Morphological and humidity sensing characteristics of SnO<Subscript>2</Subscript>-CuO,SnO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and SnO<Subscript>2</Subscript>-SbO<Subscript>2</Subscript> nanocooxides

This paper reports the synthesis of SnO₂-CuO, SnO₂-Fe₂O₃ and SnO₂-SbO₂ composites of nano oxides and comparative study of humidity sensing on their electrical resistances. CuO, Fe₂O₃ and SbO₂ were added within base material SnO₂ in the ratio 1: 0.25, 1: 0.50 and 1: 1. Characterizations of materials were done using SEM and XRD. SEM images show the surface morphology and X-ray diffraction reveals the nanostructure of sensing materials. The pellets were annealed at 200, 400 and 600°C respectively for 3 h and after each step of annealing, observations were carried out. It was observed that as relative humidity (%RH) increases, there was decrease in the resistance of pellet for the entire range of RH. Results were found reproducible. SnO₂-SbO₂ shows maximum sensitivity for humidity (12 MΩ/%RH) among other composites.     

Synthesis and crystal structure of [UO<Subscript>2</Subscript>(OH)(CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>(ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The complex [UO₂(OH)(CO(NH₂)₂)₃]₂(ClO₄)₂ (I) was synthesized. A single crystal X-ray diffraction study showed that compound I crystallizes in the triclinic system with the unit cell parameters a = 7.1410(2), b = 10.1097(2), c = 11.0240(4) Å, α = 104.648(1)°, β = 103.088(1)°, γ = 108.549(1)°, space group \(P\bar 1\), Z = 1, R = 0.0193. The uranium-containing structural units of the crystals are binuclear groups [UO₂(OH)· (CO(NH₂)₂)₃] ₂ ²⁺ belonging to crystal-chemical group AM²M ₃ ¹ [A = UO ₂ ²⁺ , M² = OH^?, M¹ = CO(NH₂)₂] of uranyl complexes. The crystal-chemical analysis of nonvalent interactions using the method of molecular Voronoi-Dirichlet polyhedra was performed, and the IR spectra of crystals of I were analyzed.     

High-temperature crystal chemistry of Na<Subscript>6</Subscript>(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript>

Thermal deformations of Na₆(UO₂)₂O(MoO₄)₄ were studied by high-temperature powder X-ray diffraction. The compound crystallizes in the triclinic system, space group Р\(\bar 1\), a = 7.636(7), b = 8.163(6), c = 8.746(4) Å, α = 72.32(9)°, β = 79.36(4)°, γ = 65.79(5)°, V = 472.74(4) ų. It is stable in the temperature interval 20–700°С. The thermal expansion coefficients (TECs) are α₁₁ = 25.5 × 10^–6, α₂₂ = 7.8 × 10^–6, and α₃₃ = 1.1 × 10^–6 (°C)^–1. The orientation of the TEC pattern relative to the crystallographic axes is a₃₃^Z = 45°, a₃₃^X = 122°, a₂₂^Z = 59°, and a₂₂^X = 66°. The anisotropy of the thermal expansion is due to specific features of the crystal structure of the compound.     

Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.     

Bingham viscosity and yield stress of molten (TeO<Subscript>2</Subscript>)<Subscript>0.78</Subscript>(WO<Subscript>2</Subscript>)<Subscript>0.22</Subscript> glass

The flow of molten (TeO₂)_0.78(WO₂)_0.22 glass in a circular-cylindrical channel has been studied at temperatures from 390 to 430°C. The variation of the measured volumetric flow rate with the gas pressure over the melt attests to non-Newtonian flow behavior. The flow rates calculated in the pseudoplastic model were used to determine the yield stress and plastic (Bingham) viscosity of the melt.     

Specific absorption coefficient of chromium in (TeO<Subscript>2</Subscript>)<Subscript>0.80</Subscript>(MoO<Subscript>3</Subscript>)<Subscript>0.20</Subscript> glass

We have prepared (TeO₂)_0.80(MoO₃)_0.20 glass samples containing 0.01 to 0.11 wt % chromium and determined their optical transmission in the range from 450 to 2800 nm. The glasses have been shown to have a strong absorption band centered at 660 nm. From the attenuation coefficient as a function of Cr³⁺ concentration in the glasses, we have evaluated their specific absorption coefficient, which has been shown to be 190 ± 2 cm^–1/wt % at the maximum of the absorption band.     

Phonons in mixed superionic fluorites (BaF<Subscript>2</Subscript>)<Subscript>1-x</Subscript>(LaF<Subscript>3</Subscript>)<Subscript>x</Subscript>

In recent years, the fluorite-structured solid solutions with the general formula, (MF₂)_1-x(RF₃)_x (M = Ca, Sr, Ba, Pb and R is a rare-earth element or Y), have been the subject of numerous experimental studies focussed on their superionic properties. The overall cubic crystal symmetry (space group Fm3m) is conserved up to x ≶ x_max, where x_max ⊁ 0.4-0.5 depending on M and R. The zone centre phonons and phonon dispersion along three symmetry directions of the mixed superionic compound (BaF₂)_1-x(LaF₃)_x have been investigated by applying de Launey angular force model for x ≶ x_max. The calculated results are compared and explained with available experimental results.     

Crystal structure of a complex of Pu(VI) nitrate with triphenylphosphine oxide, [PuO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>(OP(C<Subscript>6</Subscript>H<Subscript>5</Subscript>)<Subscript>3</Subscript>)<Subscript>2</Subscript>]

Single crystals of [PuO₂(NO₃)₂(TPPO)₂] (TPPO = OPPh₃) isostructural to the related compounds of uranyl and neptunyl were isolated, and the structure of this complex was determined. Contrary to the complexes [AnO₂(TPPO)₄](ClO₄)₂ studied previously, the interatomic distances and volumes of coordination polyhedra of An in these compounds somewhat decrease in the series U-Np-Pu. This difference was attributed to a change in the number of TPPO ligands in the compounds and weakening of their interaction with oxygen atoms of the AnO ₂ ²⁺ groups in passing from [AnO₂(TPPO)₂](ClO₄)₂ to [AnO₂(No₃)₂(TPPO)₂].     

UV detector with internal gain based on SnO<Subscript>2</Subscript>-ZnSe heterostructure

SnO₂-ZnSe heterostructures with a high current responsivity (up to 60 A/W) have been manufactured and their electrical and photoelectrical characteristics have been measured.     

Photoluminescence and raman spectra of (Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>(Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0.05</Subscript> crystals

We have measured the photoluminescence and Raman spectra of (Ga₂S₃)_0.95(Sm₂O₃)_0.05 crystals and identified the mechanism of the energy transfer from the host to the rare-earth ion and the vibrational modes of the constituent atoms.     

Vapor growth of SnO<Subscript>2</Subscript> whiskers

Tin dioxide whiskers have been prepared by vapor growth in a tube furnace in flowing argon at a constant evaporation temperature, and the effect of carrier-gas flow rate during growth on their morphology, phase composition, and IR spectrum has been studied. The whiskers are more than 0.5 mm in length and are well crystallized. Reducing the flow rate of the carrier gas during whisker growth makes it possible to reduce the fraction of phases containing tin in lower oxidation states and favors preferential whisker growth along the c axis.     

Study on simultaneous detection of CO and H<Subscript>2</Subscript> with (Pd,Fe)-modified SnO<Subscript>2</Subscript> and Pt-loaded SnO<Subscript>2</Subscript> sensors

The (Pd, Fe)-modified SnO₂ (S1) and Pt-loaded SnO₂ (S2) are synthesized via a sol–gel method. As S1 has better selectivity to CO against H₂ while S2 to H₂ against CO at 400 °C. Thus S1 and S2 can be used to detect the concentration of CO and H₂, respectively. However, neither S1 nor S2 can detect the concentration of CO and H₂ when they coexist. In this paper, S1 and S2 sensors are used simultaneously for mixed gas of CO and H₂ detection, and the respective concentration of CO and H₂ is calculated. The calculation process is explained as follows: the response of S1 (R₁) and S2 (R₂) to a fixed concentration of mixed gas of CO and H₂ is obtained in experiment, respectively. So we can calculate the concentration of CO and H₂ by using simultaneous equations with the independent variable R₁ and R₂. Contrast real values with calculated values of CO and H₂ concentration, the error margin are all less than 5%, which indicates that this method may be a promising candidate for enhancing the selectivity of semiconductor-based gas sensor to two or more gases.     

Gas-sensing properties of antimony-doped SnO<Subscript>2</Subscript>

We report a physicochemical study of the formation of thin-film and particulate SnO₂〈Sb〉 materials from film-forming solutions of Sn(II) and Sb(III) complexes during heat treatment and describe the electrical and gas-sensing properties of the films. The particle size and antimony concentration are shown to have a significant effect on carbon monoxide adsorption by the synthesized materials.     

SO<Subscript>2</Subscript> chemisorption on SnO<Subscript>2</Subscript>〈Sb〉

We have studied SO₂ chemisorption on antimony-doped SnO₂ samples annealed at 200 and 600°C. Increasing the annealing temperature from 200 to 600°C makes the sample surface more homogeneous. In the range 100–200°C, the electrical conductivity of the samples air-annealed at 600°C increases in proportion with the amount of absorbed SO₂. Doping with 0.2 at % Sb ensures the largest increase in conductivity upon chemisorption.     

A facile one step synthesis of SnO<Subscript>2</Subscript>/CuO and CuO/SnO<Subscript>2</Subscript> nanocomposites: photocatalytic application

Here novel photocatalysts, SnO₂/CuO and CuO/SnO₂ nanocomposites were successfully synthesized by chemical method at room temperature. X-ray Diffraction (XRD), transmission electron microscopy (TEM), Fourier transform Infrared (FT-IR), UV–Visible (UV–Vis) and photoluminescence (PL) spectroscopy were utilized for characterization of the nanocomposites. The photocatalytic activity of the nanocomposites was investigated. The hybrid nanocomposites exhibited high photocatalytic activity as evident from the degradation of methylene blue (MB) dye. The result revealed substantial degradation of the MB dye (92 and 69.5% degradation of SnO₂/CuO and CuO/SnO₂, respectively) under visible light illumination with short period of 30 min. Their large conduction band potential difference and the inner electrostatic field formed in the p–n heterojunction provide a strong driving force for the photogenerated electrons to move from Cu₂O to SnO₂ under visible light illumination. The excellent photodegradation of methylene blue suggested that the heterostructured SnO₂/CuO nanocomposite possessed higher charge separation and photodegradation abilities than CuO/SnO₂ nanocomposite under visible light irradiation.     

Enhanced visible light photocatalytic activity for g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/SnO<Subscript>2</Subscript>:Sb composites induced by Sb doping

In this paper, g-C₃N₄/SnO₂:Sb composite photocatalysts were fabricated by in situ loading Sb-doped SnO₂ (SnO₂:Sb) nanoparticles on graphitic carbon nitride (g-C₃N₄) nanosheets via a facile hydrothermal method. The synthesized g-C₃N₄/SnO₂:Sb composites delivered enhanced visible light photocatalytic performance for degradation of rhodamine B in comparison with g-C₃N₄/SnO₂ composites without doping Sb. Various techniques including XRD, SEM, TEM, FTIR, XPS, PL and electrochemical method were employed to demonstrate the successful fabrication of g-C₃N₄/SnO₂:Sb composite and to investigate the enhanced mechanism of photocatalytic activity. The improvement of visible light absorption and the promotion of separation efficiency and interfacial transfer of photogenerated carriers induced by Sb doping were responsible for the enhancement of photocatalytic activity. This study provides a simple and convenient method to synthesize a visible light responsive catalyst with promising performance for the potential application in environmental protection.     

Scalable fabrication of SnO<Subscript>2</Subscript>/eo-GO nanocomposites for the photoreduction of CO<Subscript>2</Subscript> to CH<Subscript>4</Subscript>

Artificial photosynthesis uses a catalyst to convert CO₂ into valuable hydrocarbon products by cleaving the C=O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide (SnO₂) nanoparticles and edge-oxidized graphene oxide (eo-GO) sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO₂ reduction compared to SnO₂ and commercialized TiO₂ (P25), respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.

Open image in new window

     

Photocurrent and Optical Transmission Spectra of Sn- and Pb-Doped (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.3</Subscript>(As<Subscript>2</Subscript>Se<Subscript>3</Subscript>)<Subscript>0.7</Subscript> Glass Films

The photocurrent and optical transmission spectra of thin (As₂S₃)_0.3(As₂Se₃)_0.7 glass films doped with Sn and Pb are reported. The strongest photoresponse is offered by the films doped with 0.010– 0.015 at % Sn or Pb. Low doping levels are shown to have a significant effect on the peak-response wavelength and band gap of the films.     

The ZrO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> phase diagram

The ZrO₂-TiO₂ phase diagram was determined experimentally between 800 and 1200°C, 1 atm, extending our knowledge of this system to temperatures previously inaccessible for equilibrium experiments due to sluggish kinetics. The crystallization of the ordered (Zr,Ti)₂O₄ phase from the oxides was facilitated by the addition of flux (CuO or Li₂MoO₄/MoO₃), and seeds. Two ordered (Zr,Ti)₂O₄ phases with different compositions were identified, and their phase relationships with TiO₂ and ZrO₂ solid solutions investigated. Structure data, superstructure reflections and composition were used to locate the ordering phase transition of (Zr,Ti)₂O₄ in equilibrium with ZrO₂ and TiO₂. At the onset of ordering between 1130 and 1080°C, (Zr,Ti)₂O₄ is of composition X_Ti = 0.495 ± 0.02, and displays a dramatic change in b-dimension. At 1060°C and below, the composition of (Zr,Ti)₂O₄ is significantly more Ti-rich and dependent on temperature, ranging from X_Ti = 0.576 at 1060°C to 0.658 at 800°C. This variability in composition of the ordered phase contrasts with previous studies that suggested the composition to be constant at either X_Ti = 0.667 [ZrTi₂O₆] or 0.583 [Zr₅Ti₇O₂₄]. When grown at low temperatures and with lithium molybdate, the crystals of ordered (Zr,Ti)₂O₄ are acicular to needle shape, and develop distinct square cross-sections and end facets.     

Mo-doped Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>@C composites for high stable sodium ion battery cathode

NASICON-type Na₃V₂(PO₄)₃ (NVP) with superior electrochemical performance has attracted enormous attention with the development of sodium ion batteries. The structural aggregation as well as poor conductivity of NVP hinder its application in high rate perforamance cathode with long stablity. In this paper, Na₃V_2-xMo _x (PO₄)₃@C was successfully prepared through two steps method, including sol-gel and solid state thermal reduction. The optimal doping amount of Mo was defined by experiment. When x was 0.15, the Na₃V_1.85Mo_0.15(PO₄)₃@C sample has the best cycle performance and rate performance. The discharge capacity of Na₃V_1.85Mo_0.15(PO₄)₃@C could reach 117.26 mA·h·g-1 at 0.1 C. The discharge capacity retention was found to be 94.5% after 600 cycles at 5 C.