Transimission Electron Microscopy Research Articles

Aerobic oxidation of 5-hydroxymethylfurfural to 2,5-difurancarboxylic acid over Pd-Au nanoparticles supported on Mg-Al hydrotalcite

A series of reconstructed hydrotalcite supported monometallic Au or Pd and bimetallic Pd-Au nanoparticles with various Pd/Au ratios were synthesized. The physicochemical properties of these catalysts were charaterized by X-ray diffraction (XRD), X-ray photoelectronic spectroscopy (XPS), Transimission electron microscopy, N2 adsorption, etc. The catalysts were used for the aerobic oxidaiton of 5-hydroxymethylfurfural(HMF) into 2,5-furandicarboxylic acid (FDCA) in an alkaline aqueous solution. The monometallic Pd or Au catalyst could not oxidize the intermediate product-5-hydroxymethyl-2-furanic acid (HMFCA), while bimetallic Pd-Au catalysts exhibited good performances for HMFCA oxidation. A high yield of FDCA up to 90% was achieved over the Pd-Au/HT catalyst with the Au/Pd ratio of 4 at 60 °C for 6 h. The enhanced oxidation activity of HMF for the bimetallic catalysts is attributed to the syneretic effect between Au and Pd nanoparticles and the formation of smaller particle size that facilicates the oxidation of HMF to FDCA. The Pd-Au/HT(1 :4) catalyst also exhibited a good stabiblity without significant loss in FDCA yield after five succesive cycles.

Effect of Ni Precipitation Method on CO Methanation over Ni/TiO2 Catalysts

A Ni/TiO2(TBT) catalyst was prepared through in situ precipitation, using tetrabutyl titanate(TBT) as the TiO2 precursor, and was studied in CO methanation. A Ni catalyst supported on commercial TiO2 was also prepared through post precipitation and studied to compare the influence of Ni precipitation conditions on the catalyst’s performance. To gain insight on their structure and physicochemical properties, the catalysts were characterized with N2-adsorption, X-ray diffraction, transimission electron microscopy, H2 temperature programmed reduction and temperature programmed desorption. The results showed that the in situ precipitation method was beneficial to the dispersion of Ni and the formation of more active sites on the Ni/TiO2 catalyst. In addition, the density of the metal- support boundary and its interaction with the active component were also increased. These characteristics of Ni/TiO2(TBT) led to a lower light-off temperature and a suppression of Ni sintering during CO methanation. As a consequence, the Ni/TiO2(TBT) exhibited better catalytic behavior, with a CO conversion of 99.4% and CH4 selectiv-ity of 90.4% under the following conditions: p=1 MPa, t=320 °C, n(H2)/n(CO)=3, gas hour space velocity (GHSV)=2×104 mL·g–1·h–1. The life test results of the two catalysts showed that Ni/TiO2(TBT) was more stable and the catalytic activity remained at its initial level after being used for 30 h.

EFFECT OF ANNEALED TEMPERATURE ON NO2 GAS-SENSING PERFORMANCES OF SnO2 NANOWIRE SENSORS

NO2 gas is a highly toxic gas and emitted from vehicles such as motocycles and internal engine transportations. It is one of the major reasons which cause air pollution in recent years, especially in big cities. Therefore, the development of NO2 gas sensor for environmental monitoring has been gained research attention in the global. In this work, we report a simple and effective method to prepare SnO2 nanowire gas sensors. The SnO2 nanowires were directly grown on the unplosihed Al2O3 substrate equipped with a pair of Pt-electrodes. The morphology and microstructure of as-grown nanowires have been investigated via X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transimission electron microscopy (TEM). The results indicated that the diameters and lengths of nanowires are about 60 – 100 nm and tens of μm, respectively. The gas-sensing performance of the SnO2 nanowires sensors annealed at different temperatures have also investigated. The results revealed that the annealed temperatures of 400 C and 500 oC do not affected on gas-sensing performance of SnO2 nanowires sensors, while the annealed temperature of 600oC results in strong decrease in NO2 gas response as compared with as-grown SnO2 nanowires sensor.

The crystal structure and physical properties of multiple components FeSe-based superconductors

The sample preparation, crystallographic structure, phase separation and superconductivity of FeSe-based superconductors are discussed here. First of all, we will introduce the ternary high tempeature superconductor K0.8Fe2− y Se2 with superconducting transition tempeature ( T c) at 31 K, which creates the record T c of FeSe-based superconductor under ambient pressure at that time. The single crystals can be grown through the self-flux method at high temperature. The crystal structure at high temperature shows the body-center tetragonal lattice with space group I4/mmm, while the superstructure developes at low tempeature with I4/m symmetry. The Fermi surface measured by angle resolution photoemission spectrum shows that K0.8Fe2− y Se2 has no any hole pockets at Fermi level, which is strikingly different from that of FeAs-based superconducors. This topology of Fermi surface implies that the superconducting mechanism of K0.8Fe2− y Se2 also should be distinguished from that of FeAs-based superconductors. The lack of interaction between electron and hole pockets would induce a possible d -wave superconducting gap. However, the mulitiple superstructure types, such as 5 × 5 , 2 × 2 , 2×2, etc, have been identified by transimission electron microscopy and neutron diffraction measurements, which reveal that K0.8Fe2− y Se2 is a phase-separated compound. Secondly, we develop the low tempeature liquid-NH3 method for synthesizing the pure FeSe-based superconducting compounds without phase separation. It is demonstrated that many alkali-metals, alkali-earth metals and rare-earth metals, such as Li, Na, Ca, Sr, Ba, Eu, and Yb, can be intercalated between FeSe layers and induce superconductivity with T c of 30–46 K, which can further enhance the record T c. In the K x (NH3) y Fe2Se2, two superconducting phases are discovered with different concentration of K ( x ≈0.3 and 0.6). The NH3 molecures play an important role in stabilizing the structures, moreover, the discrete superconducting phases implies that metal-intercalated FeSe superconductors are distinct from other FeAs-based superconductors. It is proposed that the main cause comes from their structures only being stable at particular doping levels and fine-tuning the concentrations of alkali metals may further enhance T c in the FeSe-based superconductors. Thirdly, we discuss the novel FeSe-based superconductors prepared by other metastable methods like the hydrothermal and solvent-thermal methods. The superconducting LiOHFeSe and Na x (En) y Fe2Se2 superconductors with T c over 40 K have been successfully synthesized, in which the former one shows the anti-ferromagentism at 8 K and the latter one exhibits structural tranistion at 350 K. The emergent properties from these novel high tempeature superconductors make the FeSe-based family becomes the hottest field in the community of superconductivity. In addition, the newly discovered monolayer FeSe on SrTiO3 further enhance the T c up to 65–70 K, which is close to the boiling point of liquid nitrogen. Finally, it is remarked that the structural flexibilty and weak bonds between FeSe layers are the most important advantages for exploring new superconductor with higher T c. We believe that more FeSe-based superconductors could be discovered once the new metastable methods are explored.

(Invited) Design and Realization of New Thermochemically Active Materials

Through combining predictive theory and experiment new functional materials for thermochemical cycles and reactions such as the oxygen evolution reaction. Many of these materials include metastable polymorphs of the groundstate materials and necessitate careful optimization of the inherent defect structure for that polymorph. The often exhibit multifunctional behavior. Barium nickelate, BaNiO3, and its sub-oxides have shown potential as oxygen evolution reaction catalysts. Initial results indicate performance comparable to precious metal catalysts. We have synthesized highly phase pure materials and evaluated it in a thermochemical redox cycle. In this work we examine the structural and phase changes that occur during the redox cycling of BaNiO3 at high temperature. Thermogravimetric analysis (TGA) on sol-gel synthesized powders under reducing and oxidizing conditions indicates a reversible cycling through multiple oxidation states. The structure of the BaNiO3powder as determined by synchrotron x-ray diffraction is measured prior to and after TGA analysis to track the phase changes associated with redox cycling. Transimission electron microscopy is used to track changes in the powder surface, crystal structure and morphology. The stability of this structure over a wide range of oxidation states gives this material applicability in a number of energy applications such as electrochemical water splitting, multiferroics, and solid oxide fuel cells, all of which are discussed. This work was funded by the Center for the Next Generation of Materials by Design, an U.S. Department of Energy, Office of Science EFRC under Contract No. DE-AC36-08GO28308 to NREL.

Atomic-Scale Magnetism of Cr-Doped Bi2Se3 Thin Film Topological Insulators.

Magnetic doping is the most common method for breaking time-reversal-symmetry surface states of topological insulators (TIs) to realize novel physical phenomena and to create beneficial technological applications. Here we present a study of the magnetic coupling of a prototype magnetic TI, that is, Cr-doped Bi2Se3, in its ultrathin limit which is expected to give rise to quantum anomalous Hall (QAH) effect. The high quality Bi2-xCrxSe3 epitaxial thin film was prepared using molecular beam epitaxy (MBE), characterized with scanning transimission electron microscopy (STEM), electrical magnetotransport, and X-ray magnetic circularly dichroism (XMCD) techniques, and the results were simulated using density functional theory (DFT) with spin-orbit coupling (SOC). We observed a sizable spin moment mspin = (2.05 ± 0.20) μB/Cr and a small and negative orbital moment morb = (-0.05 ± 0.02) μB/Cr of the Bi1.94Cr0.06Se3 thin film at 2.5 K. A remarkable fraction of the (CrBi-CrI)(3+) antiferromagnetic dimer in the Bi2-xCrxSe3 for 0.02 < x < 0.40 was obtained using first-principles simulations, which was neglected in previous studies. The spontaneous coexistence of ferro- and antiferromagnetic Cr defects in Bi2-xCrxSe3 explains our experimental observations and those based on conventional magnetometry which universally report magnetic moments significantly lower than 3 μB/Cr predicted by Hund's rule.

Highly efficient methylene blue dyes removal from aqueous systems by chitosan coated magnetic mesoporous silica nanoparticles

In this work, uniform chitosan coated magnetic mesoporous silica nanoparticles (CMMSNs) with good adsorption capacity and magnetic response were synthesized, and they were successfully applied to highly efficient methylene blue (MB) dyes removal. The structure and morphologies of the obtained nanoparticles were characterized by Fourier transform infrared spectroscop, X-ray diffraction, thermogravimetric analysis and nitrogen adsorption–desorption analysis and transimission electron microscopy. The CMMSNs possessed a classical core–shell structure with several Fe3O4 contained in mesoporous silica nanoparticles, and then coated by chitosan. The CMMSNs had a saturation magnetization of 12.6 emu g−1 and could be easily separated by a magnet. Taking MB as a typical organic dye, the CMMSNs were subjected as adsorbent to remove them from the polluted water. The saturated adsorption capacity of MB was 43.03 mg g−1. The MB adsorption kinetic and adsorption isotherm analysis results showed that the pseudo-second order equation was the most suitable one to describe the adsorption kinetics of MB for CMMSNs, and the adsorption isotherm model of MB onto the CMMSNs belonged to Freundlich isotherm model.

Hierarchical SAPO-11 preparation in the presence of glucose

Glucose was used as a mesoporous structure directing agent to synthesize hierarchical porous silicoaluminophosphate molecular sieves with AEL topology (SAPO-11). Nanosized SAPO-11 with numerous mesopores were confirmed by X-ray diffraction (XRD) and N2 adsorption–desorption analysis. Scanning electron microscopy (SEM) and transimission electron microscopy (TEM) are employed to reveal that inter-crystallinic meso-structures were formed from the aggregation of nanosized crystallites. A proposed mesopore construction mechanism by the addition of glucose is presented based on Energy Dispersive X-ray Spectroscopy (EDS) and CHNS analysis.

Enhanced thermoelectric properties of selenium-deficient layered TiSe(2-x): a charge-density-wave material.

In the present work, we report on the investigation of low-temperature (300-5 K) thermoelectric properties of hot-pressed TiSe2, a charge-density-wave (CDW) material. We demonstrate that, with increasing hot-pressing temperature, the density of TiSe2 increases and becomes nonstoichiometric owing to the loss of selenium. X-ray diffraction, scanning electron microscopy, and transimission electron microscopy results show that the material consists of a layered microstructure with several defects. Increasing the hot-press temperature in nonstoichiometric TiSe2 leads to a reduction of the resistivity and enhancement of the Seebeck coefficient in concomitent with suppression of CDW. Samples hot-pressed at 850 °C exhibited a minimum thermal conductivity (κ) of 1.5 W/m·K at 300 K that, in turn, resulted in a figure-of-merit (ZT) value of 0.14. This value is higher by 6 orders of magnitude compared to 1.49 × 10(-7) obtained for cold-pressed samples annealed at 850 °C. The enhancement of ZT in hot-pressed samples is attributed to (i) a reduced thermal conductivity owing to enhanced phonon scattering and (ii) improved power factor (α(2)σ).

Stimulated human mast cells secrete mitochondrial components that have autocrine and paracrine inflammatory actions.

Mast cells are hematopoietically-derived tissue immune cells that participate in acquired and innate immunity, as well as in inflammation through release of many chemokines and cytokines, especially in response to the pro-inflammatory peptide substance P (SP). Inflammation is critical in the pathogenesis of many diseases, but the trigger(s) is often unknown. We investigated if mast cell stimulation leads to secretion of mitochondrial components and whether these could elicit autocrine and/or paracrine inflammatory effects. Here we show that human LAD2 mast cells stimulated by IgE/anti-IgE or by the SP led to secretion of mitochondrial particles, mitochondrial (mt) mtDNA and ATP without cell death. Mitochondria purified fromLAD2 cells and, when mitochondria added to mast cells trigger degranulation and release of histamine, PGD2, IL-8, TNF, and IL-1β. This stimulatory effect is partially inhibited by an ATP receptor antagonist and by DNAse. These results suggest that the mitochondrial protein fraction may also contribute. Purified mitochondria also stimulate IL-8 and vascular endothelial growth factor (VEGF) release from cultured human keratinocytes, and VEGF release from primary human microvascular endothelial cells. In order to investigate if mitochondrial components could be secreted in vivo, we injected rats intraperiotoneally (ip) with compound 48/80, which mimicks the action of SP. Peritoneal mast cells degranulated and mitochondrial particles were documented by transimission electron microscopy outside the cells. We also wished to investigate if mitochondrial components secreted locally could reach the systemic circulation. Administration ip of mtDNA isolated from LAD2 cells in rats was detected in their serum within 4 hr, indicating that extravascular mtDNA could enter the systemic circulation. Secretion of mitochondrial components from stimulated live mast cells may act as “autopathogens” contributing to the pathogenesis of inflammatory diseases and may be used as targets for novel treatments.

Microwave-Assisted Synthesis of Nanocrystalline Zirconium Dioxide Using an Ionic Liquid

Zirconium dioxide (ZrO2) nanocrystals were prepared by the microwave-assisted ionic liquid method using an ionic liquid of 1-n-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM]BF4). The X-ray diffraction (XRD) patterns indicated that the crystal structure was monoclinic. The morphology of ZrO2 nanocrystals was characterized by field emission scanning electron microscopy (FESEM) and transimission electron microscopy (TEM), which showed uniform ZrO2 nanoparticles without aggregation. Thermogravimetry (TG) and Fourier transform infrared spectrometer (FTIR) curves confirmed the adsorption of organic compounds on the surface of ZrO2.

The Effect of Zn on Microstructures and Properties of Extruded Mg-Gd-Y Alloys

By using digital micro-hardness testing, mechanical testing, optical microscopy(OM), scanning electron microscopy(SEM), transimission electron microscopy(TEM), microstructure and mechanical properties of Mg-9Gd-3Y-xZn (x=0,1,2,3 wt.%) alloys during extrusion and following aging at 210 °C were investigated. The results showed that Zn can refined grains of the alloy. In T5 condition the average grains of the alloy without Zn addition were about 20.08 μm; the average grains of the alloys with 1 wt.% Zn addition and 3 wt.% Zn addition were about 15.26 μm and 10.17 μm, respectively. For the alloy with 1 wt.% Zn addition in peak-aged state, the values of tensile strength and yield strength reached 418MPa and 329 MPa, as well as ductility rate reached 5.6 %, respectively, exhibiting superior mechanical properties .

Fabrication of Core–Shell Nanostructures from Near-Infrared Electrochromic Amphiphilic Diblock Copolymers Containing Pendant Dinuclear Ruthenium Group through Assembly and Their Optical, Electrochemical, and Electroptical Properties

Novel well-defined diblock copolymers polystyrene-b-poly[benzoic acid N′-(4-vinylbenzoyl)hydrazide dinuclear ruthenium complex] (PSm-b-P(DCH-Ru)n, m = 2076, n = 417, 1024, 2432) are synthesized through two-step sequential nitroxide-mediated radical polymerization (NMRP) and postpolymerization complexation. The block copolymers containing pendant dinuclear ruthenium groups possess an amphiphilic nature. The assembly behavior of the complex block copolymers in both selective solvents acetonitrile and dioxane at various initial concentrations and block compositions were characterized by transimission electron microscopy (TEM). Spherical micelles and vesicles were observed in acetonitrile and dioxane, respectively. The photoluminescent, electrochemical, and spectroelectrochemical properties of the complex block copolymers in solution were investigated. The solvatochromism in the UV–vis region and electrochromism (EC) in the near-infrared region (NIR) were observed. Aggregates solutions in either acetonitrile or dioxane show quite different electroptical properties from that of the homogeneous solution in DMF, which might be due to spatial-confinement effect of the functional Ru pendent groups in core–shell nanostructures.

Annealing effects on the structure and electrical characteristics of amorphous Er2O3 films

Amorphous Er2O3 films are deposited on Si (001) substrates by using reactive evaporation. This paper reports the evolution of the structure, morphology and electrical characteristics with annealing temperatures in an oxygen ambience. X-ray diffraction and high resolution transimission electron microscopy measurement show that the films remain amorphous even after annealing at 700 °C. The capacitance in the accumulation region of Er2O3 films annealed at 450 °C is higher than that of as-deposited films and films annealed at other temperatures. An Er2O3/ErOx/SiOx/Si structure model is proposed to explain the results. The annealed films also exhibit a low leakage current density (around 1.38 × 10−4 A/cm2 at a bias of −1 V) due to the evolution of morphology and composition of the films after they are annealed.

Controlled deposition of Pt on Au nanorods and their catalytic activity towards formic acid oxidation

Platinum submonolayer decorated gold nanorods with controlled coverage were prepared by the addition of Au nanorods into the growth solution of Pt in the presence of NH 2OH · HCl as the growth agent. The properties of Au nanorods decorated by Pt submonolayer were investigated by various techniques including transimission electron microscopy, X-ray diffraction, and electrochemical methods. The Pt decorated Au nanorods on carbon black showed significantly higher activity on formic acid electrooxidation than the conventional Pt/C catalysts. They showed different reaction path of formic acid electrooxidation by suppressing the formation of poisoning intermediate CO.

Efficient Photocatalytic Degradation of Phenol over Co3O4/BiVO4 Composite under Visible Light Irradiation.

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Efficient Photocatalytic Degradation of Phenol over Co3O4/BiVO4 Composite under Visible Light Irradiation

Co3O4/BiVO4 composite photocatalyst with a p-n heterojunction semiconductor structure has been synthesized by the impregnation method. The physical and photophysical properties of the composite photocatalyst have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transimission electron microscopy (TEM), BET surface area, and UV-visible diffuse reflectance spectra. Co is present as p-type Co3O4 and disperses on the surface of n-type BiVO4 to constitute a heterojunction composite. The photocatalyst exhibits enhanced photocatalytic activity for phenol degradation under visible light irradiation. The highest efficiency is observed when calcined at 300 degrees C with 0.8 wt % cobalt content. On the basis of the calculated energy band positions and PL spectra, the mechanism of enhanced photocatalytic activity has been discussed.

Nanostructural M-type barium hexaferrite synthesized by spark plasma sintering method

This investigation shows that the spark plasma sintering (SPS) method may not only absolutely prevent the formation of intermediate phase α-Fe2O3 but also significantly lower the crystallization temperature of M-type barium hexaferrite. A kind of textured sample composed of major phase M-type barium hexaferrite and trace amount of BaFe0.24Fe0.76O2.88 has been successfully synthesized in one step by SPS process at 800°C for 10min. Scanning electron microscopy, energy dispersive spectroscopy, x-ray-diffraction, transimission electron microscopy, and vibrating-sample magnetometer techniques are used to study the microstructure, composition, phase formation, crystal orientation, and magnetism of the textured sample, respectively. It is confirmed that nanostructural M-type barium hexaferrites in the holes of the textured sample are in nanobelt and nanorod microstructures; these nanobelts and nanorods are nonstoichiometric and completely random and are characterized by barium or iron surplus, and that their composition may be described as BaFe12+xO19+1.5x (−4.49⩽x⩽6.60). The prolongation orientation of a nanobelt is parallel to the zone axis [101¯0]. The values of σs and Hc of the textured sample are 65.52emu∕g and 1412.17Oe, respectively. The Hc value decreases to one-fourth of that of randomly packed platelike M-type barium hexaferrite with same composition synthesized by sol-gel process at 900°C for 4h, while the σs value was independent of the synthesis conditions. This indicates that M-type barium hexaferrite magnets synthesized by SPS process may be applied to electromagnetic wave absorption and/or magnetic recording.

Ultrasonic spray pyrolysis of nano crystalline spinel LiMn 2O 4 showing good cycling performance in the 3 V range

Spherical lithium manganese oxide spinel was synthesized by an ultrasonic spray pyrolysis method, and has been characterized using X-ray diffraction, scanning electron microscopy, transimission electron microscopy and electrochemical cycling at 3 V regions. The LiMn 2O 4 powders were composed of about 10 nm-sized primary particles. The delivered discharge capacity of the synthesized nano-material was 125 mAh g −1 between 2.4 and 3.5 V and its retention was about 96% upon 50 cycling. From the high resolution transmission electron microscopic study, it was found that structural transition of the parent material did not occur even after the 50th electrochemical cycling on the 3 V region. It seems that the reversible structural change is possible for nanocrystalline LiMn 2O 4 as observed by the X-ray diffraction and transition electron microscopic observations.

Electrochemical performances of C/Fe nanocomposite and its use for mediator-free glucose biosensor preparation

C/Fe nanocomposite (CFN) was synthesized by a procedure similar to an exfoliation/adsorption process to intercalate Fe 3+ into graphite oxide (GO) layers and would be reduced in a H 2 atmosphere. The results of X-ray diffractometry (XRD) and transimission electron microscopy (TEM) show that the form of CFN is carbon nanotube–Fe nanoparticle composite with α-Fe distributed on the nanotube wall. Paste electrode has been constructed using CFN mixed with paraffin. The electrochemical characteristics of such carbon–Fe nanocomposite paste electrode (CFNPE) has been compared with that of carbon paste electrode (CPE) and evaluated with respect to the electrochemistry of potassium ferricyanide, ascorbic acid and cysteine by cyclic voltammetry. CFNPE can accelerate the electron-transfer to improve the electrochemical reaction reversibility. To fabricate the third-generation glucose biosensor, glucose oxidase (GOD) was immobilized on CFNPE surface with Nafion covered after a pretreatment. Oxygen, ascorbic acid and uric acid have no interference with the glucose detection. The biosensor displays a remarkable sensitivity and stability and the results used in the determination of glucose in the human serum samples are satisfactory.