Synthesis, characterization and dye adsorption of ilmenite nanoparticles

FeTiO₃ nanoparticles (nano-FeTiO₃ or nano-ilmenite) can be synthesized by the sol-gel method. In this study, the physical properties and dye adsorption characteristics of nano-FeTiO₃ are investigated. A synthesized nano-ilmenite has a particle size of approximately 20 to 60 nm with a polycrystalline structure. The FeTiO₃ nanoparticles exhibit weak ferromagnetism and show high adsorption capacity for methylene blue. Experimental data are fitted to pseudo-first-order and pseudo-second-order equations; the pseudo-first-order model is found to be more suitable. It also suggests that the Langmuir isotherm is more adequate than the Freundlich isotherm in simulating the adsorption isotherm of organic dye. The maximum adsorption capacity is 71.9 mg/g, therefore, the magnetic FeTiO₃ nanoparticles show a considerably high adsorption capacity for organic dyes in a solution. These findings indicate that the nano-ilmenite is an effective material for dye removal and can be used to alleviate environmental problems.     

Enhancement of the emission from TeO2 nanorods by encapsulation with ZnO

TeO₂‐core/ZnO‐shell nanorods were synthesized by a two–step process comprising thermal evaporation of Te powders and atomic layer deposition of ZnO. Scanning electron microscopy images exhibit that the core‐shell nanorods are 50 ‐ 150 nm in diameter and up to a few tens of micrometers in length, respectively. Transmission electron microscopy and X‐ray diffraction analysis revealed that the cores and shells of the core‐shell nanorods were polycrystalline simple tetragonal TeO₂ and amorphous ZnO with ZnO nanocrystallites locally, respectively. Photoluminescence measurement revealed that the TeO₂ nanorods had a weak broad violet band at approximately 430 nm. The emission band was shifted to a yellowish green region (∼540 nm) by encapsulation of the nanorods with a ZnO thin film and the yellowish green emission from the TeO₂‐core/ZnO‐shell nanorods was enhanced significantly in intensity by increasing the shell layer thickness. The highest emission was obtained for 125 ALD cycles (ZnO coating layer thickness: ∼15 nm) and its intensity was much higher than that of the emission from the uncapsulated TeO₂ nanorods. The origin of the enhancement of the emission by the encapsulation is discussed in detail. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A ZnO/TiO2 composite nanorods photoanode with improved performance for dye‐sensitized solar cells

A dye‐sensitized solar cell (DSSC) based on ZnO/TiO₂ composite nanorods (NRs) photoanode is fabricated. The power conversion efficiency (PCE) of the ZnO/TiO₂ composite NRs film DSSC is 4.36%, which is obviously higher than that of DSSCs based on pure TiO₂ NRs (0.6%) and ZnO NRs (3.10%). The enhanced performance of ZnO/TiO₂ composite NRs film DSSC can be attributed to the combined effects of ZnO and TiO₂ NRs. In this architecture, the thick ZnO NRs overlayer offers a large surface area for enough dye absorption, while the thin TiO₂ NRs underlayer not only offers a direct and quick pathway for photoinjected electron transfer along the photoanode but also acts as a blocking layer, which effectively hinders the direct contact between the substrate and the electrolyte resulting in lower carrier recombination.     

On the synthesis and characterization of La doped MgB2 superconductor

We report the synthesis of La doped MgB₂ superconductors with nominal compositions Mg_1‐xLa_xB₂ (with x = 0.01, 0.03, 0.05, 0.07) by solid state reaction at ambient pressure. A special encapsulation technique has been used by us to prepare high quality superconducting MgB₂ samples. The bulk polycrystalline samples possess superconducting transition temperature T_c(R=0) ranging between 36‐39 K. It has been found that transport critical current density J_c of the samples change significantly with the doping level of La. A high transport (J_c) value ∼1.9 x 10³ A/cm² at 15 K has been achieved for Mg_0.97La_0.03B₂ sample. The XRD and TEM investigations indicate that the samples prepared by encapsulation method are devoid of MgO, which is generally found when synthesis of MgB₂ is done through sintering of Mg and B powders. The detailed microstructural investigations of Mg_0.97La_0.03B₂ specimens by transmission electron microscopy (TEM) reveal the presence of partial dislocation network, moiré fringes and superlattice structure in the as synthesized samples. The higher transport critical current density observed in Mg_0.97La_0.03B₂ superconductor has been attributed to the partial dislocations which are capable of providing pinning centres. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Fe2O3 Doping on TiO2 Electrode for Enhancement Photovoltaic Efficiency of Dye-Sensitized Solar Cells

In this work, we report for the first time the improvement of the photovoltaic characteristics of dye-sensitized solar cells (DSSCs) by doping TiO₂ with Fe₂O₃. DSSCs were fabricated using various percentages of Fe₂O₃-doped TiO₂ composite nanoparticles. The Fe₂O₃-doped DSSCs exhibited a maximum conversion efficiency of 5.76% because of the effective electron transport. DSSCs based on Fe₂O₃-doped TiO₂ films showed better photovoltaic performance than cells fabricated with only TiO₂ nanoparticles. This result was attributed to the prevention of recombination between electrons in the TiO₂ conduction band with the dye or electrolytes. A mechanism was suggested based on impedance results, which indicated improved electron transport at the interface of the TiO₂/dye/electrolyte.     

Synthesis of ORMOSIL silica/rhodamine 6G: Powders and compacts

The sol-gel method was used to prepare a silica matrix with rhodamine 6G. This dye was chemically bonded to silica matrix by grafting reactions, obtaining ORMOSIL/R6G powder, at two different concentrations, 0.03 mmol of dye/g silica and 0.009 mmol of dye/g silica, called ORMOSIL1 and ORMOSIL2, respectively. Fluorescent compacts were also obtained, through the high-pressure processing of these powders, at 7.7 GPa and room temperature. The microstructure, chemical composition and thermal stability of the powders and compacts were comparatively studied, by N₂ adsorption/desorption isotherms, FTIR spectroscopy, thermogravimetric analyses (TGA) and elemental analyses for carbon, hydrogen, and nitrogen (CHN). The optical behavior was studied by fluorescence spectroscopy. The ORMOSIL1 compacts were completely opaque showing that the compaction was not effective, due to the high organic grade incorporated into the starting ORMOSIL1 powder. The ORMOSIL2 compacts were transparent showing an effective compaction, which are in agreement to the great surface area and porosity reduction. Additionally, it was observed in TGA results, the retention of the organics in these samples up to temperatures near 300 °C. The fluorescence emission showed that the dye was dispersed in molecular level in all samples.     

Encapsulation Characteristics of Cavitand Type Tetrabromo-Functionalized Resorcin[4]arenes in the Crystal Structure

Single crystal X-ray diffraction analysis of upper rim functionalized tetrabromo-resorcin[4]arenes are presented and their guest encapsulation abilities are discussed. The Br-atoms either attached directly to resorcinarene rim or extended by methylene group (CH₂–Br). The substituents on the upper-rim plays an important role in the guest encapsulation characteristic of the resorcinarene cavity. In the crystal structure the host–guest supramolecular systems were stabilized by C–H?O, C–H?π and C?H···Br nonbonding interactions. The Hirshfeld surfaces analysis and the related 2D fingerprint plots provided qualitative and quantitative account of the various supramolecular non-bonding interactions present within the crystal.

Graphic Abstract

Guest encapsulation characteristic of tetrabromo-functionalized resorcin[4]arenes.

     

Optical properties of Rh6G molecules ordering in the silica- and titanium dioxide mesoscopic sol-gel films

The sol-gel method has been employed for the fabrication high quality mesostructured hybrid films. The effect of the nature of the matrix on the absorption and fluorescence spectra was found. It was shown that the aggregation of the dye molecules is significantly weaker in the SiO₂-P123/Rh6G based hybrid films. In case of TiO₂-P123/Rh6G films, the loss of isosbestic points in the absorption spectra in a TiO₂ matrix suggests the formation of higher aggregates and spectra concern mostly the red shift of the fluorescence maximum. Optical properties and exited state dynamic of Rh6G make the film a good candidate for producing photonic materials.     

Phase-matched frequency doubling in a LiNbO3-sapphire waveguide

An rf-sputtered thin film of LiNbO₃ on a sapphire substrate was used as a waveguide for optical frequency doubling. Employing a Nd:YAG laser and a tunable dye laser, whose output was used to pump a stimulated Raman cell, the TM^ω₀→TM^2W₂ up-conversion process was investigated in detail and the phase matched nature of this process was demonstrated. The conversion efficiency was estimated to be about 10^?3.     

Dark-degradation of reactive brilliant blue X-BR in aqueous solution using α-Fe2O3

The precursor of Fe₂O₃ was prepared by chemical precipitation method with sodium hydroxide (NaOH) and iron chloride hexahydrate (FeCl₃ · 6H₂O). The samples annealed at different temperature were characterized by means of X-ray diffraction (XRD) and infrared absorption spectroscopy (IR). Degradation of reactive dye in aqueous solution was used to evaluate the catalytic performance of the Fe₂O₃. The experiments of degradation had been done in dark place. The experimental results indicated that the catalytic property of the precursor of α-Fe₂O₃ was excellent. The mechanism of the degradation of reactive dye in aqueous solution was investigated by comparing the data in the absence and presence of oxygen. The precursor of α-Fe₂O₃ annealed at 300 °C was the best. The degradation rate of reactive brilliant blue X-BR could exceed 95% in 8 min at 25 °C when the concentration of the precursor of α-Fe₂O₃ was 0.1 g/L. The mechanism of the catalytic oxidation reaction was investigated by comparing the X-BR catalytic oxidation data in the absence and presence of oxygen.     

Polymer dye-containing nanocomposites as photocatalysts

A significant improvement of photocatalytic efficiency is achieved by the synthesis of TiO₂/SiO₂ nanocomposites where silica matrix provides the transport of reagents to TiO₂ nanoparticles via porous structure, generation of the new active sites and thermal stability. The semiconductive films contained 10 or 30% of TiO₂ in silica matrix are synthesized by sol-gel method using concentrated anatase titania colloid. The complex composites consisted of i) the Acridine Yellow dye molecules and the polyepoxypropyl carbazole; ii) the azobenzene containing polymer covered onto the titania/silica films are obtained as photocatalytic materials. Photocatalytic activity of the composites is tested via the reduction of dichromate ions.     

Characteristics of Dye-Sensitized Solar Cells Using TiO2 Nanotube Arrays with Large Surface Area by Spin-Coating Nanoparticle

Highly ordered TiO₂ nanotube arrays (TNAs) fabricated by anodization are very attractive for use in dye-sensitized solar cells (DSSCs), because of their superior charge percolation and slow charge recombination. Highly ordered, vertically aligned TNAs have been prepared by three-step anodic oxidation. In this work, we investigated such strategies for improving the efficiency of DSSCs. Based on one of these approaches, oxide semiconductors in the form of a TNA were used as a novel method for improving electron transport through a film. A solution containing an appropriate amount of TiO₂ nanoparticles was prepared, and the mixed slurry was spin-coated on a TNA film. The coated film provided a large surface area for dye adsorption. The DSSCs achieved a light-to-electric energy conversion efficiency of 5.91% under simulated solar irradiation at 100 mW/cm² (AM 1.5).     

Aggregation of a Cationic Cyanine Dye Intercalated in the Interlayer Space of a Layered Titanate Na2Ti3O7

Abstract

A cationic cyanine dye. 1,1′-diethyl-2,2′-cyanine (PIC), was successfully intercalated into Na₂Ti₃O₇ by a guest-exchange method using a propylamine/Ti₃O₇ intercalation compound as the intermediate. Based on the XRD and chemical analytical results, it was presumed that PIC was densely packed in the interlayer space with the short axis of its quinoline-ring almost perpendicular to the host layer. Spectroscopic results revealed that the PIC formed J-aggre-gates even in the restricted space between the titanate layers.     

Orientational Order and Linear Dichroism of a Water Soluble Porphine in a Lyotropic Nematic Liquid Crystal

Aqueous lyotropic nematic liquid crystals can be homogeneously oriented by magnetic fields and are therefore well suited to be used as anisotropic solvents for optical polarization studies of water soluble dye molecules. The potassium laurate (KL)/KCl/H₂O nematic phase, composed of rod-like or cylindrical micelles, was used as a matrix for the study of orientational order and linear dichroism of a substituted free-base porphine (TPPS₄). The results indicate that a significant portion of porphine molecules are incorporated into the micelles with their planes on the average perpendicular to the optic axis of the lyotropic rods. The order parameter of TPPS₄ is much higher in this system than in other nematic lyophases such as KL/decanol/H₂O in which preferential hydrogen bonding occurs between TPPS₄ molecules and the hydroxyl groups of decanol molecules which presumably occupy the surface of the cylindrical micelles. All observed electronic transitions in the 350-700 nm range are found to be polarized in the plane of the porphine ring.     

Order Parameters of β-Substituted Anthraquinone Dyes I: 1-Amino-4-Hydroxyanthraquinone Derivatives

A study is presented of the optical order parameters and spectroscopic properties of I-amino-4-hydroxyanthraquinone derivatives containing various substituents in the 2-position in a nematic liquid crystalline mixture composed of cyanophenylcyclohexane derivatives. The results are discussed in terms of the effects of the dye structure on the order parameters. By introducing a-SCH₂-group into the 2-position, magenta dyes have been obtained which show high order parameters and solubilities. In addition, preliminary data on the solubility and photostability of the dyes are reported.     

Emission behavior of naphthalimide-coumarin cassette

ABSTRACT

In this contribution, a dye (C₈-alkyl substituted Naphthalimide-Coumarin, CNC) with naphthalimide and coumarin incorporated together with -NHN = bridge unit. The compound was fully characterized by NMR and HRMS spectroscopic techniques. Highly emissive character was investigated in detail in various polar environments. The emission maximum varied from 430 to 470 nm. In polycarbonate film, CNC is also highly emissive with 560 nm emission peak. While in sold, the emission maximum was further shifted to 580 nm due to the more tightly packing mode than that in film. The C₈-alkyl substitution enhances the solubility of CNC and also contributes most to its solid emission.     

Mixed metal oxide nanocomposites derived from layered double hydroxides as photocatalysts for C.I. Basic Blue 3 degradation under UV light

In this research we report synthesis of the heterostructure Mg‐Al‐Zn mixed metal oxide (ZnO/MMO) nanocomposite photocatalysts derived from Zn(OH)₂/Mg‐Al‐layered double hydroxides (ZLDHs) precursors. The obtained samples were characterized by the X‐ray diffraction (XRD), FT‐IR, BET surface area, ICP and TG/DTG methods. The chemical compositions and morphology of the synthesized materials were investigated by the energy dispersive X‐ray analysis (EDX) and the transmission electron microscopy (TEM). The results reveal that at the reaction time 96 h, ZLDH has the highest crystalinity which was confirmed by the X‐ray diffraction spectra. The calcined samples at 500, 600 and 700 °C for 4 h show that the crystallinity of the nanocomposite improves with the increase of calcination temperature. The photocatalytic activities of synthesized nanocomposites were compared for the degradation of C. I. Basic Blue 3 (BB3) dye under UV illumination in aqueous solution. Among the synthesized nanocomposites, ZnO/MMO calcined at 700 °C shows the highest efficiency towards the removal of dye. The effect of UV illumination on the stability of ZnO in ZnO/MMO nanocomposite and pure ZnO was also investigated. The results showed that the photostability of ZnO in ZnO/MMO nanocomposite is increased compared to the pure ZnO.     

Fluorescence Lifetimes and Site-selective Photochemistry of Anthracene Crystals Doped with 2-hydroxyanthracene

The rise and decay of the prompt fluorescence of 2-hydroxyanthracene (2-OHA) doped anthracene crystals have been investigated at 8 K following excitation with frequency-doubled pico-second pulses from a synchronously pumped dye laser. By studying fresh crystals and crystals irradiated with u-v light at 298 K so as to introduce the photodimer, the roles played by the two different sites (O₈) and (O₉) occupied by the 2-OHA, by the X-traps and by other structural defects in fluorescence and energy transfer have been elucidated. Energy transfer between impurity sites (O₈ and O₉) is slow whereas that between guest associated X-traps and impurity is rapid. For the O₉ site, both before and after photodimerization, a simple time-independent energy transfer occurs from the anthracene host to the 2-OHA guest. The transfer to O₈ sites is associated with the presence of an extended region of disorder associated with the impurity. Such regions are excited directly.     

Microwave-assisted green synthesis of SnO2 nanoparticles and their optical and photocatalytic properties

Abstract

In this study, SnO₂ has been synthesized using Andrographis Paniculata (A. Paniculata) by microwave-assisted method. It is also characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). It exhibits the tetragonal structure with average crystallite size of 27?nm. The stretching vibration peak of Sn-O-Sn is 670?cm^?1. SEM reveals the formation of nanoparticles. The bandgap was estimated by the tauc’s relation as 3.52?eV from the UV-Visible (UV-Vis) spectra. Biosynthesized SnO₂ nanoparticles show excellent photocatalytic activity against Congo red dye under sunlight irradiation.     

Dielectric characteristics of neodymium heptamolybdate crystals grown by gel encapsulation technique

Results obtained from the dielectric studies of neodymium heptamolybdate crystals grown in the system Nd(NO₃)₃ –MoO₃ –NH₄OH– HNO₃ —Na₂SiO₃ by gel encapsulation technique are presented. The variation of dielectric constant (ε′), dielectric loss (tanδ) and conductivity (σ) with frequency at different temperatures is studied. The dielectric constant of the material increases sharply, attains a peak value and then decreases rapidly, as material's temperature rises from room temperature to higher degrees. The temperature at which the peak value is attained is the transition temperature of the material. Dielectric loss (tan δ) follows almost a similar behaviour. The conductivity (σ) is also found to be temperature-and frequency-dependent. This sharp rise in ε′ is attributed to the contribution from space charge polarization. Theoretically obtained data using the expression ε′ = a₀ + a₁ T² and —In σ = a + b(T — T₀)² for T < T₀) fits very well with the experimentally obtained data indicating that space charge polarization increases as some power of temperature larger than one.