RESUMO
Molybdenum trioxide is an abundant natural, low-cost, and environmentally friendly material that has gained considerable attention from many researchers in a variety of high-impact applications. It is an attractive inorganic oxide that has been widely studied because of its layered structure, which results in intercalation ability through tetrahedral/octahedral holes and extension channels and leads to superior charge transfer. Shape-related properties such as high specific capacities, the presence of exposed active sites on the oxygen-rich structure, and its natural tendency to oxygen vacancy that leads to a high ionic conductivity are also attractive to technological applications. Due to its chemistry with multiple valence states, high thermal and chemical stability, high reduction potential, and electrochemical activity, many studies have focused on the development of molybdenum oxide-based systems in the last few years. Thus, this article aims to briefly review the latest advances in technological applications of MoO3 and MoO3-based materials in gas sensors, lithium-ion batteries, and water pollution treatment using adsorption and photocatalysis techniques, presenting the most relevant and new information on heterostructures, metal doping, and non-stoichiometric MoO3-x.
RESUMO
The physical properties of porous silica nanofibers are an important factor that impacts their performance in various applications. In this study, porous silica nanofibers were produced via solution blow spinning (SBS) from a silica precursor/polymer solution. Two polyvinylpyrrolidone (PVP, Mw = 360,000 and 1,300,000) were chosen as spinning aids in order to create different pore properties. The effect of their physical properties on the adsorption of methylene blue (MB) in an aqueous solution was explored. After forming, the nanofibers were calcined to remove the organic phase and create pores. The calcined nanofibers had a large amount of micro and mesopores without the use of additional surfactants. The molecular weight of the PVP impacted the growth of silica particles and consequently the pore size. High Mw PVP inhibited the growth of silica particles, resulting in a large volume of micropores. On the other hand, silica nanofibers with a high fraction of mesopores were obtained using the lower Mw PVP. These results demonstrate a simple method of producing blow spun silica nanofibers with defined variations of pore sizes by varying only the molecular weight of the PVP. In the adsorption process, the accessible mesopores improved the adsorption performance of large MB molecules.
RESUMO
OBJECTIVE: This work aimed at producing silica-blow-spun nanofibers containing silver nanoparticles (SiO2/Ag) and investigating the effect of their incorporation in different proportions, with or without pre-treatment with a silane coupling agent, on the mechanical, physicochemical, and biological properties of a commercial composite low-viscosity bulk-fill resin. METHODS: The production of SiO2/Ag nanofibers was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). A portion of the produced nanofibers was silanized. Scanning electronic microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), contact angle measurements, and agar diffusion tests against Streptococcus mutans were used to verify the differences between silanized and non-silanized nanofibers. Different proportions (0.5 wt% and 1 wt%) of silanized (SiO2/Ag-0.5S and SiO2/Ag-1S) and non-silanized (SiO2/Ag-0.5NS and SiO2/Ag-1NS) nanofibers were incorporated into the bulk-fill composite (Opus Bulk Fill Flow, FGM). A commercial composite was used as the control. Evaluation of the color parameters (L*, a*, and b*), radiopacity, contact angle, antimicrobial activity, Vickers microhardness, surface roughness (Sa and Sq), flexural strength, and SEM of the fractured surfaces were performed. The data were analyzed using the Mann-Whitney U test (fiber morphology), Kruskal-Wallis tests, with Dunn's post hoc test (antimicrobial activity of the specimen against S. mutans), Student's t-test (disk diffusion), one-way ANOVA and Tukey (color, radiopacity, and contact angle), and two-way ANOVA and Tukey (microhardness, surface roughness, and flexural strength) tests. All statistical analyses were performed at a significance level of 1% (α = 0.01). RESULTS: Porous nanometric SiO2/Ag fibers were successfully produced. The silanization process, confirmed by FTIR, increased the diameter and contact angle and reduced the growth inhibition halos of the nanofibers (p < 0.01). After the incorporation of nanofibers into the dental composite, all color parameters were altered in all the experimental groups (p < 0.01). All the groups presented adequate radiopacity values. No statistical difference was observed in the contact angles of the experimental composites (p > 0.01). The lowest microbial counts were obtained in the SiO2/Ag-0.5S group; although no significant difference was observed with the control group (p < 0.01). The SiO2/Ag-1S, SiO2/Ag-0.5S, and SiO2/Ag-0.5NS groups exhibited higher microhardness after 30 d of immersion in water (p < 0.01). The surface roughness (Sa-µm) resembled that of the control at baseline, except for the SiO2/Ag-1NS group. For the baseline evaluation of flexural strength, all the experimental groups exhibited lower values than the control, except for SiO2/Ag-0.5NS and SiO2/Ag-0.5S, but after 30 d of immersion in water, there was no difference (p < 0.01). SIGNIFICANCE: The incorporation of 0.5% wt. of silanized nanofibers in the commercial composite (SiO2/Ag-0.5S) seemed to be promising, especially for its greater inhibition of S. mutans, adequate roughness, and flexural strength, in addition to high hardness, even after aging in water.