RODRIGO UCHIDA ICHIKAWA

RODRIGO UCHIDA ICHIKAWA

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Influence of temperature on obtaining apatites by sol- gel method
2023 - GARCIA, JOAO I.M.M.; GOMES, ANDERSON M.; ZAMBUZZI, WILLIAN F.; ICHIKAWA, RODRIGO U.; SAEKI, MARGARIDA J.
Calcium phosphate-based ceramics (apatites) are synthetic materials that have a chemical composition similar to bone tissue, which makes them interesting to use as biomaterials [1]. In this work, the apatite precursor sols at concentrations of 0.7 mol/L and 1.4 mol/L are prepared by dissolving calcium nitrate and phosphorus pentoxide in ethanol. The sols are kept at rest for 24 hours for hydrolysis (gelatinization) under room temperature and humidity. After hydrolysis, the resulting gels are dried at 80°C to remove the organic solvent and then calcined under different temperatures (from 500°C to 1200°C, with increments of 100°C) for 8h [2]. The X-ray diffraction analysis of the samples by the Rietveld method indicates that the samples are composed of monoclinic and hexagonal hydroxyapatite (HAp), the former being predominant, and calcium β-triphosphate (TCP)[3] . For the material started from the sol with a concentration of 0.7 mol/L, the hydroxyapatite fraction increases from 28.8% to 66.5% when the calcination temperature increases from 500°C to 800°C. Above this temperature, the fraction of this phase decreases. With a concentration of 1.4 mol/L, the hydroxyapatite fraction decreases from 88.2% to 19.5% progressively with increasing temperature from 500°C to 1200°C. The micrographs revealed the formation of particulate but porous materials that agglomerate without sintering up to a temperature of 900°C, from where the formation of sintered and dense agglomerates is observed. The results of the EDX analysis showed a Ca/P molar ratio of around 1.5 for all materials. The cytotoxicity assay, using pre-osteoblast cells (MC3T3-E1, Subclone 4) by non-direct contact of 24h, showed that cell viability and adhesion did not differ from those of the control. A decrease in viability and adhesion was observed for samples prepared at a concentration of 0.7 mol/L and calcined at temperatures above 900°C.
Toward an energy-efficient synthesis method to improve persistent luminescence of Sr2MgSi2O7:Eu2+,Dy3+ materials
2021 - MERIZIO, L.G.; BONTURIM, E.; ICHIKAWA, R.U.; SILVA, I.G.N.; TEIXEIRA, V.C.; RODRIGUES, L.C.V.; BRITO, H.F.
The synthesis of persistent luminescent materials usually requires a multi-step long time annealing at high temperatures (>1200°C) in a resistive oven, causing a huge energy consumption. Also, to achieve reduced oxidation states of emitter ions (e.g., Eu3+ → Eu2+ ), the H2(g) atmosphere is often used, which can be dangerous and increase the costs of the process. Therefore, the development of a quick and new single-step green strategy, using in-situ low-risk atmosphere (e.g., CO(g)) and a microwave-assisted solid-state (MASS) method has been encouraged. In this work, we present a single-step method to synthesize the compound Sr2MgSi2O7:Eu2+,Dy3+ using the MASS method and the results were compared with those prepared by a conventional ceramic method. The luminescent material was prepared in 25 min of synthesis using carbon as a microwave susceptor and CO(g) atmosphere source at the same time. A higher concentration of Eu2+ emitter was identified by XANES in the MASS method product, which has a significant effect on the luminescence efficiency, as well as an improvement in the optical properties, leading to an emission 100 times more intense. Furthermore, to understand the Eu3+ reduction process under CO(g) atmosphere, we present here the innovative results of in-situ XANES analysis for the Sr2MgSi2O7:Eu2+,Dy3+ material. Finally, the MASS method makes it possible to prepare the materials with less than 5% of the ceramic method's duration in time. The energy-saving and better-quality persistent luminescent properties obtained in the MASS method provide viable applications on anti-counterfeiting markers, solar cell sensitizers, and other luminescent technologies.
Enhancing NIR emission in ZnAl2O4:Nd,Ce nanofibers by co-doping with Ce and Nd
2021 - ROJAS-HERNANDEZ, ROCIO E.; RUBIO-MARCOS, FERNANDO; GORNI, GIULIO; MARINI, CARLO; DANILSON, MATI; PASCUAL, LAURA; ICHIKAWA, RODRIGO U.; HUSSAINOVA, IRINA; FERNANDEZ, JOSE F.
Development of new near infrared luminescent (NIR) emitters improves our understanding of their fundamental structure–property relationships. The ability to use efficient energy transfer to convert ultraviolet or visible light photons to enhance the NIR emission has attracted a great deal of attention in down-conversion applications. Taking advantage of the sol–gel impregnation process and growth of materials along a support or template, core–shell structured nanofibers of ZnAl2O4 – based ceramic doped with cerium and neodymium were synthesized with the help of an elaborate facile and cost-efficient strategy. The color-tunable emissions make this material a suitable host for a wide range of applications, e.g., bio-imaging, security markers, imaging devices, optical coatings, and solar cells. This research correlates the defects and the remarkable optical properties of the developed structures. Specified conditions of sol–gel processing combined with the incorporation of rare-earth elements in various concentrations provide the possibility of tuning the ratio between Ce3+ and Ce4+ in the nanofibers with an average diameter of 50 nm and, therefore, their functional response. It is important to clarify the role of trivalent and tetravalent cerium cations in the modulation of NIR emission to establish the luminescence mechanism. The NIR emitter luminescent compound ZnAl2O4:Nd,Ce, which adopts a spinel-type structure, is studied using the X-ray absorption near-edge structure technique. For the first time, this study reveals the energy transfer from Ce3+ to Nd3+ and the enhancement of the NIR emission due to the presence of Ce4+ in the ZnAl2O4:Nd,Ce spinel compound. Cytotoxicity analyses suggest the viability of the synthesized nanofibers, which opens new avenues in bio-imaging applications.
Thickness estimation of TiO2-based nanotubes using X-ray diffraction techniques
2020 - FARIA, MARCELA E.M.; LEITE, MARINA M.; ICHIKAWA, RODRIGO U.; VICHI, FLAVIO M.; TURRILLAS, X.; MARTINEZ, L.G.
TiO2-based nanotubes are a very promising material with many applications in solar cells, biomedical devices, gas sensors, hydrogen generation, supercapacitors, and lithium batteries, among others. Nanotube thickness is a very important property since it is related to electronic and surface mechanics. In this sense, transmission electron microscopy (TEM) can be used. However, it can be difficult to acquire a good TEM image because the transversal section of the nanotubes needs to be visible. In this work, TiO2-based nanotubes obtained via hydrothermal synthesis were studied using X-ray line profile analysis. Scherrer and Single-Line methods provided consistent results for the thickness of the nanotubes (≃ 5 nm) when compared with TEM. Additionally, Single-Line method was also applied to estimate the microstrain. The advantage of using XRD is given by the fact that it is a quick and statistically significant analysis when compared with TEM. The results show that XRD can be used as a rapid and reliable alternative for the thickness estimation of nanotubes.
Characterization of nanostructured Mn-Zn ferrites synthesized by coprecipitation method using CTAB
2020 - MARANHAO, W.C.A.; ICHIKAWA, R.U.; TURRILLAS, X.; YOSHITO, W.K.; SAEKI, M.J.; ORLANDO, M.T.D.; MARTINEZ, L.G.
In this work it was investigated the influence of CTAB surfactant concentration on the synthesis of the compound Mn0.75Zn0.25Fe2O4 by the coprecipitation method. It was also compared the influence of hydrothermal treatment on the synthesized materials. The magnetic properties were characterized by AC susceptometry for the determination of the magnetic susceptibility and magnetic density energy. The phases, crystal structure and morphology of the nanoferrites were determined by Rietveld analysis of X-ray diffraction data. It was found the presence of two phases: Franklinite and Akaganeite and it was shown that the samples synthesized only by coprecipitation presented the tendency to increasing the crystallite sizes of the akaganeite phase and decreasing of crystallite sizes of the Franklinite phase as a function of CTAB concentration. The samples submitted to subsequent hydrothermal treatment presented a tendency to decreasing the crystallite sizes of both phases and increasing in Franklinite phase fraction, compared to the samples synthesized only by coprecipitation, suggesting that the hydrothermal treatment was effective in obtaining nanostructured materials of smaller particles.
The influence of iron content and alkaline concentration on Mn0.75Zn0.25FeyO4 structure, surface charge and acb response
2017 - MOURA, TIAGO F.A.; NAVARRO, RAPHAELLA; SHIOTSUKI, AUGUSTO K.; UTIYAMA, ANA P.M.S.; ICHIKAWA, RODRIGO U.; MATOS, RONALDO V.R.; CASTRO, GUSTAVO R.; YOSHITO, WALTER K.; MARTINEZ, L.G.; MIRANDA, JOSE R.A.; SAEKI, MARGARIDA J.
Nanotechnology applied on magnetic material provide a good opportunity to develop biomaterials as tracers for Alternating Current Biosuceptometry (ACB)and Magnetic Resonance Imaging (MRI) to diagnose certain diseases as cancer. The magnetic nanoparticles can still constitute drug carrier systems and hyperthermia agent for cancer treatment. Neverthless, the efficiency for therapy and diagnosis depends on the magnetic susceptibility. In this work, the ferrite nanoparticles with nominal composition Mn0.75Zn0.25FeyO4, where 1.5 ≤ y ≤ 2.8, were synthesized by the co-precipitation method and, the influence of iron content and concentration of precipitating agent on the structure, ACB response and surface charge was analyzed. It was noted that the synthesis using alkaline metal hydroxide between 0.1, 0.15 and 0.2 mol/L provides single-phase materials [ICSD 28515 (PDF - 742 402), space group Fd3m]. The higher concentration (0.25 mol/L) leads to materials with higher crystallinity and similar ACB response to those precipitated by lower concentration base, despite the secondary phase. A surface charge of 30 mV in module was achieved, which decreased as the concentration of the precipitating agent increased.
Cation distribution of Mn-Zn ferrite nanoparticles using pair distribution function analysis and resonant X-ray scattering
2018 - ICHIKAWA, RODRIGO U.; PARRA, JOAO P.R.L.L.; VALLCORBA, ORIOL; PERAL, INMA; YOSHITO, WALTER K.; SAEKI, MARGARIDA J.; TURRILLAS, XAVIER; MARTINEZ, LUIS G.
Mn-Zn ferrite nanoparticles were synthesized by chemical co-precipitation method and analysed using X-ray synchrotron diffraction data. Pair distribution function (PDF) analysis was used to probe the local structure and revealed that the first-neighbour distances of Fe-Fe and Mn-Zn in the 3.0 up to 3.5˚A range are different from the ones usually reported in the literature. For the sample with the best magnetic behaviour, resonant X-ray scattering (RXS) using three energies close to the absorption edges of Mn, Zn and Fe was applied to determine the cation distribution which explained the previous result from PDF analysis.
Size-strain analysis of iron-excess Mn–Zn ferrite nanoparticles using synchrotron diffraction and its correlation with magnetic saturation and isoelectric pH
2018 - ICHIKAWA, RODRIGO U.; PARRA, JOAO P.R.L.L.; MARTINS, MURILLO L.; YOSHITO, WALTER K.; SAEKI, MARGARIDA J.; TURRILLAS, XAVIER; MARTINEZ, LUIS G.
Iron-excess Mn–Zn ferrite nanoparticles were prepared by coprecipitation with sodium hydroxide (NaOH) at different concentrations (0.1, 0.2, 0.5 and 1.0 mol/L). The results of X-ray diffraction (XRD) analysis using Whole Powder Pattern Modeling (WPPM) showed that higher concentrations of NaOH promote crystallite growth and broader dispersion in crystallite sizes. Energy dispersive X-ray spectroscopy indicates that zinc loss is noticeable when [NaOH] ≥ 0.2 mol/L. XRD revealed also a significant less-crystalline phase contribution alongside the main peaks of the nanocrystalline cubic spinel ferrite phase. The less-crystalline fraction is lower for the ferrite obtained with 0.2 mol/L of NaOH, being about 50% and more than 70% for the other samples. Despite of the less-crystalline fraction and the excess of iron, no secondary phases were detected. The Warren curves showed that the concentration of NaOH significantly influences the microstrain in the crystallites, being smaller for the sample obtained with NaOH at 0.2 mol/L. The sample prepared with this condition presented the better properties to be used as magnetic tracer in clinical diagnoses combining small mean crystallite size, low microstrain, which resulted in materials with higher magnetic saturation and high surface charge under blood pH.
In situ hydration of sulfoaluminate cement mixtures monitored by synchrotron X-Ray diffraction
2018 - ROSSETTO, CLEUSA M.; ICHIKAWA, RODRIGO U.; MARTINEZ, LUIS G.; CAREZZATO, GERALDO L.; CARVALHO, ALEXANDRE M.G.; TURRILLAS, XAVIER
Mixtures of calcium sulfoaluminate and Portland clinkers with gypsum were hydrated with deionized water. The pastes were introduced in 0.7 mm borosilicate capillary tubes and kept at 40 ºC while diffraction patterns were collected every 35 s for approximately 3 hours with a monochromatic radiation of 12 keV at the XRD1 beamline of the Laboratório Nacional de Luz Síncrotron (LNLS) in Campinas, SP - Brazil. The main crystalline phases (C2S, C3S, ettringite, ye’elemite and gypsum) involved in the hydration were quantified by Rietveld analysis. The most noticeable fact was the absence of portlandite as a crystalline precipitate, most likely due to the capture of calcium ions to form ettringite.
Evidence for a core–shell configuration in Tb-doped KY3F10 nanoparticles using synchrotron x-ray line profile and pair distribution function analyses
2018 - ICHIKAWA, R.U.; LINHARES, H.S.M.D.; PERAL, I.; BALDOCHI, S.L.; RANIERI, I.M.; TURRILLAS, X.; MARTINEZ, L.G.
The microstructure of Tb-doped KY3F10 nanoparticles synthesized by coprecipitation was analysed using x-ray synchrotron diffraction data. Size-strain analysis was performed by means of x-ray line profile (XLPA) methods such as Warren–Averbach and whole powder pattern modelling. Additionally, the structural coherence of the sample was accessed using pair distribution function analysis, supporting the XLPA results. The combination of all methods revealed that the nanoparticles exhibit a more ordered core and a less ordered surface comprising a core–shell configuration.