STUDY ON THE OPTIMIZATION FOR THE SIZE OF FUEL CELL FLOW FIELD UNDER INADEQUATE AIR SUPPLY CONDITION

In this paper, the influence of the optimization for flow field size on the proton exchange membrane fuel cell (PEMFC) performance under the inadequate air supply of cathode was studied based on the three-dimensional, steady-state, and constant temperature PEMFC monomer model. Additionally, the effect of the optimization for hybrid factors, including length, width, depth and width-depth, on the PEMFC performance was also investigated. The results showed that the optimization of the flow field size can improve the performance of the PEMFC and ensure that it is close to the level under the normal gas supply.

AVALIAÇÃO DA ESTRUTURA ELETRÔNICA DA FASE MONOCLINICA DO ÓXIDO DE NIÓBIO COM BASE NO USO DE DIFERENTES FUNCIONAIS DE DENSIDADE

ASSESSMENT OF THE ELECTRONIC STRUCTURE OF THE MONOCLINIC PHASE OF NIOBIUM OXIDE BASED ON THE USE OF DIFFERENT DENSITY FUNCTIONALS. Niobium oxides, Nb2O5, are considered semiconductor materials with very attractive physical and chemical properties for applications in many areas, such as catalysis, sensors, medical, aerospace, etc. Especially, the characterization of Nb2O5-based nanostructures with monoclinic structure has received much attention in recent years. However, despite the great importance of this system, some of its fundamentals properties are still not fully understood. Hence, this work aims to apply the theoretical methodologies through Density Functional Theory (DFT) calculations in periodic models based on the use of different density functionals (like B1WC, B3PW, B3LYP, PBE0, PBESOL0, SOGGAXC, and WC1LYP) to investigate the physical and chemical properties of the monoclinic structure of Nb2O5. The band structures, energy bandgap, density of state, and vibrational properties, as well as order-disorder effects on the monoclinic structure of Nb2O5 are investigated in this study. Our theoretical results show a better agreement with experimental data for the B3LYP functional and hence lead to new perspectives on the deeper physicochemical understanding of the monoclinic Nb2O5. From these computational tools, it is possible to unravel the relations between structure and properties, which may contribute to the future development of new devices and applications based on these materials.

PLANEJAMENTO DE MISTURAS E VISUALIZAÇÃO DA REGIÃO ÓTIMA COM PLANILHAS NO EXCEL: UM TUTORIAL

MIXTURE DESIGN AND OPTIMUM REGION VISUALIZATION WITH SPREADSHEETS AT EXCEL: A TUTORIAL. This tutorial shows how to perform the data treatment for mixture design with two and multiple responses. Two data sets from the literature were used to exemplify the calculations. A template in Excel was proposed to prepare contour plot and response surface to visualize the optimum region of the mixture, which usually is made with commercial computational programs. The desirability function was used in example 2 (optimization of 5 responses simultaneously), and a code also available for download was proposed. Besides, 21 videos were prepared to show all the details for the readers and, it is available on YouTube. With this tutorial, it is possible to learn in a practical fashion how to handle the data from mixture design and, the authors hope to contribute with the researchers in this area

AVALIAÇÃO ANALÍTICA DE ANALISADOR DE COMBUSTÍVEL COMERCIAL NO CONTROLE DE QUALIDADE DE ETANOL E GASOLINA COMUM

ANALYTICAL EVALUATION OF COMMERCIAL FUEL ANALYZER IN GASOLINE AND ETHANOL FUEL QUALITY CONTROL. Brazilian news media is full of examples about fuels out of the compliances and needs to control fuel quality. This work proposed an analytical validation of a commercial near infrared photometer (Xerloq, Tech Chrom Analytical Instruments, Brazil) able to identify percentage of ethanol in fuels comparing with NBR standards. Four procedures were selected: analysis of ethanol percentage in gasoline type C samples comparing with standard method ABNT 13992; analysis of ethanol percentage in fuel ethanol samples comparing with standard method ABNT 5992; linearity correlation and selectivity of standard solution analysis. Comparisons between the photometer and standards measurements were to determine the accuracy and precision of the device which presented a little variation from the norm (ER < 1.3%, sR < 0.4%). With regard to the test for linearity, Ethanol:water mixtures was analyzed with R-squared larger than 0.999 with RMSEV less than 1%. On selectivity tests, Gasoline:Ethanol:water and Methanol:Ethanol:water mixtures were measured with bias error not exceeding 5% for regulated samples. In conclusion, this fuel analyzer can be used to analyze ethanol content in Brazilian fuels with similar results comparing with classical standard volumetric and glass densimeter analysis and may indicate adulteration gasoline and ethanol samples by anomalous data.

ALTERNATIVES FOR THE PRODUCTION OF LEVULINIC ACID OBTAINED FROM BIOMASS

Levulinic acid is a reactive polar organic compound deemed as a building block for several products with relevant applications, replacing traditional substances in the petrochemical industry. Considered a platform molecule, levulinic acid is industrially produced from the acid hydrolysis of biomass – mainly plant-based – using hydrochloric or sulfuric acid in homogenous catalysis. However, considering the World Market for levulinic acid is expected to reach US$ 71.9 million in 2027, growing annually at 14.1%, and its applications in agriculture, pharmaceuticals, plasticizers, cosmetics, and food additives, the development of alternative production processes is sought. Hence, a survey was performed on publications considering the alternatives for biomass-based levulinic acid production processes: I) alternative homogenous catalysts to avoid using noble materials in the reactor; II) heterogeneous catalysis to facilitate and reduce the catalyst’s separation and recovery costs; III) ionic liquids, exploiting their high solvency, stability, and catalytic capacity. Additionally, biomass alternatives for obtaining levulinic acid are presented, showing that other agricultural residues and animal biomass options are being considered, targeting process flexibilization while reducing costs and producing derivatives at more competitive prices. Thus, it can be stated that levulinic acid is an important platform molecule for biorefineries’ economics, replacing fossil fuels with renewable raw materials.

CONTRIBUIÇÕES À FORMAÇÃO DE PROFESSORES DE QUÍMICA PARA ATUAÇÃO EM ESPAÇO DE EDUCAÇÃO NÃO FORMAL: QUADRO ANALÍTICO COMO FACILITADOR DA AVALIAÇÃO

CONTRIBUTIONS TO CHEMISTRY TEACHER EDUCATION FOR ACTION IN NON-FORMAL EDUCATIONAL SETTING: ANALYTICAL FRAMEWORK AS AN EVALUATION FACILITATOR. This work presents an analytical framework focusing on the evaluation of contributions of formative actions to teaching practice. It consists of thirteen indicators, distributed into four levels, The framework was developed from analyzing participants’ final assignment, who attended a Specialization Course in Teaching Methodology in Natural Sciences, offered in a non-formal education setting. Potentialities and limitations related to the teacher education framework are discussed, as well as its application in the context of teaching chemistry.

APRENDIZAGEM COOPERATIVA E COLABORATIVA NO ENSINO DE EQUILÍBRIO QUÍMICO A CALOUROS

COOPERATIVE AND COLLABORATIVE LEARNING TO TEACH CHEMICAL EQUILIBRIUM TO FRESHMAN STUDENTS. This paper describes cooperative (jigsaw) and collaborative activities (Peer-Led Team Learning) carried out in the BSc degree in Chemistry at the São Carlos Institute of Chemistry, the University of São Paulo, Brazil. The dynamics of discursive interactions established among students in the cooperative and collaborative groups was investigated based on the Model proposed by Kumpulainen and Mutanen, by analyzing the following: functions of speech, cognitive processing and social processing. In this perspective, the influence of the level of structure of the activities was studied. The results obtained point to the possibility of adapting both types of activities in higher education chemistry courses.

DOPANT EFFECT ON PHENALENE BANDGAP CONTROL: A HÜCKEL MOLECULAR ORBITAL PERSPECTIVE

In this study, we investigate the effects of nitrogen and boron dopants on the properties of phenalene/phenalenyl systems based on the Hückel theory by using the Hueckel Molecular Orbital software. The dopants configurations are graphitic, pyridinic, and pyrrolic. The electronic configuration of bare phenalene confirms the delocalization of π electrons and the radical properties of the molecule, which is in good agreement with the results of previous studies. Dopant types and positions strongly affect the number of π electrons in the system, molecular orbital energy, total energy, average π-electron energy, and gap energy. The molecular energy level degeneracy strongly depends on the rotational symmetry of the system, in the order of graphitic, pyridinic, and pyrrolic. A preserved radical behavior and the number of π electrons are found for the pyridinic dopant type, while closed electronic configuration is observed for graphitic and pyrrolic types. A lower gap energy is typically found for B-doped phenalene compared to that for N-doped phenalene; this opens the possibility for the enhancement of photoluminescence intensity. This study, although qualitative, confirms the effects of dopants on the chemical and physical properties of phenalene/phenalenyl systems.

AVALIAÇÃO DE AGROTÓXICOS EM SOLO DE SISTEMAS DE PRODUÇÃO AGRÍCOLA CONVENCIONAL E AGROECOLÓGICO

EVALUATION OF AGROCHEMICALS IN SOIL OF CONVENTIONAL AND AGROECOLOGICAL AGRICULTURAL PRODUCTION SYSTEMS. At the Contestado Settlement, Lapa, PR, soil samples from agroecological and conventional environments were evaluated against the agrochemicals alachlor, atrazine, chlorpyrifos and trifluralin. For sampling, 3 depths were considered, 10 points were selected, 5 in an agroecological and 5 in the conventional environment, with sampling frequency was at 2-month intervals. The samples were characterized according to textural, chemical and fertility parameters and the data were used in the chemometric study (PCA) demonstrating that the environments are different. The method of extraction, identification and quantification was validated at the trace level. The analytes were analyzed by GC-MS/MS, the recovery values were between 83 to 113%, RSD less than 14%, LD equal to 0.01; 0.0028; 0.004 and 002 μg kg-1, LQ equal to 0.04; 0.008; 0.011 and 0.05 μg kg-1, for alachlor, atrazine, chlorpyrifos and trifluralin, respectively. Chlorpyrifos was identified in the Conv3 and trifluralin in the Agro2 and 3 and Conv2 environments. Therefore, the application of pesticides in conventional environments can contaminate agroecological environments. The effect of rain/precipitation on the samples was evaluated by simulation and it was found that the physical-chemical properties of the compounds and the soil have an influence on their behavior in the soil profile.

O USO DE MATERIAIS HIBRIDOS OU NANOCOMPÓSITOS COMO REVESTIMENTOS ANTICORROSIVOS DO AÇO

THE USE OF HYBRID OR NANOCOMPOSITE MATERIALS AS STEEL ANTICORROSIVE COATINGS. The search had as the goal to present and reflect the hybrid materials as an alternative for anticorrosive coatings of metallic surfaces, such as steel. For comparison purposes, different types of anti-corrosion coatings capable of protecting metallic surfaces, such as steel, from oxidation action were presented. Steel is a metallic material widely used by industry in different types of segments, and its corrosion is a pathology responsible for its functional loss, causing losses in its use. Through a qualitative, bibliographic and exploratory research, based on academic works, it was presented that hybrid materials or nanocomposites prove to be efficient as anticorrosive coatings capable of protecting steel against oxidation.