Synthesis of layered hierarchical porous SnO<Subscript>2</Subscript> for enhancing gas sensing performance

Layered hierarchical porous SnO₂ (LHP-SnO₂) have been synthesized by a two-step method, in which pure SnO₂ nanoparticles(NPs) with the diameter about 3.2 nm were prepared firstly through a hydro-thermal method, and then LHP-SnO₂ were prepared by utilizing polystyrene (PS) microspheres as a template and SnO₂ NPs as a precursor. The as-prepared sample consisted of porous SnO₂ layers, in which each layer presents a three-dimensional random arrangement of macropores with average pore diameter of about 260 nm. The Nitrogen adsorption–desorption analysis implied that the sample was characterized with large surface area of 140.67 m²/g and extensive micropores and mesopores structure. Compared with pure SnO₂ NPs, the LHP-SnO₂ exhibited an obvious improvement in gas sensing properties. These results indicate that the layered hierarchical porous structure possess potential application in sensing materials.     

Synthesis and characterization of monodisperse hollow SnO<Subscript>2</Subscript> microspheres and their enhanced sensing properties to ethanol

The monodisperse hollow SnO₂ (H-SnO₂) microspheres were successfully synthesized by the ion exchange method using sulfonated PS microspheres as a template. The structure and morphology were characterized by X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy, which confirms the hollow structure of the products. The H-SnO₂ microspheres are composed of numerous SnO₂ nanoparticles with a shell thickness of about 13 nm. The monodisperse H-SnO₂ microspheres have a high specific surface area of 55.54 m²/g, which improves the gas sensing properties toward ethanol. Gas-sensing measurement results indicate that H-SnO₂ microspheres exhibit an excellent sensitivity (103.1) toward 200 ppm ethanol at 260 °C, which is much higher than that (65.8) of SnO₂ nanoparticles.     

Electronic and magnetic properties of SnO<Subscript>2</Subscript>/CrO<Subscript>2</Subscript> thin superlattices

In this article, using first-principles electronic structure calculations within the spin density functional theory, alternated magnetic and non-magnetic layers of rutile-CrO₂ and rutile-SnO₂ respectively, in a (CrO₂) _n (SnO₂) _n superlattice (SL) configuration, with n being the number of monolayers which are considered equal to 1, 2, ..., 10 are studied. A half-metallic behavior is observed for the (CrO₂) _n (SnO₂) _n SLs for all values of n. The ground state is found to be FM with a magnetic moment of 2 μ_B per chromium atom, and this result does not depend on the number of monolayers n. As the FM rutile-CrO₂ is unstable at ambient temperature, and known to be stabilized when on top of SnO₂, the authors suggest that (CrO₂) _n (SnO₂) _n SLs may be applied to spintronic technologies since they provide efficient spin-polarized carriers.     

Synthesis of nanocomposite materials in the SnO<Subscript>2</Subscript>-NiO system

The SnO₂-NiO nanocomposites with the specific surface area on the order of 100 m²/g and the particle size of both phases of less than 10 nm have been synthesized by the sol-gel method with the subsequent annealing in the temperature interval 200–1000°C. It has been shown that, with an increase in the annealing temperature to 900°C, the specific surface area of the nanocomposites increases. This effect has been explained by the increase in the porosity due to the destruction of the aggregates of primary amorphous particles. The electrical conductivity has been measured and the parameters of the surface defects have been determined.     

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.     

Preparation,characterizations, and antibacterial properties of Cu/SnO<Subscript>2</Subscript> nanocomposite bilayer coatings

A nano-bilayer structure consisting of copper and SnO₂ nanocomposites was prepared by a magnetron sputtering method. A nano-SnO₂ thin layer with a thickness of 52 nm was achieved on quartz glass. A nano-copper layer was then deposited on top of the SnO₂ thin layer by the sputtering method. The thickness of the nano-copper layer was approximately 7 nm, such that the SnO₂ layer was not only completely covered by the copper layer but it also resulted in transparent bilayer films. Post-annealing was carried out at 400°C in air for 1 h to obtain a crystalline SnO₂ phase and simultaneously the copper layer was oxidized to CuO. Sputtered nanocomposites of CuO/SnO₂ bilayer films showed a synergistic effect toward E. coli inactivation under indoor light exposure. A possible mechanism for the synergistic effect with respect to the antibacterial properties of CuO/SnO₂ bilayer nanocomposites has been proposed. Incorporating CuO onto the SnO₂ layer achieves photocatalyst works under indoor light and provides an antimicrobial function even under a dark environment by the antimicrobial property of CuO itself. Reported CuO/SnO₂ sputter coating can be useful to apply, for instance, to electric devices such as touch panel displays in a hospital in order to reduce hospital-acquired infections (HAIs).     

Synthesis of PDMS-SiO<Subscript>2</Subscript> hybrids using different templates

Xerogels’ formation in the hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) was studied by varying pH through adopting three different type basic catalysts (n-octylamine, dodecylamine and tetradecylamine), respectively. The effect of different templates to the formation of xerogels was investigated and characterized by FTIR, N₂ physisorption, TG-DSC and SEM analysis. The results showed that the morphology and textural characteristics of the xerogels prepared in three kinds of organic amine solutions were quite different. The texture of xerogels became more compact after addition of hydroxyl-terminated polydimethylsiloxane (PDMS-OH). Comparing with dodecylamine and tetradecylamine, n-octylamine is more suitable as catalyst to TEOS/PDMS for stone consolidation.     

Synthesis and electrochemical properties of layered LiNi<Subscript>1/2</Subscript>Mn<Subscript>1/2</Subscript>O<Subscript>2</Subscript>prepared by coprecipitation

Spherical LiNi_1/2Mn_1/2O ₂ powders were synthesized from LiOH . H₂O and coprecipitated metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The average particle size of the powders was about 10 m and the size distribution was quite narrow due to the homogeneity of the metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The tap-density of the LiNi_1/2Mn_1/2O₂ powders was approximately 2.2 g cm_–3, which is comparable to the tap-density of commercial LiCoO₂. The LiNi_1/2Mn_1/2 O₂electrode delivered a discharge capacity of 152, 163, 183, and 189 mA h g^–1 in the voltage ranges of 2.8–4.3, 2.8–4.4, 2.8–4.5, and 2.8–4.6 V, respectively, with good cyclability. Furthermore, Al(OH)₃-coated LiNi_1/2Mn_1/2O₂exhibited excellent cycling behavior and rate capability compared to the pristine electrode.     

Synthesis and characterization of rubbery/glassy blend membranes for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> gas separation

A series of blend membranes made from the rubbery polyether block amide (Pebax®1657) and a glassy polymer, polyethersulfone (PES) or Matrimid 5218, were fabricated by solution casting with different ratios (10–40 %), in order to combine high permeability of the former with high selectivity of the latter polymer for CO₂/CH₄ gas separation. The membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and stress–strain tests. These blend membranes showed two distinct T _g s, indicating their immiscible nature as confirmed by SEM images. However, weak intermolecular interaction between polymers, as illustrated by the FTIR results, corresponds to some degree to their compatibility and improved mechanical strength, compared to the pure Pebax®. TGA analysis revealed that addition of glassy polymer improved membranes’ thermal stability. Effect of feed pressure on membrane separation, investigated by three different pressures (4, 8, and 12 bar), indicated increased permeability for higher pressures for both CO₂ and CH₄. Gas separation tests also pointed to improved separation properties of the blend membranes compared to those of the neat polymers, prepared the same way.     

Electrochemical properties of microwave-assisted reflux-synthesized Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in different electrolytes for supercapacitor applications

The nanosized Mn₃O₄ particles were prepared by microwave-assisted reflux synthesis method. The prepared sample was characterized using various techniques such as X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Raman analysis, and transmission electron microscopy (TEM). Electrochemical properties of Mn₃O₄ nanoparticles were investigated using cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge analysis in different electrolytes such as 1 M KCl, 1 M Na₂SO₄, 1 M NaNO₃, and 6 M KOH electrolytes. XRD pattern reveals the formation of single-phase Mn₃O₄ nanoparticles. The FT-IR and Raman analysis also assert the formation of Mn₃O₄ nanoparticles. The TEM image shows the spherical shape particles with less than 50 nm sizes. Among all the electrolytes, the Mn₃O₄ nanoparticles possess maximum specific capacitance of 94 F g⁻¹ in 6 M KOH electrolyte calculated from CV. The order of capacitance obtained by various electrolytes is 6 M KOH > 1 M KCl > 1 M NaNO₃ > 1 M Na₂SO₄. The EIS and galvanostatic charge–discharge results further substantiate with the CV results. The cycling stability of Mn₃O₄ electrode reveals that the prepared Mn₃O₄ nanoparticles are a suitable electrode material for supercapacitor application.     

Low-temperature anti-icing reagents in the Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O system and their properties

The polytherms of ice melting in sections of the Ca(NO₃)₂-Mg(NO₃)₂-CO(NH₂)₂-H₂O system with different component ratios were studied in the temperature interval from 0 to −40°C. A series of nitrate and nitrate-carbonate reagents that are promising for the creation of anti-acing reagents were found, which form eutectics with ice at temperatures from −25 to −39°C. Their properties, viz., melting properties with respect to ice and corrosiveness on metals and alloys, were determined. An effective corrosion inhibitor was selected.     

Nanomodification of SnO<Subscript>2</Subscript> films by doping with additives of copper and gold chlorides

The hydropyrolytic method was used to prepare samples of tin dioxide films without the doping additive, and also tin dioxide films with additives containing copper oxides and copper with gold. It was shown that by using doping additives it is possible to effectively control the ratio of the area of the film surface to its volume and, consequently, the adsorption ability of the sensor material.     

Synthesis and crystal structure of a new oxohalide CdPb<Subscript>2</Subscript>O<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

A new compound, CdPb₂O₂Cl₂, is synthesized by the method of solid-phase reactions. The compound has monoclinic symmetry, space group C2/m, a = 12.392(8) Å, b = 3.8040(14) Å, c = 7.658(5) Å, β = 122.64(5)°, and V = 304.0(3) ų. The structure contains one symmetrically independent position of the Pb²⁺ cation coordinated by three O^2? anions (Pb²⁺-O^2? = 2.29–2.34 Å) and five Cl^? anions (Pb²⁺-Cl^? = 3.35–3.57 Å). The Cd²⁺ cation has a symmetric coordination with the formation of two bonds Cd-O = 2.15 Å and four bonds Cd-Cl = 2.73 Å. The oxygen atom is tetrahedrally coordinated by three Pb²⁺ cations and one Cd²⁺ cation, which leads to the formation of oxo-centered heterometallic OPb₃Cd tetrahedra. The tetrahedra are linked together into chains through common Pb atoms and into layered complexes due to sharing of the equatorial Cd atoms. The chlorine atoms are located above the cavities of the oxo-centered layer.     

Electrolytic properties of sulfide-conducting phases based on the BaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> and CaLn<Subscript>2</Subscript>S<Subscript>4</Subscript> compounds of different structural types

The criteria for the choice of objects of investigation that possess sulfide-ion conduction, have the general formula MeLn₂S₄, and crystallize in different structural types are considered. The data obtained on the electrolytic properties of phases based on BaLn₂S₄(Ln = Nd, Sm, Tm); CaFe₂O₄ structural type), CaLn₂S₄(Ln = Y, Yb); Yb₃S₄ structural type), and CaLn₂S₄(Ln = Pr, Nd, Gd); Th₃P₄ structural type) are generalized. The performed comparative analysis of the properties of the synthesized electrolytes has demonstrated that the properties of solid electrolytes depend on the configuration of the f state of lanthanides to a greater extent than on the structure of the electrolytes under investigation. The vacancy mechanism of defects formation and sulfide-ion transfer in phases based on thiolanthanates is proposed reasoning from the data on the dependence of the electrolytic and thermodynamic properties on the composition.     

Spectroscopic investigation,cage occupancy,and gas storage capacity of hydroquinone clathrates formed with H<Subscript>2</Subscript>S-N<Subscript>2</Subscript> and COS-N<Subscript>2</Subscript> binary gas mixtures

The objective of this investigation was to determine whether hydroquinone (HQ) can form clathrate compounds with two sulfides (hydrogen sulfide (H₂S) and carbonyl sulfide (COS)) at their diluted concentrations. Hydroquinone samples obtained at ambient temperature and at two pressures (40 and 80 bar) for binary gas mixtures consisting of H₂S-N₂ and COS-N₂, were analyzed using solid-state ¹³C NMR and Raman spectroscopy. An elemental analyzer was also used to obtain quantitative information regarding the kind and amount of gas captured in the solid samples. Results show that H₂S can be concentrated within the solid clathrate from H₂S-containing gas, while COS is little captured after reaction with the COS-containing gas. This suggests that the HQ clathrate can be used to remove H₂S, and that selective separation can be achieved when two sulfides of H₂S and COS coexist. On the basis of the calculated cage occupancies of the gas components in the solid clathrate, the enclathration preference of the gas components used in this research was found to be the order of H₂S>N₂>COS.     

Synthesis,characterization and electrical properties of polypyrrole/V<Subscript>2</Subscript>O<Subscript>5</Subscript> composites

Polypyrrole (PPy) and its composites with vanadium pentoxide (V₂O₅) were synthesized in aqueous medium by chemical oxidation polymerization using FeCl₃·6H₂O as an oxidant. The materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometry (XRD), thermogravimetry analyzer (TGA), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), UV/visible spectroscopic techniques and LCR-meter. The FT-IR results confirmed the successful synthesis of PPy and PPy/V₂O₅ composites. The XRD study showed the amorphous and crystalline nature of PPy and PPy/V₂O₅ composites, respectively. The TGA analysis showed slight increase in the thermal stability of the composites. The SEM data verified the porous nature of PPy and the composites. The UV/visible spectrometry confirmed the doping of PPy in composites. The electrical properties of the materials displayed their semiconducting nature. The resistance of the samples was found to be dependent on temperature and the contents of V₂O₅ in the composites.     

Synthesis of CeO2 nanoparticles with different morphologies and their properties as peroxidase mimic

The overall objective of this work was to identify and determine the controlling factors of catalytic activity of CeO₂ nanoparticles with different properties. Therefore, four kinds of CeO₂ nanoparticles are successfully synthesized and used as peroxidase mimics. The results reveal that the catalytic activity is related to specific surface area and surface oxygen (O_sur) content. For different CeO₂ nanoparticles, specific surface area is the leading factor of catalytic activity. The catalytic activity increases with the increasing specific surface area. If the CeO₂ nanoparticles have similar specific surface area, the less O_sur contains, the lower catalytic activity will be. Meanwhile, crystallinity is not the influence factor of catalytic activity. Bamboo-like CeO₂ (B-CeO₂) nanoparticles show excellent catalytic activity and the reaction conditions are optimized. Furthermore, the catalytic activity of B-CeO₂ nanoparticles decreases very slightly after 15 cycles of the catalysis experiment. Therefore, B-CeO₂ nanoparticles can serve as effective recyclable peroxidase mimics.