Hydrothermal synthesis of WO3·H2O with different nanostructures from 0D to 3D and their gas sensing properties

In this paper, WO₃·H₂O with different nanostructures from 0D to 3D were successfully synthesized via a simple yet cost-effective hydrothermal method with the assistance of surfactants. The structures and morphologies of products were investigated by XRD and SEM. Besides, we systematically explained the evolution process and formation mechanisms of different WO₃·H₂O morphologies. It is noted that both the kinds and amounts of surfactants strongly affect the formation of WO₃·H₂O crystals, as reflected in the tailoring of WO₃·H₂O morphologies. Furthermore, the gas sensing performance of the as-prepared samples towards methanol was also investigated. 3D flower-like hierarchical architecture displayed outstanding response to target gas among the four samples. We hoped our results could be of great benefit to further investigations of synthesizing different dimensional WO₃·H₂O nanostructures and their gas sensing applications.     

Hydrothermal synthesis of Fe5(PO4)4(OH)3·2H2O microflowers for fabricating high-performance LiFePO4/C composites

Hierarchical Fe₅(PO₄)₄(OH)₃·2H₂O microflower was synthesized by a hydrothermal reaction with self-prepared β-FeOOH nanorod as raw material. The microflowers were self-assemblies of symmetric building blocks with deep grooves. The possible morphology evolution process was proposed. The microflowers morphology was retained when they were lithiated to prepare LiFePO₄/C composites through a carbothermal reduction method with citric acid as both reducing agent and carbonaceous coating conductor source. As cathode materials for lithium ion batteries, the as-obtained LiFePO₄/C composites deliver a high discharge capacity of 156 mAh g^?1 at 0.1 C rate and exhibit excellent cycling stability, which may be ascribed to the homogeneous coated carbon and the unique microflower structure with grooves.     

MnV2O6⋅V2O5 cross-like nanobelt arrays: synthesis, characterization and photocatalytic properties

Single-crystalline MnV₂O₆?V₂O₅ cross-like nanobelt arrays were successfully synthesized by hydrothermal reaction. The products were characterized by X-ray diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. The effects of the reaction conditions such as pH, V⁵⁺/Mn²⁺ ratio, carboxymethyl cellulose concentration and reaction time on the morphology of the products were studied. The band gap of the as-prepared products was calculated via diffuse reflectance spectral analysis and their activity of photocatalytic oxidation was evaluated by photodegradation of methylene blue under visible-light irradiation. The results showed that the degradation efficiency of methylene blue catalyzed by the calcinated products is remarkably enhanced due to Mn doping, suggesting that MnV₂O₆?V₂O₅ cross-like nanobelt arrays are a good candidate for visible-light-driven photocatalysts.     

Enhanced photocatalytic performance of novel self-assembled floral β-Ga2O3 nanorods

Self-assembled monoclinic phase of novel floral β-Ga₂O₃ nanorods were prepared using reflux condensation method by controlled precipitation of metal cations with urea. The structural and morphological properties were investigated by X-ray powder diffraction, Raman spectroscopy and Scanning electron microscope. Single-crystalline nanorods with size 100 nm involved in the self-assembly process to form flowery pattern have diameter ～1 μm with surface area 40.8 m²/g confirmed from transmission electron microscope and Brunauer–Emmett–Teller analysis. The band gap energy of 4.59 eV was evaluated from the UV–vis diffuse reflectance spectrum and the photoluminescence spectrum displayed the characteristic luminescence and blue-light emission peaks. Further, the photocatalytic activity of novel β-Ga₂O₃ floral nanorods towards the photodegradation of Rhodamine B in aqueous solution under ultra violet light irradiation showed better photocatalytic activity than the commercial photocatalyst Degussa P25 TiO₂.     

Optical,thermal, and structural properties of Nb2O5–TeO2 and WO3–TeO2 glasses

Glass samples from two systems, Nb₂O₅–TeO₂ and WO₃–TeO₂, were prepared at two melt quenching rates and characterized by density, DSC, UV-visible, and Raman spectroscopy. Addition of Nb₂O₅ decreased the density while increase in the WO₃ concentration increased the density. Glasses prepared at higher quenching rates had smaller densities than glasses of the same composition prepared at lower quenching rate although the short-range structure of both glasses were identical, as revealed by Raman spectroscopy. Optical studies found an intense absorption band just below the absorption edge in both the glass series. This band was attributed to electronic transitions of Nb⁵⁺ and W⁶⁺ ions and a lone pair of electrons on Te atoms. Glass transition temperature increased with increase in Nb₂O₅ and WO₃ mol% due to the increase in average bond strength in the glass network. Raman spectroscopy showed that the concentration of TeO₄ units decreased with the increase in Nb₂O₅ and WO₃ concentrations.     

Crystal and magnetic properties of the new copper-sodium borate CuNaB3O6 · 0.842H2O

A new compound CuNaB₃O₆ · 0.842H₂O was grown for the first time. Its crystal structure, magnetic susceptibility, and magnetic resonance properties are presented. It was proposed that CuNaB₃O₆ · 0.842H₂O is a spin-Peierls magnet with the transition temperature T _SP ～ 128 K and a ladder spin structure. The possibility of a structural phase transition at T < T _SP is predicted.     

Interfacial and mechanical properties of carbon fibers modified by electrochemical oxidation in (NH4HCO3)/(NH4)2C2O4·H2O aqueous compound solution

Polyacrylonitrile-based carbon fibers were electrochemical oxidized in (NH₄HCO₃)/(NH₄)₂C₂O₄·H₂O aqueous compound solution to improve its tensile strength and interfacial bounding strength with resin matrix simultaneously. AFM, XPS, XRD and Raman spectra were employed to characterize morphology, chemical states, crystallites size and ordered degree of CFs surface. The results indicated that the optimal modified condition in this paper could increase the tensile strength of CFs by 17.1%, meantime improve the interlaminar shear strength (ILSS) by 14.5%. The improvement of interlaminar shear strength not only causes by increase of surface roughness, but also causes by interaction effects of oxygen-containing and nitrogen-containing functional groups on carbon fibers. Among oxygen-containing functional groups, –COOH functional group plays an important role in enhancing the ILSS. Furthermore, after electrochemical oxidation the crystallites size decreased by 23–27%; ordered degree on CFs surface has an increase with suitable etching which did not peel off the ordered region on CFs surface and create new cracks; both above increase the tensile strength of CFs.     

Electronic structure, optical properties and lattice dynamics of MgSO3·6H2O

The electronic band structure, optical properties and lattice vibrations of MgSO(3)·6H(2)O were studied within density functional theory and compared to the experimental optical data and polarized Raman spectra. Due to the 'molecular' nature of the MgSO(3)·6H(2)O crystal all Γ-point phonon modes could be separated into groups belonging to specific structural blocks: Mg(H(2)O)(6) octahedra, SO(3) units and H(2)O molecules. All Raman lines in the experimental spectra are assigned to definite vibrations of the structure and reasonable agreement is found between theoretical and experimental mode frequencies. The temperature-dependent Raman spectra reveal at 60 °C a sharp transition from MgSO(3)·6H(2)O to anhydrous amorphous MgSO(3) without the noticeable presence of intermediate lower hydrates, such as MgSO(3)·3H(2)O.     

Hydrothermal synthesis and volatile organic compounds sensing properties of La–TiO2 nanobelts

We report the microstructure and gas-sensing properties of La–TiO₂ nanobelts prepared by the hydrothermal method. In particular, we make a comparison of the volatile organic compounds (VOCs) sensing properties between La–TiO₂ nanobelts and La–TiO₂ nanospheres. The results show that La–TiO₂ nanobelts exhibit higher gas response as well as lower working temperature as compared to that of La–TiO₂ nanospheres, suggesting that the gas sensing properties of nanocrystals can be significantly improved by tailoring the shape and the surface structure of nanocrystals.     

Synthesis of flower-shape clustering GaN nanorods by ammoniating Ga2O3 films

Flower-shape clustering GaN nanorods are successfully synthesized on Si（111） substrates through ammoniating Ga2O3/ZnO films at 950℃. The as-grown products are characterized by x-ray diffraction （XRD）, scanning electron microscope （SEM）, field-emission transmission electron microscope （FETEM）, Fourier transform infrared spectrum （FTIR） and fluorescence spectrophotometer. The SEM images demonstrate that the products consist of flower-shape clustering GaN nanorods. The XRD indicates that the reflections of the samples can be indexed to the hexagonal GaN phase and HRTEM shows that the nanorods are of pure hexagonal GaN single crystal. The photoluminescence （PL） spectrum indicates that the GaN nanorods have a good emission property. The growth mechanism is also briefly discussed.     

Microwave-assisted synthesis of Zn–WO3 and ZnWO4 for pseudocapacitor applications

Nanosized Zn–WO₃ and ZnWO₄ materials have been prepared by microwave irradiation method. The physico-chemical characterization of the prepared nanomaterials was carried out by X-ray diffraction (XRD) and high resolution-scanning electron microscopy (HR-SEM) techniques. The size and shape of the ZnWO₄ material can be controlled by changing the temperature. The XRD analysis revealed the formation of monoclinic phase of the calcined nanopowder. The HR-SEM images showed the sphere and plate shape particles. The electrochemical behavior of the ZnWO₄ modified electrodes was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) techniques. The synthesized material shows the pseudocapacitance. The specific capacitance of 35.70 F/g was achieved for the Zn–WO₃ nanopowder.     

Electrical properties of V2O5B2O3 glasses

Binary semiconducting glasses of xV₂O₅·(1−x)B₂O₃ system with x ranging from 0.6 to 0.9 have been investigated to elucidate their electronic conduction. The values of conductivity and activation energy of these glasses are in good agreement with previous results on most V₂O₅-based glasses. Arguments for the small-polaron as the charge carrier in V₂O₅B₂O₃ glasses are presented.     

Hydrolysis precipitation synthesis of monodisperse α-Fe2O3 nanorods/graphene oxide nanocomposites

A nanocomposite of graphene oxide supported by monodisperse rod-like α-Fe₂O₃ nanocrystals (GO/α-Fe₂O₃ nanocomposites) has been fabricated through a simple hydrolysis precipitation route in a water–ethanol system. The nanocomposites were characterized by X-ray diffraction, Raman spectra and transmission electron microscopy, respectively. The GO/α-Fe₂O₃ nanocomposites are GO nanosheets decorated randomly by α-Fe₂O₃ nanorods with diameters in the range of 3–5 nm and lengths of 20–30 nm, while only hollow α-Fe₂O₃ microspheres constructed by the radically oriented single-crystalline nanorods are observed in the absence of GO. Compared with pure α-Fe₂O₃ nanoparticles, α-Fe₂O₃/GO nanocomposites exhibited excellent photocatalytic activity as evident from the degradation of rhodamine B in water under UV irradiation. The superior photocatalytic activity performance of α-Fe₂O₃/GO nanocomposites could be attributed to the synergetic effect between the conducting GO nanosheets and monodisperse α-Fe₂O₃ nanorods.     

One-step simple sonochemical fabrication and photocatalytic properties of Cu2O–rGO composites

An easy, one-step synthesis of Cu₂O–reduced graphene composites (Cu₂O–rGO) was developed using a simple sonochemical route without any surfactants or templates. The morphology and structure of the Cu₂O–rGO composites were characterised using techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results indicated that the Cu₂O sphere is approximately 200 nm in diameter and composed of small Cu₂O particles approximately 20 nm in diameter. The morphology and composition of the Cu₂O–rGO composites could be well controlled by simply changing the mole ratio of the reactants under ultrasonic irradiation. The Cu₂O–rGO composites displayed better photocatalytic performance for the degradation of methyl orange (MO) than pure Cu₂O spheres, which may have potential applications in water treatment, sensors, and energy storage.     

Facile synthesis of flower-like α-Fe2O3/ZnFe2O4 architectures with self-assembled core-shell nanorods for superior TEA detection

Uniform flower-like α-Fe₂O₃ architectures with self-assembled core-shell nanorods are constructed and successfully prepared via the facile process. The concentration of Fe salt plays a great significance for morphological evolution from nanorods to self-assembled microflowers. Flower-like α-Fe₂O₃/ZnFe₂O₄ consisting of α-Fe₂O₃ core and ZnFe₂O₄ shell nanorods are derived from FeOOH/ZIF-8 precursors. The detailed studies reveal that the tunable growth of ZIF-8 nanoparticles on three-dimensional FeOOH microflowers at room temperature and the availble calcination regulation are responsible for the formation of core-shell Fe₂O₃/ZnFe₂O₄ composites. The highest response value of flower-like α-Fe₂O₃/ZnFe₂O₄ architectures to 100 ppm triethylamine (TEA) has been improved to 141 at 280 °C, which is calculated to be 6.2 times compared with flower-like α-Fe₂O₃ architectures (22.7). The enhanced gas-sensing mechanism of α-Fe₂O₃/ZnFe₂O₄ composites can be attributed to the typical microflowers structures, the large specific surface area, the effective heterojunctions between α-Fe₂O₃ core and ZnFe₂O₄ shell, and the improved electron transfer process.     

Effect of Li2O on the structure,electrical and dielectric properties of xLi2O·(20−x)CaO·30P2O5·30V2O5·20Fe2O3 glasses

Glasses of the general formula xLi₂O·(20?x)CaO·30P₂O₅·30V₂O₅·20Fe₂O₃ with x=0, 5, 10, 15 and 20 mol% were prepared; IR, density, electrical and dielectric properties have been investigated. Lithia-containing glasses revealed more (P₂O₇)^4?, FeO₆, V–O^? and PO^? groups and mostly have lower densities than those of lithia-free ones. The electrical properties showed random behavior by replacing Li₂O for CaO, which has been assigned to the change of the glass structure. The results of activation energy and frequency-dependent conductivity indicate that the conduction proceeds via electronic and ionic mechanisms, the former being dominant. The mechanism responsible for the electronic conduction is mostly thermally activated hopping of electrons from Fe(II) ions to neighboring Fe(III) sites and/or from V⁴⁺ to V⁵⁺. The dielectric constant (ε′) showed values that depend on the structure of glass according to its content of Li₂O. The (ε′) values are ranging between 3 and 41 at room temperature for 1 kHz, yet at high temperatures, glass with 20 mol Li₂O exhibits values of 110 and 3600 when measurement was carried out in the range 0.1–1 kHz, and at 5 MHz, respectively.     

Experimental study of sono-crystallisation of ZnSO4·7H2O, and interpretation by the segregation theory

Power ultrasound is known to enhance crystals nucleation, and nucleation times can be reduced by one up to three orders of magnitude for several organic or inorganic crystals. The precise physics involved in this phenomenon still remains unclear, and various mechanisms involving the action of inertial cavitation bubbles have been proposed. In this paper, two of these mechanisms, pressure and segregation effects, are examined. The first one concerns the variations of supersaturation induced by the high pressures appearing in the neighbourhood of a collapsing bubble, and the second one results from the modification of clusters distribution in the vicinity of bubble. Crystallisation experiments were performed on zinc sulphate heptahydrate ZnSO(4)·7H(2)O, which has been chosen for its pressure-independent solubility, so that pressure variations have no effect on supersaturation. As observed in past studies on other species, induction times were found lower under insonification than under silent conditions at low supersaturations, which casts some doubts on a pure pressure effect. The interfacial energy between the solid and the solution was estimated from induction times obtained in silent conditions, and, using classical nucleation theory, the steady-state distribution of the clusters was calculated. Segregation theory was then applied to calculate the over-concentrations of n-sized clusters at the end of the collapse of a 4 μm bubble driven at 20 kHz by different acoustic pressures. The over-concentration of clusters close to the critical size near a collapsing bubble was found to reach more than one order of magnitude, which may favour the direct attachment process between such clusters, and enhance the global nucleation kinetics.     

Structural and thermoelectric power properties of Na-doped V2O5·nH2O nanocrystalline thin films

X-ray diffraction (XRD), thermoelectric power (S) and at room temperature electrical conductivity (σ) of Na⁺¹-doped V₂O₅·nH₂O nanocrystalline thin films fabricated by sol gel technique (colloid route) were studied. XRD showed that the Na₂O–V₂O₅·nH₂O thin films are highly oriented nanocrystals. The average value of particle size was found to be about 7.5 nm. The thermoelectric power showed that the thermoelectric power for all present nanocrystalline thin films samples decreased with increasing Na⁺¹ content. However, the electrical conductivity increased with increasing Na⁺¹ content. There is evidence that small polarons are responsible for determining the transport properties of the Na⁺¹ doped V₂O₅·nH₂O nanocrystalline thin films samples. The high value of electrical conductivity and small value of thermoelectric power is ideal for device applications, where device to device variation of the thermoelectric power must be small. This preparation technique was demonstrated to fabricate high quality Na₂O–V₂O₅·nH₂O nanocrystalline thin films for thermoelectric device applications. However, this may be further used for deposition with an ink-jet printer.     

Structural characterization,thermal, ac conductivity and dielectric properties of (C7H12N2)2[SnCl6]Cl2·1.5H2O

(C₇H₁₂N₂)₂[SnCl₆]Cl₂·1.5H₂O is crystallized at room temperature in the monoclinic system (space group P2₁/n). The isolated molecules form organic and inorganic layers parallel to the (a, b) plane and alternate along the c-axis. The inorganic layer is built up by isolated SnCl₆ octahedrons. Besides, the organic layer is formed by 2,4-diammonium toluene cations, between which the spaces are filled with free Cl^? ions and water molecules. The crystal packing is governed by means of the ionic N—H···Cl and Ow—H···Cl hydrogen bonds, forming a three-dimensional network. The thermal study of this compound is reported, revealing two phase transitions around 360(±3) and 412(±3) K. The electrical and dielectric measurements were reported, confirming the transition temperatures detected in the differential scanning calorimetry (DSC). The frequency dependence of ac conductivity at different temperatures indicates that the correlated barrier hopping (CBH) model is the probable mechanism for the ac conduction behavior.