[en] The experimental research work was carried out in accordance with the Factorial Design Statistical Method to evaluate and analyze the influence of calcium, magnesium, silica and phosphorus on the precipitation of vanadates. precipitation was performed by neutralization with H₂ SO₄ of alkaline aqueous solutions containing vanadium pentoxide (V₂ O₅) at 60 ± 2 deg C. The experimental responses measured were percent of vanadium recovery and vanadium pentoxide content in the precipitate. These impurities are considered representative of those present in a leach liquor from the ore obtained at Campo Alegre de Lourdes (Brazil). The operational variables in this work were used optimum conditions as determined by the statistical approach. Among the impurities under study, phosphorus exhibited the highest negative influence on the experimental responses. Phosphorus diminished the percent of vanadium recovered from 98.9 to 34.5 and the vanadium oxide content in the precipitate from 91.2% to 39.3%. (author)

[en] Magnetite nanoparticles were synthesized by two methods: reverse coprecipitation and partial oxidation of ferrous ions. The particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, vibrating sample magnetometry (VSM), and thermogravimetric analysis (TGA). The prepared nanoparticles exhibited superparamagnetic properties at room temperature. The mean size of the particles was in the range of 10-29 nm. TGA curves showed different thermal decomposition behaviors depending on the synthesis method. Distinct magnetic responsiveness was observed for the TGA residue samples. Thermal decomposition kinetics was evaluated by the model-based approach using TGA curves measured at three distinct heating rates in the temperature range of 298-1173 K under a synthetic air atmosphere. The model fit resulted in a correlation coefficient of 0.998 and the order of magnitude for the estimated kinetic parameters agreed with the reported data in the literature. (author)

[en] Antimicrobial resistance (AMR) has created an unprecedented global threat to human life. Traditional antibiotics are becoming less effective in combating multidrug-resistant microorganisms that are mutating. Carbon-based nanomaterials have been discovered to exhibit potent bactericidal effects for pathogenic bacteria due to their high surface-to-volume ratio, substantial interior volume, and other distinctive chemical and physical characteristics. By encapsulating soot-derived CNPs in a water-soluble natural polypeptide, bovine serum albumin (BSA), the present study aims to create carbon nanoparticles (CNPs) encased bio macromolecular aggregates with excellent optical and antimicrobial properties. A cost-effective protocol was employed to create biopolymer BSA-stabilized carbon nanoparticles. UV–visible, FT-IR, and fluorescence spectrophotometric techniques, as well as transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses, were used to characterise the synthesised carbon nanosystems. The antibacterial efficacy evaluation of the developed CNPs was tested against selected pathogenic bacterial strains. The study established the use of carbon nanoparticles encapsulated in water-soluble and biocompatible macro-scaffold BSA as an effective antibacterial agent in order to improve the antimicrobial performance for biomedical and environmental applications. (author)

[en] The growing production of renewable fuels such as biodiesel, complementary to petroleum diesel, has intensified the search for heterogeneous catalysts containing basic sites to replace the usual homogeneous ones used in industrial transesterification. In this context, hybrid silicas are promising catalysts because of their basic property due to the presence of siloxy anions in their structure, formed by charge compensation with cetyltrimethylammonium cations (CTA+), and easy preparation procedure. Several modifications can be used in their synthesis to increase these silicas' catalytic activity. One of them is the use of alcohols as co-solvent in the reaction mixture of its synthesis, containing different numbers of carbon atoms in the linear chain (ethanol, 1-propanol, or 1-butanol), performed in this work. The hybrid silicas prepared in the presence of these alcohols were characterized to evaluate the role of alcohols on their physicochemical properties. They were also catalytically assessed in the model transesterification of ethyl acetate with methanol. The results showed that as the number of carbons in the alcohol chain used to prepare hybrid silicas increased, the value of the initial specific activity (TOF_O) increased by about 85% due to greater accessibility to the catalytic sites. The greater sites accessibility was caused by the particle size reduction and an increase in the porosity of the silicas. (author)

[en] Nb₂O₅/ZrO₂, Cu–Nb₂O₅/ZrO₂ and Ag–Nb₂O₅/ZrO₂ were prepared by incipient wetness impregnation and evaluated in the ethanol conversion into higher value-added products. The catalysts were characterized by X-ray fluorescence, X-ray diffraction, N₂-adsorption–desorption, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed desorption of CO₂ and NH₃, and FTIR pyridine adsorption. The catalytic activity and selectivities were evaluated at different temperatures and space velocities. ZrO₂ exhibited strong acid sites and led to ethylene as the main product. The addition of niobium yielded a surface Nb₂O₅ overlayer and also crystalline nanoparticles, and also increased the acid site density of the catalyst. The impregnation procedure yielded Ag and CuO nanoparticles highly dispersed over the Nb₂O₅/ZrO₂ surface, promoting ethanol dehydrogenation and consequently increasing acetaldehyde selectivity. Besides, results revealed that a decrease in temperature favors ethanol dehydrogenation to acetaldehyde, while an increase in temperature favors ethanol dehydration to ethylene. Moreover, 1,3-butadiene and ethyl acetate selectivities were increased by higher contact times. Nevertheless, the higher acid sites density and the presumable deactivation of Ag and Cu dehydrogenation sites led to high ethylene formation, which reinforces the importance of a suitable balance of acid and basic sites. (author)

[en] The thiosulfate method is a cyanide-free hydrometallurgical method for gold extraction, but the existence of copper ion in Cu²⁺–NH₃–S₂O₃^2- system is not conducive to the subsequent gold(I) recovery. This paper describes a process for improving the gold(I) adsorption capacity of mercapto-functionalized silica gel (MP-SG) by using ethylenediamine (en) as an additive to mask copper(II). The effects of en/Cu²⁺ molar ratio, contact time, and pH on adsorption were investigated. The results showed that the addition of en increased the adsorption capacity of MP-SG to gold by more than 70%. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed that the valence states of gold and copper on the adsorbent were both + 1, which confirmed the occurrence of competitive copper(II) adsorption. This could be inhibited by the addition of en without affecting the interfacial properties of MP-SG. UV–vis spectroscopy and the distribution of copper species revealed that addition of en changed the composition of the solution, forming a more stable Cu(en)₂²⁺ complex, the fraction of Cu(en)₂²⁺ increased with en content, thus reducing the competitive adsorption of Cu(II) to gold (I). The recovery rate of gold in the actual thiosulfate leaching solution was up to 92.35%, and en has almost no influence on the recycling process of the recovered leaching liquor, which proves the feasibility of this method in practical application. (author)

[en] Chalcopyrite is the most abundant copper mineral and its bioleaching has been the subject of several studies due to its refractory nature when submitted to hydrometallurgical processes. Moreover, the growing worldwide demand for copper requires the processing of low-grade ores or mining tailings for which hydrometallurgical processes are a cost-effective alternative. New approaches have shown that the use of chloride ions in chalcopyrite leaching can positively contribute to its dissolution. In this regard, the present work assessed the bioleaching of two chalcopyrite ores—containing 0.34% Cu (copper ore 1) and 1.79% Cu (copper ore 2) by the extreme thermophilic archaea Sulfolobus acidocaldarius. In addition, the effect of different NaCl concentrations (0.25 − 1.0 mol/L) on copper extraction were investigated. In the experiments with the copper ore 1, the copper extractions were higher in the abiotic experiments (from 83 to 90%) than in the biotic experiments (62–80%) for all NaCl concentrations investigated. On the other hand, the experiments with the copper ore 2 showed similar results (around 83% Cu extractions) in all abiotic tests carried out in the presence of chloride and also in the biotic experiments with 0.25 and 0.50 mol/L NaCl concentrations. However, a 97% copper extraction was observed in the biotic experiment carried out with 1.0 mol/L NaCl. Regardless of the type of ore, the lowest copper dissolutions (less than 55%) were obtained in the experiments in the absence of both microorganism and chloride. The XRD analyses of the solid residues of the bioleaching experiments did not reveal the presence of Fe(III)-precipitates such as jarosite. (author)

[en] Zeolitic imidazolate frameworks (ZIFs) containing Zn(II) cations and 2-methylimidazolate anions were synthesized at high yield in aqueous medium. Triethylamine was used as an agent for deprotonation of the organic ligand, enabling rapid formation of the microporous structure known as ZIF-8. In the absence of the deprotonator, the material formed was ZIF-L, which has a lamellar structure. The ZIFs were characterized by X-ray diffraction, CO₂ and N₂ physisorption, chloroform chemisorption, and scanning electron microscopy. The different amounts of triethylamine influenced not only ZIF structure, but also material characteristics as particle size and external area. The ZIFs were then evaluated as catalysts in the Knoevenagel condensation reaction, different catalytic performances were obtained depending on the amount of deprotonation agent used. The activation energy of ZIF-8 was estimated considering an irreversible pseudo-homogeneous first-order reaction, and was shown to be highly catalytically stable during consecutive reuses. (author)

[en] In this work, KIT-6 silica functionalized with sulfonic acid by the co-condensation method was prepared and evaluated as a catalyst in the transesterification of Brazilian cashew nut oil (BCNO) with butanol for biodiesel synthesis. The catalyst was characterized by SAXS, TEM, N₂ adsorption–desorption measurements, ²⁹Si MAS NMR and ¹³C CP-MAS NMR to prove the structural integrity of the incorporated organic group and to show the ordered structure, morphology and porosity, respectively. Small-angle XRD confirmed the formation of the mesophase of the synthesized materials. TEM images demonstrated the well-ordered arrangement of the pores and their uniformity throughout the grains, in addition to the highly ordered nature of the cubic mesostructures. The KIT-6 propylsulfonic acid catalyst was able to produce a 70% butyl ester yield, as determined by ¹H NMR spectroscopy in 6 h reaction with a BuOH/BCNO molar ratio of 30:1, 140 °C and a 6 wt% of catalyst mass relative to starting oil mass in the reaction. The KIT-6-S catalyst can be reused for two cycles without loss of catalytic activity. (author)

[en] In this study was evaluated the adsorption capacity of trivalent chromium by using commercial activated carbon as adsorbent and elephant grass (Pennisetum purpureum) as bioadsorbent, which was prior treated by steam explosion technique and surfactant impregnated. The samples were characterized by SEM, XRD, XRF and FT-IR analysis. The effect of initial concentration of metal, pH, adsorbent dosage, contact time and temperature were further investigated in batch experiments. Isotherm, kinetic and thermodynamic studies were carried out in optimal process condition. The adsorption capacity reached a maximum of 28.36 mg g^-1 for modified SEEG sample. Thermodynamic parameters reveal that Cr3⁺ adsorption is a non-spontaneous and exothermic chemical process. The Langmuir isotherm model showed a well fit unless to the in nature Elephant Grass, which fitted well to Freundlich model. Furthermore, experimental data adjusted better to PSO kinetic model. So that, it was found that the modification techniques employed significantly enhanced the adsorption capacity of Cr³⁺. (author)