Controlled synthesis of CeO<Subscript>2</Subscript> nanoparticles using novel amphiphilic cerium complex precursors

Maleic anhydride was grafted by long-chain alcohols (1-hexadecanol, 1-octadecanol) to amphiphilic mono-L cis-butene dicarboxylates (L = hexadecyl, octadecyl), i.e., MAH, MAO, respectively. Subsequently, corresponding amphiphilic cerium complexes with these two mono-L cis-butene dicarboxylate ligands (Ce(L')₃, L'= MAH, MAO) were synthesized and behaved as the precursors to prepare CeO₂ nanoparticles for both of which can form nanosized micelle-like aggregates by special self-assembly in the wet chemical process. The nanoparticles were further characterized by Fourier transform-infrared spectroscopy (FTIR), Diffuse reflectance ultraviolet-visible spectra (DRUVS), scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffraction (XRD). Both the CeO₂ nanoparticles are in a cubic fluorite structure and present regular and well-dispersion club-like morphology with average particle size in the range of 40–70 nm. Besides, the strong ultraviolet–visible absorption for these CeO₂ nanoparticles can be found at the long-wavelength ultraviolet to visible region of 200–500 nm.     

Luminescence of CaGa<Subscript>2</Subscript>Se<Subscript>4</Subscript>:Eu crystals

We have studied photoluminescence and thermoluminescence (PL and TL) in CaGa₂Se₄:Eu crystals in the temperature range 77–400 K. We have established that broadband photoluminescence with maximum at 571 nm is due to intracenter transitions 4f⁶ 5d–4f⁷ (⁸S_7/2) of the Eu²⁺ ions. From the temperature dependence of the intensity (log I–10³/T), we determined the activation energy (E _a = 0.04 eV) for thermal quenching of photoluminescence. From the thermoluminescence spectra, we determined the trap depths: 0.31, 0.44, 0.53, 0.59 eV. The lifetime of the excited state 4f6 5d of the Eu²⁺ ions in the CaGa₂Se₄ crystal found from the luminescence decay kinetics is 3.8 μsec. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 112–116, January–February, 2009.     

Silver Nanoparticle-Enhanced Chemiluminescence Method for Determining Naproxen Based on Europium(III)-Sensitized Ce(IV)-Na<Subscript>2</Subscript>S<Subscript>2</Subscript>O<Subscript>4</Subscript> Reaction

A simple and sensitive chemiluminescence (CL) method coupled with flow-injection technique is proposed to determine naproxen (NAP). The method is based upon the enhancement of the weak CL signal arising from the reaction of Ce(IV) and Na₂S₂O₄ with Eu³⁺ to form the Eu³⁺-Ce(IV)-Na₂S₂O₄ system. The CL intensity was significantly increased by the introduction of NAP into this system in the presence of silver nanoparticles (Ag NPs). Examination of the recorded UV–vis spectra and fluorescence spectra indicated that the energy of the intermediate SO₂*, which originated from the redox reaction of Ce(IV) and Na₂S₂O₄, was transferred to Eu³⁺ via NAP and that the process was accelerated by Ag NPs due to their catalytic activity. Under the optimum conditions, the CL intensity was increased with increasing NAP concentration and the correlation was linear (r = 0.9992) over the NAP concentration range of 1–420 ng mL⁻¹. The limit of detection (LOD) was 0.11 ng mL⁻¹ with a relative standard deviation (RSD) of 1.15% for 5 replicate determinations of 200 ng mL⁻¹ NAP. The method was successfully applied to determine NAP in pharmaceutical and biological samples.     

Electronic structure,ferroelectricity and optical properties of CaBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript>

Using first-principles calculations based on density-functional theory in its local-density approximation, we investigated the Electronic structure, ferroelectricity and optical properties of CaBi₂Ta₂O₉ (CBT) for the first time. It is found that CBT compound has an indirect band gap of 3.114 eV and the O 2s and 2p states are strongly hybridized with the 6s states of Bi which belong to the (Bi₂O₂)²⁺ planes. The quite strong Ta–O and Bi–O hybridization is the primary source for ferroelectricity. Our results imply that the interaction between Bi and O is highly covalent. The anisotropy occurs mainly above 4 eV in the optical properties. The different optical properties have been discussed.     

TiO<Subscript>2</Subscript> nanotube height effect on the efficiency of dye-sensitized solar cells

Performance of dye-sensitized solar cells (DSSCs) based on TiO₂ nanotubes (NTs) filled with TiO₂ nanoparticles (NPs) was studied as a function of NT height (h). The NT height was varied in the range of 1.5–7.0 μm, while the NT diameter was kept constant at ~80 nm. The studies showed that DSSC efficiency, current density, and fill factor linearly increased with h and ranged in 1.76–6.5%, 3.62–13.2 mA/cm², and 0.66–0.76, respectively, within the h range studied. The electrochemical impedance spectroscopy was also performed to study DSSC electron transport properties. Based on both photovoltaic and electrochemical impedance spectroscopy data, the results were explained as being due to the increased dye loading that led to higher light-harvesting efficiency.     

Electrical properties,equivalent circuit,and dielectric relaxation studies on [(C<Subscript>3</Subscript>H<Subscript>7</Subscript>)<Subscript>4</Subscript>N]<Subscript>2</Subscript>Cd<Subscript>2</Subscript>Cl<Subscript>6</Subscript> polycrystalline

The Ac electrical conductivity and the dielectric relaxation properties of the [(C₃H₇)₄N]₂Cd₂Cl₆ polycrystalline sample have been investigated by means of impedance spectroscopy measurements over a wide range of frequencies and temperatures, 209 Hz–5 MHz and 361–418 K, respectively. The purpose is to make a difference between the electrical and dielectric properties of the polycrystalline sample and single crystal. Besides, a detailed analysis of the impedance spectrum suggests that the electrical properties of the material are strongly temperature-dependent. Plots of (Z" versus Z') are well fitted to an equivalent circuit model consisting of a series combination of grains and grains boundary elements. Moreover, the temperature dependence of the electrical conductivity in the different phases follows the Arrhenius law and the frequency dependence of σ (ω) follows the Jonscher’s universal dynamic law. Furthermore, the modulus plots can be characterized by full width at half height or in terms of a nonexperiential decay function φ(t) = exp(t/t)^β. Finally, the imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism.     

Synthesis of uniform quasi-octahedral CeO<Subscript>2</Subscript> mesocrystals via a surfactant-free route

A facile surfactant-free nonaqueous method is presented to prepare uniform quasi-octahedral ceria, CeO₂, mesocrystals, in which only Ce(NO₃)₃ and octanol were used as the reactants at a reaction temperature of 150 °C. CeO₂ sample synthesized using this technique consists of well-dispersed quasi-octahedrons and exhibits an uniform size and morphology. Based on structural characterization, it is proposed that the CeO₂ mesostructure was formed by self-assembly of primary nanocrystals based on unique 3D oriented-attachment mechanism. Optical characterization exhibited a strong quantum confinement, revealing small size of primary nanocrystals. The thermal stability and UV–Vis study reveal CeO₂ mesocrystal has various potential for high temperature applications and optical apparatus applications.     

Structural and electrical properties of pure and H<Subscript>2</Subscript>SO<Subscript>4</Subscript> doped (PVA)<Subscript>0.7</Subscript>(NaI)<Subscript>0.3</Subscript> solid polymer electrolyte

Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)_0.7 and sodium iodide (NaI)_0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural properties of these electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric acid disrupt the semi-crystalline nature of (PVA)_0.7(NaI)_0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing sulfuric acid concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)_0.7(NaI)_0.3 matrix at room temperature was 10⁻⁵ S cm⁻¹ and this increased to 10⁻³ S cm⁻¹ with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz–1 MHz) and temperature range (300–400) K were carried out. The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration Na/SPE/MnO₂. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance of 4.5 kΩ.     

Synthesis and nanostructural investigation of TiO<Subscript>2</Subscript> nanorods doped by SiO<Subscript>2</Subscript>

TiO₂ Nano rods can be used as dye-sensitized solar cells, various sensors and photocatalysts. These nanorods are synthesized by a hydrothermal corrosion process in NaOH solution at 200°C using TiO₂ powder as the source material. In the present work, the synthesis of TiO₂ nanorods in anatase, rutile and Ti₇O₁₃ phases and synthesis of TiO₂ nanorods by incorporating SiO₂ dopant, using the sol–gel method and alkaline corrosion are reported. The morphologies and crystal structures of the TiO₂ nanorods are characterized using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) study. The obtained results show not only an aggregation structure at high calcination temperatures with spherical particles but also Ti–O–Si bonds having four-fold coordination with oxygen in SiO^4 −.     

Spectral and kinetic characteristics of CdI<Subscript>2</Subscript> and CdI<Subscript>2</Subscript>:Pb scintillators

We have studied the effect of lead dopant on the optical absorption, photoluminescence, and x-ray luminescence spectra, and the scintillation characteristics of CdI₂ at room temperature. The crystals for the study were grown by the Stockbarger-Bridgman method. Activation of CdI₂ from the melt by the compound PbI₂ leads to the appearance in the absorption spectra in the near-edge region of an activator band at 395–405 nm, which is interpreted as an A band connected with electronic transitions from the ¹S₀ state to the ³P₁ levels in the Pb²⁺ ion. For x-ray excitation, CdI₂:Pb²⁺ crystals with optimal dopant concentration (∼1.0 mol%) are characterized by a light yield with maximum in the 570–580 nm region that is an order of magnitude higher than for CdI₂ crystals in the 490–500 nm band. For α excitation, the radioluminescence kinetics for cadmium iodide is characterized by a very short (∼0.3 nsec) rise time and fast decay of luminescence, with τ₁ ≈ 4 nsec and τ₂ = 10–76 nsec. Depending on the conditions under which the crystals were obtained, the fast component fraction is 95%–99%. The crystal is characterized by a similar scintillation pulse in the case of excitation by x-ray pulses. The radioluminescence pulse shape for CdI₂:Pb in the decay stage is predominantly exponential, with luminescence decay time constants τ₁ ≈ 10 nsec and τ₂ = 200–250 nsec. This system is characterized by low afterglow, at the level for the Bi₄G₃O₁₂ scintillator. We have demonstrated the feasibility of using CdI₂:Pb as a scintillator for detecting α particles. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 825–830, November–December, 2008.     

Magnetic and dielectric properties of Mn<Subscript>0.2</Subscript>Ni<Subscript>0.8</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized by PEG-assisted hydrothermal method

We present a systematic investigation on the structural and magnetic properties of Mn_0.2Ni_0.8Fe₂O₄ nanoparticles synthesized by a polyethylene glycol (PEG)-assisted hydrothermal route. XRD, FT-IR, TEM and VSM were used for the structural, morphological, dielectric properties and magnetic investigation of the products, respectively. Average crystallite size of product was estimated using Line profile fitting as 6 ± 1 nm and particle size as 6.5 ± 1.0 nm from TEM micrographs. Magnetization measurements have shown that the particles have a blocking temperature of 134 K. Magnetization and the coercive field of the sample increase by decreasing the temperature. The conductivity measurements reveal the semiconducting behaviour for the sample. Temperature-dependent dielectric properties: dielectric permittivity (ε) and ac conductivity (σ_ac) for the sample were studied as a function of applied frequency in the range from 1 Hz to 3 MHz. These studies indicated that the dielectric dispersion curve for the sample showed usual dielectric dispersion which can be explained on the basis of Koop’s theory, which is based on the Maxwell–Wagner model for the interfacial polarization of homogeneous double structure.     

Dielectric spectroscopy study of the new compound [C<Subscript>12</Subscript>H<Subscript>17</Subscript>N<Subscript>2</Subscript>]<Subscript>2</Subscript>CdCl<Subscript>4</Subscript>

The temperature dependence of the electrical conductivity of the compound 2,4,4-trimethyl-4,5-dihydro-3H-benzo[b] [1,4] diazepin-1-ium tetrachlorocadmiate in the different phases follows the Arrhenius law. The imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism. In the temperature range 348–394 K, the activation energy of conductivity obtained from complex permittivity in regions I and II are, respectively, 1.03 and 0.33 eV, and E _m (in regions I and II are, respectively, 0.97 and 0.36 eV) obtained from the modulus spectra is close, suggesting that the ion transport is probably due to a hopping mechanism. The Kohlrausch–Williams–Watts function, j(t) = exp( - ( \fractt_\textKWW )^b ) \varphi (t) = \exp \left( { - {{\left( {\frac{t}{{{\tau_{\text{KWW}}}}}} \right)}^\beta }} \right) , and the coupling model are utilized for analyzing electric modulus at various temperatures. The decreasing of β at 373 K is due to approaching the temperatures of change in the conduction mechanism of the sample.     

Electrical characterization of the [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>][N(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>4</Subscript>]ZnCl<Subscript>4</Subscript> compound

The [N(CH₃)₄][N(C₂H₅)₄]ZnCl₄ compound has been synthesized by a solution-based chemical method. The X-ray diffraction study at room temperature revealed an orthorhombic system with P2₁2₁2 space group. The complex impedance has been investigated in the temperature and frequency ranges 420–520 K and 200 Hz–5 MHz, respectively. The grain interior and grain boundary contribution to the electrical response in the material have been identified. Dielectric data were analyzed using the complex electrical modulus M ^* for the sample at various temperature. The modulus plots can be characterized by full width at half height or in terms of a non-exponential decay function ϕ(t) = exp[(−t/τ) ^β ]. The detailed conductivity study indicated that the electrical conduction in the material is a thermally activated process. The variation of the AC conductivity with frequency at different temperatures obeys the Almond and West universal law.     

Tunneling conductivity in lithiated transition metal oxide cathode Li<Subscript>0.9</Subscript>[Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>]O<Subscript>1.95</Subscript>

Electrical complex ac conductivity of the compound Li_0.9[Ni_1/3Mn_1/3Co_1/3]O_1.95 has been studied in the frequency range 10 Hz–2 MHz and in the temperature range 93–373 K. It has been observed that the frequency dependence of the ac conductivity obeys a power law and the temperature dependence of the ac conductivity is quite weak. The experimental data have been analyzed in the framework of several theoretical models based on quantum mechanical tunneling and classical hopping over barriers. It has been observed that the electron tunneling is dominant in the temperature range from 93 K to 193 K. A crossover of relaxation mechanism from electron tunneling to polaron tunneling is observed at 193 K. Out of the several models discussed, the electron tunneling and the polaron tunneling models are quite consistent with the experimental data for the complex ac conductivity. The various parameters obtained from the fits of the experimental results for the real and imaginary parts of the conductivity to the predictions of these models are quite reasonable.     

A sonochemical-assisted synthesis and annealing temperature effect of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> nanoparticles

This paper reports on the sonochemical-assisted synthesis of La_0.7Sr_0.3MnO₃ (LSMO) nanoparticles (NPs) which have a single-crystalline perovskite structure. The average particle size of LSMO NPs was controlled from about 40 to 120 nm by changing the annealing temperatures from 750 to 1050°C. The particle size, electrical resistivity, and ferromagnetic transition temperature of LSMO NPs were strongly dependent on the annealing temperature. A substantial decrease in resistivity and an enhancement in the insulator–metal transition temperature were found on increasing the annealing temperature. Furthermore, the enhancement in magnetization and paramagnetic–ferromagnetic (PM–FM) transition temperatures was observed as the annealing temperature increases.     

Single enzyme nanoparticle for biomimetic CO<Subscript>2</Subscript> sequestration

Nanoparticle technology is being increasingly used in environmental sciences. We prepared single enzyme nanoparticle (SEN) by modifying the surface of carbonic anhydrase (CA) with a thin layer of organic/inorganic hybrid polymer. SEN-CA appears to be improving the stability of free enzyme. CA, as ubiquitously found enzyme, is involved in gaseous CO₂ sequestration and is being looked as a promising candidate for combating global warming. We report here physical characterization of SEN-CA using transmission electron microscope (TEM), Fourier-transform infrared analysis (FTIR), X-ray diffraction analysis (XRD), and energy dispersive X-ray (EDX). Average size of SEN-CA particles appears to be in the range of 70–80 nm. We also report the effect of SEN formation on the kinetic parameters of free CA such as Michaelis–Menten constant (K _m), maximum reaction velocity (V _max), and storage stability of free CA and SEN-CA. The V _max of SEN-CA (0.02857 mmol/min/mg) and free enzyme (0.02029 mmol/min/mg) is almost similar. K _m has decreased from 6.143 mM for SEN-CA to 1.252 mM for free CA. The stabilization of CA by SEN formation results in improved the half-life period (up to 100 days). The formation of carbonate was substantiated by using gas chromatography (GC). The conversion of CO₂ to carbonate was 61 mg of CaCO₃/mg of CA and 20.8 mg of CaCO₃/mg of CA using SEN-CA and free CA, respectively.     

Kinetics of electron tunneling transfer in KH<Subscript>2</Subscript>PO<Subscript>4</Subscript> and NH<Subscript>4</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> crystals with hydrogen bonds

A model of electron transfer by tunneling between trapped electron and hole centers in crystals with hydrogen bonds under the conditions of thermostimulated mobility of one carrier type in the recombination process has been developed. The proposed model describes all features in the kinetics of induced optical density relaxation observed in nonlinear optical crystals of KH₂PO₄ (KDP) and NH₄H₂PO₄ (ADP) on a wide temporal scale (10⁻⁸–10 s) under pulsed irradiation. The results of model calculations have been compared with experimental data on the photoinduced transient optical absorption (TOA) in KDP and ADP crystals in the visible and UV ranges. The nature of the radiation-induced defects, which account for the TOA, and the dependence of the TOA decay kinetics on the temperature, excitation power, and other experimental conditions have been considered.     

Photoluminescence of nanoparticles of (Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>(Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0.05</Subscript> solid solution

We have ground bulk samples to obtain nanoparticles of (Ga₂S₃)_1–x (Eu₂O₃) _x solid solutions, the sizes of which were determined using an atomic force microscope. The photoluminescence spectra of the nanoparticles were studied in the temperature interval 77–300 K. We have established the mechanisms for emission and transfer of energy from the matrix to the rare-earth ion, and we determined the Stokes shift (ΔS = 0.7 eV), the Huang–Rhys parameter (S = 16), and the optical phonon energy (ħ−ω = 23 meV).     

Optical spectra and excited state relaxation dynamics of Sm<Superscript>3+</Superscript> in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript> single crystal

Single crystals of gadolinium orthosilicate Gd₂SiO₅ containing 0.5 at% and 5 at% of Sm³⁺ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the ⁴G_5/2→⁶H_J (J=5/2–11/2) transitions of Sm³⁺ in the visible and near infrared region the ⁴G_5/2 →⁶H_7/2 one has the highest intensity with a peak emission cross section of 3.54×10⁻²¹ cm² at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd₂SiO₅:0.5 at% Sm³⁺ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the ⁴G_5/2 radiative lifetime τ _rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd₂SiO₅:5 at% Sm³⁺ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm³⁺–Sm³⁺ energy transfer C _da=1.264×10⁻⁵² cm⁶×s⁻¹.     

Dielectric relaxation and ionic conductivity studies of Ag<Subscript>2</Subscript>ZnP<Subscript>2</Subscript>O<Subscript>7</Subscript>

The complex impedance of the Ag₂ZnP₂O₇ compound has been investigated in the temperature range 419–557 K and in the frequency range 200 Hz–5 MHz. The Z′ and Z′ versus frequency plots are well fitted to an equivalent circuit model. Dielectric data were analyzed using complex electrical modulus M* for the sample at various temperatures. The modulus plot can be characterized by full width at half-height or in terms of a non-exponential decay function f( \textt ) = exp( - \textt/t )^b \phi \left( {\text{t}} \right) = \exp {\left( { - {\text{t}}/\tau } \right)^\beta } . The frequency dependence of the conductivity is interpreted in terms of Jonscher’s law: s( w) = s_\textdc + \textAwⁿ \sigma \left( \omega \right) = {\sigma_{\text{dc}}} + {\text{A}}{\omega^n} . The conductivity σ _dc follows the Arrhenius relation. The near value of activation energies obtained from the analysis of M″, conductivity data, and equivalent circuit confirms that the transport is through ion hopping mechanism dominated by the motion of the Ag⁺ ions in the structure of the investigated material.