Resumo em Português:

STRUCTURAL CHARACTERIZATION OF THE PANI-MAGNETITE COMPOSITE WITH POTENTIAL APPLICABILITY IN ELECTROCHEMICAL SESNOR. This study presents the production of a composite formed between polyaniline and magnetite (Pani-Mag) through an easy and more economical synthetic route, which satisfactorily contemplates the principles of green chemistry. The production of new materials for technological application also needs to be focused on less waste generation, and greater sustainability. FTIR and DRX analyzes confirm that the interactions between the polymeric phases and the oxide particles occurred in a synergistic way. Saturation magnetization has a value of 33.5 emu g-1, being compatible with reference values in the literature for Pani-Mag composites. The electrochemical tests indicate an electrochemically stable material with the potential to be applied as an electrochemical sensor in the determination of ascorbic acid in solution.

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Hydroxyapatite (HA) nanopowders are attracting interest for surface application to ceramic biomaterials. In this study, we developed innovative and new viable synthesis routes of calcium phosphate nanopowders from the natural calcium carbonate of chicken eggshells. Following the four routes, alternative co-precipitation, vacuum process, brushite, and calcination, we obtained the HA samples, which were then characterized by different methods. The X-ray diffraction /Rietveld method showed the HA phases, monetite and brushite crystallinity with greater symmetry, and nanoscale. Transmission electron microscopy showed the morphology of nanoparticles functionalized nanoparticles smaller than 100 nm in routes A, B and D, and Fourier-transform infrared spectrophotometry and Raman spectroscopy identified the classic chemical groups of calcium phosphates by four routes mainly groups (PO4)3- and (CO3-). Scanning electron microscopy analysis revealed a good surface topography to future cell biointeraction in A, B and D routes, and thermogravimetric analysis showed the mass loss profile inherent to each synthesis route with slot at 200 °C. Hence, the eggshell HA and brushite and the specific monetite nanoparticles with different morphology can be prepared from the four new possible and viable routes using different methods.

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NEW HYBRID NANOSTRUCTURED ADSORBENT TYPE AMINE/KIT-6 FOR CO2 CAPTURE. The present work functionalized KIT-6 mesoporous material with aminopropyltrimethoxysilane (APTMS) and tested its efficiency in CO2 capture. The KIT-6 material was synthesized by hydrothermal method and functionalized via excess solvent in APTMS concentrations of 5 and 15% to obtain the hybrid adsorbents. All adsorbent materials were characterized by XRD, TGA/DTGA, DSC, N2 adsorption/desorption, SEM and applied in the CO2 capture, varying the temperature and pressure. The KIT-6 mesoporous structure at the hybrid adsorbents was kept. Variations in textural properties denoted that the organic molecules were incorporated in mesoporous structure. In the experiments, both chemisorption and physisorption were observed, reaching the best values at 25 ºC, indicating that the temperature influences the adsorption process. The experiments showed adsorbed amounts of up to 0.8 mmol/g at atmospheric pressure, displaying the efficiency of the chemisorption provided by the CO2 interaction with the hybrid adsorbents. At high pressures, a predominance of physisorption was observed, demonstrating a better performance for the KIT-6 support, due to the superior textural properties. Finally, a well-ordered and functional hybrid adsorbent was successfully developed for the adsorption of carbon dioxide.

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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.

Resumo em Inglês:

Light oil/water/heavy oil triphase mixtures are common in industrial wastewater, while nearly all separation materials with superwettability can only separate biphase mixtures of light oil/water or/and heavy oil/water. Here, a balsa wood slice with superhydrophilic/superoleophilic property in air was fabricated by a blade-cutting and ethanol-treating process. Therefore, the slice could be dually prewetted with both water and oil and thus showed underwater superoleophobic and underoil superhydrophobic properties without any further chemical modification. Such a slice showed underoil superhydrophobicity in nonbasic environment while transition into underoil superhydrophilicity under basic condition. Combining with the porous structure possessed by wood designed to transport liquids, this superwettability of the treated wood slice could be leveraged in the continuous separation of light oil/water/heavy oil triphase mixtures only driven by gravity with a high permeation flux and separation efficiency. After each separation, the slice was easily recovered by washing with acidic solution, and it could be recycled up to 15 times without any loss of pH responsibility. During repeated cycling separation, the slice exhibited excellent separation stability.

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ELECTROSPINNING APPLIED TO THE DEVELOPMENT OF ADSORBENT NANOFIBERS AIMING AT IMPROVING SOLID PHASE (MICRO)EXTRACTION TECHNIQUES. The limitations and challenges associated with the complex analyte-matrix-interfering interactions make the development of new sorbent materials an attractive line in several research areas, ranging from the synthesis and characterization to the application of these materials. Among the different strategies for manufacturing sorbent nanomaterials, the electrospinning of nanofibers based on polymeric solutions incorporated into Metal-Organic Frameworks (MOFs), Molecularly Imprinted Polymers (MIPs) and Nanoparticles (NPs) have represented in recent years, one of the methods more versatile and promising with regard to obtaining materials with large surface area and potential for functionalization and chemical modification. In this sense, the objective of this contribution is to highlight recent work aimed at the synthesis of electrospun nanofibers applied in adsorption and sample preparation processes, highlighting the synthetic nanofiber strategies based on MOFs, MIPs and NPs and the main challenges and perspectives of the applications, although little explored, of these materials in solid phase extraction and microextraction techniques.

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OZONE APPLICATIONS AND IMPLICATIONS FOR INDUSTRY, ENVIRONMENT, AND HEALTH. Stratospheric ozone is an efficient filter for ultraviolet radiation, which damages organisms’ lives exposed to sunlight. In the troposphere, ozone is essential to oxidate volatile organic compounds, but its effects are harmful to animals and plants, particularly humans. The high reactivity of ozone with some organic compounds makes it a promising agent for several applications, such as microbiological control and the medical field. However, their contact with surfaces containing unsaturated substances and other compounds can result in the formation of products that are harmful to human health or distort the organoleptic and structural properties of food. The results available in the literature are often divergent as to their safety and economic viability. Despite this, there are many cases of dermatological applications, and as sanitizing agents in several environments. Antiviral and bactericide properties were that guided the expansion of ozone application in the current coronavirus pandemic (COVID-19). However, more studies should be carried out to comprove its effectiveness, considering possible damages resulting from these applications.

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ENVIRONMENTAL APPLICATIONS OF PERSULFATE: REMEDIATION OF CONTAMINATED GROUNDWATER AND SOILS. Environmental remediation represents a major technological challenge due to the complexity of the environmental matrices and the high treatment cost. In recent years, in situ chemical oxidation technologies (ISCO) have shown a good cost/benefit ratio, which has favored their use in the degradation of several relevant environmental pollutants. In this context, persulfate-mediated processes are of relevant importance once persulfate can be activated in situ, promoting the formation of highly oxidative radical species. Persulfate-based treatments have been frequently reported in environmental remediation studies because they guarantee the effective degradation of pollutants without producing significant changes in the remediated matrix. Given these statements, this study aims to discuss the main ways of activating persulfate and the relevant applications in the remediation of groundwater and soils contaminated with resistant organic pollutants.

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MOLECULAR NETWORKS: AN ANALYSIS ON ANNOTATIONS AND DISCOVERY OF NEW ASSETS. To speed up the discovery of bioactive natural products (NP), chemists have sought advanced approaches in analytical and computational chemistry in attempt to organize and extract information from large data sets. In this sense, the molecular networks (MN) successfully organized enormous sets of mass spectrometry (MS) data together with samples metadata information in an intuitive visualization in the spectral similarity networks format. GNPS (Global Natural Products Social Molecular Networking), a free online platform for storing and processing MSn data, is a leading application of spectral matching with public databases aimed at the dereplication and discovery of new bioactive products through molecular networks. In this review, we address the concept of GNPS spectral similarity networks, as well as their complementary computational tools, benefits and limitations applied in NP studies associated with dereplication, chemical ecology, functional genetics and determination of biosynthetic pathways.

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A HOMEMADE SPIN COATER BASED ON ELECTRONIC WASTE: A VERSATILE AND LOW COST ALTERNATIVE. High-precision equipment generally represents a significant portion of a laboratory budget, leading the access by laboratories with limited financial resources difficult. Then, adaptation of materials such as electronic trash may be a key factor to overcome financial obstacles. As the technological advancement brings with it an increase in the disposal of pieces of equipment considered obsolete, these pieces however can still be used in the construction of new equipment. The present work shows the employment of a scrapped computer HD in addition to an Arduino microcontroller and other electronic components to build a low-cost spin coater. The thickness of films obtained in the handmade equipment presented approximately five percent of difference in relation to films obtained in a commercial equipment.

Resumo em Inglês:

Molecular absorbance and fluorescence measurements are usually performed by benchtop or portable USB spectrophotometers or fluorometers. However, even the simplest configuration of these instruments requires considerable financial input, which is not affordable to many universities and research groups especially when public politics withdraw funds from science. Light-emitting diodes (LEDs) based devices can be an interesting alternative for low-cost, portable yet reliable measurements of absorbance of fluorescence. Especially if associated with the fabrication of 3D structures by additive manufacturing techniques. Although there are many reviews in the literature dedicated to discussing the theoretical aspects and analytical performance of LED-based devices, we consider that these reviews are not easily applicable for beginners in electronics. It results in the intimidation to employ such powerful tools which could have a huge impact mainly to small and/or initial groups. In this tutorial, we present a guide that will help students and researchers to construct “lab-built” devices based on simple optoelectronic components and 3D printing to perform molecular absorbance and fluorescence measurements for analytical methods. Finally, with this tutorial guide, we anticipate a large spread of the usage of LED devices for reliable analytical measurements that can be extensively used in many scenarios.

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LOW-COST ROBOTIC SYSTEM FOR PREPARATION OF LAYER-BY-LAYER FILMS. Layer-by-Layer is an efficient technique for the deposition of thin films used in several devices such as sensors, solar cells, and other systems. A robotic system improves the process reproducibility, be a stand-alone system, and does not demand human participation during the deposition process. On the other hand, the commercially available equipment is expensive. In this work, we present a low-cost robotic system built by using materials commonly found that allows performing several bathing, drying steps and deposition cycles of the substrates necessary for the formation of LbL films. This technical note presents the electronic assembly scheme and the program developed for an experiment. The number of baths, the time necessary for the deposition, and repetitions to result in the formation of the desired film; can be easily modified in this program. The films prepared in this experiment were successfully employed for the preparation of compact layers for perovskite solar cells. Therefore, the equipment can be easily customized to the needs of each research group that uses it.

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PROMOTING THE TEACHER EDUCATION OF POST-GRADUATE STUDENTS IN CHEMISTRY: A CASE STUDY IN THE DISCIPLINE OF INTERNSHIP TEACHING. The objective of this work was to identify evidences related to the teacher knowledge and professional identity characteristics developed by post-graduate students in Chemistry during a discipline of Teaching Internship and Teaching Methodology in Chemistry from a Federal University. The activities carried out were leaned on the discussion of chemistry teaching aspects, planning, developing and reflection about teaching experiences. The teacher education process was analyzed by students themselves by means of metacognitive reports that was employed as data research and examined using content analysis to investigate their teacher knowledge development. The results pointed out the appropriation as much teacher knowledges as aspects of teacher professional identities: search for a flexible and singular didactic-pedagogical profile; belief in constant training/qualification; difficulties and social obligation of the profession. Such results show that the activities proposed can be useful and adaptable to the reality of each post-graduate program in Chemistry. The approach is an opportunity and an incentive for post-graduate students to seek other teaching qualifications during the journey to become a university professor. Despite having contributed to teacher development, just a discipline is not enough to encompass the complexity of this process.

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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.

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CHEMICAL ETHICS AND ITS TEACHING TO CHEMISTRY STUDENTS. This paper aims at broadening the understanding of scientific ethics by addressing chemical ethics, which deals with the benefits, risks and uncertainties associated with or arising from chemical activities. Chemical ethics is a theme of the Philosophy of Chemistry and its discussion has been recommended in Chemical Education. The purpose of its teaching is to recognize and analyze ethical problems, as well as to evaluate the possible paths that can be followed to make better decisions. In this paper, the implementation of a didactic intervention based on a historical case and on a hypothetical case in an undergraduate course is described. The aim of the intervention was to promote the development of ethical reasoning, instead of prescribing a specific ethical path, solution, or behavior. The historical case allowed students to understand the risks and uncertainties associated with the use of chemical substances. The hypothetical case made it possible to make ethical decisions by dealing with a problem situation, in which the characters’ possible decisions and their consequences were analyzed. Results show that the different approaches enable complementary understandings, which favor the development of students’ ethical reasoning.

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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.