangement allow to modify the LUMO’s energy of the dyes, while the HOMO's energy is slightly affected. <![CDATA[ORGANOPHILIZATION AND SILANIZATION OF BENTONITE CLAY]]> Clays have been used in several technological areas. One of the most usual applications is their incorporation into organic materials. Nonetheless, natural clays are hydrophobic being incompatible with organic medium. Clay organophilization can be reached by several methods such as by exchange of the interlayer sodium cations by organic cations, and by silanization of the clay layers. In this study the bentonite clay was organophilized by the addition of the methoxymethyltriphenylphosphonium chloride (CTFF). Further, the organoclay was silanized with (3-glycidyloxypropyl) trimethoxysilane (GPTMS). X-ray fluorescence results, infrared and XPS spectroscopy showed the presence of phosphorus in the organophilic clay. The interlayer space, obtained by X-ray diffraction, increased in 55% after the CTFF addition showing the cationic exchange in the clay lamellar region. After the silanization of the organoclay the interlayer space was slightly reduced from 1,78 nm to 1,72 nm, indicating that the silane molecules were preferential bound in the clay edges. <![CDATA[THE USE OF POLYSACCHARIDES EXTRACTED FROM SEED OF <em>Persea americana</em> var. Hass ON THE SYNTHESIS OF ACRYLIC HYDROGELS]]> This paper reports the use of polysaccharides extracted from seed of Persea americana var. Hass in the synthesis of acrylic hydrogels. The effects of the chemical composition (acrylamide/acrylic acid), the concentration of crosslinking agent (glycerol diacrylate) and the type of initiation (redox, photoinitiation) of the hydrogels were evaluated with and without polysaccharides. Xerogels were characterized by FTIR spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), while for the swollen hydrogels the swelling kinetic and mechanical properties were evaluated. The kinetic parameters were obtained using the second order equation proposed by Schott, where it is reported that by increasing the concentration of the crosslinking agent, the degree of swelling is reduced because of the greater structural level. The increase of the amount of acrylamide and the amount of polysaccharides causes also a decrease in the swelling degree. The type of initiation also affected the hydrogels swelling kinetic, the photoinitiated hydrogels were the ones that captured less water. Moreover, the increasing of the glass transition temperature and the compression modulus with the crosslinking agent concentration and molar ratio AAm/AAc are observed for hydrogels with and without polysaccharides. The results demonstrate a successful incorporation of polysaccharides into the polymeric network. <![CDATA[MORE ACTIVE AND SULFUR RESISTANT BIMETALLIC Pd-Ni CATALYSTS]]> The influence of the kind of metal precursor and the sequence of impregnation on the properties of Pd-Ni catalysts was evaluated during the test reaction of selective hydrogenation of styrene to ethylbenzene by means of physicochemical characterization. The focus was put on the final hydrogenating activity and the resistance to deactivation by sulfided compounds (thiophene). The used techniques of characterization were ICP, XPS, XDR, TPR, CO chemisorption and TEM. XPS results indicated the presence of different Pd species: Pdδ-, Pdº and Pdδ+. In the case of the Ni containing catalysts, Niº and NiO species were also detected. These palladium and nickel species would be responsables of the variation of activity and sulfurresistance of the catalysts. NiClPd catalysts had a higher resistance to deactivation by sulfur poisoning. This was associated to a higher concentration of Pdη+ClxOy species that would prevent the adsorption of thiophene by both steric and electronic effects. It could also be due to the lower concentration of Pdº and Niº on these catalysts, as compared to those shown by the PdNiCl catalysts. Both the Pdº and Niº species are more prone to poisoning because of their higher electronic availability. <![CDATA[EVALUATION OF ASPHALTENE PRECIPITATION IN DIFFERENT CONDITIONS OF COMPOSITION, TEMPERATURE, AND PRESSION]]> Asphaltenes are a heavy fraction of petroleum with the ability for self-association, a phenomenon that can occur spontaneously in the reservoirs or in any of the various stages of production and processing, depending on variations in pressure, temperature, composition and shearing, among others. In this work, it was evaluated the precipitation of asphaltenes in two oils (P01 and P02) in different conditions of temperature and pressure and in the absence or presence of CO2. Under high pressure and temperature conditions, the precipitation of asphaltenes was observed in the presence of CO2 in mixtures with methane, while the addition of propane induced precipitation in the absence of CO2. The results of analyses elemental (CHNO), SEM, FTIR and LDI-MS were consistent with the structure assigned to samples of this nature (oils, maltenes and fractions of asphaltenes insoluble in n-pentane, C5I, and n-heptane, C7I). <![CDATA[ELECTROCOAGULATION-FLOTATION PROCESS: INVESTIGATION OF OPERATIONAL PARAMETERS FOR WASTEWATER TREATMENT FROM FISHERY INDUSTRY]]> The objective of this study was the utilization of an electrocoagulation-flotation process to evaluate the treatment of a real wastewater from fish industries (Brazil - SC). This type of effluent is usually treated by conventional processes, which are often not sufficient to meet the desired final quality of legal environmental requirements. The effect of current density, pH and treatment time was evaluated. The best experimental conditions for the process were current of 5 A, potential of 15 V and distance between electrodes equal to 10 mm. Under these conditions, the removal of the contaminants were expressive for all analyzed parameters as follows: average color reduction of 95.5%; turbidity of 96.9%; COD 93.3; BOD5 of 97.5%; phosphorus of 88.5% and oils and greases of 93.6%. <![CDATA[BIOCONVERSION OF CELLULOSE INTO HYDROGEN, BIOGAS AND ORGANIC ACIDS USING MICROBIAL CONSORTIUM FROM A PULP AND PAPER MILL WASTEWATER TREATMENT PLANT]]> This study evaluated the potential of a microbial consortium collected from a pulp and paper mill wastewater treatment plant (WWTP) for converting cellulose to hydrogen, biogas and organic acids. Fermentation tests were conducted in batch reactors fed with different concentrations of cellulose as substrate: (C1) 2.0 g L -1; (C2) 5.0 g L -1 and (C3) 10.0 g L -1. The parameters investigated were hydrogen, biogas, organic acids, carbohydrates and pH. The maximum hydrogen production was 14.77, 39.25 and 22.53 mmol L -1, and the maximum methane was 4.40, 3.72 and 9.56 mmol L -1, for C1, C2 and C3, respectively. Butyric acid was the main metabolite generated, with maximum concentrations of 2.2, 1.8 and 2.2 g L -1 for C1, C2 and C3, respectively. The decrease in hydrogen production was accompanied by the production of methane, acetic acid and hydrogen sulfide in the three tests, probably related to hydrogenotrophic methanogenesis, homoacetogenesis and sulfidogenesis, respectively. The phylogenetic characterization of the bacterial community was performed by cloning and sequencing analysis. The microorganisms identified in the consortium were similar (&gt; 95%) to Clostridium sp., Klebsiella sp., Routella sp. and Desulfovibrio sp. These genera were associated with hydrogen production, degradation of cellulosic substrates, and/or hydrogen-consuming microorganisms. <![CDATA[PROCESSING OF SPENT ZINC-MnO<sub>2</sub> DRY CELLS IN VARIOUS ACIDIC MEDIA]]> This paper describes a route for recovering manganese and zinc from spent zinc-MnO2 dry cells via acid leaching. Sulfuric, hydrofluoric and formic acids were used as leachants. Hydrogen peroxide was added as reductant, except for formic acid since it is itself a reductant. Experiments were run at 25-40 ºC for 1-3 h. Under the best optimal conditions, over 95 wt.% of zinc and manganese were leached irrespective of the leachant. Leaching of contaminants was strongly dependent on the leachant due to the insolubility of salts or complexing reactions. Zn(II) was best extracted with D2EHPA diluted in n-heptane at pH &gt; 1, particularly from the leachates of weak acids. Mn(II) was much more co-extracted from sulfuric leachates, but was easily scrubbed with dilute leachant (~2 mol L -1). Zn(II) striping was possible using 5 mol L -1 H2SO4. Manganese was isolated as MnO2 carrying the leached contaminants. High-purity sodium salts of the anions of the leachants were recovered after slow evaporation of the final solution. <![CDATA[NEW DEGRADED QUINONE DITERPENOID FROM THE STEMS OF <em>Byrsonima coccolobifolia</em> Kunth. (Malpighiaceae)]]> A chemical investigation of two specimens of Byrsonima coccolobifolia collected in the southeast cerrado and from central Brazil was performed. A new degraded diterpenoid, byrsonimaquinone, was isolated from the stems along with known compounds. This is the first study on the roots of B. coccolobifolia, and several triterpenes, such as α-amyrin, β-amyrin, oleanolic acid, and glochidonol, along with a mixture of stigmasterol, β-sitosterol and campesterol, were identified. These compounds were identified by spectroscopic analysis techniques, including 1D and 2D NMR, GC-MS and high-resolution mass spectrometry. <![CDATA[THE VERSATILITY OF THE HANGING MERCURY DROP ELECTRODE IN ANALYTICAL CHEMISTRY - A REVIEW ABOUT RECENT APPLICATIONS]]> Voltammetry using mercury electrode as working electrode has been employed in the determination of organic and inorganic compounds in several samples. A review on the applications of this analytical tool is present, covering the period of the last ten years. The emphasis of this work is directed to the hanging mercury drop electrode (HMDE), its advantages, disadvantages and applications. Voltammetric measurements are easily carried out, and present low cost. The review discusses that the use of mercury in the measurements can be a limitation due the toxicity of the element. However, nowadays the necessary of volume of Hg in the measurements is very small, and it can be reused. Thus, the correct disposal of the small amount of waste generated can be minimize environmental risks and human health, according to the principles of Green Chemistry. <![CDATA[CHEMINFORMATICS: AN INTRODUCTION]]> Cheminformatics is an interdisciplinary field between chemistry and informatics, which has evolved considerably since its inception in the 1960s. Initially, the cheminformatics community dealt primarily with practical and technical aspects of chemical structure representation, manipulation, and processing, while modern research explores a new role: the exploration and interpretation of large chemical databases and the discovery of new compounds with desired activity and safety profiles. Despite the recent release of several hallmark reviews addressing methods and application of cheminformatics written in Portuguese, so far there are no scientific articles presenting cheminformatics research to the Brazilian scientific community yet. To address this gap, we aim to introduce the field of cheminformatics to both students and researchers in a simple and didactic way by narrating important historical facts and contextualizing information within the scope of various applications. <![CDATA[OPTIMIZATION OF SOLID-LIQUID EXTRACTION WITH LOW TEMPERATURE PARTITION FOR DETERMINATION OF CARBOFURAN IN CUCURBITA PEPO L (“ZUCCHINI”) BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY]]> According to results of the Program of Analysis of Pesticide Residues in Foods of the National Agency of Sanitary in Brazil (2013 to 2015) the zucchini, Cucurbita pepo L is one of the non-hardy vegetables, that presented higher contamination index by pesticides residues. One of these agrochemicals is carbofuran, which although not authorized for this crop, is commonly and illegally used for whitefly control. The objective of this study was to optimize the solid-liquid extraction method with low temperature partitioning (SLE/LTP) for the determination of carbofuran residues in zucchini by high performance liquid chromatography with ultraviolet detector (HPLC-UV). The optimization was performed with a complete factorial design, 2³ to evaluate the simultaneous performance of three factors in two levels, in triplicate. The optimized SLE/LTP-HPLC/UV method showed to be selective, simple and efficient, consuming a small amount of sample and solvent extractor. The average recovery percentage was 75.88%. Samples of zucchini purchased in the Itumbiara-GO trade, Brazil, and submitted to the optimized method did not present carbofuran residues. <![CDATA[UNA DEFENSA DE LA PERSPECTIVA FORMATIVA DEL DESARROLLO PROFESIONAL DOCENTE EN LA PRÁCTICA EDUCATIVA DE LOS PROFESORES DE QUÍMICA]]> Teachers’ Professional Development (TPD) has been defined as learning opportunities, insights and discussions that improves the personal, social and pedagogical growing of the teachers, whose main goal is the enhancement of their knowledge about teaching strategies and research skills around educational practice. The above topics are needed to change the learning and teaching forms in chemical education; however, the tie between TPD and the classroom practice of the chemistry teachers still has not been greatly discussed in the literature. Thus, this paper seeks to generate a perspective upon theoretical issues related with TPD and their relevance in the chemistry teaching, where the teacher as researcher is put forward as a promoter of classroom research projects, which he joins chemical, pedagogical and practical knowledge for the improvement of learning process of his students. Moreover, the fruitful relationship between TPD and teaching of chemistry educators with the aim to make teachers’ communities around their professional development is analyzed. <![CDATA[PEDAGOGICAL LINK-MAKING IN HIGHER EDUCATION SCIENCE CLASSROOMS]]> The higher Education, when compared to basic Education, deals with much more specialized knowledge, usually thought in more technical terms. This specialization of the disciplinary fields that are objects of the graduate courses and the technical character present in most of these courses tend to compartmentalize the knowledge. We developed this work with the aim of analyzing the pedagogical link-making, as proposed by Scott, Mortimer and Ametller (2011), used by four professors of Higher Education, when teaching a class. We observe that the links between the content and the context depend on the area in which the professor acts. Micro and meso continuity links, in turn, do not depend on the area of knowledge, but on the performance of the professor. Macro relations, which could help build a coherent idea of the curriculum, are little present in the lessons of all the professors analysed. <![CDATA[PHENOMENOLOGICAL APPROACHES TO STUDY LEARNING IN THE TERTIARY LEVEL CHEMISTRY LABORATORY]]> Despite the widespread notion amongst chemistry educators that the laboratory is essential to learn chemistry, it is often a neglected area of teaching and, arguably, of educational research. Research has typically focused on secondary education, single institutions, and isolated interventions that are mostly assessed quantitatively. It has also honed in on compartmentalised features instead of searching understanding of broader aspects of learning through experimentation. This paper contends there is a gap in subject specific, tertiary level research that is comprehensive and learning-centred instead of fragmented and instruction-based. A shift in focus requires consideration of methodological approaches that can effectively tackle the challenges of researching complex learning environments. This paper reckons qualitative approaches, specifically phenomenology, are better suited for this purpose. To illustrate this potential, it summarises an exemplar phenomenological study that investigated students’ experience of change in instructional style from an expository (traditional) laboratory program to one that was cooperative and project-based (reformed). The study suggests the experience was characterised by a transition from a learning environment that promoted mindless behaviour to one in which students were mindfully engaged in their learning. Thus, this work puts forth the use of Mindfulness Theory to investigate and support design of laboratory experiences.