Characterization of Cr/SiO2 catalysts and ethylene polymerization by XPS

Cr/SiO₂ catalysts with 1 or 3 wt.% Cr loadings and different chromium precursors were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). A method to determine chromium species in the sample was developed through the decomposition of the Cr 2p XPS spectrum in Cr⁶⁺ and Cr³⁺ standard spectra. The results of the binding energy from the Cr 2p region and of the distribution of chromium species allowed to evaluate the dynamic photo-reduction of the surface chromium species during XPS analysis. Photo-reduction of surface Cr⁶⁺ to Cr³⁺ species was verified for all samples supported in silica, depending on the precursor and chromium content. Bulk CrO₃ and Cr₂O₃ standards did not reveal variation in the binding energy of Cr 2p_3/2, but a physical mixture of CrO₃ with SiO₂ presented photo-reduction. The behavior of this mixture resembled to the catalysts and suggests the participation of the surface hydroxyls of silica in the photo-reduction process. XPS intensity measurements for assessing dispersion of chromium oxide were used to compare the calcined and reduced catalysts to different chromium precursors. Polyethylene chains were detected by in situ XPS, while oligomerization products were not observed.     

Preparation of superparamagnetic γ-Fe2O3 nanoparticles in nonaqueous medium by γ-irradiation

Superparamagnetic γ-Fe₂O₃ nanocrystallites have been prepared by γ-irradiating ferrocene in the presence of isopropyl alcohol to get Fe nanoparticles in nitrogen atmosphere and at room temperature, followed by oxidization in air to obtain γ-Fe₂O₃. The final black powder was characterized with X-ray powder diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). From XRD pattern and XPS spectrum, we can confirm to get γ-Fe₂O₃. The particle size is several nanometers as shown in TEM image. Magnetic hysteresis loop measurements exhibited that the γ-Fe₂O₃ nanoparticles display superparamagnetism. However, a trace black powder was obtained in kerosene oil using the same method. A possible formation mechanism of the γ-Fe₂O₃ nanoparticles was suggested.     

Preparation, characterization and luminescence properties of porous Si3N4 ceramics with Eu2O3 as sintering additive

Porous Si₃N₄ ceramics with photoluminescence properties were prepared by pressureless sintering using α-Si₃N₄ powder as raw material and Eu₂O₃ as sintering additive. Chemical composition, phase formation, microstructure and photoluminescence properties of porous Si₃N₄ ceramics were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence measurements (PL/PLE). The results show that single Eu₂O₃ additive promotes α→β transformation but not significant densification. A broad band emission center at 570 nm assigned to Eu²⁺ is observed, Eu³⁺ in Eu₂O₃ is (partially) converted to Eu²⁺ by reaction with Si₃N₄, which results in a lower β aspect ratio and β-content compared to the other Ln (Ln=lanthanide) oxide additives.     

Synthesis and surface characteristics of CeTbO3+δ induced by femtosecond laser irradiation

This work describes the use of focused, high-intensity light from a Ti:sapphire laser that generates femtosecond pulses to irradiate mixture of CeO₂ and Tb₄O₇ under ambient conditions. The prepared samples were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). XRD and XPS measurement results demonstrated that solid solution CeTbO_3+δ with cubic fluorite structure has been synthesized on the irradiated target surface. SEM micrographs showed that the ultra-short laser irradiation resulted in the formation of foamy structure and spherical particles with size varying from about 30 to 200 nm. The formation mechanism has been discussed in detail.     

Photophysical and enhanced daylight photocatalytic properties of N-doped TiO2/g-C3N4 composites

N-doped TiO₂/C₃N₄ composite samples were synthesized by heating the mixture of the hydrolysis product of TiCl₄ and C₃N₄ at different weight ratios. The samples were characterized by X-ray diffraction (XRD), Raman spectrum, UV–vis absorption spectrum, photoluminescence spectrum, X-ray photon electron spectrum (XPS) and surface photovoltage spectrum (SPS). The XRD and Raman results indicate that the introduction of C₃N₄ could inhibit the formation of rutile TiO₂. The composite samples show slight visible light absorption due to the introduction of C₃N₄. The XPS result reveals that some amount of nitrogen is doped into TiO₂, and C₃N₄ exists in the composite sample. The intensities of the SPS signal in the composite samples decrease with the rise in the amount of C₃N₄ in the samples. The photocatalytic activity was evaluated from the Rhodamine B (RhB) degradation under fluorescence light irradiation. The composite samples show significantly enhanced photocatalytic activities and the RhB self-sensitized photodegradation in this system was observed by measuring the photocurrent in the dye sensitized solar cell using the composite as the working electrode.     

Synthesis and luminescence properties of Tb:NaGd(WO4)2 novel green phosphors

Tb³⁺:NaGd(WO₄)₂ (Tb:NGW) phosphors with different Tb³⁺ concentrations have been synthesized by a mild hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence excitation and emission spectra and decay curve were used to characterize the Tb:NGW phosphors. XRD analysis confirmed the formation of NGW with scheelite structure. SEM study showed that the obtained Tb:NGW phosphors appeared to be nearly spherical and their sizes ranged from 1 to 1.5 μm. The excitation spectra of these systems showed an intense broad band with maximum at 270 nm related to the O→W ligand-to-metal charge-transfer state. Photoluminescence spectra indicated the phosphors emitted strong green light centered at 545 nm under UV light excitation. Analysis of the photoluminescence spectra with different Tb³⁺ concentrations revealed that the optimum dopant concentration for Tb³⁺ is about 15 at% of Tb³⁺ ions in Tb:NGW phosphors.     

Nd:YAG laser synthesis of nanostructural V2O5 from vanadium oxide sols: Morphological and structural characterizations

Vanadium oxide thin films were prepared by sol-gel method, then subjected to Nd:YAG laser (CW, 1064 nm) radiation. The characteristics of the films were changed by varying the intensity of the laser radiation. The nanocrystalline films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD revealed that above 102 W/cm² the original xerogel structure disappears and above 129 W/cm² the films become totally polycrystalline with an orthorhombic structure. From TEM observations, we can see that due to laser radiation, the originally fibrillar-like particles disappear and irregular shaped, layer structured V₂O₅ particles are created. From XPS spectra we can conclude that due to laser radiation the O/V ratio increased with higher intensities.     

Synthesis and characteristics of natural zeolite supported Fe-TiO2 photocatalysts

Natural zeolite supported Fe³⁺-TiO₂ photocatalysts were synthesized for the sake of improving the recovery and photocatalytic efficiency of TiO₂. The as-prepared materials were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflection spectroscopy (UV-vis DRS), scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). Methyl orange was used to estimate the photocatalytic activity of the samples. The results showed that zeolite inhibited the growth of TiO₂ crystallite sizes. The Fe³⁺ concentration played an important role on the microstructure and photocatalytic activity of the samples. The iron ions could diffuse into TiO₂ lattice to the form Fe-O-Ti bond and gave TiO₂ the capacity to absorb light at lower energy levels. The photocatalytic activity of the samples could be enhanced as appropriate dosages of Fe³⁺ were doped.     

Synthesis of earth-abundant Cu2SnS3 powder using solid state reaction

Cu₂SnS₃ (CTS) powder has been synthesized at 200 °C by solid state reaction of pastes consisting of Cu and Sn salts and different sulphur compounds in air. The compositions of the products is elucidated from XRD and only thiourea is found to yield CTS without any unwanted CuS_x or SnS_y. Rietveld analysis of Cu₂SnS₃ is carried out to determine the structure parameters. XPS shows that Cu and Sn are in oxidation states +1 and +4, respectively. Morphology of powder as revealed by SEM shows the powder to be polycrystalline with porous structure. The band gap of CTS powder is found to be 1.1 eV from diffuse reflectance spectroscopy. Cu₂SnS₃ pellets are p-type with electrical conductivity of 10⁻² S/cm. The thermal degradation and metal–ligand coordination in CTS precursor are studied with TGA/DSC and FT-IR, respectively, and a probable mechanism of formation of CTS has been suggested.     

Al2O3/SiO2 films prepared by electron-beam evaporation as UV antireflection coatings on 4H-SiC

Al₂O₃/SiO₂ films have been deposited as UV antireflection coatings on 4H-SiC by electron-beam evaporation and characterized by reflection spectrum, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The reflectance of the Al₂O₃/SiO₂ films is 0.33% and 10 times lower than that of a thermally grown SiO₂ single layer at 276 nm. The films are amorphous in microstructure and characterize good adhesion to 4H-SiC substrate. XPS results indicate an abrupt interface between evaporated SiO₂ and 4H-SiC substrate free of Si-suboxides. These results make the possibility for 4H-SiC based high performance UV optoelectronic devices with Al₂O₃/SiO₂ films as antireflection coatings.     

Microstructural, dielectric and spectroscopic properties of Li2O-Nb2O5-ZrO2-SiO2 glass system crystallized with V2O5

Li₂O-Nb₂O₅-ZrO₂-SiO₂ glasses mixed with different concentrations of V₂O₅ were crystallized. The samples were characterized by XRD, SEM and DTA techniques. The SEM pictures indicated that the samples contain well defined and randomly distributed crystal grains. The X-ray diffraction studies have revealed the presence of several crystalline phases in these samples. Optical absorption, ESR and photoluminescence spectral studies on these samples have indicated that a considerable proportion of vanadium ions do exist in V⁴⁺ state in addition to V⁵⁺ state and the redox ratio seems to be increasing with increase in the concentration of crystallizing agent V₂O₅. The infrared spectral studies have pointed out the existence of conventional SiO₄, ZrO₄, NbO₆, VO structural units in the glass ceramic network. The study of dielectric properties suggested a decrease in the insulating character of the glass ceramics with increase in the crystallizing agent. A.C. conductivity in the high temperature region seems to be connected mainly with the polarons involved in the process of transfer from V⁴⁺↔V⁵⁺ ions.     

Effect of calcination temperature on the structure and hydroxylation activity of Ni0.5Cu0.5Fe2O4 nanoparticles

Nanocrystalline Ni_0.5Cu_0.5Fe₂O₄ was synthesized by sol-gel method with varying calcination temperature over the range of 500-1000. The powders obtained were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In addition, thermal analysis (TG-DTG-DTA) of the precursor was carried out. The study reveals the simultaneous decomposition and ferritization process at rather low temperature (280-350). For the crystalline structure investigated, single cubic spinel is gained when the precursor was decomposed at 800-1000, whereas separated crystal CuO formed when calcination temperature is below 800. The increase of calcination temperature favors the appearance of Fe_B³⁺, Cu_A²⁺ and O on the spinel surface. The hydroxylation activity is relative to the amount of Cu_B²⁺ species on the spinel surface. The lattice oxygen species on the spinel surface are favorable for the deep oxidation of phenol.     

Structure and electrical properties of CdIn2O4 thin films prepared by DC reactive magnetron sputtering

CdIn₂O₄ thin films were prepared by direct-current (DC) reactive magnetron sputtering. The structure, surface morphology and the chemical composition of the thin films were analyzed by X-ray diffraction (XRD), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The electrical properties of the films prepared in different oxygen concentration and annealing treatment were determined, and the effects of the preparing conditions on the structure and electrical properties were also explored. It indicates that the CdIn₂O₄ thin films with uniform and dense surface morphology contain mainly CdIn₂O₄, In₂O₃ phases, and CdO phase is also observed. The XPS analysis confirms the films are in oxygen-deficient state. The electrical properties of these films significantly depend on the preparing conditions, the resistivity of the films with the oxygen concentration of 4.29% is 2.95 × 10⁻⁴ Ω cm and the Hall mobility is as high as 60.32 cm²/V s. Annealing treatment can improve the electrical performance of the films.     

Removal of organic dye by air and macroporous ZnO/MoO3/SiO2 hybrid under room conditions

A new macroporous ZnO/MoO₃/SiO₂ hybrid was synthesized by a method involving sol-gel technology and biomimetic synthesis. It was characterized by Elemental analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS) and scanning electron microscopy (SEM). Chemical degradation of 0.3 g/L Safranin T (ST) by air oxidation over macroporous ZnO/MoO₃/SiO₂ hybrid was studied. It was found that the decolorization efficiency and the chemical oxygen demand (COD) removal of ST reached above 95.3% and 93.2%, respectively, within 25 min at room temperature and atmospheric pressure. And the organic pollutant was mineralized to simple inorganic species such as HCO₃⁻, Cl⁻ and NO₃⁻, while the total organic carbon (TOC) decreased 95.4%. The structure and morphology of the catalyst were still stable after six cycling runs and the leaching test showed negligible leaching effect.     

Sol-gel derived S,I-codoped mesoporous TiO2 photocatalyst with high visible-light photocatalytic activity

A mesoporous S,I-codoped TiO₂ photocatalyst with high visible light photocatalytic activity was synthesized through the hydrolysis and condensation of titanium isopropoxide with thiourea and iodic acid as the precursors. The as-prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-vis diffuse reflectance (DRS), X-ray photoelectron spectroscopy (XPS), Fourier translation infrared spectroscopy (FT-IR), and N₂ adsorption. The results showed that the cations of S⁶⁺ and I⁵⁺ could substitute for some of the lattice titanium (Ti⁴⁺). The S,I-codoping forms the new bands above the valence band and narrows the band-gap of the TiO₂, then shifts the absorption edge from UV light region to visible light range. The activity of the catalyst was examined by photodegradation of methylene blue in an aqueous solution under visible light irradiation. The activity of the S,I-codoped catalyst is far superior to that of single S or I-doped TiO₂ counterpart. The high visible light photocatalytic activity could be attributed to the strong absorption of light, well-crystalline anatase phase, and mesoporous microstructure.     

A facile method to the cube-like MnSe2 microcrystallines via a hydrothermal process

A convenient hydrothermal process was applied to prepare the cube-like MnSe₂ microcrystallines through the reaction of MnSO₄·H₂O with Se and NaH₂PO₂·H₂O in aqueous solution at 160 °C for 12 h. Powder X-ray diffraction (XRD) analysis confirmed that the product was the cubic phase of MnSe₂ with cell parameter a=6.440 Å. The chemical composition of the MnSe₂ was determined by XPS. The Raman spectrum of MnSe₂ presented the peaks of the Se-Se stretching mode at 232.44 and 266.58 cm⁻¹. The images of scanning electron microscope (SEM) and transmission electron microscope (TEM) showed the cube-like morphology of the product with the edge length ranging from 20 to 30 μm. The formation mechanism of the MnSe₂ microcrystallines was discussed as well.     

Growth and characterization of Y2O3 thin films

Y₂O₃ thin films were grown on silicon (1 0 0) substrates by pulsed-laser deposition at different substrate temperatures and O₂ pressures. The structure and composition of films are studied by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Y₂O₃ thin films deposited in vacuum strongly oriented their [1 1 1] axis of the cubic structure and the film quality depended on the substrate temperature. The magnitude of O₂ pressure obviously influences the film structure and quality. Due to the silicon diffusion and interface reaction during the deposition, yttrium silicate and SiO₂ were formed. The strong relationship between composition and growth condition was discussed.     

Aqueous electrochemical insertion of Na into the tungsten oxide hybrid WO3(4,4′-bipyridyl)0.5

Aqueous electrochemical insertion of M⁺ (Na⁺ and H⁺) species into WO₃(4,4′-bipyridyl)_0.5 has been carried out. The chemical states and structure of the resulting product were analysed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). XPS showed the presence of W⁶⁺ as well as the usual reduced W species (W⁵⁺) which is responsible for a change in colour. Moreover, the presence of these intercalates correlates with the evolution of the reduced W species. The bulk structure of the layered hybrid, as determined by powder X-ray diffraction, showed no alteration after electrochemistry, in contrast to the same measurements on tungsten trioxide (WO₃). This however concurs with single-crystal X-ray studies, which show little change in lattice parameters with Na⁺ insertion. Four-probe resistance measurements of the layered hybrid coated film display a drop in resistance after electrochemistry, which can be attributed to the injection of charge-carriers into the conduction band.     

Preparation of alkaline solid polymer electrolyte based on PVA-TiO2-KOH-H2O and its performance in Zn-Ni battery

A novel composite alkaline polymer electrolyte based on poly(vinyl alcohol) (PVA) polymer matrix, titanium dioxide (TiO₂) ceramic fillers, KOH, and H₂O was prepared by a solution casting method. The properties of PVA-TiO₂-KOH alkaline polymer electrolyte films were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and AC impedance techniques. DSC and XRD results showed that the domain of amorphous region in the PVA polymer matrix augmented when TiO₂ filler was added. The SEM result showed that TiO₂ particles dispersed into the PVA matrix although some TiO₂ aggregates of several micrometers were formed. The alkaline polymer electrolyte showed excellent electrochemical properties. The room temperature (20 °C) ionic conductivity values of typical samples were between 0.102 and 0.171 S cm⁻¹. The Zn-Ni secondary battery with the alkaline polymer electrolyte PVA-TiO₂-KOH had excellent electrochemical property at the low charge-discharge rate.     

Optical study of Sr2SnO4:Eu phosphor

This work presents the influence of europium dopant on optical properties of Sr₂SnO₄:Eu³⁺ powders fabricated by a facile low temperature method. Powders were obtained from the same amounts of Eu³⁺ doping into the different concentrations of Sr(NO₃)₂. Powders were examined by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL). SEM measurements different Eu concentrations in fabricated powders was determined to found different morphologies. XRD analysis revealed the existence of crystalline Sr₂SnO₄ in the form of tetragonal and the diffraction intensity was remarkably changed. PL studies showed a red luminescence of Sr₂SnO₄:Eu³⁺ powders. The intensity of luminescence increased with better crystallinity. This approach provides economically viable route for large-scale synthesis of this kind of nanopowders.