The stabilization of nanoparticles in solution is a challenge of major proportions, and avoiding ... more The stabilization of nanoparticles in solution is a challenge of major proportions, and avoiding the formation of aggregates and eventual coalescence of particles is directly linked to the conservation of its unique properties. In this work, we reported the synthesis of two hexakis-heterocyclic compounds, containing the tetrazole or 2-amino-1,3,4-thiadiazole group, respectively. The hexa-heterocyclic compounds were used in the synthesis and stabilization of Au and Ag nanoparticles. To obtain these molecules was used phosphonitrilic chloride trimer compound as core, which reacted with phenols properly substituted in the para position with either cyano or aldehyde group. The cyano group was successfully converted to the corresponding tetrazole using a 1,3-dipolar cycloaddition reaction with ammonium azide generated in situ. In the case of aldehyde derivative, it was converted to the corresponding thiosemicarbazone, which was further cyclized using FeCl3. Compounds were characterized b...
Ion-exchange polymers find wide applications in fuel cells, electro-organic synthesis, catalysis ... more Ion-exchange polymers find wide applications in fuel cells, electro-organic synthesis, catalysis and nanoparticles synthesis. We report on the use of aqueous solutions of an low molecular weight ion-exchange polymer containing phosphonic acid groups; the poly(p-acryloylaminobenzylphosphonic acid), for the synthesis of Ag particles at room temperature without using additional protective reagent. The process of formation of the Ag particles using the ion-exchange polymer start as an initial complexation of polymer to Ag+, followed by the very slow reduction of the metal ions to the Ag metallic. Our results indicate that this ion-exchange polymer is capable of protect the Ag particles in the solution, permitting us to obtain large-size cubes and rectangular prisms in colloidal solutions which are stable for several months.
... Chem. Soc., 125 (2003), p. 4430. [12] U. Pal and P. Santiago. J. Phys. Chem. ... [16] D. Bane... more ... Chem. Soc., 125 (2003), p. 4430. [12] U. Pal and P. Santiago. J. Phys. Chem. ... [16] D. Banerjee, JL Lao, DZ Wang, JY Huang, D. Steeves, B. Kimball and ZF Ren. Nanotechnology, 15 (2004), p. 404. [17] K. Vanhusden, CH Seager, WL Warren, DR Tallant and JA Voigt. Appl. Phys. ...
The optical constants of Si/ZnO composite films grown on quartz glass substrates were determined ... more The optical constants of Si/ZnO composite films grown on quartz glass substrates were determined in the spectral range 1.5–5.0 eV by spectroscopic ellipsometry using a rotating-analyzer ellipsometer. The structure of the samples was modeled by a two-phase (substrate–film) model, and the optical functions of the film were parameterized through different effective medium approximations. The results allowed us to estimate the microstructural film parameters, such as film thickness, the volume fractions of each of the constituents, and optical constants.
We studied the correlations among size, defects, and photoluminescence emissions in ZnO nanoparti... more We studied the correlations among size, defects, and photoluminescence emissions in ZnO nanoparticles of sizes ranging from 25 to 73 nm. The impurities and defects were characterized by Fourier-transform infrared spectroscopy and Raman spectroscopy. Particles of larger size revealed fewer surface impurities and enhanced E2 mode of hexagonal ZnO crystals, while the oxygen vacancy centers did not vary significantly with particle size. A simultaneous increase of excitonic luminescence and defect luminescence intensities with the increase of particle size is shown, indicating both emissions are subjected to nonradiative quenching by near surface defects. The study on the size-dependent green luminescence in our samples suggests that the emission might be a bulk property instead of having a surface origin in nanostructured ZnO. Two different radiative recombination processes are involved in the excitonic emission of ZnO. While the slow decay component (370 ps) did not depend on particle ...
Los cristales líquidos (CLs) son compuestos que presentan propiedades tanto de materiales líquido... more Los cristales líquidos (CLs) son compuestos que presentan propiedades tanto de materiales líquidos como de cristales. Hasta ahora no existe una predicción exacta de cuales moléculas o compuestos se comporten como CLs. Sin embargo los CLs tienen ...
The stabilization of nanoparticles in solution is a challenge of major proportions, and avoiding ... more The stabilization of nanoparticles in solution is a challenge of major proportions, and avoiding the formation of aggregates and eventual coalescence of particles is directly linked to the conservation of its unique properties. In this work, we reported the synthesis of two hexakis-heterocyclic compounds, containing the tetrazole or 2-amino-1,3,4-thiadiazole group, respectively. The hexa-heterocyclic compounds were used in the synthesis and stabilization of Au and Ag nanoparticles. To obtain these molecules was used phosphonitrilic chloride trimer compound as core, which reacted with phenols properly substituted in the para position with either cyano or aldehyde group. The cyano group was successfully converted to the corresponding tetrazole using a 1,3-dipolar cycloaddition reaction with ammonium azide generated in situ. In the case of aldehyde derivative, it was converted to the corresponding thiosemicarbazone, which was further cyclized using FeCl3. Compounds were characterized b...
Ion-exchange polymers find wide applications in fuel cells, electro-organic synthesis, catalysis ... more Ion-exchange polymers find wide applications in fuel cells, electro-organic synthesis, catalysis and nanoparticles synthesis. We report on the use of aqueous solutions of an low molecular weight ion-exchange polymer containing phosphonic acid groups; the poly(p-acryloylaminobenzylphosphonic acid), for the synthesis of Ag particles at room temperature without using additional protective reagent. The process of formation of the Ag particles using the ion-exchange polymer start as an initial complexation of polymer to Ag+, followed by the very slow reduction of the metal ions to the Ag metallic. Our results indicate that this ion-exchange polymer is capable of protect the Ag particles in the solution, permitting us to obtain large-size cubes and rectangular prisms in colloidal solutions which are stable for several months.
... Chem. Soc., 125 (2003), p. 4430. [12] U. Pal and P. Santiago. J. Phys. Chem. ... [16] D. Bane... more ... Chem. Soc., 125 (2003), p. 4430. [12] U. Pal and P. Santiago. J. Phys. Chem. ... [16] D. Banerjee, JL Lao, DZ Wang, JY Huang, D. Steeves, B. Kimball and ZF Ren. Nanotechnology, 15 (2004), p. 404. [17] K. Vanhusden, CH Seager, WL Warren, DR Tallant and JA Voigt. Appl. Phys. ...
The optical constants of Si/ZnO composite films grown on quartz glass substrates were determined ... more The optical constants of Si/ZnO composite films grown on quartz glass substrates were determined in the spectral range 1.5–5.0 eV by spectroscopic ellipsometry using a rotating-analyzer ellipsometer. The structure of the samples was modeled by a two-phase (substrate–film) model, and the optical functions of the film were parameterized through different effective medium approximations. The results allowed us to estimate the microstructural film parameters, such as film thickness, the volume fractions of each of the constituents, and optical constants.
We studied the correlations among size, defects, and photoluminescence emissions in ZnO nanoparti... more We studied the correlations among size, defects, and photoluminescence emissions in ZnO nanoparticles of sizes ranging from 25 to 73 nm. The impurities and defects were characterized by Fourier-transform infrared spectroscopy and Raman spectroscopy. Particles of larger size revealed fewer surface impurities and enhanced E2 mode of hexagonal ZnO crystals, while the oxygen vacancy centers did not vary significantly with particle size. A simultaneous increase of excitonic luminescence and defect luminescence intensities with the increase of particle size is shown, indicating both emissions are subjected to nonradiative quenching by near surface defects. The study on the size-dependent green luminescence in our samples suggests that the emission might be a bulk property instead of having a surface origin in nanostructured ZnO. Two different radiative recombination processes are involved in the excitonic emission of ZnO. While the slow decay component (370 ps) did not depend on particle ...
Los cristales líquidos (CLs) son compuestos que presentan propiedades tanto de materiales líquido... more Los cristales líquidos (CLs) son compuestos que presentan propiedades tanto de materiales líquidos como de cristales. Hasta ahora no existe una predicción exacta de cuales moléculas o compuestos se comporten como CLs. Sin embargo los CLs tienen ...
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