BARBARA PEREZ GONCALVES SILVA

BARBARA PEREZ GONCALVES SILVA

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Development of flexible magnetic films by the incorporation of Ni/Ni3C nanoparticles in a matrix of Amazonian tannic extract (Myrcia atramentifera)
2024 - SILVA, CRYSTIAN W.C. da; SOUZA, KATIUSSE S. de; SILVA, BARBARA P.G.; FREITAS, RAFAEL S. de; LAZAR, DOLORES R.R.; PASCA, GABRIEL A.C.; CARBONARI, ARTUR W.; OTUBO, LARISSA
The development of nanostructured magnetic materials based on Ni and its compounds (Ni/Ni3C) has been the objective of scientific research due to the versatility of applications that these materials. In this context, magnetic films can be applied in a variety of technologies such as data storage, flexible spintronics, chemical detection, and magnetic sensors.[1] Additionally, the growing prospect of obtaining environmentally eco-friendly materials has promoted the use of vegetable matrices for film synthesis, such as tannins, for example. In this work, we report the fabrication of flexible magnetic films on paper substrates by adding Ni/Ni3C nanoparticles to the tannin extract matrix of the Amazonian species Myrcea atramentífera.[2] The tannin extract solution was obtained by processing the species' bark through grinding, sieving, and water extraction for 8 hours at 70°C, followed by filtration and concentration. After this step, a tannin extract suspension containing 0.1% Ni/Ni3C was prepared by dispersion in an ultrasonic processor. The suspension was dispersed onto a paper substrate and dried at 30 °C for 10 minutes. The films were characterized by XRD, SEM, AFM, and TGA/DSC measurements. The structural and morphological results indicate the formation of continuous films with dispersed nanoparticles. Thermal analysis results suggest that the nanoparticles dispersed in the films maintain structural stability up to 350 °C. The films present macroscopic magnetic response at room temperature, which can be attributed to the presence of nanoparticles with a coercive field of 100 Oe and saturation magnetization of 26 emu/g. [3]
The influence of halide ions in the silver nanowires synthesis using polyol method
2024 - SILVA, BARBARA P.G.; SILVA, CRYSTIAN W.C. da; OTUBO, LARISSA
Silver nanowires (AgNWs) have been studied due to their great optical and electrical properties, making them potential materials to be applied in transparent conductive films (TCFs). Halide ions, such as chloride (Cl-) and bromide (Br-), have been investigated in the synthesis of AgNWs by many researchers.¹ Cl- are commonly used to control the AgNWs growth by facilitating AgCl formation and controlling Ag+ in the solution thereby inhibiting the growth of silver particles (AgNP). Similarly, Br- are also being investigated as a capping agent due to their ability to adsorb onto the (100) crystal plane of Ag, analogous to the capping agent polyvinylpyrrolidone (PVP). In this study, we investigate the influence of Brand Cl- ions in the synthesis of AgNWs using the polyol method, employing ethylene glycol (EG) as solvent and reducing agent, silver nitrate (AgNO3) as the metallic precursor and PVP as the capping agent. In the absence of halide salts, pyramids and rod structures were observed. When only Cl- is added in the reaction, a mixture of pyramids rods and wires were formed. The addition of Br-resulted in the formation of particles (d=133,7 ± 1,6 nm) attributed to the adsorption of Br- ions on the {100}, {110} and {111} crystal planes of fcc silver. The Uv-vis spectrum of sample with Br- exhibited a band at 430 nm, consistent with literature reports for AgNP. The spectra obtained for samples without halides and sample with Cl- are consistent with larger structures. However, when both halides are introduced in the reaction, longer and thinner AgNWs were produced,as observed through SEM, AFM and UV-vis, stating their important role in the silver nanowires growth. Enhancing our comprehension on the growth process and morphological control is important for optimizing the technological application of AgNWs, especially for TCFs.
Simple and fast preparation of transparent conductive films of silver nanowires obtained by a salt assisted polyol method
2024 - SILVA, BARBARA P.G.; SILVA, WILLIAN C. da; SARAIVA, STEFANY R.; OTUBO, LARISSA
Silver nanowires thin films have gained attention due to their excellent optical and electrical properties, being a potential material to be applied in optoelectronic devices as transparent conductive films, deposited on a substrate in a such way that forms a percolated network. We report the synthesis of silver nanowires with average length of 9.5 ± 0.4 μm and diameter of 75 ± 3 nm by a modified polyol method and fabrication of transparent and conductive thin films using a simple and low-cost technique as drop-casting. Additionally, we examined the influence of the drop-casting method in function of number of deposition cycles on the optical and electrical properties of the films through optical absorption and electrical resistance measurements using the two-point methodology. Increasing the number of silver nanowire deposition layers, the optical transmittance decreased from 97 (for one layer) to 60% (for five layers), and electrical resistance decreased from 940 ± 0.35 Ω for the 2-layer film to 32 ± 0.02 Ω, for the 5-layer film. Due to the electrical conductivity range of the produced silver nanowires films, we suggested their application in low-voltage circuits.
The influence of PVP molecular weight in the synthesis of silver nanowires using a salt-assisted polyol method
2023 - SILVA, BARBARA P.G.; OTUBO, LARISSA
In the last decades, the demand for new materials to be used in electronic devices has increased. Among the materials that can be used in transparent conductive films (TCFs), are the silver nanowires (AgNWs). This class of material, when supported in glass or PET, e.g., has good conductivity, thermal and mechanical properties and also high transparency. In this work, the AgNWs were synthesized using the polyol method assisted by a salt and the influence of molecular weight of the capping agent polyvinylpyrrolidone (PVP) in the morphology and structure of Ag crystals was investigated. Different molecular weight of PVP (40 K, 120 K, 360 K and 1300 K MW) was used in the synthesis. The surface morphology of the products was observed by scanning electron microscopy and atomic force microscopy. The phase composition and structure were analyzed by X-ray diffraction (XRD) and the XRD patterns diffraction peaks correspond with the face-centered-cubic (fcc) crystalline phase of silver. Transmission electron microscopy was used to analyze the crystal structure, and UV-visible spectroscopy was used to follow the formation of Ag structures. The results indicate that PVP and its chain length have an important role in the formation of silver nanocrystals due to the adsorption and steric effects [1] and as high is the molecular weight of PVP, longer and thinner are the AgNWs as observed by other authors [2]. Different morphologies were obtained when changing the size of PVP chain. For smaller MW of PVP, particles and short wires were formed. Increasing the MW, nanorods and pyramidal particles were formed, and finally, forming nanowires when using the highest MW PVP of the experiments.Improving the aspect ratio of silver nanowires is important to construct TCFs, since the conductivity and transparency properties are improved when they are thinner and longer.
Graphene deposited on glass fiber using a non-thermal plasma system
2023 - GOMES, PAULO V.R.; BONIFACIO, RAFAEL N.; SILVA, BARBARA P.G.; FERREIRA, JOAO C.; SOUZA, RODRIGO F.B. de; OTUBO, LARISSA; LAZAR, DOLORES R.R.; NETO, ALMIR O.
This study reports a bottom-up approach for the conversion of cyclohexane into graphene nanoflakes, which were then deposited onto fiberglass using a non-thermal generator. The composite was characterized using transmission electron microscopy, which revealed the formation of stacked few-layer graphene with a partially disordered structure and a d-spacing of 0.358 nm between the layers. X-ray diffraction confirmed the observations from the TEM images. SEM images showed the agglomeration of carbonaceous material onto the fiberglass, which experienced some delamination due to the synthesis method. Raman spectroscopy indicated that the obtained graphene exhibited a predominance of defects in its structure. Additionally, atomic force microscopy (AFM) analyses revealed the formation of graphene layers with varying levels of porosity.