In this paper, we have combined the various experimental results and first-principles calculations with a new and interesting discussion to explain the photocatalytic and antibacterial activities of α-Ag 2 WO 4 crystals, which were obtained using the microwave-hydrothermal (MH) method with anionic surfactants. The advantages of the insights gained through the present work are two-fold. First, the mechanism and origin of the photocatalytic and antibacterial activities can be rationalized. Second, this facile and controllable synthetic method is expected to encourage the synthesis of complex metal oxides with specific active facets, and these insights can contribute to the rational design of new materials for multifunctional applications. X-ray diffraction and Rietveld refinement analysis confirmed that all the crystals have an orthorhombic structure without deleterious phases. Ultraviolet-visible diffuse reflectance spectroscopy indicated the presence of intermediary energy levels and a variation in the optical band gap values (3.09-3.14 eV) with the crystal growth process.The geometry, electronic properties of the bulk, and surface energies of these crystals were evaluated using first-principles quantum mechanical calculations based on the density functional theory. The crystal shapes was experimentally and theoretically modeled based on Rietveld refinement data, emission scanning electron microscopy images, and Wulff construction. To obtain a wide variety of crystal shapes, the morphologies were gradually varied by tuning the surface chemistry, i.e., the relative stability of the faceted crystals. The growth mechanisms of different α-Ag 2 WO 4 crystals and their facet-dependent photocatalytic and antibacterial performances were explored in details. The combination of experimental and theoretical data revealed the presence of (110) and (011) planes with high surface energies together with the disappearance of faces related to the IJ010)/IJ010) planes in α-Ag 2 WO 4 crystals are key factors that can rationalize both the photocatalytic and antibacterial activities. The different activities may be attributed to the different number of unsaturated superficial Ag and W atoms capable of forming the main active adsorption sites. Finally, we discuss how knowledge of surface-specific properties can be utilized to design a number of crystal morphologies that may offer improved performance in various applications.
Saccharomyces cerevisiae strains from different regions of Minas Gerais, Brazil, were isolated and characterized aiming at the selection of starter yeasts to be used in the production of cachaça, the Brazilian sugar cane spirit. The methodology established took into account the screening for biochemical traits desirable in a yeast cachaça producer, such as no H 2 S production, high tolerance to ethanol and high temperatures, high fermentative capacity, and the abilities to flocculate and to produce mycocins. Furthermore, the yeasts were exposed to drugs such as 5,5,5؆-trifluor-D,L-leucine and cerulenin to isolate those that potentially overproduce higher alcohols and esters. The utilization of a random amplified polymorphic DNA-PCR method with primers based on intron splicing sites flanking regions of the COX1 gene, as well as microsatellite analysis, was not sufficient to achieve good differentiation among selected strains. In contrast, karyotype analysis allowed a clear distinction among all strains. Two selected strains were experimentally evaluated as cachaça producers. The results suggest that the selection of strains as fermentation starters requires the combined use of biochemical and molecular criteria to ensure the isolation and identification of strains with potential characteristics to produce cachaça with a higher quality standard.Cachaça (pronounced "kha-sha-ssa"), the sugar cane spirit, is the most popular distilled beverage produced in Brazil. The annual production reaches 1.3 billion liters, with 15% being produced in more than 8,500 distilleries in the state of Minas Gerais.Traditional cachaça production relies on a spontaneous fermentative process that is mediated by the microbiota present in the cane juice wort and on the surface of equipments used in the productive process. It has been already demonstrated that in such systems there occurs a succession of yeasts, with Saccharomyces cerevisiae being the predominant species. Cachaça quality depends on the ecology of the microbial populations during an initial spontaneous fermentation (18,29,31,32,39). The fermentative process occurs through a continuously open fermentative process which is completed within 24 h and generally takes place from May to November, corresponding to the sugar cane harvesting period.Considering the conditions of production usually found in the cachaça distilleries, fermenting yeast populations have to face different types of stress (osmotic, high temperature, and high ethanol concentration). Besides, they might also present some characteristics such as a good fermentative power, no H 2 S production, killer activity, flocculation ability, and production of flavoring compounds. Taking all of these factors into account, we have developed a strategy to select yeast strains with appropriated characteristics to produce cachaça with potentially higher-quality standards (52). Parallel to the selection and development of S. cerevisiae strains toward ethanolic fermentations, molecular methods were developed and validated to study...
Bacteria are the microorganisms that most frequently cause infectious diseases in humans. The synthesis of silver nanoparticles (AgNPs) has attracted interest due to the new and different physical and chemical characteristics with applications in new fields. AgNPs, alone or supported on ceramic, are used as antimicrobial fillers in textiles and polymers for food-packaging and biomedical applications, for antimicrobial paints, and potentially for drug delivery. The evaluation of mesoporous nanostructures or nanocomposites as FDU-12/lignin/silver was effective in inhibiting Staphylococcus aureus, E. coli, Enterococcus faecalis, and Candida albicans. The best results were achieved against the inhibition of E. coli and with the structures FDU-12/silver. In plates with FDU-12/lignin/silver, FDU-12, FDU-12/lignin, and the positive control, it was enumerated at 0, 6, 14, and 27 colonies, respectively. While the development of resistance to a new antibiotic is expected, the time course and degree of resistance are uncertain and depend on various factors. The application of AgNPs as nanocomposites can alter the expression of bacterial proteins and could be used for inactivation. This review explores such aspects and a number of factors arising like the use of nanostructures against E. coli, from the knowledge acquired.
Controlling the bioaerosol present in indoor environments has been evidenced to be extremely necessary. An alternative is to develop filter media for air conditioners that have biocidal properties. This study aimed to verify the biocidal effect of a high-efficiency particulate air (HEPA) filter medium modified with the deposition of nanoparticles on its surface. For this purpose, Ag, TiO 2 , and Ag/TiO 2 nanoparticles were used and the antimicrobial activities of these nanomaterials against Escherichia coli , Staphylococcus aureus , and Candida albicans microorganisms were evaluated, as well as the biocidal efficacy of the modified HEPA filter with these nanomaterials in a real environment. The percentages of elimination obtained for the Ag, TiO 2 , and Ag/TiO 2 nanomaterials, respectively, were 53%, 63%, and 68% ( E. coli ); 67%, 67%, and 69% ( S. aureus ); and 68%, 73%, and 75% ( C. albicans ). The HEPA filter media had their surfaces modified by aspersion and deposition of Ag, TiO 2 , and Ag/TiO 2 nanomaterials. We could conclude that the nanoparticles adhered to the filter medium do not affect its permeability. The modified filters were arranged in an internal environment (bathroom) for the collection of the bioaerosols, and after the collection, the filter cake was plated and arranged to grow in a liquid medium. The results showed that the filters have 100% of biocidal action in passing air, and 55.6%, 72.2%, and 81% of inhibition to microbial growth in their surface for modification with Ag, TiO 2 , and Ag/TiO 2 , respectively, compared to unmodified filters.
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