Morphology and photoluminescence properties of phenolic epoxy resin coating on KH550-modified SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript> powder in the presence of triarylsulfonium hexafluoroantimonate

In this study, the amino silane coupling agent (KH550)-modified SrAl₂0₄: Eu²⁺, Dy³⁺ phosphor powder coated with phenolic epoxy resin (EOCN) in the presence of triarylsulfonium hexafluoroantimonate catalyst was prepared using the combination of organic–inorganic composite dip-coating and UV curing coating methods. The results of SEM, TEM, and FTIR showed that the organic coating was a layer of compact membrane with a thickness of 20–50 nm, which can be named silane-modified epoxy monomer generated by the KH550 and the EOCN. Furthermore, it was observed that afterglow and spectrum properties of the coated phosphor powder had good long-afterglow luminescence properties, and revealed two emission peaks at 435 nm and 520 nm under the same excitation wavelength of 360 nm, respectively. More interesting, the emitting color of the coated sample was located in the area of cyan light on CIE1931 chromaticity diagram, which led to a slight blue shift rather than the yellow–green color of the pure SrAl₂0₄: Eu²⁺, Dy³⁺ phosphor powder.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>: Eu<Superscript>2+</Superscript>,<Emphasis Type="Italic">RE</Emphasis><Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and Dy³⁺ codoped strontium aluminates SrAl₂O₄: Eu²⁺,Dy³⁺ were prepared by a solid-state reaction. The UV-excited photoluminescence, persistent luminescence, and thermoluminescence of the SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors with different compositions and ion doping was studied and compared. The results showed that the Eu²⁺ ion doped in SrAl₂O₄: Eu²⁺,Dy³⁺ phosphors is not only the UV-excited luminescent center but also the persistent luminescent center. The Dy³⁺ ion introduced into SrAl₂O₄: Eu²⁺ crystal matrix can hardly yield any luminescence under UV excitation but acts as an electron trap with a suitable depth for persistent luminescence. The Dy³⁺ codoping would effectively enhance the persistent luminescence and thermoluminescence. Different codoping RE ³⁺ ions have a different effect on persistent luminescence. Only the RE ³⁺ ions (for example, Dy³⁺ and Nd³⁺), which have suitable optical electronegativity, can form suitable electron traps and effectively improve the persistent luminescence of SrAl₂O₄: Eu²⁺. Based on the above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated. The text was submitted by the authors in English.     

Thermal and neutron shielding properties of <Superscript>10</Superscript>B<Subscript>2</Subscript>O<Subscript>3</Subscript>/polyimide hybrid materials

In this study, ¹⁰B₂O₃/polyimide (PI) hybrid materials were synthesized with the aim to improve their thermal stability and neutron shielding properties. 3,3′-Diaminodiphenyl sulfone (DADPS) reacted with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl-2-pyrrolidone (NMP) and mixed with amine functionalized ¹⁰B₂O₃ to prepare a series of poly (amic acid), meanwhile, corresponding PIs were obtained via the thermal imidization procedures. The morphologies and structures of the prepared hybrid materials were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The thermooxidative and flame retardancy properties of the PI films were examined by thermogravimetric analysis (TGA) and limiting oxygen ındex (LOI). The experimental results showed that as the amount of functionalized ¹⁰B₂O₃ was increased, flame retardant properties of the hybrid films were increased. Hybrid materials were also irradiated with thermal neutrons. The neutron shielding properties increasing depends on the amount and the distribution of the ¹⁰B isotope.     

Interaction of O<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and H<Subscript>2</Subscript>O<Subscript>2</Subscript> with an activated carbon

The results of the modification of AG-OV-1 activated carbon under various conditions (by atmospheric oxygen at elevated temperatures and by hydrogen peroxide or ozone) are given. The effect of the used modifier on changes in the porosity, surface state, and adsorption capacity of activated carbon is evaluated.     

Size-dependent luminescent properties of hollow and dense BaMgAl<Subscript>10</Subscript>O<Subscript>17</Subscript>: Eu blue phosphor particles prepared by spray pyrolysis

Hollow and dense BaMgAl10O17: Eu₂₊ (BAM) phosphor particles were synthesized by a spray pyrolysis process and their luminescent properties were investigated under vacuum ultraviolet (VUV) excitation as varying the average particle size. The dependence of the luminescent intensity on the particle size was greatly influenced by the morphology of BAM particles. For the BAM particles with a hollow structure, the luminescent intensity linearly increased with increasing the particle size. However, no significant change in the luminescent intensity was observed for dense particles as the particle size changed. Also, all dense BAM particles had higher photoluminescence intensity than that of the hollow ones regardless of the particle size. The luminescent intensity of BAM phosphor particles prepared by spray pyrolysis was found to have a linear relationship with the crystallite size. Therefore, it was concluded that suppressing the formation of a hollow structure and increasing the crystallite size are needed to obtain high luminous BAM phosphor particles with a spherical shape and fine size of less than 1 Μm. On the basis of penetration depth of VUV, a simple relation equation between the particle size and the luminescent intensity was derived and correlated with experimental results in order to interpret the luminescent behavior of BAM phosphor as the particle size changes.     

Ni<Superscript>2+</Superscript> reduction under solar irradiation over CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/TiO<Subscript>2</Subscript> catalysts

The photo-electrochemical characterization of the hetero-system CoFe₂O₄/TiO₂ was undertaken for the Ni²⁺ reduction under solar light. The spinel CoFe₂O₄ was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V_SCE) is more cathodic than the potential of Ni²⁺/Ni couple (-0.6 V_SCE), thus leading to a feasible nickel photoreduction. TiO₂ with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni²⁺ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni²⁺ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10^-2 min^-1 according to the Langmuir-Hinshelwood model.     

Dehydration of aldoximes on rare earth exchanged (La<Superscript>3+</Superscript>, Ce<Superscript>3+</Superscript>, RE<Superscript>3+</Superscript>, Sm<Superscript>3+</Superscript>) Na–Y zeolites: A facile route for the synthesis of nitriles

Rare earth exchanged Na–Y zeolites, H-mordenite, K-10 montmorillonite clay and amorphous silica-alumina were effectively employed for the continuous synthesis of nitriles. Dehydration of benzaldoxime and 4-methoxybenzaldoxime were carried out on these catalysts at 473 K. Benzonitrile (dehydration product) was obtained in near quantitative yield with benzaldoxime whereas; 4-methoxybenzaldoxime produces both Beckmann rearrangement (4-methoxyphenylformamide) as well as dehydration products (4-methoxy benzonitrile) in quantitative yields. The production of benzonitrile was near quantitative under heterogeneous reaction conditions. The optimal protocol allows nitriles to be synthesized in good yields through the dehydration of aldoximes. Time on stream (TOS) studies show decline in the activity of the catalysts due to neutralization of acid sites by the basic reactant and product molecules and water formed during the dehydration of aldoximes.     

Structure and properties of glasses in the MgSO<Subscript>4</Subscript>-Na<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>-KPO<Subscript>3</Subscript> system

A glass formation region has been established in the MgSO₄-Na₂B₄O₇-KPO₃ system. This region is located in the borate-phosphate part of the concentration triangle and occupies ∼40% of the triangle area. Based on the spectral data obtained (nuclear magnetic resonance, IR and Raman spectroscopy), a model is proposed in terms of which the physicochemical properties (such as the linear thermal expansion coefficient, the softening temperature, and the glass transition temperature) of the samples are discussed.     

Gd<Superscript>3+</Superscript> doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles with proper magnetic and supercapacitive characteristics: A novel synthesis platform and characterization

A novel electrochemical procedure was developed for the facile preparation of Gd-doped iron oxide nanoparticles (GdIO-NPs). A simple galvanostatic deposition (i=10 mA cm^-2) was done in an additive-free aqueous solution containing FeCl₂·4H₂O, Fe(NO₃)₃·9H₂O and GdCl₃·6H₂O. The XRD, FE-SEM, EDS and TEM characterizations showed that the product is composed of 15% GdIO-NPs with 10 nm in size. VSM analysis proved that the GdIO-NPs are superparamagnetic. The cyclic voltammetry and charge-discharge tests showed that the prepared GdIO-NPs are capable to deliver specific capacity as high as 190.1 F g^-1 at 0.5A g^-1 and capacity retention of 95.1% after 2000 cycling. Based on the results, it was concluded that the developed electrochemical strategy acts as an efficient procedure for the preparation of lanthanide doped MNPs with proper magnetic and supercapacitive characters.     

Preparation of surface-crystallized optical glass-ceramics SrO · 2B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The physicochemical features of the phase formation upon crystallization of monolithic glasses of the strontium diborate stoichiometric composition are investigated. It is demonstrated that the first phase crystallizing on the surface of the SrO · 2B₂O₃ glass is the strontium borate Sr₄B₁₄O₂₅, which plays the role of a precursor for the subsequent crystallization of the SrB₄O₇ borate. The temperature corresponding to the maximum crystal nucleation rate on the surface and the time of complete “operation” of nuclei are determined using differential thermal analysis. The optical glass-ceramics prepared by the two-stage crystallization are surface-crystallized glasses in which the filling density of the surface is approximately equal to 30% and the content of the main phase SrB₄O₇ is as high as ∼ 70%. No second harmonic generation of neodymium laser radiation in the glass-ceramics is observed because of both the absence of the preferred orientation of SrB₄O₇ nonlinear optical crystals and the small crystal sizes (considerably smaller than the coherence length of the SrB₄O₇ crystal) in the direction perpendicular to the glass surface.     

Visible up-conversion luminescence of CaWO<Subscript>4</Subscript>: Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> and emission enhancement by tri-doping of Li<Superscript>+</Superscript> ions

Er³⁺,Yb³⁺ co-doped CaWO₄ polycrystalline powders were prepared by a solid-state reaction and their up-conversion (UC) luminescence properties were investigated in detail. Under 980 nm laser excitation, CaWO₄: Er³⁺,Yb³⁺ powder exhibited green UC emission peaks at 530 and 550 nm, which were due to the transitions of Er³⁺ (²H_11/2)→Er³⁺ (⁴I_15/2) and Er³⁺ (⁴S_3/2)→Er³⁺ (⁴I_15/2), respectively. Effects of Li+ tri-doping into CaWO₄: Er³⁺,Yb³⁺ were investigated. The introduction of Li⁺ ions reduced the optimum calcinations temperature about 100 °C by a liquid-phase sintering process and the UC emission intensity was remarkably enhanced by Li⁺ ions, which could be attributed to the lowering of the symmetry of the crystal field around Er³⁺ ions.     

A Resumable Fluorescent Probe BHN-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> Hybrid Nanostructure for Fe<Superscript>3+</Superscript> and its Application in Bioimaging

A multifunctional fluorescent probe BHN-Fe₃O₄@SiO₂ nanostructure for Fe³⁺ was designed and developed. It has a good selective response to Fe³⁺ with fluorescence quenching and can be recycled using an external magnetic field. With adding EDTA (2.5?×?10^?5 M) to the consequent product Fe³⁺-BHN-Fe₃O₄@SiO₂, Fe³⁺ can be removed from the complex, and its fluorescence probing ability recovers, which means that this constituted on-off type fluorescence probe could be reversed and reused. At the same time, the probe has been successfully applied for quantitatively detecting Fe³⁺ in a linear mode with a low limit of detection 1.25?×?10^?8 M. Furthermore, the BHN-Fe₃O₄@SiO₂ nanostructure probe is successfully used to detect Fe³⁺ in living HeLa cells, which shows its great potential in bioimaging detection.     

Thermal oxidation of A<Superscript>III</Superscript>B<Superscript>V</Superscript> semiconductors with V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanolayers on the surface

The specific features of the interaction of vanadium(V) oxide nanofilms with the surface of gallium arsenide and indium phosphide semiconductors under thermal oxidation conditions have been considered. The kinetics and mechanism of thermal oxidation of GaAs and InP with deposited V₂O₅ layers 15 and 25 nm in thickness have been studied. It has been revealed that vanadium(V) oxide exerts a specific effect on the oxidation of gallium arsenide and indium phosphide as compared to other d-metal oxides. It has been established that the oxidation occurs with the formation of a phase predominantly consisting of indium phosphates or gallium arsenates and intermediate products based on vanadium compounds in different oxidation states. Schemes have been proposed for the development of the oxidation processes with due regard for the chemical nature of vanadium(V) oxide.     

High-temperature crystal chemistry of α-Na<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> and β-NaB<Subscript>3</Subscript>O<Subscript>5</Subscript> layered borates

The thermal expansion of two layered sodium borates is investigated using high-temperature X-ray powder diffraction. It is established that both compounds are characterized by strong anisotropy of thermal expansion due to the hinge mechanism. Special (singular) points are revealed in the temperature dependences of the angular lattice parameters for the α-Na₂B₄O₇ compound. The temperature of manifestation of these singularities corresponds to the glass transition temperature of the melt of the same chemical composition. The assumption is made that the angular lattice parameters (angles between atomic rows) in compounds with a considerable degree of ionic bonding are more sensitive to variations in temperature as compared to the linear lattice parameters (interatomic distances). It is experimentally in situ demonstrated with high-temperature X-ray diffraction that the β-NaB₃O₅ borate is peritectically melted at a temperature of 725 ± 10°C with the formation of the α-Na₂B₈O₁₃ octaborate.     

Sorption studies of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, N<Subscript>2</Subscript>, CO,O<Subscript>2</Subscript> and Ar on nanoporous aluminum terephthalate [MIL-53(Al)]

Aluminum terephthalate, MIL-53(Al), metal–organic framework synthesized hydrothermally and purified by solvent extraction method was used as an adsorbent for gas adsorption studies. The synthesized MIL-53(Al) was characterized by powder X-Ray diffraction analysis, surface area measurement using N₂ adsorption–desorption at 77 K, FTIR spectroscopy and thermo gravimetric analysis. Adsorption isotherms of CO₂, CH₄, CO, N₂, O₂ and Ar were measured at 288 and 303 K. The absolute adsorption capacity was found in the order CO₂>CH₄>CO>N₂>Ar>O₂. Henry’s constants, heat of adsorption in the low pressure region and adsorption selectivities for the adsorbate gases were calculated from their adsorption isotherms. The high selectivity and low heat of adsorption for CO₂ suggests that MIL-53(Al) is a potential adsorbent material for the separation of CO₂ from gas mixtures. The high selectivity for CH₄ over O₂ and its low heat of adsorption suggests that MIL-53(Al) could also be a compatible adsorbent for the separation of methane from methane–oxygen gas mixtures.     

Preparation and properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods as supercapacitor material

Co₃O₄ nanorods have been successfully synthesized by thermal decomposition of the precursor prepared via a facile and efficient microwave-assisted hydrothermal method, using cetyltrimethylammonium bromide (CTAB) with ordered chain structures as soft template for the first time. The obtained Co₃O₄ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The results demonstrate that the as-synthesized nanorods are single crystalline with an average diameter of about 20 to 50 nm and length up to several micrometers. Preliminary electrochemical studies, including cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) measurements, are carried out in 6 M KOH electrolyte. Specific capacitance of 456 F g⁻¹ for a single electrode could be achieved even after 500 cycles, suggesting its potential application in electrochemical capacitors. This promising method could provide a universal green chemistry approach to synthesize other low-cost and environmentally friendly transition metal hydroxide or oxide.     

Synthesis and properties of flux-cast refractories in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Details are given of the synthesis and testing of flux-cast refractory materials in the alumina-rich region of the Al₂O₃-MgO-B₂O₃ system; XRD and petrography indicate that the main structure-forming phases are corundum and magnesian spinel. In subordinate amounts there are the boroaluminate 9Al₂O₃·2B₂O₃ and the previously unknown compound 4Al₂O₃·MgO·2B₂O₃, whose composition has been established by microprobe analysis. Corrosion tests showed that three-component systems containing magnesium and boron oxides at levels of 5–10% do not increase the corrosion resistance of refractories in molten sodium-calcium-silicate glass and electrovacuum borosilicate glass. __________ Translated from Novye Ogneupory, No. 3, pp. 161–163, March, 2008.     

Physicochemical properties of nanocrystalline composites based on ZrO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and rare-earth oxides

Powder precursors have been prepared by means of the sol-gel technique and codeposition, and nanoceramics in the ZrO₂-Al₂O₃-rare-earth (RE) oxide system (RE = Ce, Sc, or Y) based on them have been obtained. Physicochemical properties of the resulting ceramic composites have been investigated. The energy model for oxygen-ionic transport processes in a solid solution based on ZrO₂, which relies on computer simulation procedure, has been proposed, and the structural, strength, and electrophysical characteristics of the solid solution have been calculated. The obtained materials are promising as high-melting electrochemical sensors in molten oxides.     

Properties of a melt of the eutectic composition in the NaPO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>-LiF system

Physical (density, viscosity) and thermophysical (heat capacity, thermal conductivity) properties of a melt of the eutectic composition (wt %) 84NaPO₃ · 8Na₂B₄O₇ · 8LiF have been investigated. It has been demonstrated that this eutectic mixture is a promising material for the use as a high-temperature heat-transfer agent.