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The aim of this paper was the syntheses and characterizations of functionalized zeolite materials with undoped and nitrogen-doped TiO2 nanocrystals. These materials were obtained by using alternative methods, namely sol-gel and hydrothermal, directly from precursors. The synthesis of TiO2 by sol-gel and hydrothermal methods was achieved in order to compare the crystalline structures and morphologies of TiO2 on the surface of the zeolite within the obtained hybrid materials. The obtained materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), and scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDAX). The XRD results revealed that the natural zeolite used for the synthesis is mostly clinoptilolite and the anatase form of TiO2 for both applied methods. As it was desired, no the rutile phase of TiO2 was evidenced. The surface morphology observed by SEM analysis showed that TiO2 (spherical form) nanocrystals were attached on the zeolite surface. Therefore, the IR spectra confirmed the presence of TiO2 in to the zeolite lattice. The presence of the nitrogen ion in the materials obtained by both synthesis methods was also confirmed by EDAX spectra.

Cobalt ferrite is characterized by a partial inverse spinellic structure, which makes it a material with special magnetic properties that vary as a function of the cobalt concentration. The special magnetic properties represent one of the parameters due to which cobalt ferrite is of a great interest. In the present paper, we studied these properties from the perspective of the effect produced by the precursors of CoxFe3-xO4 nanomaterial synthesis on magnetic properties, shape, and morphology characteristics to these nanomaterials. Magnetic measurements were achieved with a SQUID magnetometer, while the structural and morphological characterization was achieved by X-ray diffraction (XRD), SEM- EDAX and AFM.

Zinc gallate (ZnGa2O4) is a normal spinel crystal structure (space group Fd3m). ZnGa2O4 has attracted much attention due its multitude of possible applications regarding field emission display, electroluminescent devices, and in the last decade mostly sensor domain. ZnGa2O4 nanoparticles were obtained by the hydrothermal method using Ga2O3 and Zn(NO3)2 x 6H2O precursors in basic medium using a Teflon-lined stainless steel autoclave tightly sealed. The synthesys was effectuated at 210°C for 4 h. The hydrothermal method is one of the most promising solution chemical methods. Thus, the size of particles and their distribution, phase homogeneity, and morphology could be well controlled. These powders were characterized by X-ray diffraction (XDR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDAX), and atomic force microscopy (AFM). Photoluminescence (PL) measurements were obtained with a conventional lamp as an excitation source.

Two samples of ZnxMn1−xFe2O4 (x = 0, sample A; and x = 0.4, sample B) were synthesized by the hydrothermal method. From complex impedance measurements in the range 100 Hz–2 MHz and for temperatures T between 30 and 130 °C, the barrier energy between localized states ΔErelax was determined for the first time in these samples. For sample B, a single value of ΔErelax was highlighted (0.221 eV), whilst, for sample A, two values were obtained (0.012 eV and 0.283 eV, below 85 °C and above 85 °C, respectively), associated with two zones of different conductivities. Using the Mott's VRH model and the CBH model, we determined for the first time both the bandgap energy barrier (Wm) and the hopping (crossover) frequency (ωh), at various temperatures. The results show that, for sample A, Wm has a maximum equal to 0.72 eV at a temperature between 70 and 80 °C, whilst, for sample B, Wm has a minimum equal to 0.28 eV at a temperature of 60 °C, the results being in good agreement with the temperature dependence of the static conductivity σDC(T) of the samples. By evaluating σDC and eliminating the conduction losses, we identified, using a novel approach, a dielectric relaxation phenomenon in the samples, characterized by the activation energy EA,rel. At various temperatures, we determined EA,rel, which ranged from 0.195 eV to 0.77 eV. These results are important, as understanding these electrical properties is crucial to various applications, especially in technologies where temperature variation is significant. [ABSTRACT FROM AUTHOR]

The synthesis, thermal behavior and electrical properties of a series of undoped and 1% Ga- or Y-doped lanthanum manganite compounds, obtained via the sol–gel technique, are reported. Scanning electron microscopy (SEM/EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analyses were performed on all synthesized samples. The XRD results confirmed a good crystallinity for all studied samples, and a change in the crystal structure of Ga- or Y-doped lanthanum manganite (Pm-3m space group) was observed compared to the pristine sample (R-3c space group). Thermal analysis highlighted a different behavior of the doped samples compared to the undoped sample, observed by the different mass losses in the analyzed temperature range. For these materials, it is shown for the first time that the static electrical conductivity, σDC, of Ga- or Y-doped LaMnO3 compounds increases compared to the σDC of the pristine sample, and the thermal activation energy of the process of electrical conduction, EA,cond, increases linearly with the temperature for all three studied samples. [ABSTRACT FROM AUTHOR]

LaMnO3 and 1% Pd-, Ag-, or Y-doped perovskite type nanomaterials were prepared by the sol-gel method, followed by heat treatment at a low temperature (600 °C for 6 h). The investigation through X-ray diffraction and FT-IR spectroscopy indicated that all samples were well crystallized, without secondary phases, and that the transition metal doping changed the crystal structure from the R-3c space group for the undoped LaMnO3 to the Pm-3m space group for the doped perovskite compounds. In this research paper, the efficiencies of the perovskite LaMnO3 materials for methyl orange removal were analyzed, wherein the effect of the doping ions and of the pH on the catalytic activity were studied together with a kinetic approach for the LaMnO3 materials at different values of the pH. Moreover, in the catalytic activity, it should be noted that a slightly better performance was obtained for the Ag-doped materials compared to the Y- and Pd-doped perovskite samples. The results presented for the perovskite LaMnO3 nanomaterials reinforce the interest in these multifunctional materials to be used in industrial applications; e.g., in water treatment. [ABSTRACT FROM AUTHOR]

Present day scientific research is focused on the identification of renewable and clean alternatives to fossil fuels, with hydrogen being a promising energy source that fulfills both requirements. Given this context, the current work investigates the water splitting electrocatalytic properties of two hydrothermally synthesized transition metal oxides: MnO2 and Fe3O4. Electrodes were obtained by modifying graphite substrates with suspensions in ethanol containing the catalytic materials as such or in compositions, and their activity for the O2 and H2 evolution reactions (OER and HER) was studied in alkaline medium. Out of the MnO2-based electrodes, the one modified with the suspension containing 2 mg MnO2, 1 mg Carbon Black and 10 μL Nafion solution displayed an OER overpotential (ηO2) value, at i = 10 mA/cm2, of 0.53 V, while the one manufactured using the suspension with 4 mg MnO2 and 10 μL Nafion solution showed a HER overpotential (ηH2) of 0.427 V (at i = -10 mA/cm2). From the Fe3O4-based electrodes, the one modified with the suspension containing 2 mg Fe3O4 and 2 mg Carbon Black evidenced the highest catalytic activity for both reactions (ηO2 = 0.51 V and ηH2 = 0.43 V). [ABSTRACT FROM AUTHOR]

This work reports the change in the structural and electrical behavior of partial substitution of manganese by palladium in LaMnO3 perovskite materials synthesized through sol–gel method. X-ray diffraction analysis reveals that all the obtained materials crystallize in the orthorhombic perovskite structure (Pnma space group). Morphological investigations show the presence of fine nanometric particles of similar shape and high tendency to agglomerate, and the elemental analysis highlights the presence of palladium. Detailed study of complex impedance measurements in the frequency range 20 Hz–2 MHz and different temperatures between (30 and 120) °C indicate the presence of electrical relaxation in materials; the activation energy of relaxation decreases from 0.207 eV (0.05% Pd–LMO–Pd1) to 0.102 eV (0.15% Pd–LMO–Pd3) when the x concentration of Pd increases from 0.05 to 0.15. The electrical conductivity analyses indicate that the conduction mechanisms in the low-frequency range (f < 100 kHz) are activated thermally and were explained using the Mott's variable-range-hopping (VRH) model. In the high-frequency range (f > 100 kHz), the conduction mechanism is due to the charge carriers hopping between the nearest neighboring states, in agreement with the CBH model (correlated barrier hopping). Based on this model, the bandgap energy, Wm was determined. The results show that by increasing the Pd concentration, the value of Wm of the sample increases, from 0.229 eV (LMO–Pd1) to 0.298 eV (LMO–Pd3), in agreement with the decreasing of electrical conductivity of samples. Highlights: Partial substitution of Mn by palladium in LaMnO3 perovskite materials. Heat treatment was performed at low temperature. Detailed studies of impedance and electric conductivity have been performed. [ABSTRACT FROM AUTHOR]

Ultrasound-assisted co-precipitation method is used for the first time to prepare F e 3 2 + (PO4)2·8H2O polycrystalline materials which crystallise at room temperature in a monoclinic structure (C2/m space group). The frequency and temperature dependence of the electrical conductivity σ of the Fe3(PO4)2·8H2O sample was determined, and they follow Jonscher's law. The results show that, in the low frequency range (below 10 kHz), the conduction mechanism can be explained by the Mott's variable-range-hopping model; a change of slope of the conductivity is observed at ≈ 110 °C, which may be associated with a change in the crystal structure, due to the loss of water molecules from the sample. Based on Mott's model, the density of localized states near the Fermi level, N(EF), the hopping distance, R, and the hopping energy, W, were computed. The results show that, at a constant frequency (below 10 kHz), N(EF) does not depend on temperature, while R decreases and W increases with the increase in temperature. Over 200 kHz, the correlated barrier hopping model is characteristic to the conductivity for this type of materials and the calculated band gap energy is 1.072 eV, in the (25–110) °C range and 0.821 eV, in the (110–220) °C range. [ABSTRACT FROM AUTHOR]

Sodium niobate (NaNbO3) fine powders were synthesized by hydrothermal method using ammonium niobate (V) oxalate hydrate (C4H4NNbO9 x H2O), sodium hydroxide (NaOH) and sodium citrate hydrate (C6H9Na3O9) as precursors. The samples were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), AFM (Atomic Force Microscopy), UV-VIS spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). X-ray diffraction for powder obtained by hydrothermal method revealed three phases mixture (NaNbO3, Nb2O5, Na2C2O4). In order to obtain a material with perovskite structure, the powder was treated for 6 h at 600°C. After calcination, the X-ray powder diffraction (XRD) patterns shown reflections of a pure cubic structure (space group Pm-3m) with lattice parameters (a=b=c=3.909Å) comparable to those reported in the literature. The average particle sizes estimated by SEM image were 2-3 micrometers. [ABSTRACT FROM AUTHOR]

Abstract: ZnGa2O4 phosphor doped with Eu3+ ions was synthesized by hydrothermal method using two concentrations: 3.34mol% and 1.67mol% of Eu3+. The crystal structure was investigated by means of X-ray diffraction, scanning electron microscopy and atomic force microscopy. The results indicate that the material consisting of ZnGa2O4:Eu3+ nanoparticles exhibits good crystalinity, with cubic spinel structure. The powders were found to have 4.74eV of ZnGa2O4:Eu3+ (3.34mol%) and 4.69eV of ZnGa2O4:Eu3+ (1.67mol%) band gaps, respectively. The luminescent analysis of the materials shows that the trivalent europium ions doped in this material are localized in different sites, substituting both Zn2+ and Ga3+. The emission spectra of the europium-doped samples, originating from 5D0–7F J (J =0–4) transitions, suggests the existence of three different site symmetry of Eu3+ ions, tetrahedral (Zn2+), distorted octahedral (Ga3+) and low octahedral (Ga3+) sites, respectively. [Copyright &y& Elsevier]

Two samples of NaTaO3 perovskite materials were prepared by the standard hydrothermal method at the same reaction temperature (600 °C) but with different sintering times: 6 hours for sample S1 and 12 hours for sample S2. Using X-ray diffraction (XRD), it shows that samples S1 and S2 are mixtures of Na-Ta oxides (Ta2O5 and the prevailing phase NaTaO3). The scanning electron microscopy analysis (SEM), shows that the grains are connected each other in agglomerated clusters of size about few hundred nanometers. The frequency (f) dependencies of complex impedance, Z(f) = Z'(f) – i Z''(f) of the samples, over the frequency range 20 Hz – 2 MHz, at room temperature are presented. The real component Z' of the complex impedance decreases with increasing frequency and the imaginary component Z'' has two maximum corresponding to two relaxation processes. The results obtained from the complex impedance spectroscopy, Z''(Z') showed the appearance of two semicircles, corresponding to grain and grain boundary mechanism. Experimental results have been fitted with two parallel RC equivalent circuits connected in series and the parameters R and C have been evaluated. [ABSTRACT FROM AUTHOR]