ÁLVARO ANTONIO ALENCAR  DE QUEIROZ

ÁLVARO ANTONIO ALENCAR DE QUEIROZ

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Magneto-optical properties of iron-bulk metallic glasses sustainably produced from iron-rich sand sludge
2024 - QUEIROZ, ALFREDO A.A.E. de; CAVALLARO, FRANCISCO de A.; QUEIROZ, ALVARO A.A.
A large amount of sand sludge (SS) from rivers polluted with heavy metals is continuously dredged and often dumped into landfills, resulting in environmental pollution of soil and water. This work examines the feasibility of the utilization of iron-enriched SS from dredged polluted rivers to produce Fe-based bulk metallic glasses (Fe-BMG). Fe-BMG was prepared from SS by melt-quenching technique, and their magnetic and photochromic properties were studied. The chemical composition of the Fe-BMG was determined by X-ray fluorescence (XRF). The structural properties have been analyzed using the Raman spectroscopy (RS), vibrating sample magnetometer (VSM) and ultraviolet-visible (UV-VIS) spectroscopy. XRF results shows that Fe-BMG contains an iron proportion of 38.8% (wt.) as the hematite (α-Fe2O3), and magnetite (Fe3O4) phases. The Raman “fingerprints” of α-Fe2O3 and Fe3O4 were identified at 1330 cm−1, and 300-600 cm-1, respectively. The measured saturation magnetization of Fe-BMG samples is 3.0 emu/g at 60 kOe. A UV-VIS analysis of the Fe-BMG exposed to sunlight simulator reveals an enhanced transmission of light in the 400-700 cm-1 region. These findings confirmed the successful conversion of the hazardous SS into Fe-BMG with promising magneto-optical characteristics for a wide variety of technological applications.
Probing the epoxy insulation of smoothing reactors with graphene ink
2024 - FARIA, GABRIEL H. de; ARAUJO, LIVIA C. dos P.; LOPES, GUSTAVO P.; WANDERLEY NETO, ESTACIO T.; LEYVA, MARIA E.; QUEIROZ, ALVARO A.A. de
Electrically conductive inks (ECIs) are up to now a growing research field, to create flexible circuits for power engineering. As a result, research into screen printing of conductive electrodes onto fiberglass-epoxy-reinforced laminates (FGERLs) has emerged. In this study, an ECI based on reduced graphene oxide (rGO) is proposed for screen printing of conductive electrodes on FGERL used in insulation of the high-voltage direct current smoothing reactors (HVDCSRs). The electrically conductive reduced graphene oxide ink (ECrGOI) was fabricated by mixing rGO, hyperbranched polyglycerol (HPGL) as an adhesion promoter, and poly (vinyl alcohol) (PVA) as a binding agent. The ECrGOI electrodes exhibited adhesion strength of 3.7 ± 0.3 N/mm2 and conductivity of 1.2.10-4 S/cm at percolation threshold starting at less than 7.5 wt.% of rGO. The thermogravimetric analysis (TGA) indicates that ECrGOI exhibited good thermal stability at 400 °C. The attractive electric, thermal, and adhesive properties, combined with the ease of preparation and solution-processing capability, indicate that ECrGOI may have great potential applications in analysis of insulation produced by FGERL used in encapsulation of smoothing reactors.
Electrical properties of silver-silicone rubber nanocomposites for high-voltage outdoor insulators
2024 - ARAUJO, LIVIA C. dos P.; LEYVA, MARIA E.; WANDERLEY NETO, ESTACIO T.; QUEIROZ, ALVARO A.A. de
Currently, the selection of high-temperature vulcanizing silicone rubber (HTVSiR) formulations resistant to the growth of microorganisms and which suitable electrical properties plays an important role in the manufacture of the polymeric high-voltage outdoor insulators (HVOIs) with high lifetime. In this work, silver-HTVSiR nanocomposites (AgHTVSiR) formulations are prepared and their electrical and antimicrobial properties are presented. Ag nanoparticles were electrochemically synthesized and characterized by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), UV-visible (UV-Vis), and X-ray (XRD) spectroscopies. Thermogravimetric (TG/DTG) analysis is undertaken with the purpose of determining the thermal behavior of AgHTVSiR. The complex impedance analyses were conducted to investigate the electrical conduction mechanism of the AgHTVSiR nanocomposites via electrochemical impedance spectroscopy (EIS) within a frequency range from 0.1 Hz to 0.1 MHz. XRD revealed Ag nanoparticles of 50 nm in diameter size. The images of SEM-EDS evinced the homogeneity of Ag nanoparticles dispersion into the HTVSiR matrix. The incorporation of silver nanoparticles does not change the thermal stability of the AgHTVSiR nanocomposite as compared to neat HTVSiR. The AgHTVSiR nanocomposites have maximal values for real part (Z') at low frequencies. Z' is found to decrease as the frequency of the applied alternating electric field increases. Furthermore, there is an improvement in the permittivity values for the AgHTVSiR nanocomposites with an increase in the concentration of 0.1 wt.%-0.3 wt.% of the Ag nanoparticles. Also, the AgHTVSiR shows excellent antimicrobial efficacy against Trichoderma spp fungus. The impedance characteristics of the AgHTVSiR nanocomposite along with its high dielectric permittivity and excellent antimicrobial property make it suitable for application in HVOI.
Higher electrical conductivity of functionalized graphene oxide doped with silver and copper (II) ions
2023 - PEREIRA, NELSON G.A.; GONZALEZ, MARIA E.L.; QUEIROZ, ALVARO A.A. de; OLIVEIRA, ADHIMAR F.; WANDERLEY NETO, ESTACIO T.
This study presents a new methodology for graphene oxide (GO) synthesis through electrochemical exfoliation of graphite, followed by phthalic anhydride functionalization (PhA-GO) and doping with Cu2+ and Ag+ ions. The synthesis of GO involved the use of an electrochemical cell with H2 SO4 as the electrolyte, with a gradual increase in potential from 2.3 V to 10 V. Extensive characterization techniques confirmed the successful incorporation of oxygen-containing functional groups, verifying the oxidation of graphite. PhA-GO functionalization was confirmed by thermogravimetric analysis, Differential Scanning Calorimetry, Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDX), which confirmed the presence of Cu2+ and Ag+ ions. The Scherrer equation determined a grain size of 75.85 nm for GO. The electrical properties exhibited semiconductor and semimetal behavior, particularly in PhA-GO/Ag+ composites, making them suitable for electronic devices over a wide temperature range, presenting a promising pathway for advanced materials in electronic applications.
Poly(vinyl alcohol)/poly(glycerol) dendrimer hydrogel mediated green synthesis of silver nanoparticles
2022 - MARCONDES, POLLYANA; ROSAS, GISELA H.; GONZALEZ, MARIA E.L.; QUEIROZ, ALVARO A.A. de; MARQUES, PAULO S.
In this paper, we report the synthesis and evaluation of a poly(vinyl alcohol)/poly(glycerol) dendrimer hydrogel incorporated with green synthesized silver nanoparticles (PVA/PGLD-AgNPs) using Cinnamomum verum extract as the reducting agent (Cz-extract). The Cz-extract was prepared using ultrasonic technique. UV-visible (UV-vis) spectra of Cz-extract confirmed the presence of cinnamaldehyde. PVA/PGLD-AgNPs films were prepared using 5, 10 and 20 mL of Cz-extract and characterized by UV-vis, Fourier transform infrared spectroscopy, Thermogravimetric analysis and X-ray diffraction (XRD). The surface plasmon resonance band in the UV-vis spectra confirmed the formation of AgNPs. XRD pattern confirmed the presence of silver, with average crystallite sizes calculated by Scherrer equal to 13.64 nm, 16.63nm and 20.27 nm for AgNPs prepared with 5 mL, 10 mL and 20 mL of Cz-extract, respectively. AgNPs release kinetic was studied by Korsmeyer– Peppas model. The antimicrobial results revealed that the PVA/PGLD-AgNPs hydrogels showed good antibacterial activity behavior against Escherichia coli.
Physicochemical and biological properties of nanohydroxyapatite grafted with star-shaped poly(ε-caprolactone)
2022 - KAIRALLA, ELENI C.; BRESSIANI, JOSE C.; BRESSIANI, ANA H. de A.; RIBELA, MARIA T. de C.P.; HIGA, OLGA Z.; QUEIROZ, ÁLVARO A.A. de
To overcome the disadvantages generated by the lack of interfacial bonding between hydroxyapatite nanocrystals (HAPN) and agglomeration of particles in the development of biodegradable nanocomposites a chemical grafting method was applied to modify the surface of HAPN through grafting of the three-arms star-shaped poly(ε-caprolactone) (SPCL) onto the nanoparticles. The chemical grafting of SPCL onto HAPN (SPCL-g-HAPN) has been investigated using Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy (TEM), photoelectron spectroscopy, X-ray diffraction, zeta potential (ZP) and contact angle (CA). TEM micrographs of the SPCL-g-HAPN revealed the existence of hybrid organic/inorganic (O/I) nanoscale domains. The results of albumin (HSA) and fibrinogen (HFb) adsorption indicate resistance to HFb adsorption by SPCL-g-HAPN relatively to unmodified HAPN. The ZP and CA measurement suggest a heterogeneous topology for SPCL-g-HAPN likely due to the existence of hydrophobic-hydrophilic regions on the nanocomposite surface. The enzyme degradation by cholesterol esterase and lipase indicates that the rates of hydrolysis for SPCL-g-HAPN were very slow relative to the SPCL/HAPN blends. The in vitro biological studies showed that the human osteoblast-like cells (MG-63) cells had normal morphology and they were able to attach and spread out on SPCL-g-HAPN surfaces. A higher overall cellular proliferation was observed on SPCL-g-HAPN scaffolds compared to pure HAPN or SPCL materials.
In vitro cytotoxic data on Se-methylselenocysteine conjugated to dendritic poly(glycerol) against human squamous carcinoma cells
2022 - CORREA, NICOLI D.G.; SILVA, FELIPE D.; VIEIRA, DANIEL P.; SOARES, CARLOS R.J.; QUEIROZ, ALVARO A.A. de
Polymeric nanoparticles acting as sources of selenium (Se) are currently an interesting topic in cancer chemotherapy. In this study, polyglycerol dendrimer (DPGLy) was functionalized with seleno-methyl-selenocysteine (SeMeCys) by means of Steglich esterification with 4-dimethylaminopyridine/(l-ethyl-3-(3-dimethylaminopropyl)carbodiimide) (EDC/DMAP) and cerium chloride as cocatalyst in acetonitrile at quantitative yields of 98 ± 1%. The SeMeCys coupling DPGLy efficiency vs. time were determined by Fourier Transform infrared spectroscopy (FTIR) and ultraviolet–visible (UV–Vis) spectroscopy. The cytotoxic effects of SeMeCys–DPGLy on the Chinese Hamster ovary cell line (CHO-K1) and head and neck squamous cell carcinoma (HNSCC) cells line were assessed by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay. No signs of general toxicity of SeMeCys–DPGLy against CHO-K1 cells were detectable at which cell viability was greater than 98%. MTS assays revealed that SeMeCys–DPGLy reduced HNSCC cell viability and proliferation at higher doses and long incubation times.
Fabrication of hyperbranched polyglycerols microcapsules from microfluidics guided by artificial neural networks
2021 - ALVES, ANDRESSA A.; QUEIROZ, ÁLVARO A.A. de; QUEIROZ, ALFREDO A.A.E. de
In recent years, the microfluidic approach has received a lot of attention from the scientific community due to the simple and efficient synthesis of highly monodisperse microcapsules used in a variety of applications in biotechnology and medicine such as, for example, materials synthesis, drug encapsulation, among others [1,2]. Thus, in this work, hyperbranched polyglycerol microcapsules (HPGM) were developed using microfluidic technology. Artificial neural network (ANN) feed-forward using multilayer perceptron architecture was trained and applied to model and predict the microfluidic process. The HPGM produced were characterized by scanning electron microscope (SEM), attenuated total reflection-Fourier transform infrared (ATR-FTIR) and thermogravimetric analysis (TGA). The fabricated HPGM showed spherical size and monomodal distribution with an average diameter of 29 μm. The developed ANN proved to be efficient predictor, showing well agreement with the experimental data (R2=0.9983). Based on these results in this research, it was found that the microfluidic device for producing HPGM was successfully developed since it was possible to synthesize microcapsules with targeted properties, monodispersed with high stability and low porosity. In this way, microfluidic technology guided by ANN can be used to synthesize HPGM for biotechnology processes.
Biophysical properties of electrospun chitosan-grafted poly(lactic acid) nanofibrous scaffolds loaded with chondroitin sulfate and silver nanoparticles
2022 - JUNIOR, ALEXANDRE F.; RIBEIRO, CHARLENE A.; LEYVA, MARIA E.; MARQUES, PAULO S.; SOARES, CARLOS R.J.; QUEIROZ, ALVARO A.A. de
The aim of this work was to study the biophysical properties of the chitosan-grafted poly(lactic acid) (CH-g-PLA) nanofibers loaded with silver nanoparticles (AgNPs) and chondroitin-4-sulfate (C4S). The electrospun CH-g-PLA:AgNP:C4S nanofibers were manufactured using the electrospinning technique. The microstructure of the CH-g-PLA:AgNP:C4S nanofibers was investigated by proton nuclear magnetic resonance (1H-NMR), scanning electron microscopy (SEM), UV-Visible spectroscopy (UV-Vis), X-ray diffraction (XRD), and Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR and 1H-NMR confirm the CH grafting successfully by PLA with a substitution degree of 33.4%. The SEM measurement results indicated apparently smooth nanofibers having a diameter range of 340 ± 18 nm with porosity of 89 ± 3.08% and an average pore area of 0.27 μm2. UV-Vis and XRD suggest that silver nanoparticles with the size distribution of 30 nm were successfully incorporated into the electrospun nanofibers. The water contact angle of 12.8 ± 2.7° reveals the hydrophilic nature of the CH-g-PLA:AgNP:C4S nanofibers has been improved by C4S. The electrospun CH-g-PLA:AgNP:C4S nanofibers are found to release ions Ag+ at a concentration level capable of rendering an antimicrobial efficacy. Gram-positive bacteria (S.aureus) were more sensitive to CH-g-PLA:AgNP:C4S than Gram-negative bacteria (E. coli). The electrospun CH-g-PLA:AgNP:C4S nanofibers exhibited no cytotoxicity to the L-929 fibroblast cells, suggesting cytocompatibility. Fluorescence microscopy demonstrated that C4S promotes the adhesion and proliferation of fibroblast cells onto electrospun CH-g-PLA:AgNP:C4S nanofibers.
Microfluidic caging lipase in hyperbranched polyglycerol microcapsules for extracorporeal treatment of enzyme pancreatic insufficiency
2021 - ALVES, ANDRESSA A.; QUEIROZ, ALFREDO A.A.E. de; SOARES, CARLOS R.J.; QUEIROZ, ALVARO A.A. de
Lipase cartridges are currently the mainstay of treatment to improve fat absorption related to pancreatic insufficiency (PI) in patients receiving enteral nutrition feedings. Enzyme immobilization is an essential prerequisite for designing lipase cartridges systems for efficient enzymatic fat hydrolysis. A microfluidic approach has been adopted to produce lipase (LIP) caged in hyperbranched polyglycerol microcapsules (HPGly). The resulting HPGly-LIP microcapsules are spherical and had an average diameter of 29 µm with monomodal size distribution. The optimum conditions determined by artificial neural networks were HPGly concentration of 10 wt.%, LIP loading of 20% (wt) and total flow rate in microfluidic cell of 1.0 mL/h. Under these conditions, the maximum capacity of the LIP that can be microencapsulated is around 85% with respect to the HPGly concentration of 10 wt.% and total flow rate in microfluidic cell of 1.0 mL/h. This resultant HPGly-LIP exhibited Michaelis–Menten coefficients of 1.138,14 mM (Km) and 0.49 U/mg (Vmax) showing higher activity compared to free LIP. Finally, the robust HPGly-LIP microcapsules showed excellent recyclability. The in vitro Analysis of the HPGly-LIP cytotoxicity showed that microcapsules had no cytotoxic effect to L929 fibroblasts cells and behaved very similar to the negative control. These features will be useful for the facile construction of biocatalytic systems with high efficiency, excellent recyclability and adequate biocompatibility for treatment of patients with PI receiving enteral nutrition feedings.