Laser-induced thermal effects in hexagonal MoO3 nanorods

Laser-induced thermal effects on the hexagonal MoO₃ nanorods at different power density levels were studied using Raman spectroscopy and scanning electron microscopy techniques. The structural features of the nanorods were accompanied by varying the incident laser power from 8.0 to 600 mW by using a gradual increasing rate and a sudden increasing incident laser power. It was shown that the photoeffects observed on the MoO₃ nanorods critically depends on the exposure rate. By gradually increasing the incident laser power up to 600 mW, morphology of the nanorods were completely preserved, and the observed thermal behavior was discussed on the basis of thermal contact at nanoscale. However, when the irradiation intensity was suddenly increased, it was observed that overheating of h-MoO₃ nanorods at relatively lower laser powers (80 mW) sublimate the nanorods around the laser spot region. The MoO₃ molecules on vapor-phase at high temperatures condense and crystallize next to the laser spot on the orthorhombic (α-MoO₃) and monoclinic (β-MoO₃) phases. Furthermore, the nanorods closest to the laser spot region undergo a structural phase (and morphological) transition from h-MoO₃ phase to α-MoO₃ phase.     

High-pressure Raman scattering on Fe2(MoO4)3 microcrystals obtained by a hydrothermal method

This study reports on the effect of high hydrostatic pressure on the vibrational spectra of Fe₂(MoO₄)₃ microcrystals using Raman scattering in combination with a membrane diamond-anvil cell. The ferric molybdate was obtained by the conventional hydrothermal method, and the structural and morphological properties of the sample were characterized using additionally X-ray diffraction, scanning electron microscopy, as well as energy dispersive spectroscopy. The X-ray diffraction measurements have shown that the crystals have a monoclinic structure. At pressures higher than 4.8 GPa, the disappearance of external modes was observed, suggesting that pressure has induced a breakdown in the translational symmetry of the crystal system. The high-pressure amorphous phase is reversible and attributed to an incomplete crystal-amorphous transformation.     

Microwave-assisted hydrothermal synthesis and electrochemical studies of α- and h-MoO<Subscript>3</Subscript>

Two modifications of molybdenum trioxide with orthorhombic (α-MoO₃) and hexagonal (h-MoO₃) crystal structure have been synthesized by a microwave-assisted hydrothermal method, facilitated by formic acid. Characterization by means of X-ray diffraction, scanning electron microscopy, specific surface analysis, and Fourier-transform infrared, Raman, and UV-Vis spectroscopy reveals phase-pure crystalline powder samples of hexagonal h-MoO₃ microrods and of α-MoO₃ nanobelt bundles, respectively. The electrochemical properties of the MoO₃ compounds, studied by cyclic voltammetry and galvanostatic cycling vs. Li/Li⁺, strongly depend on the structure and the applied potential range. In the range of 1.5–3.5 V, Li⁺-ions can be reversibly intercalated into the α-MoO₃ nanobelts. Utilizing the material in this way as intercalation cathode material yields an initial discharge capacity of 295 mA h g^?1 at 100 mA g^?1 and comparably moderate capacity fading of 25% between cycles 20 and 100. Extending the potential range to 0.01–3.0 V induces the conversion reaction to Mo, which for both modifications yields high initial capacities of around 1500 mA h g^?1 but is associated with much stronger capacity fading.     

Hydrothermal synthesis,characterization, and photocatalytic performance of W-doped MoO<Subscript>3</Subscript> nanobelts

Orthorhombic MoO₃ and W-doped MoO₃ nanobelts were successfully synthesized by a hydrothermal method. The effect of W dopant on the photocatalytic performance of W-doped MoO₃ nanobelts was studied. The phase, morphology, and oxidation state of the products were characterized by X-ray diffraction analysis, Fourier-transform infrared and Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. In this research, MoO₃ and W-doped MoO₃ exhibited the same phase and morphology of orthorhombic nanobelts with growth along the [001] direction, including detection of Mo⁶⁺, O^2?, and W⁶⁺ in the 3 mol% W-doped MoO₃ sample. The photocatalytic performance of the as-synthesized MoO₃ and W-doped MoO₃ nanobelts was monitored through photodegradation of methylene blue (MB) under visible radiation. W-doped MoO₃ nanobelts showed better photocatalytic performance than pure MoO₃. The 3 mol% W-doped MoO₃ photocatalyst exhibited very good visible-light-driven activity for photodegradation of MB, as high as 99 % within 60 min.     

Local and Remote Charge‐Transfer‐Enhanced Raman Scattering on One‐Dimensional Transition‐Metal Oxides

The one‐dimensional (1D) transition‐metal oxide MoO₃ belt is synthesized and characterized with X‐ray diffraction, scanning electron microscopy, and Raman spectroscopy. Charge‐transfer‐(CT) enhanced Raman scattering of 4‐mercaptobenzoic acid (4‐MBA) on a 1D MoO₃ belt was investigated experimentally and theoretically. The chemical enhancement of surface‐enhanced Raman scattering (SERS) of 4‐MBA on the MoO₃ belt by CT is in the order of 10³. The SERS of 4‐MBA was investigated theoretically by using a quantum chemical method. The remote SERS of 4‐MBA along the 1D MoO₃ belt (the light excitation to one side of the MoO₃ belt, and the SERS spectrum is collected on the other side of the MoO₃ belt) is also shown experimentally, which provides potential applications of SERS. The incident polarization dependence of remote SERS spectra has also been investigated experimentally.     

The photocatalytic properties of Ti–Mo oxides prepared by a simple sol–gel route

Powders containing mixtures of titania and molybdite in different ratios were prepared by sol–gel processing. The sols were dried and subsequently calcined at 300, 500 and 700 °C. Depending on the ratio of Ti and Mo in the initial sol and the calcination temperature, Ti-doped MoO₃, TiO₂/MoO₃ or Mo-doped TiO₂ have been formed. The as prepared samples were characterised by scanning electron microscopy with attached X-ray dispersive energy analysis, X-ray diffractometry, Raman spectroscopy, gas adsorption and optical characterisation by ultraviolet/visible spectroscopy. The latter was used for the analysis of the photocatalytic properties on the decolourisation of methylene blue solutions under visible light irradiation. The phase composition, the specific surface and the photocatalytic activity were influenced by the molybdenum content and the calcination temperature. The final molybdenum content in the samples additionally depends on the calcination temperature. The optimum photocatalytic properties were observed or Ti-doped MoO₃.     

Synthesis and evolution of novel double tower-like ZnO by a simple method

Delicate double tower-like ZnO have been fabricated through the decomposition of the zinc nitrate hexahydrate (Zn(NO₃)₂6H₂O). The phase transformation and morphology evolution of the products were carefully studied and investigated with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectra. The resultant results indicated that the obtained double tower-like ZnO materials possess pure wurtzite hexagonal phase, growing along the [100] direction. A reasonable formation mechanism was also presented in this paper.     

MoO3纳米带/RGO复合材料的制备及其电化学性能研究

以水杨酸为模板剂和还原剂,采用水热法制备得到了一种MoO₃纳米带/RGO复合材料。利用XRD、SEM、TEM、拉曼光谱、恒流充放电、交流阻抗等手段对样品的结构、形貌以及电化学性能进行表征。测试结果表明,MoO₃纳米带/RGO复合材料作为锂离子电池负极材料,在50mA·g^-1的电流密度下可逆比容量为1000mAh·g^-1,循环50次后比容量还保持在950mAh·g^-1,相比于MoO₃纳米带其容量保持能力和循环性能得到了显著改善。     

Electrochemical performance of new α-MoO3 nanobelt cathode materials for rechargeable Li-ion batteries

The orthorhombic molybdenum trioxide (α-MoO₃) nanobelts and polyvinyl pyrrolidone (PVP) surfactant MoO₃ nanobelts with high quality were prepared through hydrothermal synthesis. The morphology and microstructure of the samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The nanobelts with rectangular cross-section have an orthorhombic phase structure, preferentially grow in [001] direction. The results showed that the H atoms in polyvinyl pyrrolidone are H-bonded with the O atoms in the MoO bonds of MoO₃ nanobelts. When MoO₃ is modified by the intercalation of PVP, it is effectively shielded against electrostatic interaction between the MoO₃ interlayer and Li⁺ ions. The specific capacity of pure MoO₃ nanobelts battery and (PVP)_0.2MoO₃ nanobelts exhibit as 195 mAh g⁻¹ and 237 mAh g⁻¹, respectively after 14 cycles, suggests that the stability of surfactant material is worthy.     

MoO_3纳米带/RGO复合材料的制备及其电化学性能研究

以水杨酸为模板剂和还原剂,采用水热法制备得到了一种MoO3纳米带/RGO复合材料。利用XRD、SEM、TEM、拉曼光谱、恒流充放电、交流阻抗等手段对样品的结构、形貌以及电化学性能进行表征。测试结果表明,MoO3纳米带/RGO复合材料作为锂离子电池负极材料,在50 m A·g-1的电流密度下可逆比容量为1 000 m Ah·g-1,循环50次后比容量还保持在950 m Ah·g-1,相比于MoO3纳米带其容量保持能力和循环性能得到了显著改善。     

Synthesis and characterization of sol–gel derived ZrV2O7 fibers with negative thermal expansion property

Novel ZrV₂O₇ fibers with negative thermal expansion were prepared via combination of sol–gel process and thermal decomposition. The as-prepared fibers were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy and Raman spectroscopy. The results showed that the synthetic pH value had little influence on the crystal structure of products while showed significant effect on morphology. The fibers obtained at pH = 9 exhibited cylindrical morphology and its mean diameter was about 1 μm. The thermal expansion property of the as-prepared fibers was investigated by in situ XRD and thermal mechanical analyzer. All of the as-prepared fibers showed positive thermal expansion first and then negative thermal expansion, resulting from a phase transition from 3 × 3 × 3 superstructure to 1 × 1 × 1 cubic structure. The macro thermal expansion coefficients of ZrV₂O₇ ceramic rods increased with decreasing of fiber diameter. The mechanism of the phase transition was also discussed.     

Liquid phase deposition synthesis of hexagonal molybdenum trioxide thin films

Hexagonal molybdenum trioxide thin films with good crystallinity and high purity have been fabricated by the liquid phase deposition (LPD) technique using molybdic acid (H₂MoO₄) dissolved in 2.82% hydrofluoric acid (HF) and H₃BO₃ as precursors. The crystal was found to belong to a hexagonal hydrate system MoO₃.nH₂O (n~0.56). The unit cell lattice parameters are a=10.651 Å, c=3.725 Å and V=365.997 Å³. Scanning electron microscope (SEM) images of the as-deposited samples showed well-shaped hexagonal rods nuclei that grew and where the amount increased with increase in reaction time. X-ray photon electron spectroscopy (XPS) spectra showed a Gaussian shape of the doublet of Mo 3d core level, indicating the presence of Mo⁶⁺ oxidation state in the deposited films. The deposited films exhibited an electrochromic behavior by lithium intercalation and deintercalation, which resulted in coloration and bleaching of the film. Upon dehydration at about 450 °C, the hexagonal MoO₃.nH₂O was transformed into the thermodynamically stable orthorhombic phase.     

Mn3O4 nanoplates and nanoparticles: Synthesis, characterization, electrochemical and catalytic properties

Mn₃O₄ hexagonal nanoplates and nanoparticles were synthesized via a solvent-assisted hydrothermal oxidation process at low temperature and a solvothermal oxidation method, respectively. The synthesized product was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), electron diffraction (ED), Fourier transform infrared (FT-IR) spectroscopy. Their capability of catalytic oxidation of formaldehyde to formic acid at room temperature and atmospheric pressure and electrochemical properties by cyclic voltammogram (CV) were compared. The results showed that Mn₃O₄ hexagonal nanoplate is a better catalyst, and the hexagonal nanoplates and nanoparticles modified electrodes blended with carbon black have a higher specific capacitance.     

Influence of mechanochemical activation on structure and some properties of mixed vanadium�Cmolybdenum oxides

Mechanochemical activation of individual V₂O₅, MoO₃ and mixed vanadium-molybdenum oxide system in various media (air, water, and ethanol) has been studied. Powder X-ray diffraction, nitrogen adsorption?Cdesorption, thermogravimetric and chemical analysis, FTIR and Raman spectroscopy, and scanning electron microscopy have been used for research of prepared milled samples. The electrokinetic properties (dependence zeta potential??pH, position of isoelectric point) of individual V₂O₅, MoO₃ and mixed vanadium?Cmolybdenum oxide system, synthesized via mechanochemical treatment in various medium, in aqueous solutions of electrolytes also have been determined. Initial, milled, and spent samples are characterized with the help of XRD, FTIR and Raman spectroscopy, and SEM and adsorption of nitrogen. The catalytic properties of vanadium?Cmolybdenum oxide composition activated in different media have been investigated in reaction of oxidation dehydrogenation of propane.     

Temperature-dependent Raman spectroscopy studies of phase transformations in the K2WO4 and the MgMoO4 crystals

Temperature-dependent Raman spectroscopy studies of K₂WO₄ and MgMoO₄ polycrystals were performed in order to obtain information about vibrational and structural changes in these materials as a function of temperature. The stability of the monoclinic phase for both K₂WO₄ and MgMoO₄ samples was assessed and our results indicated that this phase is stable in the 295–723 K and 300–770 K ranges for K₂WO₄ and MgMoO₄, respectively. It was observed that both samples underwent two phase transformations above room temperature. The first phase transformations which occur at about 633 K and 640 K for K₂WO₄ and MgMoO₄, respectively, is most likely connected with weak tilting and/or rotations of WO₄/MoO₄ tetrahedral units that lead to a disorder in the oxygen sublattice. Raman spectroscopy data also indicated that K₂WO₄ and MgMoO₄ exhibited a first-order phase transition at around 723 K and 770 K, respectively, changing from monoclinic to hexagonal symmetry.     

Physical and chemical properties of silicon carbonitride nanocrystalline films

Nanocrystalline transparent films SiC_xN_y were obtained by plasma-enhanced chemical deposition within the temperature range 473–1173 K from low pressure gas phase from a mixture of hexamethyldisilazane vapor, ammonia, and helium. Physical chemical properties of the films obtained were studied by IR and Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron spectroscopy and synchrotron radiation powder diffaction. Voltage-capacity and voltage-current measurements were also made. The dependence of chemical and phase composition of the films on deposition conditions was determined, and the formation of approximately 2 nm sized spherical nanocrystals within the films was established. The nanocrystals are formed by a phase similar to usual α-Si₃N₄, with silicon atoms partially substituted by carbon ones.     

MOF-808/Bi2MoO6复合材料的构筑及其光催化性能

采用简单的两步水热法制备出了锆基金属有机骨架和钼酸铋的复合材料MOF-808/Bi₂MoO₆。通过X射线粉末衍射、傅里叶红外光谱、扫描电子显微镜、透射电子显微镜、X射线光电子能谱、紫外可见漫反射光谱、N₂吸附-脱附测试和电化学测试对所制备材料的组成、微观结构、光学性质以及光生载流子的复合效率进行了分析。与纯Bi₂MoO₆和MOF-808相比,0.5%-MOF-808/Bi₂MoO₆复合材料展示出了较高的光催化活性,在可见光照射120 min时对抗生素环丙沙星(CIP)的降解率达89.7%。通过自由基捕获实验,证明了·O₂^-是主要活性物种,基于此我们提出了可能的光催化降解机理。     

MOF-808/Bi2MoO6复合材料的构筑及其光催化性能

采用简单的两步水热法制备出了锆基金属有机骨架和钼酸铋的复合材料MOF-808/Bi₂MoO₆。通过X射线粉末衍射、傅里叶红外光谱、扫描电子显微镜、透射电子显微镜、X射线光电子能谱、紫外可见漫反射光谱、N₂吸附-脱附测试和电化学测试对所制备材料的组成、微观结构、光学性质以及光生载流子的复合效率进行了分析。与纯Bi₂MoO₆和MOF-808相比,0.5%-MOF-808/Bi₂MoO₆复合材料展示出了较高的光催化活性,在可见光照射120 min时对抗生素环丙沙星(CIP)的降解率达89.7%。通过自由基捕获实验,证明了·O₂^-是主要活性物种,基于此我们提出了可能的光催化降解机理。     

Spectroscopic studies of the phase transition in ammonia borane: Raman spectroscopy of single crystal NH3BH3 as a function of temperature from 88 to 330 K

Raman spectra of single crystal ammonia borane, NH3BH3, were recorded as a function of temperature from 88 to 300 K using Raman microscopy and a variable temperature stage. The orthorhombic to orientationally disordered tetragonal phase transition at 225 K was clearly evident from the decrease in the number of vibrational modes. However, some of the modes in the orthorhombic phase appeared to merge 10-12 K below the phase transition perhaps suggesting the presence of an intermediate phase. Factor group analysis of vibrational spectra for both orthorhombic and tetragonal phase is provided. In addition, electronic structure calculations are used to assist in the interpretation and assignment of the normal modes.     

Selective self-propagating combustion synthesis of hexagonal and orthorhombic nanocrystalline yttrium iron oxide

Macroporous nanocrystalline YFeO₃ was prepared by a self-propagating combustion method using yttrium nitrate and iron nitrate as precursors and glycine as a fuel. The phase structure of the product can be selectively controlled to be hexagonal or orthorhombic by simply adjusting the ratio of glycine to nitrate. The samples were characterized by X-ray diffraction (XRD) analysis, N₂ adsorption, micro-Raman spectroscopy, Fourier transform infrared absorption spectroscopy (FT-IR), thermal analysis (TGA/DSC), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and magnetic property analysis. Photocatalytic activity for the degradation of methylene blue in water under visible light irradiation shows that the orthorhombic YFeO₃ is superior to the hexagonal form. More adsorbed oxygen and ferromagnetism of the orthorhombic sample may explain its high activity.