Showing papers on "Transmission electron microscopy published in 2017"

Atomic structure of sensitive battery materials and interfaces revealed by cryo–electron microscopy

Abstract: Whereas standard transmission electron microscopy studies are unable to preserve the native state of chemically reactive and beam-sensitive battery materials after operation, such materials remain pristine at cryogenic conditions. It is then possible to atomically resolve individual lithium metal atoms and their interface with the solid electrolyte interphase (SEI). We observe that dendrites in carbonate-based electrolytes grow along the (preferred), , or directions as faceted, single-crystalline nanowires. These growth directions can change at kinks with no observable crystallographic defect. Furthermore, we reveal distinct SEI nanostructures formed in different electrolytes.

Phase segregation enhanced ion movement in efficient inorganic CsPbIBr2 solar cells

Abstract: Organic–inorganic hybrid perovskite solar cells with mixed cations and mixed halides have achieved impressive power conversion efficiency of up to 22.1%. Phase segregation due to the mixed compositions has attracted wide concerns, and their nature and origin are still unclear. Some very useful analytical techniques are controversial in microstructural and chemical analyses due to electron beam-induced damage to the “soft” hybrid perovskite materials. In this study photoluminescence, cathodoluminescence, and transmission electron microscopy are used to study charge carrier recombination and retrieve crystallographic and compositional information for all-inorganic CsPbIBr2 films on the nanoscale. It is found that under light and electron beam illumination, “iodide-rich” CsPbI(1+x)Br(2−x) phases form at grain boundaries as well as segregate as clusters inside the film. Phase segregation generates a high density of mobile ions moving along grain boundaries as ion migration “highways.” Finally, these mobile ions can pile up at the perovskite/TiO2 interface resulting in formation of larger injection barriers, hampering electron extraction and leading to strong current density–voltage hysteresis in the polycrystalline perovskite solar cells. This explains why the planar CsPbIBr2 solar cells exhibit significant hysteresis in efficiency measurements, showing an efficiency of up to 8.02% in the reverse scan and a reduced efficiency of 4.02% in the forward scan, and giving a stabilized efficiency of 6.07%.

Sensitive and selective NO2 gas sensor based on WO3 nanoplates

Abstract: Gas sensors based on a chemiresistive metal oxide semiconductor are widely used including nitrogen dioxide (NO 2 ) at a moderate temperature. In this work efforts are taken to fabricate NO 2 gas sensor using thin films of tungsten oxide (WO 3 ) grown directly on to a soda-lime glass substrate without assistance of any seed layer by a simple and a facile hydrothermal technique. As per our knowledge, the deposition of nanostructured WO 3 thin films without assistance of any seed layer on the glass substrate was rarely reported. The WO 3 thin film samples were synthesized at various deposition times ranging from 3 h to 7 h and were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV–vis spectroscopy and Brunauer-Emmett-Teller techniques. The surface morphological and structural characterization showed the two dimensional (2D) nanoplate-like structure of as synthesized WO 3 thin films with plate thickness ranging from 90 to 150 nm and had an orthorhombic structure, respectively. Moreover, the 2D nanoplates of WO 3 exhibited a gas response ∼10 for 5 ppm for toxic NO 2 gas at relatively low operating temperature. The new synthesis route and sensing behavior of as synthesized WO 3 nanoplates revealed a promising candidate for the fabrication of the cost effective gas sensors.

Unravelling surface and interfacial structures of a metal–organic framework by transmission electron microscopy

Abstract: Metal-organic frameworks (MOFs) are crystalline porous materials with designable topology, porosity and functionality, having promising applications in gas storage and separation, ion conduction and catalysis. It is challenging to observe MOFs with transmission electron microscopy (TEM) due to the extreme instability of MOFs upon electron beam irradiation. Here, we use a direct-detection electron-counting camera to acquire TEM images of the MOF ZIF-8 with an ultralow dose of 4.1 electrons per square angstrom to retain the structural integrity. The obtained image involves structural information transferred up to 2.1 A, allowing the resolution of individual atomic columns of Zn and organic linkers in the framework. Furthermore, TEM reveals important local structural features of ZIF-8 crystals that cannot be identified by diffraction techniques, including armchair-type surface terminations and coherent interfaces between assembled crystals. These observations allow us to understand how ZIF-8 crystals self-assemble and the subsequent influence of interfacial cavities on mass transport of guest molecules.

Observation of stable Néel skyrmions in cobalt/palladium multilayers with Lorentz transmission electron microscopy.

Abstract: Neel skyrmions are of high interest due to their potential applications in a variety of spintronic devices, currently accessible in ultrathin heavy metal/ferromagnetic bilayers and multilayers with a strong Dzyaloshinskii–Moriya interaction. Here we report on the direct imaging of chiral spin structures including skyrmions in an exchange-coupled cobalt/palladium multilayer at room temperature with Lorentz transmission electron microscopy, a high-resolution technique previously suggested to exhibit no Neel skyrmion contrast. Phase retrieval methods allow us to map the internal spin structure of the skyrmion core, identifying a 25 nm central region of uniform magnetization followed by a larger region characterized by rotation from in- to out-of-plane. The formation and resolution of the internal spin structure of room temperature skyrmions without a stabilizing out-of-plane field in thick magnetic multilayers opens up a new set of tools and materials to study the physics and device applications associated with chiral ordering and skyrmions. Neel skyrmions are spin textures with a magnetization that rotates from in- to out-of-plane with distance from its centre. Here, the authors show that Lorentz transmission electron microscopy can be used to directly image Neel skyrmions with high resolution in thick exchange-coupled magnetic multilayers.

In Situ Transmission Electron Microscopy Study of Electron Beam-Induced Transformations in Colloidal Cesium Lead Halide Perovskite Nanocrystals

Abstract: An increasing number of studies have recently reported the rapid degradation of hybrid and all-inorganic lead halide perovskite nanocrystals under electron beam irradiation in the transmission electron microscope, with the formation of nanometer size, high contrast particles. The nature of these nanoparticles and the involved transformations in the perovskite nanocrystals are still a matter of debate. Herein, we have studied the effects of high energy (80/200 keV) electron irradiation on colloidal cesium lead bromide (CsPbBr3) nanocrystals with different shapes and sizes, especially 3 nm thick nanosheets, a morphology that facilitated the analysis of the various ongoing processes. Our results show that the CsPbBr3 nanocrystals undergo a radiolysis process, with electron stimulated desorption of a fraction of bromine atoms and the reduction of a fraction of Pb2+ ions to Pb0. Subsequently Pb0 atoms diffuse and aggregate, giving rise to the high contrast particles, as previously reported by various groups. T...

Layer-by-Layer Self-assembly of Co3O4 Nanorod-Decorated MoS2 Nanosheet-Based Nanocomposite toward High-Performance Ammonia Detection.

Abstract: This article is the first demonstration of a molybdenum disulfide (MoS2)/tricobalt tetraoxide (Co3O4) nanocomposite film sensor toward NH3 detection. The MoS2/Co3O4 film sensor was fabricated on a substrate with interdigital electrodes via layer-by-layer self-assembly route. The surface morphology, nanostructure, and elemental composition of the MoS2/Co3O4 samples were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive spectrometry, and X-ray photoelectron spectroscopy. The characterization results confirmed its successful preparation and rationality. The NH3 sensing properties of the sensor for ultra-low-concentration detection were investigated at room temperature. The experimental results revealed that high sensitivity, good repeatability, stability, and selectivity and fast response/recovery characteristics were achieved by the sensor toward NH3. Moreover, the MoS2/Co3O4 nanocomposite film sensor exhibited significant enhancement in ammonia...

Antibacterial Activity of Graphene Oxide/g-C3N4 Composite through Photocatalytic Disinfection under Visible Light

Abstract: Carbon-based nanomaterials have been widely developed into innovative antimicrobial agents due to their advantages of high surface-to-volume ratio, extremely high mechanical strength, and distinct physicochemical properties. Here, the nanocomposite of graphene oxide/graphitic carbon nitride (GO/g-C3N4), a free-metal photocatalyst, was fabricated through sonication at room temperature and its antibacterial activity against Escherichia coli (E. coli) was investigated. The 100 μg/mL GO/g-C3N4 composite was found to kill 97.9% of E. coli after 120 min visible light irradiation, which was further confirmed by fluorescent-based cell membrane integrity assay. Additionally, the holes produced by photocatalysis were confirmed by electron spin resonance (ESR) spectra and trapping experiments to participate in photocatalytic sterilization as principal active species and were further verified by transmission electron microscopy (TEM) and scanning electron microscope (SEM) to lead to the distortion and rupture of cell...

Selective Electroreduction of CO2 toward Ethylene on Nano Dendritic Copper Catalysts at High Current Density

Abstract: In situ deposited copper nanodendrites are herein proven to be a highly selective electrocatalyst which is capable of reducing CO2 to ethylene by reaching a Faradaic efficiency of 57% at a current density of 170 mA cm−2. It is found that the desired structures are formed in situ under acidic pH conditions at high electrode potentials more negative than −2 V versus Ag/AgCl. Detailed investigations on the preparation, characterization, and advancement of electrode materials and of the electrolyte have been performed. Catalyst degradation effects are intensively followed by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) characterization methods and found to be a major root course for selectivity losses.

Direct observation of intrinsic twin domains in tetragonal CH 3 NH 3 PbI 3

Abstract: Organic–inorganic hybrid perovskites are exciting candidates for next-generation solar cells, with CH3NH3PbI3 being one of the most widely studied. While there have been intense efforts to fabricate and optimize photovoltaic devices using CH3NH3PbI3, critical questions remain regarding the crystal structure that governs its unique properties of the hybrid perovskite material. Here we report unambiguous evidence for crystallographic twin domains in tetragonal CH3NH3PbI3, observed using low-dose transmission electron microscopy and selected area electron diffraction. The domains are around 100–300 nm wide, which disappear/reappear above/below the tetragonal-to-cubic phase transition temperature (approximate 57 °C) in a reversible process that often ‘memorizes’ the scale and orientation of the domains. Since these domains exist within the operational temperature range of solar cells, and have dimensions comparable to the thickness of typical CH3NH3PbI3 films in the solar cells, understanding the twin geometry and orientation is essential for further improving perovskite solar cells. Using low dose transmission electron microscopy, Rothmann, Li, Zhuet al. report direct evidence for twin domains in tetragonal CH3NH3PbI3perovskite. The relevant scale and transition temperature of these twin domains could have implications for perovskite solar cells.

Electrochemical Dissolution of Iridium and Iridium Oxide Particles in Acidic Media: Transmission Electron Microscopy, Electrochemical Flow Cell Coupled to Inductively Coupled Plasma Mass Spectrometry, and X-ray Absorption Spectroscopy Study

Abstract: Iridium-based particles, regarded as the most promising proton exchange membrane electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO2 particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer.

Highly sensitive and low detection limit of ethanol gas sensor based on hollow ZnO/SnO2 spheres composite material

Abstract: Heterostructure ZnO/SnO2 composites material with a hollow nanostructure was synthesized by solution method. The obtained products were characterized by X-ray diffraction (XRD), field-emission electron scanning microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that ZnO nanoparticles could be clearly observed on the surface of SnO2 hollow spheres and the surface oxygen chemisorbed ability of ZnO/SnO2 composites was much higher than that of single-component SnO2. The as-synthesized composites as sensing material was investigated and the results revealed that such composites had an excellent sensing performance to ethanol, and the response to 30 ppm ethanol was nearly 7-times higher than that of pristine SnO2 at its optimum temperature. Moreover, it is noteworthy that such gas sensor showed a low detection limit (ppb-level). The enhanced sensing properties might be attributed to the formation of heterojunction and synergistic effect between SnO2 and ZnO.

Study of structural, optical and magnetic properties of cobalt doped ZnO nanorods

Abstract: Cobalt doped zinc oxide nanoparticles (NPs) and nanorods (NRs) were synthesized by a simple chemical method. An increase in the formation of nanorods with an increase in cobalt doping is found to occur from scanning electron microscopy and transmission electron microscopy studies. Powder X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction confirm the formation of a wurtzite crystal structure of ZnO. Shifting and broadening of the bands at 437 cm−1 and 579 cm−1 in the micro-Raman study of Co-doped ZnO nanostructures indicates the incorporation of Co in ZnO. Shifting of the absorption edge to lower wavelength and blue shift of the band gap is observed in UV-visible spectra of Co-doped ZnO samples. Field-dependent magnetization measurements exhibit diamagnetic behavior down to 2 K in the case of ZnO whereas Co-doped ZnO samples show coexistence of superparamagnetic and ferromagnetic behavior at room temperature and at 2 K. The observed ferromagnetism may have originated due to the exchange interaction between the localized d electrons in Co2+ atoms and free carriers generated due to Co-doping as well as due to cobalt clustering in the Co-doped samples.

Defining the radiation chemistry during liquid cell electron microscopy to enable visualization of nanomaterial growth and degradation dynamics.

Abstract: We present a critical review of methods for defining the chemical environment during liquid cell electron microscopy investigation of electron beam induced nanomaterial growth and degradation. We draw from the radiation chemistry and liquid cell electron microscopy literature to present solution chemistry and electron beam-based methods for selecting the radiolysis products formed and their relative amount during electron irradiation of liquid media in a transmission electron microscope. We outline various methods for establishing net oxidizing or net reducing reaction environments and propose solvents with minimal overall production of radicals under the electron beam. Exemplary liquid cell electron microscopy experiments in the fields of nanoparticle nucleation, growth, and degradation along with recommendations for best practices and experimental parameters are reported. We expect this review will provide researchers with a useful toolkit for designing general chemistry and materials science liquid cell electron microscopy experiments by 'directing' the effect of the electron beam to understand fundamental mechanisms of dynamic nanoscale processes as well as minimizing radiation damage to samples.

Potential of an Alumina-Supported Ni3Fe Catalyst in the Methanation of CO2: Impact of Alloy Formation on Activity and Stability

Abstract: A promising bimetallic 17 wt % Ni3Fe catalyst supported on γ-Al2O3 was prepared via homogeneous deposition–precipitation for the application in the methanation of CO2 to gather more detailed insight into the structure and performance of the catalyst compared to state-of-the-art methanation systems. X-ray diffraction (XRD) analysis, detailed investigations using scanning transmission electron microscopy (STEM) combined with energy dispersive X-ray spectroscopy analysis (EDX) of single particles as well as larger areas, high-resolution transmission electron microscopy (HRTEM) imaging, temperature-programmed reduction (H2-TPR), and in-depth interpretation of Raman bands led to the conclusion that a high fraction of the Ni and Fe formed the desired Ni3Fe alloy resulting in small and well-defined nanoparticles with 4 nm in size and a dispersion of 24%. For comparison, a monometallic catalyst with similar dispersion using the same preparation method and analysis was prepared. Using a fixed-bed reactor, the Ni3F...

Chemical Ni-C Bonding in Ni-Carbon Nanotube Composite by a Microwave Welding Method and Its Induced High-Frequency Radar Frequency Electromagnetic Wave Absorption.

Abstract: In this work, a microwave welding method has been used for the construction of chemical Ni–C bonding at the interface between carbon nanotubes (CNTs) and metal Ni to provide a different surface electron distribution, which determined the electromagnetic (EM) wave absorption properties based on a surface plasmon resonance mechanism. Through a serial of detailed examinations, such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectrum, the as-expected chemical Ni–C bonding between CNTs and metal Ni has been confirmed. And the Brunauer–Emmett–Teller and surface zeta potential measurements uncovered the great evolution of structure and electronic density compared with CNTs, metal Ni, and Ni–CNT composite without Ni–C bonding. Correspondingly, except the EM absorption due to CNTs and metal Ni in the composite, another wide and strong EM absorption band ranging from 10 to 18 GHz ...

Facile Preparation of Core–Shell Fe3O4@Polypyrrole Composites with Superior Electromagnetic Wave Absorption Properties

Abstract: Core–shell Fe3O4@polypyrrole (PPy) composites with excellent electromagnetic wave absorption properties have been prepared by a sequential process of etching, polymerization, and replication. Templating from pre-prepared Fe3O4 microspheres, ferric ions were released from the skin layer of the microspheres by acid etching and initiated the oxidative polymerization of pyrrole in suit. The morphological and textural evolution of core–shell Fe3O4@PPy composites depending on etching time was investigated by scanning and transmission electron microscope. A maximum reflection loss of as much as −41.9 dB (>99.99% absorption) at 13.3 GHz with a matching layer thickness of 2.0 mm was achieved when the etching time was 5 min. In comparison with other conductive polymer-based core–shell composites reported previously, the Fe3O4@PPy composites in this study not only possess better reflection loss performance but also demonstrate a wider effective absorption bandwidth (<−10.0 dB) over the entire Ku band (12.0–18.0 GHz)...

Nickel-metal organic framework/MWCNT composite electrode for non-enzymatic urea detection

Abstract: A porous composite catalyst based on nickel-metal organic framework (Ni-MOF) and multiwalled carbon nanotubes (MWCNTs) was synthesized for non-enzymatic urea detection. The Ni-MOF was characterized by Fourier transform infrared spectroscopy, X-ray photo electron spectroscopy and X-ray diffraction techniques. The morphology and the structure of the Ni-MOF were studied using scanning electron microscopy and transmission electron microscopy. The Ni-MOF/MWCNTs coated indium tin oxide glass was used as a novel electrochemical sensor for urea detection. The Ni-MOF/MWCNT electrode showed a very high sensitivity of 685 μAmM −1 cm −2 , low detection limit of 3 μM and a response time of 10 s. Moreover, the sensor showed remarkable stability with no loss in activity after 30 days of storage under ambient conditions. Overall, the novel hybrid inorganic–organic material showed notable potential for designing of micro-scale point of care diagnostic devices for urea sensing applications.

The Use of Graphene and Its Derivatives for Liquid-Phase Transmission Electron Microscopy of Radiation-Sensitive Specimens.

Abstract: One of the key challenges facing liquid-phase transmission electron microscopy (TEM) of biological specimens has been the damaging effects of electron beam irradiation. The strongly ionizing electron beam is known to induce radiolysis of surrounding water molecules, leading to the formation of reactive radical species. In this study, we employ DNA-assembled Au nanoparticle superlattices (DNA-AuNP superlattices) as a model system to demonstrate that graphene and its derivatives can be used to mitigate electron beam-induced damage. We can image DNA-AuNP superlattices in their native saline environment when the liquid cell window material is graphene, but not when it is silicon nitride. In the latter case, initial dissociation of assembled AuNPs was followed by their random aggregation and etching. Using graphene-coated silicon nitride windows, we were able to replicate the observation of stable DNA-AuNP superlattices achieved with graphene liquid cells. We then carried out a correlative Raman spectroscopy a...

Capture the growth kinetics of CVD growth of two-dimensional MoS 2

Abstract: Understanding the microscopic mechanism is fundamental for function-oriented controlled chemical vapor deposition growth of two-dimensional (2D) materials. In this work, we reveal the growth kinetics of 2D MoS2 by capturing the nucleation seeds, evolving morphology, edge structure, and edge terminations at the atomic scale during chemical vapor deposition growth using the transmission electron microscopy and scanning transmission electron microscopy. The direct growth of few-layer and mono-layer MoS2 onto graphene-based transmission electron microscopy grids helped us to perform the subsequent transmission electron microscopy characterization without any solution-based transfer. Two seeding centers are observed: (i) Mo-oxysulfide (MoO x S2−y ) nanoparticles either in multi-shelled fullerene-like structures or as compact nanocrystals for the growth of fewer-layer MoS2; (ii) Mo-S atomic clusters. In the early stage growth, irregular polygons with two primary edge terminations, S-Mo Klein edges and Mo zigzag edges, appear approximately in equal numbers. The morphology evolves into a near-triangle shape in which Mo zigzag edges predominate. Results from density-functional theory calculations are consistent with the inferred growth kinetics, and thus support the growth mechanism we proposed. In general, the growth mechanisms found here should also be applicable in other 2D materials, such as MoSe2, WS2 and WSe2. The growth kinetics of two-dimensional (2D) molybdenum disulfide (MoS2) atomic layers has been captured using atomic-resolution transmission electron microscopy (TEM). In a regular process, 2D growth is usually performed on a silicon dioxide substrate. This makes studying the atomic-scale structures difficult because small layers can be damaged while transfering onto TEM grids. A team led by Chuanhong Jin at Zhejiang University, China, grew atomic layers of MoS2 directly on graphene-layer-based TEM grids in a regular chemical vapor deposition system. With this method intermediate and few-nanometer scale layers have been successfully monitored. These results are important for understanding the growth mechanism of MoS2 and other relevant 2D materials.

Highly Uniform Atomic Layer-Deposited MoS2@3D-Ni-Foam: A Novel Approach To Prepare an Electrode for Supercapacitors

Abstract: This article takes an effort to establish the potential of atomic layer deposition (ALD) technique toward the field of supercapacitors by preparing molybdenum disulfide (MoS2) as its electrode. While molybdenum hexacarbonyl [Mo(CO)6] serves as a novel precursor toward the low-temperature synthesis of ALD-grown MoS2, H2S plasma helps to deposit its polycrystalline phase at 200 °C. Several ex situ characterizations such as X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and so forth are performed in detail to study the as-grown MoS2 film on a Si/SiO2 substrate. While stoichiometric MoS2 with very negligible amount of C and O impurities was evident from XPS, the XRD and high-resolution transmission electron microscopy analyses confirmed the (002)-oriented polycrystalline h-MoS2 phase of the as-grown film. A comparative study of ALD-grown MoS2 as a supercapacitor electrode on 2-dimensional stainless steel and on 3-dimensional (3D) Ni-foam substrates clearly reflects the...

Hierarchical Assembly of α-Fe2O3 Nanorods on Multiwall Carbon Nanotubes as a High-Performance Sensing Material for Gas Sensors

Abstract: This paper presents a facile hydrolysis reaction and annealing for preparing a novel hierarchical nanoheterostructure via assembly of α-Fe2O3 nanorods onto multiwall carbon nanotubes (MWCNTs) backbones. The as-synthesized nanocomposites were characterized using XRD (X-ray diffraction), FESEM (Field emission scanning electron microscopy), TEM (Transmission electron microscopy), XPS (X-ray photoelectron spectroscopy) and BET (Surface Area and Porosity System). The observations showed uniform α-Fe2O3 nanorods approximately 100–200 nm in length and 50–100 nm in diameter that were hierarchically assembled onto the surface of the MWCNTs. The formation of the heterostructure was investigated by observing the evolution of the microstructure of the products at different reaction times. The X-ray photoelectron spectra (XPS) showed that the ability of the absorbing oxygen was enhanced by the formation of the heterostructure composites. Moreover, as a proof-of-concept presentation, the novel CNTs@α-Fe2O3 hierarchical...

Kinetic Analysis of the Reduction of 4-Nitrophenol Catalyzed by CeO2 Nanorods-Supported CuNi Nanoparticles

Abstract: CuxNi100–x (x = 0, 20, 40, 60, 80, and 100) nanoparticles were uniformly grown on the surface of CeO2 by the liquid impregnation method. The as-prepared nanocomposite abbreviated CuxNi100–x–CeO2 was characterized by various techniques including, X-ray powder diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Brunauer–Emmett–Teller surface area analyzer, and transmission electron microscopy. The catalytic activity of CuxNi100–x–CeO2 nanocomposites was investigated in 4-nitrophenol (4-NP) reduction reaction. Among the synthesized nanocomposites, Cu60Ni40–CeO2 exhibited the best catalytic activity (rate constant as 0.1654 s–1) with high recyclability for five consecutive runs. The mechanism of the reduction was studied, and the adsorption equilibrium constant of 4-NP (K4-NP) and borohydride (KBH4–) was calculated by using the Longmuir–Hinshelwood model. The energy of activation (Ea) and thermodynamic parameters such as activation enthalpy (ΔH⧧), entropy (ΔS⧧), and...

Enhancement of the isopropanol gas sensing performance of SnO2/ZnO core/shell nanocomposites

Abstract: Pure SnO2, ZnO nanoparticles, and a SnO2/ZnO core/shell nanocomposite (NC) were prepared via a sol–gel technique. The structure and morphology of the obtained materials were characterized by X-ray diffraction (XRD), micro-Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). The results showed that highly crystalline materials were formed, and the resulting composites exhibited core/shell structure with a size of 30 nm, whereas the fabricated films exhibited porous morphology. The gas sensing performance of the SnO2, ZnO nanoparticles, and the SnO2/ZnO NC films was investigated for different volatile organic compound (VOC) vapors in the temperature range from 150 to 350 °C. The gas sensing results confirmed that the SnO2/ZnO NC film shows a high selectivity, sensitivity, good stability, and fast response time towards isopropanol at the optimum operating temperature of 300 °C.

Advances in Atomic Resolution In Situ Environmental Transmission Electron Microscopy and 1 Angstrom Aberration Corrected In Situ Electron Microscopy

Abstract: Advances in atomic resolution in situ environmental transmission electron microscopy for direct probing of gas-solid reactions, including at very high temperatures are described. In addition, recent developments of dynamic real time in situ studies at the Angstrom level using a hot stage in an aberration corrected environment are presented. In situ data from Pt and Pd nanoparticles on carbon with the corresponding FFT (optical diffractogram) illustrate an achieved resolution of 0.11 nm at 500 C and higher in a double aberration corrected TEM and STEM instrument employing a wider gap objective pole piece. The new results open up opportunities for dynamic studies of materials in an aberration corrected environment.