Er:YAl(3)(BO(3))(4) glassy thin films from polymeric precursor and sol-gel methods: Waveguides for integrated optics

This paper presents the characterization of single-mode waveguides for 980 and 1550 nm wavelengths. High quality planar waveguide structure was fabricated from Y(1-x)Er(x)Al(3)(BO(3))(4) multilayer thin films with x = 0.02, 0.05, 0.1, 0.3, and 0.5, prepared through the polymeric precursor and sol-gel methods using spin-coating. The propagation losses of the planar waveguides varying from 0.63 to 0.88 dB/cm were measured at 632.8 and 1550 nm. The photoluminescence spectra and radiative lifetimes of the Er(3+) (4)I(13/2) energy level were measured in waveguiding geometry. For most samples the photoluminescence decay was single exponential with lifetimes in between 640 mu s and 200 mu s, depending on the erbium concentration and synthesis method. These results indicate that Er doped YAl(3)(BO(3))(4) compounds are promising for low loss waveguides. (C) 2009 Elsevier B.V. All fights reserved.

Effect of Lithium Nitrate on the Alkali-Silica Reaction Gel

Lithium nitrate has been used to prevent and to mediate the expansion caused by alkali-silica reaction (ASR). However, there is limited information on how it affects the existing reaction products caused by ASR. The aim of the present work is to determine the modifications caused by the LiNO3 treatment on the structure of the gel produced by ASR. ASR gel samples obtained from a concrete dam were exposed to an aqueous solution of lithium nitrate and sodium hydroxide with molar LiNO3/NaOH = 0.74, and the resulting products were analyzed by X-ray diffraction, infrared spectroscopy, and solid-state nuclear magnetic resonance of Si-29, Na-23, and Li-7. The treatment of the gel samples produces significant structural modifications in ASR products. A new amorphous silicate compound incorporating Li+ ions is formed, with an average silicate network that can be described as linear in contrast with the layered structure of the original gel. This elimination of the layered structure after the Li-based treatments may be related to the reduction of the tendency of the gel to expand. Also, several crystalline compounds containing potassium indicate the release of this species from the original ASR gel.

Magnetic resonance study of a vanadium pentoxide gel

In this work we report results from continuous-wave (CW) and pulsed electron paramagnetic resonance (EPR) and proton nuclear magnetic resonance (NMR) studies of the vanadium pentoxide xerogel V2O5:nH(2)O (n approximate to 1.6). The low temperature CW-EPR spectrum shows hyperfine structure due to coupling of unpaired V4+ electron with the vanadium nucleus. The analysis of the spin Hamiltonian parameters suggests that the V4+ ions are located in tetragonally distorted octahedral sites. The transition temperature from the rigid-lattice low-temperature regime to the high temperature liquid-like regime was determined from the analysis of the temperature dependence of the hyperfine splitting and the V4+ motional correlation time. The Electron Spin Echo Envelope Modulation (ESEEM) data shows the signals resulting from the interaction of H-1 nuclei with V4+ ions. The modulation effect was observed only for field values in the center of the EPR absorption spectrum corresponding to the single crystals orientated perpendicular to the magnetic field direction. At least three protons are identified in the xerogel by our magnetic resonance experiments: (I) the OH groups in the equatorial plane, (ii) the bound water molecules in the axial V=O bond and (iii) the free mobile water molecules between the oxide layers. Proton NMR lineshapes and spin-lattice relaxation times were measured in the temperature range between 150 K and 323 K. Our analysis indicates that only a fraction of the xerogel protons contribute to the measured conductivity.

Sol-gel prepared AlPO(4) with incorporating Rhodamine 6G

Rhodamine 6G (RH6G) laser dye-doped AlPO(4) xerogel and glass were prepared via a simple sol-gel route by one-step process and two-step process, respectively. The aggregating behavior of dyes in xerogel and glass was studied by excitation and emission spectra. The results indicated the dye aggregates become significantly weak in AlPO(4) glass than in xerogel, which might be attributed to the enhanced interactions between dye and AlPO(4) network as well as the nano-scale separation of dye by the mesoporous structure of AlPO(4) glass. The (27)Al MAS NMR of AlPO(4) glass confirms the interaction of RH6G with AlPO(4) glass network. Incorporation of RH6G into AlPO(4) glass converts Al(4) to Al(6) units, resulting in the increase of Al(6) concentration with the doped RH6G concentration. (C) 2010 Elsevier B.V. All rights reserved.

Tryptophan photooxidation promoted by new hybrid materials prepared by condensation of naphthalene imides with silicate by the sol-gel process

Three novel hybrid organic/inorganic materials were synthesized from 4-substituted (NO(2), Br, H) 1,8-naphthalene imide-N-propyltriethoxysilane by the sol-gel process. These materials were obtained as a xerogel and partially characterized. The ability to photosensitize the oxidation and degradation of tryptophan indole ring by these materials was studied through photophysical and photochemical techniques. Although the derivatives containing Br and NO(2) as substituent do not cause efficient tryptophan photodamage, the hybrid material obtained from 1,8-naphthalic anhydride is very efficient to promote tryptophan photooxidation. By using laser flash photolysis it was possible to verify the presence of naphthalene imide transient radical species. The presence of oxygen causes an increase of the yield of radical formation. These results suggest that the mechanism of photodegradation of tryptophan occurs by type I, i.e. the transient radical (TrpH(center dot+)) formed by the direct reaction of the triplet state of the naphthalene imide moiety with tryptophan. Thus a inorganic-organic hybrid material that can be used to promote the oxidation of biomolecules was obtained. (C) 2009 Elsevier B.V. All rights reserved.

Iron oxyhydroxide nanostructured in montmorillonite clays: Preparation and characterization

Akaganeite is a very rare iron oxyhydroxide in nature. It can be obtained by many synthetic routes, but thermohydrolysis is the most common method reported in the literature. In this work, akaganeite-like materials were prepared through the thermohydrolysis of FeCl(3)center dot 6H(2)O in water and suspensions containing clay minerals. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) data show that the clays determine the crystal phase and size of the iron oxyhydroxide crystals. According to XRD and FTIR data, beta-FeO(OH) (akaganeite) is the main metal oxyhydroxide phase. Considering the small basal spacing (d(0 0 1)) displacement observed when comparing the XRD patterns of pristine clays with the composites containing beta-FeO(OH), the iron oxyhydroxide should be mostly located on the basal and edge surfaces of the clay minerals. UV-Vis electronic absorption spectra indicate that the preferred phase of the iron oxyhydroxide is determined by the nature of the clay minerals. (C) 2010 Elsevier Inc. All rights reserved.

Preparation and characterization of colloidal Ni(OH)(2)/bentonite composites

A conductive and electrochemically active composite material has been prepared by the combination of bentonite and nickel hydroxide precursor sol. This material exhibits the characteristic intercalation properties of the clay component and the electrochemical and optical properties of nickel hydroxide. The clay particles seem to induce the aggregation of nickel hydroxide, leading to the formation of a layer of alpha-Ni(OH)(2) exhibiting needle like morphology. The composite forms stable films and has been conveniently used for the preparation of modified electrodes exhibiting intercalation and electrochemical properties, thus providing an interesting material for the development of amperometric sensors. (C) 2008 Elsevier Ltd. All rights reserved.

Luminescent nanoparticles of MgAl(2)O(4):Eu, Dy prepared by citrate sol-gel method

MgAl(2)O(4):Eu, Dy nanoparticles were prepared by citrate sol-gel method and thermally treated at 600, 700, 800 and 900 degrees C. The trivalent europium ion is partially reduced to the divalent state at 700 and 800 degrees C. Infrared spectra of the phosphors showed bands around 700 and 520 cm(-1) corresponding to the AlO(6) groups. X-ray diffraction patterns present sharp reflections of samples heated from 700 to 900 degrees C indicating the MgAl(2)O(4) spinel phase. Grain size in the range 20-30 nm were observed by measurement of transmission electron microscopy (TEM). The emission spectra of the phosphors show a broadened band at 480 nm assigned to the 4f(G)5d -> 4f(7) ((8)S(7/2)) transition of Eu(2+) ion overlapped to the (4)F(9/2) -> (6)H(15/2) transition of the Dy(3+) ion. Besides, the (4)F(9/2) -> (6)H(13/2) transition (579 nm) of Dy(3+) ion is overlapped with the (5)D(0) -> (7)F(0) (578 nm) and (5)D(0) -> (7)F(1) (595 nm) transitions from the Eu(3+) ion. Excitation spectra of the sample heated at 900 degrees C monitoring the excitation at 615 nm of (5)D(0) -> (7)F(2) transition of Eu(3+) ion exhibit a broad band assigned to the O -> Eu(3+) ligand-to-metal charge-transfer states (LMCT) around 280 nm. The samples present green persistent luminescence after exposure to UV radiation. The chromaticity coordinates were obtained from the luminescence emission spectrum. (C) 2008 Elsevier B.V. All rights reserved.

Oxidation of anilinium ions intercalated in montmorillonite clay by electrochemical route

Resonance Raman, FTIR, X-ray diffraction, UV-vis-NIR, electron paramagnetic resonance, X-ray absorption at Si K-edge and electron microscopy were employed for characterizing the products formed through electrochemical oxidation of intercalated anilinium ions inside the cationic montmorillonite (MMT) clay. The layer silicate structure was not affected by the anilinium oxidation between the layers. The intercalated products present only an electronic absorption band at 400 nm, very low conductivity (ca. 10(-7) S cm(-1)) and their Raman spectrum displays bands, with high relative intensities, assigned to the benzidine dication, indicating that this product was formed in high amount. Nevertheless, bands that can be correlated to phenazine-like segments and 1,4-phenylenediamine repeat units (PANI like segments) are also observed. The very low EPR signal indicates that diamagnetic species are predominant. All results are compared to those obtained by anilinium-MMT chemically oxidized by persulfate and the differences are pointed out. (C) 2008 Elsevier B.V. All rights reserved.

Spectroscopic study of the polymerization of intercalated anilinium ions in different montmorillonite clays

The polymerization of the intercalated aniline ions was studied in three different clays, Swy2-montmorillonite (MMT), synthetic mica-montmorillonite (Synl) and pillarized Swy2-montmorillonite (PILC). PANI is formed between the MMT and Syn1 clay layers, being confirmed by the shift of d(001) peak in the X-ray pattern. X-ray Absorption near to Si K edge (Si K XANES) data show that the structures of clays are preserved after the polymerization process and in addition to the SEM images show that morphologies of the clays are maintained after polymerization, indicating no polymerization in their external surface. UV-vis-NIR and resonance Raman data display that the PANI formed in Syn1 galleries has higher amount of phenazinic rings than observed for PANI intercalated in montmorillonite (MMT) clay. No polymer formation was detected in the PILC. N K XANES and EPR spectroscopies show the presence of azo and radical nitrogen in intercalated PAN! chains. Hence, the results are rationalized considering the structural differences between the clays for understanding the role of the anilinium polymerization within the clays galleries. (C) 2011 Elsevier B.V. All rights reserved.

Influence of neodymium ions on photocatalytic activity of TiO(2) synthesized by sol-gel and precipitation methods

Titanium dioxide with and without the addition of neodymium ions was prepared using sol-gel and precipitation methods. The resulting catalysts were characterized by thermal analysis, X-ray diffraction and BET specific surface area. Neodymium addition exerted a remarkable influence on the phase transition temperature and the surface properties of the TiO(2) matrix. TiO(2) samples synthesized by precipitation exhibit an exothermic event related from the amorphous to anatase phase transition at 510 degrees C, whereas in Nd-doped TiO(2) this transition occurred at 527 degrees C. A similar effect was observed in samples obtained using sol-gel method. The photocatalytic reactivity of the catalysts was evaluated by photodegradation of Remazol Black B (RB) under ultraviolet irradiation. Nd-doped TiO(2) showed enhanced photodegradation ability compared to undoped TiO(2) samples, independent of the method of synthesis. In samples obtained by sol-gel, RB decoloration was enhanced by 16% for TiO(2) doped with 0.5% neodymium ions. (C) 2010 Elsevier B.V. All rights reserved.

External polyacrylate-coating as alternative material for preparation of photopolymerized sol-gel monolithic column

Photopolymerized sol-gel monolithic columns for use in capillary electrochromatography were prepared in 125 mu m i.d. polyacrylate-coated fused-silica capillaries. The polyacrylate-coating, unlike the polyimide one, is transparent to the radiation used (approximate to 370 nm), and thus, no coating removal is necessary. This is a very important particularity since intrinsic capillary column characteristics, such as flexibility and mechanical resistance, are unchanged. A mixture containing metacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photoinitiator was irradiated at 370 nm for 20 min inside the capillaries to prepare the columns through sol-gel approach. The versatility and viability of the use of polyacrilate as a new capillary external coating were shown through preparation of two columns under different conditions, which were tested in electrochromatography for separation of standard mixture containing thiourea (marker compound), propylbenzene, phenanthrene and pyrene. (C) 2008 Elsevier B.V. All rights reserved.

Effect of sonication on the particle size of montmorillonite clays

This paper reports on the effect of sonication on SAz-1 and SWy-1 montmorillonite suspensions. Changes in the size of the particles of these materials and modifications of their properties have been investigated. The variation of the particle size has been analyzed by DLS (dynamic light scattering). In all cases the clay particles show a bimodal distribution. Sonication resulted in a decrease of the larger modal diameter, as well as a reduction of its volume percentage. Simultaneously, the proportion of the smallest particles increases. After 60 min of sonication, SAz-1 presented a very broad particle size distribution with a modal diameter of 283 nm. On the other hand, the SWy-1 sonicated for 60 min presents a bimodal distribution of particles at 140 and 454 nm. Changes in the properties of the clay suspensions due to sonication were evaluated spectroscopically from dye-clay interactions, using Methylene Blue. The acidic sites present in the interlamellar region, which are responsible for dye protonation, disappeared after sonication of the clay. The changes in the size of the scattering particles and the lack of acidic sites after sonication suggest that sonication induces delamination of the clay particles. (c) 2008 Elsevier Inc. All rights reserved.

Anticorrosive cerium-based coatings prepared by the sol-gel method

The development of efficient anti-corrosion and environmentally friendly coating systems are needed for the replacement of the highly toxic Cr-based conversion coatings for corrosion protection of aluminum alloys. In this study, we demonstrate that the direct application of ceramic cerium-based sol-gel coatings to AA7075-T6 substrates produces high-performance anti-corrosion layers. Electrochemical experiments and analyses of the microstructure demonstrate that the protective layers are very efficient for the passivation of the alloy surfaces operating as both passive and active barrier for corrosion protection.

Plasticized pectin-based gel electrolytes

Pectin is a natural polymer present in plants and, as all natural polymers has biodegradation properties. Chemically, pectin is a polysaccharide composed of a linear chain of 1 -> 4 linked galacturonic acids, which is esterified with methanol at 80%. The pectin-based gel electrolytes in a transparent film form were obtained by a plasticization process with glycerol and addition of LiClO(4). The films showed good ionic conductivity results, which increased from 10(-5) S/cm for the samples with 37 wt.% of glycerol to 4.7 x 10(-4) S/cm at room temperature for the sample with 68 wt.% of glycerol. The electrochemical behaviors of the samples were studied by electrochemical impedance spectroscopy (EIS), and Nyquist graphs are showed and discussed. The obtained pectin-based samples also presented good adherence to the glass, flexibility, homogeneity (SEM) and transparency (about 70% in the vis) properties. They are good candidates to be applied as gel electrolytes in electrochromic devices. (C) 2009 Elsevier Ltd. All rights reserved.