β-Cyclodextrin-assisted preparation of hierarchical walnut-like CeOHCO3 and CeO2 mesocrystals

The hierarchical walnut-like CeOHCO₃ mesocrystals were prepared by a facile hydrothermal method under low temperature with β-cyclodextrin (β-CD) as assistant agent. The hierarchical walnut-like CeO₂ mesocrystals were obtained by thermal decomposition of CeOHCO₃ mesocrystals. The crystal phase, morphology, and structure of CeOHCO₃ and CeO₂ mesocrystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The time-dependent experimental results indicated that the morphology transformation from shuttle-like to walnut-like and the crystal phase transformation from orthorhombic to hexagonal simultaneously occurred in the formation processes of CeOHCO₃ mesocrystals. On the basis of the morphological and crystal phase evolution processes, the formation mechanism of hierarchical walnut-like CeOHCO₃ mesocrystals, including dissolution-recrystallization processes, was discussed. β-CD was believed to play an important role in the formation of the hierarchical walnut-like CeOHCO₃ mesocrystals. The effects of reaction temperature, β-CD amount, and concentration of reactants on the morphologies of the products were systematically studied. CeO₂ mesocrystals exhibited the distinct red-shift phenomenon in UV-vis absorption spectra.     

Characterizations of electrodeposited Ni–CeO2 nanocomposite coatings

The expansion of current machinery requires metallic materials with better surface properties. In the present investigation, CeO₂ reinforced nickel nanocomposite coatings were deposited on mild steel substrate by direct current electrodeposition process employing nickel acetate bath. The effect of incorporation of CeO₂ particles in the Ni nanocomposite coatings on the micro hardness and corrosion behaviour has been evaluated. Smooth and compact nanocomposite deposits containing well-distributed cerium oxide particles were obtained. The crystallite structure was fcc for electrodeposited nickel and Ni–CeO₂ nanocomposite coatings. It has been observed that, the presence of CeO₂ nanoparticles favours the [111] and [200] texture of nickel matrix. The co-deposition of CeO₂ nanoparticles with nickel was found to be favoured at applied current density of 8 A dm⁻². The micro hardness values of the nickel nanocomposite coatings (725 HV) was higher than that of pure nickel (265 HV).The decrease in I_corr values and increase in Constant Phase Element values were investigated in 3.5% NaCl solution which showed the higher corrosion resistant nature of Ni–CeO₂ coatings.     

SnO2–Au nanocomposite synthesized by successive ionic layer deposition method: Characterization and application in gas sensors

A possibility of synthesizing the SnO₂–Au nanocomposite by the successive ionic layer deposition (SILD) method is demonstrated in this article. It is shown that as a result of successive treatments in solutions of Sn(OH)_xF_yCl_z and HAuCl₄ the SnO₂–Au nanocomposite with a Sn/Au ratio varying from 1:1 to 6:1 can be formed on the surface of substrates. It is found that the value of this ratio depends on the concentration of F ions in solution. The gold in the indicated composite is in the metallic state. The growth of the SnO₂–Au composite takes place through the formation of 3-D precipitates, which form a continuous film after 13 deposition cycles. As a result, a layer with averaged thickness of up to 20 nm is formed on the surface. Nanocomposite films, even after treatment at an annealing temperature T_an ∼ 600 °C, have finely dispersed structure. The size of the Au clusters incorporated in the SnO₂ matrix is in the range from 3 to 15 nm. Gas sensing characteristics of SnO₂ films modified by SnO₂–Au nanocomposites are discussed as well. It is shown that surface modification by SnO₂–Au nanocomposites can be used for improving operating characteristics of conductometric SnO₂-based gas sensors.     

Morphology and crystal structure of CeO2-modified mesoporous ZrO2 powders prepared by sol–gel method

Mesoporous ZrO₂ powder modified by CeO₂ has been prepared by sol–gel method combined with novel heat-treatment without any templates. The morphology and crystal structure were characterized by Fourier transform infrared spectrophotometer (FT-IR), thermal gravimetry/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), Raman spectroscope, N₂ absorption–desorption, scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM). It was demonstrated that the morphologies and crystal structures were varied with the CeO₂ content and calcination temperatures. Some circular grooves with diameter about 300–500 nm and thickness of 150–200 nm were observed for 30 mol% CeO₂ modified samples. Tetragonal ZrO₂ and cubic (Ce,Zr)O₂ solid solution were in turn observed with CeO₂ content increasing. The oxygen storage capacity (OSC) of the mesoporous powders was determined by thermalgravimetry (TG) under cyclic thermal treatments.     

Synthesis and properties of magnetic solid superacid: SO4/ZrO2–B2O3–Fe3O4

A magnetic SO₄²⁻/ZrO₂–B₂O₃–Fe₃O₄ solid superacid catalyst is prepared via a simple chemical co-precipitation approach. The obtained materials were characterized in detailed by X-ray powder diffraction, thermogravimetric analysis–different scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM), and Mossbauer spectra. Powder X-ray diffraction patterns show that in this composite oxide the transformation temperature of ZrO₂ from tetragonal to monoclinic phase is higher compared to the pristine SO₄²⁻/ZrO₂ material. The introduction of Fe₃O₄ endows the superacid with a super-paramagnetic property while in a ferromagnetic state after calcination. The superacid exhibits high catalytic activity in forming ethyl acetate by esterification.     

Superior DeNO x activity of V2O5–WO3/TiO2 catalysts prepared by deposition–precipitation method

V₂O₅–WO₃/TiO₂ catalysts were prepared by incipient wetness impregnation and deposition–precipitation (DP) methods. The catalysts were characterized by N₂ physisorption, X-ray powder diffraction, Fourier transform infra red spectroscopy, electron paramagnetic resonance spectroscopy, transmission electron microscopy, H₂-temperature programmed reduction and NH₃-temperature programmed desorption. The catalysts exhibited only crystalline TiO₂ phases with the active metal and promoter in highly dispersed or amorphous state. The 3 wt% V₂O₅–10 wt% WO₃/TiO₂ catalyst prepared by DP using ammonium carbamate as a precipitating agent was found to be the most active and selective to N₂. The superior activity of the catalyst can be ascribed to the altered acidic and redox properties of vanadium. The catalysts did not show increased potassium resistance with the change in preparation method or with increasing vanadium concentration. Furthermore, potassium-poisoned catalysts showed above stoichiometric loss of surface acidity. Thus, these modified formulations are suggested to be used in coal/natural gas-fired power plants where there is a demand for high selective catalytic reduction activity and selectivity to N₂.     

Preparation and characterization of α-Fe2O3 nanorod-thin film by metal-organic chemical vapor deposition

Alpha iron oxide (α-Fe₂O₃) films were grown on catalyst-free silicon substrate using a vertical type metal-organic chemical vapor deposition process. X-ray powder diffraction and field-emission transmission electron microscopy measurements showed that these α-Fe₂O₃ films consisted of bundles of one dimensional (1D) nanorods and the nanorods in these α-Fe₂O₃ films were single crystalline with a well-ordered rhombohedral structure. The nanorods showed a preferred growth orientation in the [104] direction. Magnetic force microscopy image suggests that spin domains were formed in the α-Fe₂O₃ nanorods. Photo-catalytic property of these nanorod films was confirmed through the photo-degradation of Rhodamine B by UV irradiation. These α-Fe₂O₃ film/nanorod materials could be used as building blocks for nanodevice applications.     

XAS characterization of the RuO2–Ta2O5 system local (crystal) structure

The influence of the preparation method on the structural properties of the RuO₂–Ta₂O₅ system was investigated. Both thin films on Ti substrates and powder samples of nominal composition Ti/RuO₂–Ta₂O₅ (Ru:Ta = 100:0, 90:10, 80:20, 30:70, and 0:100 at.%) were prepared through thermal decomposition of polymeric precursors (DPP). The thin films and powder samples were investigated using X-ray absorption spectroscopy (XAS). XANES analyses showed that Ru and Ta are present in the Ru(IV) and Ta(V) oxidation states. EXAFS signals of all the samples were analyzed, to obtain the average bond length (r), coordination number, and the Debye–Waller factor (σ²) for each Ru–O, Ru–Ru, Ta–O nearest-neighbor. The first shell Ru–O distance was found at 1.91–1.92 Å with coordination number of 1.8–2.1, and at 2.01–2.02 Å with coordination number of 3.9–4.1. The Ta–O distance obtained for all the samples and in both modes (transmission and fluorescence) had significantly different values from the theoretical ones. The results revealed that the local structure around both the Ru and Ta sites are similar, and that they consist of distorted M–O₆ octahedra (where M = Ru or Ta).     

Preparation and characterization of single-phase α-Fe2O3 nano-powders by Pechini sol-gel method

In this work, single-phase α-Fe₂O₃ nano-particles were first synthesized via Pechini sol-gel method using citric acid and polyethylene glycol-6000 as chelating agents. The structural coordination of as-prepared polymeric intermediates was investigated by FTIR analysis. Thermal behavior of the polymeric intermediates was studied by TG-DTG-DSC thermograms. The structure of the powders calcined at different temperatures was characterized by XRD and FESEM. The single-phase α-Fe₂O₃ nano-powders with uniform size were prepared when the polymeric intermediate calcined at 600 °C, and the lowest particle size was found to be 30 nm.     

Preparation and characterization of Au/CeO2–Al2O3 monoliths

Porous CeO₂–Al₂O₃ monoliths with hierarchical pore structure were prepared by mixing boehmite particles with solutions containing different amounts of cerium chloride and aluminum nitrate. The monoliths were functionalized with gold nanoparticles using the incipient wetness method. The resulting materials were characterized by X-ray diffraction, nitrogen sorption, mercury porosimetry, UV–vis spectroscopy and transmission electron microscopy. The catalysts were tested in liquid phase glucose oxidation, comparing continuously stirred batch reactor and continuous-flow fix-bed reactor setups.     

Preparation and characterization of Y2O3–Sm2O3 co-doped ceria electrolyte for IT-SOFCs

Y₂O₃–Sm₂O₃ co-doped ceria (YSDC) powder was synthesized by a gel-casting method using Ce(NO₃)₃·6H₂O, Sm₂O₃ and Y₂O₃ as raw materials. Phase structure of the synthesized powders was characterized by X-Ray diffraction analysis. Sinterability of the powders was investigated by testing the relative density and observing the microstructure of the sintered YSDC samples. Electrical conductivity of the sintered YSDC samples was measured using impedance spectra method. Single solid oxide fuel cells based on the YSDC electrolyte were also assembled and tested. The results showed that YSDC powders with single-phase fluorite structure can be obtained by calcining the dried gelcasts at temperature above 800 °C. Average particle size of the YSDC powder is 50–100 nm. Relative density of more than 95% of the theoretical can be achieved by sintering the YSDC compacts at temperature above 1400 °C. The sintered YSDC sample has an ionic conductivity of 4.74 × 10⁻² S cm⁻¹ at 800 °C in air. Single fuel cells based on the YSDC electrolyte with 50 μm in thickness were tested using humidified hydrogen as fuel and air as oxidant, and maximum power densities of about 190 and 112 mW cm⁻² were achieved at 700 and 600 °C, respectively.     

Optical properties and structure of R2O–Ga2O3–SiO2 and RO–Ga2O3–SiO2 glasses

Refractive index and molar refraction of Li₂O–, Na₂O–, CaO–, and BaO–Ga₂O₃–SiO₂ glasses have been used to test the validity of a structural model of silicate glasses containing Ga₂O₃ glasses. Ga₂O₃ enters these types of glass in a similar manner as Al₂O₃. It is assumed that, for (SiO₂/Ga₂O₃) >1 and (Ga₂O₃/R₂O) ≤1, Ga₂O₃ associates primarily with modifier oxides to form GaO₄ units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values suggest another structure for (Ga₂O₃/SiO₂) ≥1.     

High-speed preparation of c-axis-oriented YBa2Cu3O7-δ film by laser chemical vapor deposition

YBa₂Cu₃O_7-δ (YBCO) films were prepared by laser chemical vapor deposition using Y(DPM)₃, Ba(DPM)₂/Ba(TMOD)₂ and Cu(DPM)₂ as precursors with enhancement by a continuous wave Nd:YAG laser. A c-axis-oriented YBCO film almost entirely in a single phase was obtained. The YBCO film consisted of rectangular grains about 30 μm in size. The highest deposition rate was about 100 μm h^− 1, which was 10-1000 times higher than that of conventional MOCVD.     

Single step synthesis of nanosized CeO2–MxOy mixed oxides (MxOy?=?SiO2, TiO2, ZrO2, and Al2O3) by microwave induced solution combustion synthesis: characterization and CO oxidation

Various CeO₂ –M _x O _y (M _x O _y  = SiO₂, TiO₂, ZrO₂, and Al₂O₃) mixed oxides were prepared by microwave induced solution combustion method and analyzed by different complimentary techniques, namely, X-ray diffraction (XRD), Raman spectroscopic (RS), UV–Vis diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG-DTA), and BET surface area. XRD analyses revealed that CeO₂ –SiO₂ and CeO₂ –TiO₂ mixed oxides are in slightly amorphous form and exhibit only broad diffraction lines due to cubic fluorite structure of ceria. XRD lines due to the formation of cubic Ce_0.5Zr_0.5O₂ were observed in the case of CeO₂ –ZrO₂ sample. RS results suggested defective structure of the mixed oxides resulting in the formation of oxygen vacancies. The UV-DRS measurements provided valid information about Ce⁴⁺ ← O²⁻ and Ce³⁺ ← O²⁻ charge transfer transitions. XPS studies revealed the presence of cerium in both Ce³⁺ and Ce⁴⁺ oxidation states. The ceria–zirconia combination exhibited better oxygen storage capacity (OSC) and CO oxidation activity when compared to other samples. The significance of present synthesis method lays mostly on its simplicity, flexibility, and the easy control of different experimental factors.     

Meso-macroporous monolithic CuO–CeO2/γ-Al2O3 catalysts and their catalytic performance for preferential oxidation of CO

Meso-macroporous monolithic CuO–CeO₂/γ-Al₂O₃ catalysts were prepared and tested for preferential oxidation of carbon monoxide in hydrogen-rich gases. The catalysts were characterized with photographs, SEM, N₂ adsorption–desorption, XRD, HRTEM, and TPR techniques. CuO–CeO₂ catalysts were evenly coated onto the walls of γ-Al₂O₃ monolith macropores with ceria and copper oxide highly dispersed. The prepared meso-macroporous monolithic CuO–CeO₂/γ-Al₂O₃ catalysts can remove CO from H₂-rich gases to ppm level at high space velocity, indicating that they are a kind of promising structured catalyst.     

Physico-chemical and electrochemical characterization of Ti/RhOx–IrO2 electrodes using sol–gel technology

Sol–gel technology has been successfully used for the incorporation of RhO_x–IrO₂ on a Ti substrate. RhO_x–IrO₂ was prepared from chloride precursors of Rh and Ir, for surface studies. These metal oxides were then immobilised on solid Ti substrates via dip withdrawal coating methods to form thin films. The Ti/RhO_x–IrO₂ thin films were extensively characterized in terms of surface characterization and chemical composition and used in the oxidation of phenol. Thermo-gravimetric analysis (TGA) determined the calcination temperature at 700 °C where no further structural changes occurred due to mass loss. The rhodium oxide showed two-phase formations, RhO₂ and Rh₂O₃, which were attributed to high calcinated temperatures compare to one phase IrO₂ which was stable at lower temperatures. The scanning electron microscopy (SEM) showed that the morphology of the film was found to be rough with a grain-like appearance in the 150-nm range. The phase composition of these metal oxides was determined by X-ray diffraction (XRD) technique and found to have crystalline structures. The results obtained from Rutherford backscattering spectrometry (RBS) revealed information regarding the chemical composition of the metal oxides and confirmed the diffusion of Rh and Ir into the Ti substrate. Electrochemical characterization of the Ti/RhO_x–IrO₂ electrode, via cyclic voltammetry (CV), showed distinctive redox peaks: anodic and cathodic peaks associated with the oxidation and reduction of the ferricyanide–ferrocyanide couple was seen at 250 and 100 mV respectively; the peak observed at 1000 mV was associated with oxygen evolution and a broad reductive wave at −600 mV can be ascribed to the Ti/RuO_x–IrO₂ reduction, which proved that the Ti/RhO_x–IrO₂ electrode were electroactive and exhibit fast electrochemistry.     

Ferroelectric and ferromagnetic properties of Gd-doped BiFeO3–BaTiO3 solid solution

The solid solutions of Bi_1−x−yGd_xBa_yFe_1−yTi_yO₃ have been prepared via solid-state reaction method with the aim to obtain magnetoelectric coupling (i.e., linear relation between magnetization and electric field) at room temperature. Optimum calcination and sintering strategies for obtaining pure perovskite phase, high density ceramics and homogeneous microstructures have been determined. All the samples of the composition Bi_1−x−yGd_xBa_yFe_1−yTi_yO₃ (x = 0.1 and y = 0.1, 0.2, and 0.3) reported in the present work are tetragonal at room temperature. The maximum ferroelectric transition temperature (T_c) of this system was 150–170 °C with the dielectric constant peak of 2300 at 100 kHz for y = 0.1. Above T_c the dielectric constant is decreasing up to a certain temperature and then increasing with temperature similar to that observed in other perovskites due to chemical inhomogeneities in both A and B sites of the ABO₃ cell. The variation of ferroelectric and magnetic properties was followed by piezoresponse force microscopy and vibrating sample magnetometer, respectively. Well-saturated piezoelectric loops were observed for all composition indicating room temperature ferroelectricity.     

Microwave dielectric properties of BaO–TiO2–TeO2 ternary system

Besides the applications as optical functional materials, tellurium oxides also have attracted interest as microwave dielectric materials. Most TeO₂-based binary and ternary system have large negative temperature coefficient of resonant frequency (τ_f), which is not compatible for the low-temperature cofired ceramic. To compensate τ_f close to zero, two single-phase predecessors of BaTe₄O₉ and TiTe₃O₈ are synthesized in air at 530–560 and 620–680 °C, respectively. The two predecessors show exceptional dielectric properties and their τ_f are opposite. The BaO–TiO₂–TeO₂ ternary system compounds are investigated by adjusting the ratio of BaTe₄O₉ and TiTe₃O₈ and sintered at 520–580 °C to develop the microwave properties and compensate the τ_f. After sintered at 560 °C, the ceramic sample with the composition of 0.47BaTe₄O₉–0.53TiTe₃O₈ exhibits a dielectric permittivity of 28, a Q × f-value of 12,200 GHz, and a τ_f of 4.0 ppm/°C measured at 10 GHz.