Resumo em Inglês:

ZrO2-WO3 mixed metal oxides are important solid acid catalysts, and typically, ammonia gas calcination reduces their acidity. However, in this study, we introduce an updated NH3 calcination technique that can increase the acidity of mesoporous ZrO2-WO3 solid acids. Their structures and acid properties were thoroughly characterized through X-ray diffraction (XRD), N2 adsorption measurement, pyridine-adsorbed infrared spectroscopy (Py-IR), temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis-DRS) analysis. The resulting materials exhibit remarkable activity in the Friedel-Crafts (F-C) reaction of anisole and benzyl alcohol. Our investigations showed that the subnanometer WOx clusters act as the most active sites for the F-C reaction, and NH3-air calcination is essential for the formation of WOx clusters. This treatment not only enhances acidity but also provides a novel method of obtaining acidic ZrO2-WO3 mixed metal oxides. Most importantly, it presents a fresh approach for regulating the formation of WO3 clusters and catalytic activity.

Resumo em Inglês:

This work aims to synthesize the alloy Co64Nb30B6 through mechanical alloying using a planetary ball mill. A disc rotation per minute and a ball/powder weight ratio of 300 rpm and 10:1 were used, with a milled time of 10 h, respectively. The characterization of the Co64Nb30B6 alloy was performed by X-ray diffraction (XRD), examined by scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), thermoanalytical techniques (TGA/DTA), vibrating sample magnetometer (VSM) and confirmed by Braunauer, Emmet e Teller (BET) method type IV isotherms with a hysteresis loop for mesoporous materials. The results indicated that the evolution of the amorphous phase in the Co64Nb30B6 composition through the mechanical alloying process exhibited good soft magnetic properties with the addition of the metalloid element B and its excellent unique ferromagnetic properties. Through thermoanalytical analysis (TGA/DTA), it was shown that at higher temperatures, Co and Nb ions are oxidized by the environment and, therefore, the mass can be slightly increased to 14.9% and a probable contribution of boron in evolution stability thermal and magnetic in the amorphous phase, respectively. This suggests that the newly developed high-performance amorphous alloy Co64Nb30B6 has great application potential.

Resumo em Inglês:

In this work, babassu FAME samples were synthesized by transesterification reaction under alkaline catalysis with sodium glyceroxide and by two steps process with KOH followed by H2SO4 as catalysts. A sequential multi-element method for determination of Zn, Fe, Mg, Ca, Na and K in synthesized babassu FAME by high resolution continuum source flame atomic absorption spectrometry (HR CS FAAS) was developed. The proposed method is based on a microemulsion formation by mixing the babassu FAME samples with 1-propanol and aqueous phase. The mass proportion of the added components was evaluated through a ternary diagram. External and matrix-matching calibration techniques with inorganic and organic standard were investigated. In the five-level spike-recovery test, satisfactory results were obtained by performing the matrix-matching calibration along with inorganic standard solutions. By using the optimized conditions, limits of detection in the range of 0.002-0.12 mg kg-1 were obtained. Accuracy was attested by the agreement of the results obtained in the analysis of three certified reference materials. By applying the microemulsion system and HR-CS FAAS, the sequential determination of six elements was achieved. Therefore, the proposed method was a suitable alternative for metal determination in babassu FAME samples, with good sensitivities, accuracy, and a wide linear working range.

Resumo em Inglês:

Solid and liquid fractions of hydrothermally pretreated sugarcane bagasse (SCB) were simultaneously used as substrate of a novel continuous compartmentalized reactor. The effect of four (56, 42, 28, and 14 h) hydraulic retention time (HRT) and three (0.5, 3.0, and 9.0 g L-1) chemical oxygen demand (COD) levels were evaluated on hydrogen (H2) and organic acids production. Higher H2 production and yield (686 mL and 1.63 mol mol-1 carbohydrate, respectively) were obtained under an HRT of 28 h, probably due to the Clostridium and Thermoanaerobacterium metabolisms, which accounted for almost 60% of the microbial relative abundance. Under lower and higher HRT (14 and 56 h, respectively) lactic acid prevailed without hydrogen production. Other value-added chemicals such as citric, valeric and caproic acids were also obtained according to the HRT. From the functional point of view, enzymes from the glycoside hydrolases group (GHs) potentially performed important roles in the lignocellulosic biomass bioconversion.

Resumo em Inglês:

The synthesis of oxides using plant extracts as precursors has attracted attention as it is an economical, efficient, and ecological route. Euterpe oleracea Mart, available in the Legal Amazon, has great potential due to its composition, rich secondary metabolites. Therefore, this work aimed to investigate the potential of aqueous açaí leaf extract as precursors in synthesizing FexOy-type oxides. The synthesis was developed in two stages to obtain the hematite phases (step 1) and the magnetite phase (step 2). The effect of pH on phase formation and structure was evaluated in step 1. Then, the material was obtained in step 2 by precipitation with pH adjustment. The powders were characterized by thermal analysis, X-ray diffraction, infrared spectroscopy, and scanning electron microscopy. The results showed that pH played a significant role in the thermal behavior, crystallite sizes, and structural parameters of hematite, with neutral or acidic pH being more attractive for obtaining crystallites between 21 and 24 nm. Magnetite with 21.51 nm crystallites was precipitated, indicating possible capping of the Fe3O4 particles and preserving their magnetic characteristics.

Resumo em Inglês:

Photosynthetic microorganisms have been widely studied as an alternative technology for CO2 capture. Aiming to overcome some operational challenges in the application of these microorganisms for gas treatment on a large scale, the immobilization of microalgae in solid matrices emerges as an alternative to facilitate effective management of microalgae culture during harvesting process. In this work, different matrices for microalgae immobilization composed of silica/alginate were obtained varying silica precursors. The synthesized materials were characterized in terms of their specific surface area, cell viability, transparency and physical-chemical properties. Additionally, a new methodology was developed to evaluate the CO2 capture by microalgae using a pressurized system with natural gas mixture. Tests were carried out exploring the influence of some variables, such as headspace volume, cell concentration, stirring and pressure. Once the optimized parameters were established, the amount of CO2 captured by immobilized microalgae was investigated for 7 days by determining the CO2 relative concentrations using gas chromatography. The results of immobilized microalgae showed levels of CO2 removal of 41.4%. This work proved the potential application of the studied biomaterial for natural gas processing, making even more feasible the adoption of this technology for selective capture of CO2 on an industrial scale.

Resumo em Português:

INFLUENCE OF THE PROCEDURE FOR GRANULOMETRIC SAMPLE ADJUSTMENT OF RED CERAMIC AGGREGATED WITH DIMENSION STONE WASTES FOR CLASSIFICATION ACCORDING TO THE ABNT CRITERIA’S. In order to clarify questions about the granulometric preparation of samples for the classification of solid wastes according to the Brazilian technical standard (NBR 10004/04), solubilization tests were carried out on red ceramic specimens made with conventional clay aggregated with ornamental rock residues. Samples were prepared by fragmentation and milling to verify the effects on metals releasing to the extractor medium. The specimens were made with 80% clay, 20% residue and 10% (m/m) moisture and sintered at 1000 °C. The data show that ceramics made with conventional clay, when discarded, will produce non inert wastes, as well as the ceramics made with dimension stone wastes added to the conventional raw material, according to the granulometry of its particles. After all, the metals concentration in the solubilization test are influenced by the sample granulometry. This paper shows that the method of granulometric adjustment should be detailed in the technical standard for solubilization tests (NBR 10006/04), in order to ensure the reliability of the method for classification of solid wastes.

Resumo em Inglês:

In this work, microwave-assisted ring opening polymerization (ROP) of lactide (LA) and glycolide (GA) initiated by magnesium lactate was investigated. The influence of microwave power, temperature, and reaction time on homopolymers and copolymer’s structure and thermal properties is discussed. Polymerization of L-lactide (LLA) initiated by the magnesium compound resulted in yields up to 78% and poly(L-lactic acid) (PLLA) with average molar mass of up to 30,600 g mol−1. Homopolymerization of glycolide generate poly(glycolic acid) (PGA) in yields up to 90% and in L-lactide/glycolide copolymerizations yields between 34-82%. PLLA prepared with the initiator presented microstructure with significant amount of stereo errors as the result of a racemization process during polymerization as well as low glass transition temperature (Tg) and melting temperature (Tm), while the PGAs presented high Tg, due to high crystallinity, and Tm in accordance with the literature. LLA and GA copolymerization result in poly(lactic acid-co-glycolic acid) (PLGA) with composition close to polymerization feed composition.

Resumo em Inglês:

Silicon catalysts have very low catalytic activity in polyester (PET). However, titanium catalysts have high catalytic activity in polyester. The simultaneous use of titanium and silicon catalysts is effective in reducing the activity of a single titanium catalytic base agent. In addition, the glycol salts of titanium and silicon (Ti-EG and Si-EG) prepared in the present invention for use in the polyester catalytic process can avoid the introduction of other groups of impurities during the polyester catalytic process, which would lead to premature capping of the polyester in the process of polycondensation and chain building and make it difficult to increase the molecular weight, and thus affect the quality of the polyester. It has been verified that the ratio of Ti:Si is 1:1 (mol), and total amount added to the catalyst is 0.15% of the raw material amount, and the polycondensation temperature was 260-280 °C for 60 min. Compared with the single Ti-EG catalyst, the b* value of the synthesized PET was significantly reduced, and the molecular weight and other indexes did not change too much. In addition, at the end of catalysis, the catalyst was uniformly dispersed in the reaction system, which could be used as a matting agent for PET.

Resumo em Inglês:

The recycling of waste electrical and electronic equipment (WEEE) is a worldwide challenge and this is one of the biggest issues debated on 21st century, motivating the participation of governments research institutions and also the private sector in order to develop technologies based on the cleaner production (C + P) concept so that the eco-efficiency of the electronics industry is improved. In this work, the manual dismantling and mechanical processing steps, including grinding, magnetic and electrostatic separations were the procedures employed for this. Subsequently, the physical and chemical printed circuit board (PCB) characterizations was carried out by particle size classification and inductively coupled plasma optical emission spectroscopy/scanning electron microscopy-energy dispersive spectroscopy (ICP OES/SEM-EDS) analyses, respectively in order to confirm the release, separation and concentration of metal content. After magnetic separation, the percentages of the magnetic and non-magnetic fractions were 15.18 and 56.70%, respectively. In the magnetic fraction, the concentration of iron, nickel, silver and gold reached 1.26 ± 0.33%, 1.24 ± 0.27%, 650.03 ± 77.60 mg kg-1 and 504.88 ± 18.53 mg kg-1, respectively. In the case of copper, the magnetic fraction had a content of 11.27 ± 1.41%, corresponding to about 50% of the value obtained in the non-magnetic fraction. Hence, iron, nickel, silver and gold were concentrated in the magnetic fraction, while copper was concentrated in the non-magnetic fraction.

Resumo em Inglês:

The article establishes a three-dimensional multiphase proton exchange membrane single-cell model and investigates the impact of precision flow field design on the electrochemical characteristics, heat mass transfer properties, and phase change characteristics of fuel cells. The simulation model is analyzed using COMSOL 6.0 multiphysics software and validated using experimental data under the same operating conditions. The research results indicate that precision flow field design can enhance the electrochemical characteristics of proton exchange membrane fuel cells (PEMFC) by reducing concentration overpotentials through improved gas mass transfer, thus increasing the performance of cell. Precision flow field design improves gas and current density distribution uniformity, promoting more uniform electrochemical reactions and enhancing cell durability. Finally, precision flow field design increases gas mass transfer rates, effectively removing liquid water from the interior and facilitating smoother gas transport to the active regions. This study provides new insights into flow field design for fuel cells.

Resumo em Português:

Over the years it has been possible to notice the growth of applications for educational purposes available on digital platforms. Many of these apps are used in teaching and learning processes, however few are evaluated regarding their theoretical and practical aspects. In this context, in chemistry teaching, specifically the area of organic chemistry, it is inferred that apps can help build knowledge of this Science through visualization and interaction with them, but little is discussed about how these apps are evaluated in practice. Therefore, the present work proposes a new model based on technical and pedagogical aspects, based on evaluation models for educational digital games and Bloom’s digital taxonomy, called the educational application evaluation model (EAEM). In addition, organic chemistry applications available on the Google Play® platform through EAEM are analyzed. The results indicate that the EAEM was efficient in evaluating organic chemistry apps, configuring itself as an alternative for choosing educational apps regardless of the subject, where teachers can analyze the characteristics of the apps according to their pedagogical activities.

Resumo em Inglês:

Carbon dioxide and the related species bicarbonate and carbonate are known for centuries and are deeply involved with modern chemistry knowledge from the beginning. Carbonic acid, by its turn, was intuited more than a century before being synthesized for the first time, which was not obtained, however, without stumbles and mistakes. The equilibrium between HCO3− and CO32− in aqueous medium is free of disputes. However, the interconversion of the other three species is rather controversial. Several papers starting in the beginning of the 19th century until the present days are critically reviewed in order to understand the controversial history of the CO2/H2O system. Finally, experimental evidence and theoretical calculations allow us to place HCO3− as the central species as the conjugate acid for CO32− and conjugate base for two different acids: H2CO3 and CO2.

Resumo em Inglês:

In the most recent simulations on the formation of the Moon by the collision of a protoplanet, approximately the size of Mars, called Theia, with the proto-Earth, 4.5 billion years ago, it is observed that the remains of Theia are deposited on the proto-Earth. This explains the presence of significant quantities of heavy elements in the Earth's crust, such as the transition elements of the first series (V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and Mo, essential for life. This very special collision shaped the structure and, mainly, the chemical constitution of the Earth's crust, allowing the development of highly evolved life forms that would not have formed without this availability. As we observe the heat waves that are causing severe damage today in various parts of the world, the awareness that life on Earth was produced by a cosmic condition with a very low probability of occurring in other planetary systems constitutes a new argument in favor of all actions aimed at stopping global warming. All of us, all of humanity, need to sacrifice our way of life to preserve life on our planet, which is a much more special place than previously assumed.

Resumo em Inglês:

Given the importance of chemistry to society, we sought to understand how the perception of chemistry has been portrayed in academic literature. To this end, we conducted a literature review, analyzing 54 scientific articles published between 1996 and 2022 in 36 journals and written by 135 authors. The results show that this subject is still under-researched, with occasional publications. If, on the one hand, the publications focus on investigating students' perceptions of chemistry, with a more disciplinary approach and focused on understanding the content or the relationship with the discipline, on the other hand, there are few efforts to investigate the attitudes and social representations of chemistry as an area of knowledge.