Repositório RCAAP

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

In this work, thin and compact films of TiO2, Nb2O5 and WO3 nanoparticles were prepared to be used as contact/blocking layer in dye sensitized solar cells (DSCs). The films were produced by deposition of 30 bilayers of TiO2(ac)/TiO2(bas), TiO2(ac)/Nb2O5(bas) and TiO2(ac)/WO3(bas) using the layer-by-layer technique (LbL) from nanoparticle sols of TiO2 (pH = 2 and 10), Nb2O5 (pH = 10) and WO3 (pH 10) prepared by sol-gel method. The TiO2/TiO2 and TiO2/Nb2O5 underlayers resulted in an increase of 25% and 87% respectively, in the efficiency of DSCs when compared to those without the contact/blocking layers. The application of TiO2/WO3 films did not result in any improvement of DSC efficiency. Factors such as thickness, nanoparticles homogeneity, oxides concentration on the films and roughness directly influence on the efficiency of such films as contact/blocking layer. Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM) images, confirmed that all films are constituted by spherical nanoparticles with homogeneous diameters smaller than 20 nm, resulting on compact and low porous surfaces. This morphology ensures a physical barrier between the electrolyte and the conductive glass used as electrode in DSCs. The TiO2/TiO2 and TiO2/Nb2O5 films also exhibited higher roughness than the surface of the conductive glass without the bilayers, which increases the interaction with the mesoporous TiO2 film. The molar ratios of the species present on the films are controlled by the pH employed during deposition, and were determined by X- ray photoelectron spectroscopy (XPS). The Ti4+/Nb5+ and Ti4+/W6+ ratios were 1.6 and 19 respectively, which evidences a higher concentration of TiO2 nanoparticles on the films. For a better understanding of the role of the bilayers on the charge transfer processes, the substrates were analyzed by Electrochemical Impedance Spectroscopy (EIS). The electronic properties of the oxides also influence the efficiency of the LbL films as contact/blocking layers. Due to its higher band gap, Nb2O5 nanoparticles impose an electronic barrier to the electrons transfer from the conductive substrate to the electrolyte, additionally to the physical barrier.

The nanobiosensors are devices of detection that have as recognition elements a biological material. This work is a proposal of the nanobiossensor to detect specific inhibitor herbicides acetyl co-enzyme A carboxylase (ACC), whose has effectively proved in detecting herbicide diclofop compared with the presence of atrazine in the sample to being analyzed. This nanobiossensor consists of an atomic force microscopy (AFM) that has its tip functionalized with the enzyme ACC; and the detection is performed by measures the force between the AFM tip and the sample studied, which is originated in interaction strength of the enzyme-herbicide. Due to these interactions, which occur between enzyme and substrate, the advantage of the nanobiosensor is its selectivity and sensitivity for detecting concentrations that would not be accounted for in conventional methods of sensors and biosensors. Given the use of nanobiosensor with functionalized AFM tip, this study aimed to verify the selectivity of it for two specific classes of herbicides that are inhibitors of ACCase: the aryloxyphenoxypropionates (fops) and cyclohexanediones (dims). For this, molecular docking calculations with 12 herbicides were made, and this methodology evaluated the best conformation of the complex enzyme-substrate and free energy of interaction. This study also proposed to verify the effect that the presence of water causes on the selectivity and sensitivity of detection, making necessary the use of Molecular Dynamics simulation of the ACC with subsequent docking calculations. The results show that the best interaction energies of the complexes were formed with the fops and dims herbicides, however two other herbicides, imazaquin and metsulfuron, showed a comparable binding energy of specific inhibitors, primarily due to the similarity in the type intermolecular interactions thought hydrogen bonding interactions with the ILE-1735 and ALA-1627, so these herbicides may interfere in detection for the nanobiosensor. The presence of water molecules increases the bind energy, making them more unfavorable for the specific inhibitors herbicides, which can slightly affect the sensitivity of detection. In general, the selectivity was not affected because the fops and dims continued with more favorable energy values when compared with other herbicides.

In previous work regenerated cellulose membranes produced from the cellulose extracted from sugar cane bagasse were prepared from an adaptation of the Cuprammonium method. Although it has been possible to produce the membranes, it showed high levels of Cu (II) ions, fact that can impossible their application in medical field. In this work, the preparation of these membranes was realized through changes in the methodology as the removal of an intermediate stage (alkaline bath) and the increase in time in the acid bath for cellulose regeneration. Two membranes were produced: MBAG (using cellulose extracted from sugar cane bagasse) and MROD (using cellulose from Pinnus pulp supplied by Rhodia). With the changes in methodology, the copper (II) percentage on the membrane of MBAG (0.0236%) showed a decrease of about 15 times for the membranes produced in previous works (0.3634%). The cell viability data obtained by the technique of incorporation of vital dyes showed that the membranes MBAG and MROD have no toxicity to cell cultures studied. These results indicate a positive way in order to reuse the sugar cane bagasse cellulose for production of devices used in medicine as membranes for hemodialysis therapy.

This research investigated the conceptions of a small group of teachers, graduates from the Federal University of Uberlândia on the Chemistry course, related to the teaching and learning process of electrochemistry. For data collection we conducted interviews collectively, with approaches to the methodology of focus group, which included five teachers. The interviews were recorded on audio and video and then transcribed to perform the analysis of participants\' speech that was made by crossing with the information obtained from the literature. From this analysis we identified some conceptions of teachers about science and electrochemistry teaching. Through the analysis of the statements of the research participants and the information obtained from the literature, we found that they had an apprenticeship with several gaps during them basic education. We also note that the degree in chemistry, did not impact learning electrochemistry of participants, which shows a failure in the development of the curriculum of the course in question. However, the professional experiences with the electrochemistry in the classroom, or the knowledge acquired in other subjects during graduation, allowed the participants a broader view of education and consequently on teaching electrochemistry. Teachers showed experience different teaching materials for teaching electrochemistry, discuss possible topics for teaching electrochemistry, and also recognize the limitations and difficulties in teaching this content.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

The ANP (National Agency of Petroleum, Natural Gas and Biofuels) inspects only the levels of iron and copper in fuel ethanol, however the determination of manganese is also necessary due to the negative effects of metals that accelerate the formation of gums and sediments inside engines and storage tanks. The metal alloys employed since the manufacturing until to distribution of this fuel are composed of carbon steel and / or stainless steel which contain considerable amounts of manganese in their chemical composition. This work proposed the determination of manganese by square-wave cathodic stripping voltammetry employing a glassy-carbon electrode as detector. The voltammetric characterization was accomplished between -1,0 and +1,5 to verify the electrochemical behavior oh manganese. For its determination, the following conditions were employed: deposition potential of 1.2 V for 180 seconds, conditioning potential of -0.5 V for 30 seconds, 0.04 mol L-1 Britton-Robinson buffer solution at pH 4, ethanol ratio in the electrochemical cell of 2.5% (v/v), amplitude of 100 mV, frequency of 30 Hz, a step of 10 mV and stirring speed of 2250 rpm. Some parameters for the validation of method were evaluated, such as repeatability, linearity, recovery test, limits of detection and quantification. The following results were obtained: repeatability with standard deviation of 5.58 % for 10 readings, analytical frequency of 16 analysis h-1, recovery values between 90.8 % and 110.9 %, linear range between 3 and 175 μg L-1, detection limit of 0.9 μg L-1 and quantification limit of 3 μg L-1. The content of manganese in the analyzed fuel ethanol samples were below the detection limit of the proposed method. Searching for the development of an alternative method for the determination of manganese, the fuel ethanol samples were pretreated by complete evaporation followed by acid digestion of the organic residue with an oxidant mixture (H2O2 + HNO3). However, this method did not provide acceptable recovery values (111 160%) employing the same optimized conditions to the use of glassy carbon for the direct analyses of fuel ethanol, which indicates a possible matrix effect resulting from the sample pretreatment.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

In this work, blends of starch, carboxymethyl cellulose and hydroxypropyl methylcellulose with latex were produced and characterized according to their physicochemical properties. The blends were prepared in the proportions in percentage of 12.5%/87.5%; 25%/75%; 37.5%/62.5%; 50%/50%; 62.5%/37.5%; 75%/25%; 87.5%/12.5%. The characterization techniques used were Spectroscopy in the Infrared region Fourier transform (FTIR), scanning electron microscopy (SEM), Thermogravimetric Analysis (TGA) and Dynamic-Mechanical Analysis (DMA). The latex was collected in a farm located in the rural town of Silver - MG, and then immediately treated with ammonium hydroxide (NH4OH) to prevent clotting. The Hidroxipropilmetlcelulose, Carboximetlcelulose and starch polymers were solubilized in deionized water, and for the procedure with the starch was necessary warming of about 50 °C and shaking to its total dissolution. The FTIR analyzes revealed changes in band shift in the blends starch25%/latex75%, CMC50%/latex50% and in the other, changes in the intensity of the peaks in the spectra according to the variations in the proportions of the polymers in the blends. The SEM images generally show stages in the formation of mixtures of starch/latex and CMC/latex, and for HPMC/latex was more homogeneous structures indicating good compatibility. The results observed from TGA curves show that the addition of latex and hydroxypropyl starch in leads to a change in thermal stability of the resulting blends, while for the blends with carboxymethylcellulose no significant differences in the thermal stability. Dynamic-mechanical analysis showed an increased resistance of the blends, thus changing the properties of the films being shown in the values of E\' and Tanδ. The results showed that the blends of HPMC/latex have greater compatibility and miscibility in comparison with other mixtures investigated, discussing the limitations of pure film and the improvement of the properties of the blends obtained.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This study aims to understand the influence of selection processes for entry to Higher Education Institutions (HEIs) on the teaching practice in Basic Education programs. Therefore, we use the methodology of phenomenological nature. For building data, we conducted semi-structured interviews with teachers, the transcription of audio taped interviews, and document analysis from the documents provided by the school, the Regional Superintendent of Education of Uberlândia - MG, and those drawn from the information portals of Department of Education of the State of Minas Gerais which discuss the Advancement of Studies, a program that, among other goals, aims to mainly prepare the student for selection processes. From the data analysis, it was possible to conclude that the teacher\'s pedagogic practice of Basic Education is exaggeratedly influenced by selective processes of HEI programs because, in practice, the teacher gives greater emphasis on preparing the student for success in such processes, as opposed to a practice that aims to train the student to effectively play its role as a citizen in your community. Thus, we could confirm the propositions of scholars who point out that high school is not an end in itself, but is introductory. We believe that the necessary changes pervade political and socio-cultural issues and need to occur in various areas of management education in the country. Carried out, these changes reflected in the Basic Education and therefore in the classroom, providing advances in educational processes, new organizational structures that support the practice of the teacher in accordance with the most legitimate aspirations that justify the existence of areas of education.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

The coffee is one of the main agricultural products that move the agribusiness in Brazil. The 2004/2005 production revealed that Brazil was responsible for 38.630 million processed bags, being 30.461 million bags of the arabic coffee and 7.803 million bags of the conillon coffee. The production and commercialization of coffee occupies about 20 million people in the world and it involves great disputes for the current and future markets. The importance and presence in the daily of most of the people, it is waited that the drink of coffee has quality, aroma and pleasant flavor. This work presents the study of the chemical composition, antioxidant activity and potential odorific of a coffee (Coffea canephora) conillon variety 2003/2004, produced in south Espírito Santo State and a comparative analysis with (Coffea arabic) arabic variety of the cerrado Minas Gerais State. The sample of coffee was roasted in three diferent degrees of roasted: light, average and strong, and in a house mill. The antioxidant activity and total phenols demonstrated that conillon coffee beans lightly toasted presents superior values than the others, and it also presents ligher values than those in arabic coffee. The analyses of the powerfull odorants presents in roasted coffee beans, identified by GC/MS showed that conillon coffee weak roasts has the largest odorific activity, justified basically for the ligher concentration of ß-damascenone. The conillon coffee presented odorific activity higher than arabic coffee. The analyses by HPLC showed that the lightly roasts conillon coffee presented more trigoneline and chlorogenic acid than other roasts. The caffeine concentration didn't present significant differences between ther roasts. The arabic coffee have higher trigoneline concentration and the conillon coffee higher caffeine and chlorogenic acid content. Those results indicate that the best drinking of coffee would be a blend of lightly roasted arabic with conillon coffee. The conillon coffee show higher antioxidant activity and the arabic coffee have more pleasant flavor.