São Cristóvão, Brazil
São Cristóvão, Brazil

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Pereira S.C.,Programa de pos graduacao em Quimica | Paranhos M.M.,Programa de pos graduacao em Quimica | Eduardo A.C.,Programa de pos graduacao em Quimica | Santos M.A.B.,Curso de Quimica | And 4 more authors.
Ceramica | Year: 2014

Through the polymeric precursor method were synthesized samples Ca0.98Sr0.01X0.01TiO3 (X= Eu3+, Sm3+ and Pr3+), which under different heat treatments were obtained with levels of distinct structural order-disorder. The synthesized materials were characterized by X-ray diffraction, confirming the obtaining of ahomogeneous material with perovskite-type orthorhombic structure. This characterization allowed evaluating the average crystallite size of the samples that varies depending on the rare-earth ion. The results of photoluminescence emission confirmed the presence of this optical phenomenon at room temperature and its relationship to the level of order-disorder structural system. The photoluminescence emission is more intense in samples annealed at 500 ° C (independent on the dopant ion), the variation of the dopant influence on the emission intensity due to charge transfer between the host and emitting rare-earth ion, where the doped with Pr3+ ion has charge transfer more efficient and hence more intense emission in the photoluminescence. Another factor that favors the optical property of the samples is the charge compensation, as it contributes to the increase in structural disorder due to formation of Ca2+ vacancies.


Santana Andrade G.R.,Programa da Pos graduacao em Ciencia e Engineering de Materiais | Da Cunha Nascimento C.,Programa da Pos graduacao em Ciencia e Engineering de Materiais | Da Cunha Nascimento C.,Instituto Federal Of Educacao | Xavier P.A.,Programa de Pos graduacao em Quimica | And 3 more authors.
Optical Materials | Year: 2014

CdS and ZnS nanocrystals were grown over specific binding sites onto a thiolated silica-gel aiming to favor defect emission processes. This strategy was found to be effective in yielding ZnS nanocrystals with simultaneous blue and blue-green emissions owing to different types of defects. The effects of doping with copper ions have been observed on the photoluminescence properties. The intensity of defect-related emissions from both semiconductor nanocrystals increased with increasing dopant concentration from 0.25% to 1.5% copper, consistent with the presence of sulfur vacancies. Higher dopant concentrations lead to concentration quenching. © 2014 Elsevier B.V. All rights reserved.


Vasconcelos D.A.,Programa de Pos graduacao em Quimica | Kubota T.,Programa de Pos graduacao em Quimica | Kubota T.,Laboratorio Of Sintese Of Polimeros Derivados Of Carboidratos | Santos D.C.,Programa da Pos graduacao em Ciencia e Engineering de Materiais | And 3 more authors.
Carbohydrate Polymers | Year: 2016

Here we report the use of β-cyclodextrin polyurethane nanosponges cross-linked with 1,6-hexamethylene diisocyanate as a template for the preparation of Aun quantum clusters, by the core-etching of glutathione-capped Au nanoparticles. The study of temporal evolution of the core-etching process using different Au concentrations indicated that formation of Aun clusters embedded in the nanosponge is favored by the use of lower Au concentrations, since it began at shorter times and lead to higher cluster loading. An estimation of the number of Au atoms based on the maximum photoluminescence wavelength suggested that, depending on the Au concentration and the core etching time, clusters with 11-15 atoms were formed. After excluding the possibility of an inclusion complex formation, evaluation of the catalytic activity of nanosponge-loaded Aun clusters toward the reduction of 4-nitrophenol has shown that the reaction is catalyzed by the Aun clusters with no induction time, following the Langmuir-Hinshelwood kinetic model. © 2015 Elsevier Ltd. All rights reserved.


Da Costa L.M.,Programa de Pos Graduacao em Quimica | Amorim R.M.,Programa de Pos Graduacao em Quimica | Amorim R.M.,Instituto Nacional Of Propriedade Industrial | De Macedo Cruz M.T.,Federal University of Rio de Janeiro | And 2 more authors.
Computational and Theoretical Chemistry | Year: 2012

Quantum chemical calculations using the B3LYP/6-31+G(d) method were carried out for the pentaaqua Ca 2+-phosphoryl complexes [Ca(H 2O) 5L] 2+. Two sets of phosphoryl ligands were studied: with trivalent (OPR and OPPhR) and with pentavalent (OP(R) 3 and OP(PhR) 3) phosphorous atoms, where RNH 2, OCH 3, OH, CH 3, H, F, Cl, Br, CN and NO 2. In the OPPhR and OP(PhR) 3 cases the R group is bonded to the para position of a phenyl ring. The nature of the metal-ligand bond was investigated with an energy decomposition analysis (EDA). The decomposition of the bond energy into its five components (electrostatic, exchange, polarization, dispersion and repulsion) shows that the electronic nature of the substituent is strongly correlated with the total interaction energy. Complexes with electron donating substituents (RNH 2, OCH 3, OH, CH 3) have the strongest metal-ligand interaction energies. The electrostatic, polarization and repulsion energies are the components of the interaction most strongly affected by inductive and resonance effects of the R groups, whereas the exchange and dispersion components are almost constants along each set of complexes. Both electrostatic and the covalent terms are important components to dictate the magnitude of the interaction. NBO analysis shows that the nature of the substituent is also correlated with the s/p character of the orbital in the ligand that is responsible for the interaction. © 2012 Elsevier B.V.


PubMed | Programa de Pos graduacao em Quimica, Programa da Pos graduacao em Ciencia e Engineering de Materiais and Laboratorio Of Sintese Of Polimeros Derivados Of Carboidratos
Type: | Journal: Carbohydrate polymers | Year: 2015

Here we report the use of -cyclodextrin polyurethane nanosponges cross-linked with 1,6-hexamethylene diisocyanate as a template for the preparation of Aun quantum clusters, by the core-etching of glutathione-capped Au nanoparticles. The study of temporal evolution of the core-etching process using different Au concentrations indicated that formation of Aun clusters embedded in the nanosponge is favored by the use of lower Au concentrations, since it began at shorter times and lead to higher cluster loading. An estimation of the number of Au atoms based on the maximum photoluminescence wavelength suggested that, depending on the Au concentration and the core etching time, clusters with 11-15 atoms were formed. After excluding the possibility of an inclusion complex formation, evaluation of the catalytic activity of nanosponge-loaded Aun clusters toward the reduction of 4-nitrophenol has shown that the reaction is catalyzed by the Aun clusters with no induction time, following the Langmuir-Hinshelwood kinetic model.

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