Papers by Author: P.T.A. Santos

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Authors: P.T.A. Santos, Cristiane M. Furtado, M.O. Rodrigues, A.C.F.M. Costa
Abstract: ZnAl1.,9Eu0.1O4 nanoparticles were functionalization used of the 3-aminopropyltrimethoxysilane silane and chitosan, in 5:1 proportion of the nanoparticles to chitosan, in order to obtain hybrid materials for the development of luminescent markers. The samples were characterized by XRD, FTIR, TEM, excitation and emission. After functionalized the nanoparticles showed formation of crystalline phase of spinel and chitosan. TEM results have revealed that the samples presented before particle size less than 100 nm and after functionalization was observed that the particle size increases. Emission peak of Eu centered at 614 nm, corresponding to the transition 5D0 7F2. Nanoparticles before and after functionalization showed the spectral lines characteristics of Eu ion 5D0 7Fj where (J = 0,1,2,3,4). After functionalization the sample presented an increase of luminescence intensity.
Authors: Joelda Dantas, A.S. Silva, P.T.A. Santos, J.R.D. Santos, D.C. Barbosa, Simoni Margareti Plentz Meneghetti, Ana Cristina Figueiredo de Melo Costa
Abstract: This study aimed to assess the performance of the solid catalyst Ni0.4Cu0.1Zn0.5Fe2O4, synthesized by combustion reaction, over the methyl esterification reaction of the fatty acids present in cottonseed oil. The catalyst was characterized by XRD, FTIR pyridine absorption, Raman spectroscopy, and SEM. The reactions were conducted at 140 and 180°C with molar ratios of 1:3, 1:6 and 1:9, with 2% of catalyst and reaction time of 2 h. The XRD results showed that the single phase ferrite was obtained with surface area of 87 m2/g and with mesoporous characteristic. It was observed from the FTIR pyridine absorption only the presence of Lewis acid sites. The Raman spectra confirm the presence of the inverse spinel phase. The results indicated that at 180°C and molar ratio of 1:9, the conversion of free fatty acids was about 87%.
Authors: P.T.A. Santos, Hélio Lucena Lira, Lucianna Gama, F. Argolo, Heloysa Martins Carvalho Andrade, Ana Cristina Figueiredo de Melo Costa
Abstract: The selective reaction of CO oxidation (PROX) was named as the most attractive way to reduce the CO concentration, thereby purifying the hydrogen. The aim of this work is to make the structural and morphologic characterization of the NiFe2O4 spinel synthesized by combustion reaction, using glycine as fuel, and to evaluate as catalyst in the reaction of selective oxidation of carbon monoxide in the presence of hydrogen, oxygen and carbon monoxide. The powder was prepared by using a vitreous silica crucible on a hot plate at 480°C and according to stoichiometry established by theory of propellants and explosive. The powder was characterized by X-ray diffraction (XRD), FTIR, textural analyses, transmission electron microscopy (TEM) and catalytic measurements. The results from XRD show characteristic peaks of spinel phase without presence of secondary phases. The morphologic results show surface area of 3.1 m2/g and particle size calculated by TEM of 21.72 nm. The catalyst was active and selective for O2, reaching 100% of conversion.
Authors: Valmir José da Silva, P.T.A. Santos, Lucianna Gama, Ruth Herta Goldsmith Aliaga Kiminami, Daniel R. Cornejo, A. Azevedo, Ana Cristina Figueiredo de Melo Costa
Abstract: This work involved a morphological, microstructural and magnetic characterization of nanosized powders and sintered samples of Ni-Zn ferrite doped with chromium. The effect of substituting Fe3+ for Cr3+ on the final characteristics of the powders and sintered samples was investigated. The Ni-Zn ferrite powders were prepared by combustion reaction using nitrates and urea as fuel, based on the concepts of propellant chemistry. The samples were uniaxially compacted by dry pressing (385 MPa) and sintered at 1200oC/2h, using a heating rate of 5°C/min. The Ni-Zn powders and compacted samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the measures of their magnetic properties. The results revealed the formation of the cubic crystalline phase of the inverse spinel of Ni-Zn-Cr ferrite. The average crystallite size was 21 nm and 57 nm while the saturation magnetization was 47.0 and 73.1 emu/g for the powder and the sintered sample, respectively.
Authors: P.T.A. Santos, Daniel Cornejo, P.T.A. Santos, Hélio Lucena Lira, Ana Cristina Figueiredo de Melo Costa
Abstract: Ni0.5Zn0.5Fe1.97Al0.3O4 ferrites were synthesized by combustion reaction method and after calcined at 700°C/1 h, with the aim to investigate how the Al3+ ions substitution byNi2+ ions can influence the magnetic properties. The results from X-ray diffraction showed the formation of a unique Ni-Zn ferrite phase with average crystallite size of 8 and 22nm, before and after calcination, respectively. The synthesize samples presented a superparamagnetic behavior, with saturation magnetization of 0.9 emu/g, and coercive field of 0.05 kOe, and after calcination the samples presented soft magnetic behavior with saturation magnetization of 40.0 emu/g and coercive field of 0.04 kOe.
Authors: P.T.A. Santos, Joelda Dantas, P.M.A.G. Araújo, P.T.A. Santos, A.C.F.M. Costa
Abstract: In this paper we propose nanoferrites Ni-Zn silanization with 3-aminopropyltrimethoxysilane using the method of reflux and evaluate the effect of silanization on the structure, morphology and magnetism of the magnetic nanoparticles aimed at biological applications. The samples as synthesized and after silanization were characterized by XRD, FTIR, SEM and testing magnetic attraction. The results indicated a single phase inverse spinel Ni-Zn ferrite, high intensity of diffraction peaks and a high basal width of all reflections observed, indicating that the samples are crystalline, and formation of nanoparticles. Morphologically, for nanoferrites Ni-Zn synthesized observed formation of large agglomerates in the form of spongy blocks of frail and after silanization was observed with respect dense pellets, indicating that most particles were rigidly connected by the presence of the agent silane. The characteristic bands of the spinel were observed for the Ni-Zn nanoferrites before and after silanization, and also observed the characteristic bands of silane in confirming the ferrites silanized functionalization of ferrites with the silane agent. Nanoparticles ferrite as synthesized and after silanized were strongly attracted by the presence of a magnet, immediately after the presence thereof indicating that the silane is effective is not interfere with the magnetic particles, maintaining the same magnetic behavior.
Authors: P.M.A.G. Araújo, P.T.A. Santos, P.T.A. Santos, F.N. Silva, A.C.F.M. Costa, E.M. Araújo
Abstract: This work reports the development and characterization by SEM, XRD, FTIR, emission and excitation chisonan/ZnAl1.9Eu0.05O4 films with a mass proportion of 1:1. The powders were deagglomerated and passed 325 mesh screens and added to the diluted chitosan in 1% acetic acid. The materials were filtered and placed in petri dishes and placed in an oven at 60°C for solvent evaporation. After drying the film, a solution of 1M sodium hydroxide was added in order to obtain a film with neutral pH. With the XRD, it has been verified that the chitosan/ZnAl1.9Eu0.05O4 films presented the chitosan peaks and ZnAl2O4. Through the SEM, it has been observed that the chitosan/ZnAl1.9Eu0.05O4 presented a protruding surface. The results presented in emission and excitation spectra suggest that the film chitosan/ ZnAl1.9Eu0.05O4 exhibit good luminescence properties, and are promising to be applied as a luminescent marker in future applications in the field of biomaterials.
Authors: P.T.A. Santos, Ana Cristina Figueiredo de Melo Costa, Heloysa Martins Carvalho Andrade
Abstract: This paper aims to synthesize and characterize nanosized nickel and zinc ferrites (NiFe2O4 and ZnFe2O4) samples by a combustion reaction method, using glycine as fuel. The performance in HT-WGRS reaction the samples was investigated. The results showed that the combustion reaction was effective in the production of major phases of the spinel ferrite (crystallite sizes of 44 and 27 nm) and presence of the secondary phases, such as Ni and ZnO, with surface area 3 and 115 m2/g for NiFe2O4 and ZnFe2O4, respectively. HT-WGSR activity was achieved (80%) to NiFe2O4 ferrite in the temperature range of 300 - 500°C.
Authors: Pascally M.A. Guerra de Araújo, P.T.A. Santos, Ana Cristina Figueiredo de Melo Costa, Edcleide Maria Araújo
Abstract: The present work intends to prepare ZnAl2O4/chitosan films with a mass proportion of 3:1and evaluate the influence of the ZnAl2O4 filler on the chitosan films morphology, structure and thermogravimetric properties. The films were characterized by XRD, SEM, TG and FTIR. With the XRD, it has been verified that both the chitosan and the ZnAl2O4/chitosan films presented the chitosan peaks. However, the ZnAl2O4/chitosan film also presented the ZnAl2O4 peaks. Through the SEM, it has been observed that the chitosan film presented a flat surface. On the other hand, the ZnAl2O4/chitosan presented a protruding surface. The TGA/DTA curves of the ZnAl2O4/chitosan film showed an increase in the thermal stability at temperatures greater than 720oC, comparing with the chitosan film.
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