Repositório RCAAP

Universidade Federal de Uberlândia

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This paper intends to discuss the teaching of chemistry for Youngsters and Adults. Focusing on the learning subjects, we tried to figure out their wills, fears and expectations. For that matter, a qualitative research was made, based on the Life Stories of 10 learning subjects, evaluating a written memorial made by each one of them, as well as semistructured interviews for the analyses of the results. We considered that listening to these learning subjects makes emerge their specificities, learning time and forms of learning, also it brings up the ways they interact to the world and with the world, understanding how these subjects maintain and build themselves in the different historic periods. We used Freire, as epistemological matrix, for the comprehension of the relations among the learning subjects of how they deal with the backwards and forwards from the school environment. We identified that the limit-situations that made them quit school are related mainly to their dedication to their children, seeking for a job and for random personal reasons. Seeking for a better life style and to get a good job, these subjects return to school, as a limit-act of overcome the issues they had during their primary educational process. We were also able to verify how our learning subjects started to build their own wills, fears and expectations which will be revealed at the conclusion of their dreams and desires, as for example, being able to go to college. We observed that work is responsible for these subjects come back to school or leave it; other than that, women with partners the majority of our study universe showed that their return to school is an attempt to fight for their dignity and for better work conditions, trying to have the same opportunities than men. In this scenery the chemistry classes happen. We observed the difficulties in understanding the chemistry contents, because of its specific language, its symbols and codes. This difficulty is mostly shown in the process of comprehension of the chemical phenomenon, because the apprentices can identify them, however they cannot explain them, even after didactic exercises. The interests in chemistry reflect the aspects the learning subjects can emphasize in their daily basis activities. We believe that for a construction of a meaningful chemistry learning is necessary to consider these points, what according to Freire, would contribute for the formation of their wills, fears and expectations, and particularly in this case, in the chemistry classes. This way, we would be able to build didactic strategies which will be able to contribute for the formation of critical and conscious citizens.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

This paper presents a qualitative and quantitative nature documentary, uestions of chemistry of National Secondary Education Examination (Enem) and vestibular Federal University of Uberlândia (UFU) in the period of 2001-2010. After mapping the evidence and mount a database, which analyzed the material focusing on the contextual approaches that were focused on issues of chemistry, as well as possible interdisciplinary and cross situations. We used several authors for reasons of our discussions that seek to investigate: How contextual approaches are arranged on the issues of chemical vestibular Federal University of Uberlândia (UFU) and the National Secondary Education Examination Average (Enem)? Which focus, theme and show interest in these approaches and how they relate to the chemical content present in these processes? To this end, we divide the analysis in some parts, we observe, first, the relationship between phenomena, theories and chemical representations , seeking to understand how knowledge emerges from the chemical structure of scientific knowledge, correlating, and levels of chemical and relations involving the axes constituting fundamental chemical transformations, the materials and their properties and explanatory models. We also look for the presence or absence of interdisciplinarity and transversality, and the possible influences of these issues in chemistry, and the presence of some other contextual approaches that could be part of these issues. The results indicate a predominance of questions of General Chemistry (HQ), which shows that both tests select students who has a broader view of chemical knowledge, but to dominate and skills that make up each task. However, the analysis to detail about how knowledge emerges from the chemical structure of scientific knowledge, we note that the issues from both the vestibular UFU as Enem, reference levels and the axes of the chemical constituent, however, the slightly differently. The Enem presents both levels as the axes constituent in isolation, thus hampering the construction of knowledge by students. Since the vestibular UFU can merge more levels within the issues, working also in a less separated axes, which can help in the construction of chemical knowledge. We also investigate the more specific context of trying to find such evidence in the presence of at least some forms of context, which will certainly serve to enrich the questions. However, both studies the relationships bring technological, social and environmental, as a mere illustration of the theories and scientific concepts. When we think in relations with the daily and experimentation, this scenario is somewhat different, because both contextual approaches only appear in most issues of the two tests, when carrying out subsequent to the start of the New Enem.Also evaluated the presence of both interdisciplinarity as the transverse and the possible influences of them on these issues, which is explicit and ratified in Enem, which presents a series of cross-cutting issues, especially on the topic Environment. The Health theme also appeared in some issues, but in smaller proportions. Interdisciplinarity was also evident on several issues Enem, which makes clear the concern of the examination to correlate to the subjects, causing students to gain knowledge of how to build the most extensive and complete. However, when we look at the issues of chemical vestibular UFU, we could not find cross-cutting issues, interdisciplinary or what we prevented a more detailed study of the subject, this selection process. Thus, we see that both tests have strengths and weaknesses, the questions of chemistry. However, the contextual approaches appear subtly in both selection processes, mainly in the analysis made in recent years. This fact may show that some changes are occurring in these tests and the contextual approaches are becoming priority in the preparation of these issues, which may assist in a closer knowledge of chemicals linked to student s lives.

This paper presents new analytical procedures for fast determination (in less than a minute) of codeine (COD), diclofenac (DCF) and its counter-ions sodium, potassium, diethylammonium (DEA) and phosphate by capillary electrophoresis coupled with contactless conductivity detection (CE-C4D). The proposed methods can be used in quality control of raw materials and pharmaceutical formulations which have such compounds in their composition. Two different methods were developed, one for the fast and simultaneous determination DCF and its counter-ions (sodium, potassium and DEA) using TRIS / TAPS 10 mmol L-1 (pH 8.2) as the background electrolyte (BGE), and another for fast determination of DCF, COD and its counter-ions (sodium and phosphate) using TEA / oxalate 10/1,8 mmol L-1 (pH 8.4) as BGE. Both methods had low relative standard deviations of the peak areas and migration times. In the determination of DCF and its counter-ions, the calculated values ranged from 2.1 to 5.7% and from 0.69 to 0.85% and in the determination of DCF and COD between 0.72 to 2.7% and 0 0.23 to 0 39%, respectively. The calculated resolutions for each analyte were the following: 2.06 for sodium, 1.99 for DEA; 4.72 for DCF, and 7.11 for COD. All resolutions can be considered satisfactory. The calibration curves for all analytes showed correlation coefficients greater than 0.992. The results obtained from the commercial pharmaceutical samples analysis using the proposed methods were compared with those obtained by HPLC or flame photometry. At a confidence level of 95%, the calculated t values (paired t-Student test) were lower than the theoretical critical value (2.78, n = 3) in all analysis, which indicates no significant differences between the results of the proposed methods and the standard methods (HPLC or flame photometry).

The effect of the insertion of silver ions on the photocatalytic activity of TiO2 was studied in this work, considering the degradation of tartrazine, a food coloring in the class of azo-compounds, with sulfonic groups in its structure, being highly soluble in water. Characterization techniques such as differential thermal analysis, x-ray diffraction, Raman Spectroscopy, difuse reflectance UV-Vis spectroscopy, surface area analysis, and scanning electron microscopy were used to understand the relationship between structure and photocatalytic activity for the oxides synthesized by homogeneous precipitation method in ultrasound, with different nominal concentrations of silver ions (0.0, 0.5, 2.0, and 5.0% m/m). According to the analysis by X-ray diffraction, anatase crystalline phase is predominant in all compounds synthesized. The band gap of the oxides synthesized showed displacement to smaller energies as increased percentage of doping ions. Raman Spectroscopy data suggest the existence of active modes of anatase and smaller particle size, when compared to TiO2 P25. The surface area was increased by the addition of silver ions and also by the method of synthesis used. The oxides synthesized presented porous and partially aggregated structure, which contributes to its application in heterogeneous photocatalysis, due to the availability of active sites. Photocatalytic degradation of the dye tartrazine, catalyzed by oxides synthesized, was evaluated under three different conditions of pH: 3.00, 6.90 (solution without pH correction), and 8.00. The best photocatalytic performance was observed when using TiO2 doped with 5% m/m of silver ions under pH without correction (~6.90).

This study is an analysis of documentary stamp as it investigates, through sampling, ten subprojects chemistry of the first edition (2007) Programa Institucional de Bolsa de iniciação à Docência - Pibid. This analysis aimed to determine the main concepts related to teacher training (technical rationality and practical rationality) that emerge from such documents. In this perspective, initially, it was necessary to carry out a detailed study on the scope and philosophy of the program in the wake Pibid national. Then it became expedient for achieving a deeper investigative reporting on the technical and practical rationalism, the bias of teacher training, since these two types of matrices epistemological rationales are adopted to carry out the following survey. From conceptions assimilated the light of the two kinds of rationalities study, an analysis was made of two subprojects chemistry Capes scholarship program in each region of Brazil, totaling ten documents. This analysis included the approaches advocated in the first edition of subprojects chemistry Pibid. It was also possible to correlate either explicitly sometimes implicitly, the philosophy adopted by the subprojects with the two types of rationales studied in this thesis. One of the most important contributions of this study is to help outline what assumptions related to teacher training in chemistry, the Federal Institutions of Higher Education of Brazil adopted to form their future educators. Thus, we can commensurate to the importance that the program has Pibid, in current time, for the training system of teachers in our country.

In this work were prepared zinc oxide (ZnO) samples by microwave - hydrothermal (MH) method and realized a structural analysis and morphology of the samples assessing the effect of different experimental parameters used: heating method, synthesis temperature, reaction time, heating rate and addition of surfactants. The samples were characterized structurally by the techniques of X-ray diffraction (XRD) and Raman spectroscopy. The particle size and morphology were investigated by scanning electron microscopy by field emission (FEG-SEM). The optical properties were analyzed by photoluminescence spectroscopy (PL). The results of XRD showed the formation of crystalline structures related to ZnO wurtzite phase, indicating a periodic structural organization at long range. The Raman active modes that characterize the hexagonal structure of ZnO were observed and the presence of structural defects showed the short-range influence on the optical properties of the obtained materials. Samples showed photoluminescent properties with maximum emission in the green region of the visible spectrum, which is related to structural defects in the medium and short ranges, the oxygen vacancies, Zn2+ interstitials in the ZnO crystal lattice, which are types of defects that can be generated during the synthesis process. The addition of urea synthesis led to the formation of nanoparticles rounded and more uniform than the samples obtained in presence of polyethylene glycol. The materials prepared in this work have potential application in optical devices, catalysis, gas sensors and solar cells.

This work contributes to the study of the production of biodiesel from sunflower oil, starting with oil analysis and obtaining biodiesel using methyl and ethyl routes from the transesterification reaction. The catalysts used were homogeneous and basic. For the optimization of reaction conditions, the variables examined were: molar ratio, speed, reaction time, catalyst type, catalyst concentration and temperature. For ethyl biodiesel, time, rotation and catalyst concentration are the variables most important operational, while for methyl biodiesel, the catalyst concentration, time and temperature are most relevant. The conditions for maximum yield were determined by factorial design: potassium hydroxide (KOH) as the catalyst, molar ratio of alcohol: oil 6:1; rotation of 260 rpm catalyst concentration of about 0.19% (w / w); temperature of 308 K and reaction time of 35 min, for ethyl biodiesel . For biodiesel methyl were: potassium hydroxide (KOH) as the catalyst, molar ratio of alcohol: oil 6:1; rotation of 189 rpm; temperature of 319 K; catalyst concentration of about 0.42% (w / w) and reaction time of 60 min. The process has a tolerance for the variables of greatest influence on the reaction, which means that small variations quantitative individual conditions do not significantly affect the overall yield, allowing greater control of the process. The biodiesels optimized were characterized (physical-chemical analysis) according to standards of the ANP - National Agency of Petroleum, Natural Gas and Biofuels. Through the thermal expansion coefficients of biodiesels obtained mathematical algorithms for biodiesel methyl and ethyl, respectively, μT = μ measured 0,7330 × (T T measured) e μT = μ measured 0,7340 × (T T measured). These algorithms allow the correction of the specific mass of biodiesel, important business transactions. You can observe significant differences between the mathematical models established compared to the results by standard EN 14214.

Corncob (SM) is an agro-industrial waste available in large quantities in Brazil which deserves to be better and/or properly used. This work evaluates the use of SM as a source of cellulose to obtain cellulose nanocrystals (NC) by acid hydrolysis in order to obtain a material suitable to be a reinforcement agent in the manufacture of nanocomposites. The hydrolysis were performed at 45 °C for 30, 60 and 90 min, using 15 mL of H2SO4 (9.17 M) for each gram of fiber. The resulting NC of corncob (NCSM) were characterized by crystallinity index (ICr), morphology and thermal stability; and its ability to strengthen was evaluated as the maximum tensile strength (RTM), the initial degradation temperature (Tonset), transparency and optical transmittance (Tr) and the permeability to water (PH) using poly (vinyl alcohol) (PVA) as the polymeric matrix. The NCSM obtained with 60 min of hydrolysis (NCSM60) endowed the PVA/NCSM nanocomposites with a significantly improved tensile strength of 140.2% when only 9% (wt%) NCSM60 was incorporated. The addition of NCSM60 in the PVA matrix improved the Tonset of the nanocomposite tested, and the PVA film loaded with 6 wt% NCSM60 showed an Tonset around 242 °C. The results of (Tr) films in the region of ultraviolet-visible spectrum showed excellent Tr in the visible region maintaining the transparency of the nanocomposite films substantially equal to pure PVA film. The nanocomposite films with 3%, 6% and 9% filler showed increasing improvement in the reduction of PH of 6.93%, 19.97% and 28.73% respectively, and this may be an indication that the NCSM60 were well dispersed and adhered in the polymer matrix. The NCSM60 presented a needle-shaped nature, high crystallinity (83.7%), good thermal stability (236 °C), average length (L) of 210.8±44.2 nm, diameter (D) of 4.15±1.08 nm, and aspect ratio (L/D) of 53.4±15.8. The results show that the more suitable filler were NCSM60. Since NCSM60 has the highest crystallinity among the NCSM samples, but does not have the highest aspect ratio, these results suggest that the difference in the ICr has a greater influence on the tensile properties than the aspects ratio, in this case. Cellulose nanocrystals obtained from corncob have great potential as reinforcing agents for the manufacture of nanocomposites.

The pineapple leaf (PL) is an agricultural waste with annual output and available in abundance, whereas in 2011 were produced about three million tons, being rarely used and currently has a low commercial value. Therefore, this agro-waste deserves to be better and/or properly used. The aim of this study was to explore PL as a source of raw material for the production of cellulose nanocrystals (CN). The CN were extracted by acid hydrolysis at 45°C for 5, 30 and 60 minutes, using 20 mL of H2SO4 (9.17 M) for each gram of material. The resulting CN were characterized by crystallinity index, morphology (shape and size) and thermal stability. Among the hydrolysis conditions carried out, the best extraction time was 30 minutes, with yield of 65%. At this extraction time, the CN presented a needle-shaped nature, high thermal stability (225 °C) when compared to the thermoplastic processing temperature (about 200 °C), high crystallinity (87.3%) relative to other sources CN cellulosic derived from agricultural residues (e.g., soy hull 73.5%), an average length of 249.7 ± 51.5 nm and a diameter of 4.45 ±1.41 nm, giving an aspect ratio (L/D) of around 60. Therefore, CN obtained from PL has great potential as reinforcement in the manufacture of nanocomposites. The production of CN from this underutilized agro-waste has commercial application potential that can add value to the pineapple cultivation, generate extra income for farmers and also help in agribusiness diversification. In addition, the reuse of these residues allows a significant reduction in both the volume of waste accumulated in the environment and in the extraction of raw materials, which is against the concept of sustainable development.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

An environmentally-friendly flow system was developed for the determination of fluoride in natural waters, based on its reaction with zirconium ions and trisodium salt of acid 1,8-dihydroxy-2-(4-sulfophenylazo)-3,6-naphthalene-disulfonate (SPADNS). The flow system was designed with solenoid valves in order to increase the versatility and improve the analytical performance, since each device handles the solution independently leading to more efficient use of reagents. The minimization of reagent consumption and waste generation favors the development of a system based on the principles of Green Chemistry. Under optimized conditions, a linear response was observed within the range of 0.1 2.2 mg L-1, with the detection limit, coefficient of variation and sampling rate estimated as 0.02 mg L-1, 4.1% and 60 determinations per hour, respectively. In comparison with other methods, the proposed system offers advantages such as wider analytical range (1.7 to 2.2 times), higher sample throughput (1.5 to 4.0 times), and quantification limit (by a factor of 5 to 68). Along with the consumption of reagents being 20 to 55 times lower and the generation of wastes is 1.2 to 3.0 times lower, which contributes to the development of a greener system. This method is fast, amenable to automation, environmentally-friendly and of low-cost, and it could be successfully applied to the determination of fluoride in water samples, the results obtained being in agreement with those of the ion selective electrode (ISE) method.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

In the present work, the process of thermal decomposition of bagasse Cane Sugar (BCA) was used to understand the behavior of the raw material for the production of bio-oil (BO) from Fast Pyrolysis process. The study was objectified on two fronts: i) characterization of the BCA and ii) Characterization of BO. BCA was characterized by elemental analysis and has the chemical composition according to the formula CH1,48O0,71N0,0054 The test results shown BCA shown that this is an important potential source lignocellulose for the production of BO, since this has a low ash content (3.7%) and high content of volatile materials (81.8%), moreover, the calorific value of the BCA was 15.9 MJ/kg, a value close to that obtained with other lignocellulosic sources. The thermal decomposition of BCA was assessed through thermogravimetric curves in inert atmosphere and in synthetic air. The curves show that the presence of oxygen has an influence on the final products of decomposition and the values of activation energy (Ea) for the process. The kinetic study was performed using the methods isoconversionais Ozawa-Flynn-Wall (OFW) and Vyazovkin (V). The present study aimed to contribute information about the kinetics of thermal decomposition of BCA in the presence of oxygen, considering the process on a pilot scale, held oxidative pyrolysis with atmospheric air, becoming self-sufficient through the release of energy by combustion Part of biomass for energy production. For the decomposition reaction conversions higher than 60%, the Ea of the process in synthetic air increases dramatically, indicating that the presence of oxygen lead to the formation of oxidation products is difficult to decompose. The BO produced in fast pyrolysis plant (PPR) acquired by the company Bioware presents chemical composition compatible with the formula CH1,48O0,39N0,008. This result shows a reduction in the percentage of oxygen, a fact that enhances the characteristics of BO for use as fuel. The calorific value is increased the production of BO 15,9 MJ/kg (BCA) to 20,4 MJ/kg, which confirms the increase of the potential use of bio-oil as fuel. Considering this aspect, to preserve the quality of BO and energetically promote the process, lower oxygen concentrations should be employed in the process of decomposition.

The present study sought to compare the performance of a composite based on association between the TiO2 P25 and zinc phthalocyanine (TiO2/FtZn 1.6%), and TiO2 P25 in the photocatalytic degradation and mineralization of the dye Ponceau 4R (C.I. 16255), P4R. The result in laboratory scale presented by composite, in the absence of hydrogen peroxide, is about three times higher than that presented by TiO2 P25, resulting in 50% of mineralization dye after 120 minutes of reaction. This performance has been attributed to the synergy between zinc phthalocyanine aggregates and the surface of the catalyst. Additional studies conducted in laboratory scale to define the most appropriate concentration of hydrogen peroxide to accelerate the mineralization of P4R, were made using just the composite. It was observed that when a concentration of 0.1 mL/L (9.7 x 10-4 M or 33 mg of H2O2 per litre of solution) in terms of H2O2 was used, the performance of the reaction was improved. The role of the pH of the medium on the degradation and mineralization of P4R, promoted by the composite and also by TiO2 P25, was also evaluated. To P4R degradation, pH showed no significant effect. However, for mineralization the best performance occurred at pH 6.0 in both cases. Photocatalytic tests on a large scale, made under action of solar radiation using a CPC (Compound Parabolic Collector) reactor under the best conditions of pH and concentration of H2O2, defined in laboratory scale, reinforce the higher efficiency of the composite TiO2/FtZn 1.6%.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais