EDUARDO DE LIMA CORREA

EDUARDO DE LIMA CORREA

Página do item completo

Resultados de Busca

Agora exibindo 1 - 7 de 7

High-saturation magnetization in small nanoparticles of Fe3O4 coated with natural oils
2020 - CORRÊA, BRUNO S.; COSTA, MESSIAS S.; CABRERA-PASCA, GABRIEL A.; SENA, CLEIDILANE; PINTO, RAFAEL H.H.; SILVA, ANA P.S.; CARVALHO JUNIOR, RAUL N.; ISHIDA, LINA; RAMON, JONATHAN G.A.; FREITAS, RAFAEL S.; SAIKI, MITIKO; MATOS, IZABELA T.; CORRÊA, EDUARDO L.; CARBONARI, ARTUR W.
The enhancement of nanoparticle’s magnetic properties with a suitable coating is the main tool to increase their potential as an effective candidate for applications in different areas, especially in biomedicine. In the work here reported, Fe3O4 nanoparticles coated with natural oils were synthesized by iron (III) acetylacetonate thermal decomposition and the effects of the coating on the magnetic properties of these particles have been investigated. The oils were extracted from three Amazon fruits seeds: açaí, ucuúba, and bacaba by CO2 supercritical extraction process, and the relative percentage composition of fatty acids were determined by gas chromatography. A systematic study of crystalline, morphological, and magnetic properties revealed a saturation magnetization (Ms) enhancement and high values of the anisotropy constant for Fe3O4 samples when coated with açaí and ucuúba oils, which present a large percentage of saturated total fatty acid. Our results indicate that nanoparticles with sizes smaller than around 5 nm present Ms values as high as that found for bulk Fe3O4 and, consequently, much higher than Ms values for nanoparticles usually coated with oleic acid. The nuclear techniques neutron activation analysis and perturbed angular correlations were used to better characterize the nanoparticles.
Can natural oils improve the properties of magnetic nanoparticles?
2019 - CORREA, B.S.; COSTA, M.S.; CABRERA-PASCA, G.; SENA, C.; PINTO, R.H.; CARVALHO JUNIOR, R.N.; FREITAS, R.S.; SAIKI, M.; CORREA, E.; CARBONARI, A.W.
The use of nanoparticles coated with different materials have been studied by many researchers to improve the quality of nanomaterials for biomedical applications such as controlled drug delivery, image contrast and treatment of cancer by magnetic hyperthermia [1]. In this work, we used oils extracted from ucuúba (Virola surinamensis), bacaba (Oenocarpus bacaba Mart.) and açaí (Euterpe oleracea Mart.) to coat Fe3O4 nanoparticles. The ucuúba, bacaba and açaí are native trees of the Amazon forest, whose oils are rich in fatty acids, such as lauric, myristic, steatic, oleic, palmitic, and linoleic acid, with different proportions. These pure oils, free of solvents, were obtained by the extraction method with carbon dioxide in the supercritical state [2], and then added during the synthesis process of iron oxide nanoparticles by thermal decomposition method [3]. The results of X-ray diffraction confirmed the formation of Fe3O4 single phase. The average size around 3 nm and spherical morphology of the magnetite nanoparticles was determined by transmission electron microscopy. The study of magnetic properties revealed a saturation magnetization (Ms) enhancement and high values of the anisotropy constant for Fe3O4 samples when coated with açaí (91.4 emu.g-1; 4.6 105 J.m-3) and ucuúba (80.6 emu.g-1; 9.3 105 J.m-3) oils, which present a large percentage of saturated total fatty acid. The results indicate that nanoparticles with sizes smaller than around 5 nm present Ms values as high as those found in bulk Fe3O4 and higher than those usually obtained for nanoparticles coated with oleic acid [4]. The neutron activation analysis (NAA) nuclear technique was used to determine with high accuracy the mass of Fe in the Fe3O4 core of nanoparticles in order to normalize the magnetization values [5]. These results show that natural oils have a great potential to produce stable and quality nanoparticles as compared with conventional coated.
Magnetic field at Ce impurities in La sites of LaBaMn2O6 double perovskites
2019 - BOSCH-SANTOS, B.; NASCIMENTO, N.; SAIKI, M.; CORREA, E.L.; SALES, T.S.; PEREIRA, L.F.; CABRERA-PASCA, G.A.; CARBONARI, A.W.
Magnetic behavior in LaBaMn2O6 double perovskite compounds has been investigated with various techniques, due to the rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine field at the 140Ce nucleus of Ce impurities occupying La sites. The radioactive 140La nuclei with a half-life of 40.8 h were produced by direct activation of natural La present in the samples through the irradiation with neutrons in the IEA-R1 nuclear research reactor of IPEN. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. This double perovskite samples were synthesized by sol-gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group. This phase occurs due to an oxygen deficiency. The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites, which can be ascribed to the contribution of 4f band of Ce to Bhf at low temperatures due to the increase in its localized character.
Magnetic field at Ce impurities in La sites of La0.5Ba0.5MnO3 double perovskites
2019 - BOSCH-SANTOS, B.; NASCIMENTO, N.M.; SAIKI, M.; CORREA, E.L.; SALES, T.S.N.; PEREIRA, L.F.D.; CABRERA-PASCA, G.A.; SAXENA, R.N.; SCHELL, J.; CARBONARI, A.W.
Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol- Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and a pure antiferromagnetic interaction below 100 K. Moreover, it also indicates an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites measured with 140Ce probe nuclei, which can be ascribed to the contribution of 4f band of Ce to Magnetic Hyperfine Field (Bhf) at low temperatures due to the increase in its localized character.
Synthesis and atomic scale characterization of Er2O3 nanoparticles
2018 - CORREA, EDUARDO L.; BOSCH-SANTOS, BRIANNA; FREITAS, RAFAEL S.; POTIENS, MARIA da P.A.; SAIKI, MITIKO; CARBONARI, ARTUR W.
In the investigation reported in this paper a modified thermal decomposition method was developed to produce very small Er2O3 nanoparticles (NPs). Particles structure, shape and size were characterized by x-ray diffraction and transmission electron microscopy which showed that the synthesis by thermal decomposition under O2 atmosphere produced very small and monodisperse NPs, allowing the investigation of finite-size and surface effects. Results of magnetization measurements showed that the smallest particles present the highest values of susceptibility that decrease as particle size increases. Specific heat measurements indicate that the sample with the smallest NPs (diameter ∼5 nm) has a Néel temperature of 0.54 K. The local structure of particles was investigated by measurements of hyperfine interactions with perturbed angular correlation spectroscopy using 111Cd as probe nuclei replacing the cationic sites. Results showed that the relative population of sites 8b increases in both the core and surface layer of particles.
Determination of gadolinium and erbium in Gd2O3 and Er2O3 nanoparticle samples by neutron activation analysis
2017 - CORREA, E.L.; BOSCH-SANTOS, B.; SAIKI, M.; NASCIMENTO, N.M.; EFFENBERGER, F.B.; CARBONARI, A.W.; POTIENS, M.P.A.
Along these years the applications of nanoparticles (NPs) in medicine as radiosensitizers have been widely studied, so several methods for its syntheses are presented. One of the best synthesis methods for this application is by thermal decomposition, which produces small NPs size (3-5 nm) with a narrow size distribution. On the other hand NPs synthetized by this method are covered by an organic material, hence making their mass measurement impossible by conventional means. In this study neutron activation analysis (NAA) was applied to determine Gd and Er concentrations in their NP oxides. The analysis of NPs composition is not commonly carried out. However these determinations are of great importance when the NPs are used in radiosensitization tests and magnetization measurements. NPs were synthetized by the method of thermal decomposition, which consisted in adding and mixing Gd and Er acetate in an organic solution by stirring and heating at high temperature (about 573 K) for about six hours. After cooling at room temperature the solution was centrifuged to obtain the NPs that were separated from the liquid. For NAA about 5 mg of post-synthesis and 873 K annealed samples of Gd2O3-NP and Er2O3-NP were irradiated together with their respective element standard. One-minute irradiations were carried out at the IEA-R1 research nuclear reactor. Element concentrations were determined by measuring 159Gd and 171Er gamma ray activities (energy of 363.56 keV and 308.3 keV respectively). Concentration of (19.88 ± 0.43) % of Gd and (23.53 ± 0.82) % of Er were obtained in the Gd2O3-NP and Er2O3-NP samples, respectively. These results are useful and have been used to establish experimental conditions for NPs magnetization and irradiation in radiotherapy beams for dose enhancement factor determination.
Síntese de nanopartículas de óxido de ferro utilizando óleo de ucuúba
2015 - CORREA, BRUNO S.; SILVA, ANA P.S.; CORDEIRO, RENATO M.; MATOS, IZABELA T.; CORREA, EDUARDO L.; EFFENBERGER, FERNANDO B.; SENA, CLEIDILANE; CARVALHO JUNIOR, RAUL N.; SAIKI, MITIKO; CARBONARI, ARTUR W.