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Fe2O3–SiO2 composites obtained by sol–gel synthesis

The present work deals with the synthesis of Fe2O3–SiO2 composites, obtained by embedding iron oxide particles in a silica matrix, through sol–gel method based on hydrolysis and condensation of a silicon alkoxide and thermal treatment. Methods employed in characterisation of the materials obtained at different iron concentration and at suitable thermal treatments are infrared spectroscopy, X-ray diffraction analysis and SEM analysis. In purpose to evaluate magnetic properties of these composites, static magnetic and Mossbauer spectra measurements were carried out.

Synthesis, Spectroscopic and Self-Assembling Characterization of Novel Photoactive Mixed Aryl-Substituted Porphyrin

The present report is concerned with the designing, obtaining and characterization of novel light -sensitive molecules, belong- ing to second generation meso-tetraarylporphyrin derivatives. A new structure of A3B porphyrin, namely: 5-(4-pyridyl)-10,15,20-tris(4- phenoxyphenyl)-porphyrin was synthesized in fair yield by multicomponent reaction and characterized by 1 H-NMR, FT-IR, UV-vis, fluo- rescence, MS, HPLC, TLC, AFM and XRD techniques. Tailoring porphyrins by introducing a pyridyl substituent in one of the meso-aryl groups confers some degree of hydrophilicity and may cause absorption and fluorescence emission bands in the long wavelength region. Besides, as it was expected, because of the relatively rigid planar structure, due to substitution with three phenoxy substituents, this por- phyrin is characterized by a value of 0.219 for fluorescence quantum yield, a higher value in comparison with usual porphyrins. In solu- tion, by UV-vis and fluorescence spectra, the effects of pH and concentration upon H and J aggregates of the porphyrin are discussed. X- ray diffraction and atomic force microscopy investigations proved that this newly synthesized porphyrin is able to generate stable self- assembly in preferred orientations, such as multilayer of lamellar triangles, densely packed and homogeneous, with dimensions around 440 nm, finally forming pyramidal type structures. CHCl3 favors the spiral organization of the pyramids so that rings and even tubes of various diameters ranging from 1μm to 4.5 μm were formed.

Optical properties of ZnAl2O4 nanomaterials obtained by the hydrothermal method

Nanocrystalline zinc aluminate, ZnAl2O4, was obtained by the hydrothermal method. After hydrothermal treatment the samples were heated at different temperatures. The precursors used in the hydrothermal synthesis of ZnAl2O4 were zinc nitrate hexahydrate and aluminum nitrate nonahydrate. Sodium hydroxide was used as a basic source. The obtained samples were analyzed by x-ray diffraction. The optical properties of nanocrystalline zinc aluminate were also determined by photoluminescence and photoluminescence excitation measurements taken with a conventional lamp as the excitation source and by UV/vis/NIR spectroscopy.

Nanostructured Glasses Based on Hybrid Silica Materials Incorporating a New Asymmetrical Phenyl-Substituted Porphyrin

The new asymmetrical, phenyl substituted porphyrin structure, namely: 5,10,15-tris(3-hydroxy-phenyl)-20- (3,4-dimethoxy-phenyl)-21H,23H-porphyrin, along with the nanostructured glasses and silica-based nanoparticles embedded with this compound were synthetized and characterized as to be designated for potential use in construction of advanced optoelectronic devices or electrochemical sensors. This porphyrin was synthesized by a multicomponent Adler- Longo type reaction using two different substituted aldehydes, and next characterized by HPLC, TLC, MS, UV-vis, fluorescence spectroscopy, AFM, 1 H-NMR and 13 C-NMR analysis. The observed changes in UV-vis and emission spectra were also discussed in terms of various pH conditions. The series of novel porphyrin-silica nanomaterials have been prepared by using silica matrices obtained in two variable sol-gel processes, i.e. via the one step acid- or two steps acid- base-catalyzed hydrolysis and condensation of tetraethylorthosilicate. Especially, the hybrid monolithic glass nanomaterials obtained here via the one step acid-sol-gel procedure exhibited a high intensity of the emission spectra bands and, besides, a very sharp bathochromic shift in the red region towards 723 nm, thus making also these nanoparticles as the valuable source of potential second generation photosensitizers. In the atomic force microscopy (AFM) measurements this hybrid nanomaterials displayed the spherical and highly monodispersed particles of ultra low size (less than 70 nm and with an average height of 20 nm), controlled shape, high porosity, and superior stability as the potential water-insoluble photosensitizers.

Molecular Properties and Aggregation of Porphyrin-modified Polysiloxane in Solutions

Molecular properties and aggregation behavior of a polysiloxane with grafted side chain groups consisting of asymmetrical hydroxy-functionalized porphyrin were studied in dilute solutions. In order to understand the mechanism of aggregation of the polymeric porphyrin derivatives, several analyses of chloroform solutions were performed permitting comparison of the data obtained by means of different techniques. Molar mass and hydrodynamic size of the macromolecules were obtained using the methods of analytical ultracentrifugation, isothermal translational diffusion, and viscometry. Long distance interactions between macromolecules in dilute solutions were detected with static light scattering. With increasing the concentration of the solutions, the electronic and fluorescence spectra bands assigned to generation of H and J aggregates became apparent. The organization of aggregates, which seemed to be favored by chloroform, was visualized by atomic force microscopy images that displayed sponge-like morphology, small triangular particles, characteristic of H aggregates, and nano or micro-structured ring geometries obtained by the side-by-side J-process, coexisting together.