Scanning Transmission Electron Microscopy Energy Dispersive X-ray Spectroscopy Research Articles

Contrasting shell thickness-dependent magnetic behaviors of CoFe2O4@Fe3O4 and Fe3O4@CoFe2O4 core/shell nanoparticles

The magnetic properties of bi-magnetic core/shell nanoparticles (NPs) have been a subject of extensive investigation. Yet, the role of shell thickness in hard/soft and soft/hard core/shell NPs, corresponding to conventional and inverse structures, remains incompletely elucidated. In this study, we synthesized two sets of core/shell NPs, namely Fe3O4@CoFe2O4 (IF@CF) and CoFe2O4@Fe3O4 (CF@IF), featuring a fixed core diameter of approximately 11 nm and varying shell thicknesses up to 5 nm. These NPs were synthesized via a seed-mediated particle growth approach. The formation of the core/shell configuration of typical NPs in both sets was directly verified through scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) imaging. Notably, the saturation magnetization (MS) of IF@CF NPs exhibited a significant increase compared to that of the IF core across all shell thickness variations, whereas it remained largely unchanged for CF core and CF@IF NPs. Conversely, the coercivity (HC) showed an opposite trend in the two structures with increasing shell thickness. We observed the emergence of a transition from constricted to smooth hysteresis loops in the conventional structure when the shell thickness reached 5 nm. The systematic evolution of hysteresis loops with escalating shell thickness in both structures closely correlates with distinct magnetic reversal mechanisms, influenced significantly by interparticle interactions. Our study presents a pathway for modulating the magnetic properties of bi-magnetic core/shell NPs, thereby opening avenues for advanced applications in magnetic imaging, sensing, drug delivery, and magnetic hyperthermia.

Atomic-level investigation of structure and formation process of Y3Al5O12 with super-high content of Ce emitting anomalous orange-red emissions

Ce-doped yttrium aluminum garnet (YAG:Ce, Y3Al5O12:Ce) is the most commonly used yellow phosphor in white light-emitting diodes. Recently, we found that (Y1–xCex)3Al5O12:Ce with a super-high content of Ce (x = 0.11–0.21) can be prepared by a polymerized complex method and exhibits anomalous orange–red emission. To understand the nature of this anomalous behavior from the atomic level, we applied high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and scanning transmission electron microscopy–energy dispersive X-ray spectroscopy (STEM-EDS), a state-of-the-art technique that enables analysis of the atomic-level elemental distributions of Al, Y, and Ce. STEM-EDS images on the atomic level were successfully obtained for YAG:Ce. It was found that Ce in Y site has spatially uneven for few nanometers. Ce–K edge extended X-ray absorption fine structure (EXAFS) analysis was also conducted, which revealed a high level of asymmetry around Ce. By combining the STEM-EDS and EXAFS results, a dynamic model for the red emission was proposed. STEM-EDS also revealed that CeO2 nanocrystals were firstly formed with low-temperature annealing and that the reaction of Y with the CeO2 nanocrystals subsequently yielded YAG:Ce, unlike in the conventional one-step high-temperature synthesis.

Contributions to the mechanistic understanding of the microstructural evolution in irradiated U-Mo dispersion fuel

Advanced microstructural characterization techniques, such as scanning electron microscopy (SEM) and scanning transmission electron microscopy - energy dispersive x-ray spectroscopy (STEM-EDS), were used to interpret the fuel microstructure evolution and fission products behavior in U-Mo dispersion fuel irradiated in the Advanced Test Reactor (ATR) as part of the European Mini-Plate Irradiation Experiment (EMPIrE) test. The larger as-fabricated fuel grain size achieved by heat-treating the U-Mo powder resulted in slower high burnup structure (HBS) development and reduced fission gas porosity. Slower HBS kinetics was observed at the fuel kernels’ periphery, which contained smaller and less fission gas bubbles at all fission densities (FDs) investigated and was attributed to a locally reduced damage density and fission products concentration, as corroborated with Monte Carlo simulations. The non-refined grains at the fuel kernel periphery hosted a perfectly ordered fission Gas Bubble Superlattice (GBS) up to 6.3 × 1021 fissions/cm3. Nano-scale STEM-EDS analysis presented in this study provided useful information on the GBS characteristic morphology and evolution in U-Mo fuel. The concentration of fission gas in the GBS progressively increased with FD, pointing to an evolution of the nanobubble pressure status with irradiation. A possible connection between the GBS collapse and HBS onset is proposed for which there exists a threshold in the misorientation of the refined sub-grains above which the GBS stability during irradiation is no longer preserved, resulting in the GBS collapse.

Control of side reactions using LiNbO3 mixed/doped solid electrolyte for enhanced sulfide-based all-solid-state batteries

Control of side reactions is a critical issue for obtaining all-solid-state lithium batteries (ASSLBs) with comparable performance to lithium-ion batteries (LIBs). In particular, the interfacial reaction at the cathode/sulfide electrolyte interface and decomposition of the sulfide electrolyte lead to a significant deterioration in the electrochemical performance of ASSLBs. Surface-coated cathodes have been used in ASSLBs to mitigate these side reactions. However, the generally used LiNbO3 coating, a representative coating for ASSLBs, is expensive because of the high price of the source materials, and perfect coverage of the entire cathode surface by coating is practically very difficult. In this study, we introduced a LiNbO3 mixed/doped Li6PS5Cl solid electrolyte, instead of surface coating on the cathodes, to improve the resistance against side reactions concerning the sulfide electrolyte. The source material used for LiNbO3 mixing/doping is cheaper than that used for LiNbO3 coating. Partial doping of LiNbO3 was confirmed by laser Raman spectroscopy and field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy (EDS) analysis. An optimum LiNbO3 mixed/doped electrolyte (4 mol.% of electrolyte) showed enhanced ionic conductivity than that of Li6PS5Cl solid electrolyte without LiNbO3. Moreover, the interfacial reaction at the cathode/electrolyte interface and the sulfide electrolyte decomposition were decreased owing to the LiNbO3 mixing/doping effect. The suppression of ion exchange between the cathode and electrolyte was also confirmed by the scanning transmission electron microscopy - energy dispersive X-ray spectroscopy (STEM-EDS) line profile. These results contributed to the increased discharge capacity and improved rate capability of the cell using 96LPSCl-4LNO (4 mol.% LiNbO3 mixing/doping), compared to those of the cell using pristine Li6PS5Cl.

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for Analysis of Surface and Interface Chemistry of Porous Transport Layers

As the United States energy infrastructure moves towards the integration of hydrogen energy, the reliable production of hydrogen through water electrolyzers is imperative. In proton exchange membrane water electrolyzes (PEMWE’s), the porous transport layer (PTL) plays an important role. When choosing PTL material, one should consider corrosion resistance, electrical conductivity, and ability to support the structure of the electrochemical cell. Due to these requirements, titanium is the current state-of-the-art anode PTL material. However, titanium quickly forms a layer of titanium oxide which significantly decreases conductivity of the PTL and respectively decreases the overall efficiency of the PEMWE system. Coatings are commonly applied to the PTL to combat this complication, but the use of noble metals leads to cost concerns. Additionally, the degradation of coated PTLs is not yet well known.Advanced physicochemical characterization of PTLs at various stages of fabrication and testing is vital to understand their properties and the impact on electrochemical performance in order to improve durability and meet cost targets. Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) is currently used to cross section areas of the PTL for subsequent analysis with Scanning Transmission Electron MicroscopyEnergy-dispersive X-ray Spectroscopy (STEM-EDS) analysis to visualize the elemental information of the PTL materials and PTL coatings, specifically looking at detrimental oxide layer formation. Unfortunately, this approach is time-consuming and difficult, motivating the development of alternative approaches that allow the characterization of wide sample sets more efficiently. Additionally, STEM-EDS analysis only provides elemental information, so if several oxide layers preside, it can be difficult to differentiate them. Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiling is a very powerful technique that has been commonly used to characterize thin films and buried interfaces. Unlike the FIB-SEM and STEM-EDS combination, ToF-SIMS can be performed relatively quickly in several areas of the PTL, provides chemical information, and is sensitive to trace elements. An added advantage of ToF-SIMS is ability to do 2D and 3D chemical analysis on different scales. This enables visualization of elemental and chemical distribution on both larger scale (70x70 um) areas, and smaller areas (20x10 um) which provides more detailed surface and interface information. This allows for detailed tracking of all major constituents of the PTL and coating. It also allows to follow changes in oxide layers upon fabrication and after electrochemical testing, as well as track homogeneity of the surface and oxide layer interfaces throughout different parts of the PTL. This presentation will demonstrate capabilities of this technique for characterization of PTLs, along with progress and potential challenges. ToF-SIMs results will be compared to TEM analysis of cross-sections obtained with FIB-SEM. This study will highlight similarities and differences between the techniques, technique optimization for these morphologically challenging samples, and paths for future investigation moving forward.

In-situ characterization of porcine fibroblasts in response to silver ions by Raman spectroscopy and liquid scanning transmission electron microscopy

Since silver ion is known for its antimicrobial function, most of the research has focused mainly on toxicity effects rather than the role of silver ion in general biology and the behind mechanism of actions of silver ion in mammalian cells. Moreover, a conventional in vitro approach to estimate the effects of silver ion on cells does not provide information about the biochemical changes and might accompany artifacts due to invasive and destructive sample preparation processes. In the present study, in-situ real time approaches were applied to evaluate the impact of silver ion (0.57, 1.34, 1.96, 2.33 mg/L) on fibroblast cells. Raman spectroscopy analysis showed that Raman peak intensities of proteins and nucleic acids significantly increased in the cells after exposure to silver ion for 21 h, especially at relatively higher levels 1.34, 1.96, and 2.33 mg/L. Raman peak at 1585 cm−1 and liquid scanning transmission electron microscopy energy-dispersive x-ray spectroscopy (STEM-EDS) analysis revealed the fate of silver ion that was taken up by the cell and reduced into metallic silver accumulating in the cell as silver nanoparticles. These results suggest cells were undergoing different activities such as enhanced metabolic activities rather than cell apoptosis or cell death. Additionally, Raman spectroscopy predicted the level of silver ion exposed to the cell at 2.11 ± 0.38 and 1.73 ± 0.26 mg/L by the PLS prediction model, compared with the results measured by inductively coupled plasma mass spectrometry (ICP-MS), 2.14 ± 0.07 and 1.87 ± 0.07 mg/L respectively, suggesting Raman spectroscopy can provide a new and fast approach to determine and measure the concentration of silver ion or probably other tested molecules treated to the cell for the future research.

Ultra-fast high-temperature sintering of strontium titanate

Ultrafast High-temperature Sintering (UHS) is a novel sintering process enabling extremely high heating rates by direct contact of sample to electrically heated thin carbon strips. Using strontium titanate as a model system, the densification behavior by UHS was investigated. Controlled experiments via maximum current limitation were used to study the influence of the applied current on the degree of densification and resulting final grain size. Simulations by Finite Element Modeling (FEM) allow estimating the sample temperature reached during UHS, which is in good agreement with the experimental data. Moreover, the FEM simulations show a self-stabilization of the sample temperature by thermal radiation. UHS results suggest that rapid densification can be achieved with an extremely high heating rate. The microstructure of the undoped strontium titanate samples shows exaggerated grain growth and pore-boundary separation, which results in pore entrapment inside grains. The addition of 2 mol% iron in strontium titanate is beneficial by limiting the grain growth during the UHS sintering cycle. Uniform densification and grain growth in the sample is consequently observed. Scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDS) is utilized to analyze grain boundary segregation. Measurement of the electrical conductivity of the UHS sintered samples by impedance spectroscopy suggest that rapid densification by UHS enables full access to the functional properties of strontium titanate as compared to the conventionally sintered material.

Surface segregation of 3 mol % yttria-doped tetragonal zirconia particle studied by atomic-resolution scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy

Atomic structure of the surfaces in commercial 3 mol % yttria-doped tetragonal zirconia (TZP) nano-particulate powders were studied by atomic resolution scanning transmission electron microscopy (STEM), and the surface segregation of Y were investigated by STEM energy-dispersive X-ray spectroscopy (EDS) at atomic scale. STEM-EDS observations revealed that the Y cations tend to segregate on the top surface layer, forming a monolayer segregation structure. Static lattice calculations revealed that the surface segregation of Y is energetically favorable. These results indicate that Y surface segregation occurs in the TZP powders, which might partially account for the grain boundary segregation in the sintered body of TZP ceramics.

Tungsten Oxide-Modified SSZ-13 Zeolite as an Efficient Catalyst for Ethylene-To-Propylene Reaction

Among the zeolitic catalysts for the ethylene-to-propylene (ETP) reaction, the SSZ-13 zeolite shows the highest catalytic activity based on both its suitable pore architecture and tunable acidity. In this study, in order to improve the propylene selectivity further, the surface of the SSZ-13 zeolite was modified with various amounts of tungsten oxide ranging from 1 wt% to 15 wt% via a simple incipient wetness impregnation method. The prepared catalysts were characterized with several analysis techniques, specifically, powder X-ray diffraction (PXRD), Raman spectroscopy, temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and N2 sorption, and their catalytic activities were investigated in a fixed-bed reactor system. The tungsten oxide-modified SSZ-13 catalysts demonstrated significantly improved propylene selectivity and yield compared to the parent H-SSZ-13 catalyst. For the tungsten oxide loading, 10 wt% loading showed the highest propylene yield of 64.9 wt%, which was 6.5 wt% higher than the pristine H-SSZ-13 catalyst. This can be related to not only the milder and decreased strong acid sites but also the diffusion restriction of bulky byproducts, as supported by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) observation.

Investigation of the Effects of Forming Gas Annealing on Al2O3/GaN Interface

In this work, the effects of post-deposition annealing in forming gas ambient on the structure of the Al2O3/GaN interface are investigated. Using capacitance–voltage (C–V) and conductance–frequency (G–f) measurements, the quality of Al2O3/GaN metal–insulator–semiconductor (MIS) devices subjected to different annealing conditions was assessed. Annealing at 350°C for 10 and 20 min resulted in the lowest density of trap states (< 1011 cm−2eV−1), while higher-temperature annealing resulted in increased density of interface traps. Scanning transmission electron microscopy, energy-dispersive x-ray spectroscopy (STEM/EDS), and x-ray photoelectron spectroscopy (XPS) were used to determine the impact of the anneal on the structure of the oxide and interface. It was found that after annealing at 600°C for 20 min, the oxide structure was not significantly changed, though the density of interface states was found to increase by nearly an order of magnitude. These results suggest that the post-deposition annealing of Al2O3/GaN in forming gas passivates defects at the interface but does not cause significant structural change away from the interface.

Microstructure and microchemistry study of irradiation-induced precipitates in proton irradiated ZrNb alloys

Proton irradiation induced Nb redistribution in Zr-xNb alloys (x = 0.4, 0.5, 1.0 wt%) has been investigated using scanning transmission electron microscopy/energy dispersive X-ray spectroscopy (STEM/EDS). Zr-xNb alloys are mainly composed of Zr matrix, native Zr–Nb–Fe phases, and β-Nb precipitates. After 2 MeV proton irradiation at 350 °C, a decrease of Nb content in native precipitates, as well as irradiation-induced precipitation of Nb-rich platelets (135 ± 69 nm long and 27 ± 12 nm wide) were found. Nb-rich platelets and Zr matrix form the Burgers orientation relationship, [11¯1]//[21¯1¯0] and (011)//(0002). The platelets were found to be mostly coherent with the matrix with a few dislocations near the ends of the precipitate. The coherent strain field has been measured in the matrix and platelets by the 4D-STEM technique. The growth of Nb-rich platelets is mainly driven by coherency and dislocation-induced strain fields. Irradiation may both enhance the diffusion and induce segregation of interstitial Nb to the ends of the irradiation induced platelets, further facilitating their growth.

Tiny Ruthenium‐Cobalt‐Cobalt Hydroxide Nanoparticles Supported on Graphene for Efficiently Catalyzing Naphthalene Complete Hydrogenation

AbstractThe nanocatalyst of graphene‐supported ruthenium/cobalt/cobalt hydroxide nanoparticles (denoted as Ru/Co/Co(OH)2/G) was obtained at ambient temperature by using chemical reduction with hydrazine hydrate as reducing agent and galvanic replacement reaction methods. The nanostructure of Ru nanoclusters‐on‐cobalt‐on‐cobalt hydroxide nanoparticles (NPs) has been proved in Ru/Co/Co(OH)2/G by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), high resolution TEM (HRTEM), scanning transmission electron microscopy‐energy dispersive X‐ray spectroscopy (STEM‐EDS) elemental line scanning and mapping analysis, and high‐sensitivity low‐energy ion scattering (HS‐LEIS) measurement techniques. The Ru/Co/Co(OH)2/G catalyst showed excellent catalytic activity and 100% selectivity toward decalin for naphthalene hydrogenation reaction at the reaction temperature of 100 °C under initial 4.48 MPa hydrogen pressure probably owing to the synergetic effect of Ru, Co and Co(OH)2 active sites.

High-temperature structural change and microtexture formation of sillimanite and its phase relation with mullite

Abstract Synchrotron powder X-ray diffraction (XRD) experiments and transmission electron microscopy (TEM) observations of heat-treated sillimanite at various pressures were conducted to clarify the detailed phase relation between sillimanite and mullite. Under TEM, heat-treated sillimanite frequently showed anti-phase boundary (APB)-like textures with a displacement vector of ½[001]sil. Additional scanning TEM energy-dispersive X-ray spectroscopy analysis of regions with APB-like texture showed that they were clearly enriched in Al and accompanied by very fine, Si-rich glass inclusions, which indicates that the APB-like textures are composed of fine mullite. Moreover, synchrotron XRD patterns of these samples clearly showed double peaks of newly formed mullite and remnant sillimanite, indicating that the compositional transformation from sillimanite to mullite and glass is discontinuous. We separately determined the cell parameters of the sillimanite and mullite from the XRD pattern and found that the b axial length of the sillimanite increased with the treatment temperature, reflecting disordering of tetrahedral Al and Si in the sillimanite. In contrast, the positions of the deconvoluted mullite peaks indicated that the a axial length of mullite decreased as experimental pressure increased, owing to enrichment of the Si component. By projecting the cell parameters onto the a–b axial plane, the detailed changes in the crystallographic state of the sillimanite and mullite could be easily and comprehensively identified. On the basis of our results, we propose a new P-T diagram for the Al2SiO5 system that shows the transformation boundary between sillimanite and mullite + SiO2-rich melt and the contour of the Al/Si order parameter of sillimanite.

Athabasca oil sands region snow contains efficient micron and nano-sized ice nucleating particles

The Athabasca Oil Sands Region (AOSR) in Alberta, Canada, is an important source of atmospheric pollutants, such as aerosols, that have repercussions on both the climate and human health. We show that the mean freezing temperature of snow-borne particles from AOSR was elevated (−7.1 ± 1.8 °C), higher than mineral dust which freezes at ∼ −15 °C and is recognized as one of the most relevant ice nuclei globally. Ice nucleation of nanosized snow samples indicated an elevated freezing ability (−11.6 ± 2.0 °C), which was statistically much higher than snow-borne particles from downtown Montreal. AOSR snow had a higher concentration (∼2 orders of magnitude) of >100 nm particles than Montreal. Triple quadrupole ICP-(QQQ)-MS/MS analysis of AOSR and Montreal snow demonstrated that most concentrations of metals, including those identified as emerging nanoparticulate contaminants, were much more elevated in AOSR in contrast to Montreal: 34.1, 34.1, 16.6, 5.8, 0.3, 0.1, and 9.4 mg/m3 for Cr, Ni, Cu, As, Se, Cd, and Pb respectively, in AOSR and 1.3, 0.3, 2.0, <0.03, 0.1, 0.03, and 1.2 mg/m3 in Montreal snow. High-resolution Scanning Transmission Electron Microscopy/Energy-dispersive X-ray Spectroscopy (STEM-EDS) imaging provided evidence for various anthropogenic nano-materials, including carbon nanotubes resembling structures, in AOSR snow up to 7–25 km away from major oil sands upgrading facilities. In summary, particles characterized as coming from oil sands are more efficient at ice nucleation. We discuss the potential impacts of AOSR emissions on atmospheric and microphysical processes (ice nucleation and precipitation) both locally and regionally.

Enhanced activity of Pd–Cu(Ni) bimetallic catalysts for oxidative carbonylation of phenol

Pd–Cu(Ni) bimetallic catalysts supported on Pb-doped manganese oxide octahedral molecular sieves(Pb-OMS-2) were prepared by deposition-precipitation method, and the activities of those bimetallic catalysts were evaluated in the oxidative carbonylation of phenol to diphenyl carbonate (DPC). The physico-chemical properties of catalysts were evaluated by various characterization techniques such as X-ray diffraction (XRD), Transmission electron microscope (TEM), Scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDS), Temperature-programmed reduction of hydrogen (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The results showed that superior activity of bimetallic catalyst was accomplished by the addition of second metal Cu(Ni) compared to monometallic Pd catalyst. The metal particles of bimetallic catalysts were dispersed homogeneously on the surface with small particle size (3∼5 nm). The high activity and stability of bimetallic catalyst were achieved due to the formation of very active Pd–Cu(Ni) interfaces. The oxidation state of active species increased via the strong interaction between bimetallic components, and the redox capacity of Pd became stronger with the addition of the second metal. The highest DPC yield was 23.4% for Pd1Cu2 and 22.9% for Pd1Ni4 catalysts, respectively. After 20 h of reaction time, even though the DPC yield stopped growing for the monometallic catalysts, it continued to increase for the bimetallic catalysts, and the DPC yield reached about 50.0% at 24 h.

Biosynthesized Highly Stable Au/C Nanodots: Ideal Probes for the Selective and Sensitive Detection of Hg2+ Ions.

The enormous ongoing industrial development has caused serious water pollution which has become a major crisis, particularly in developing countries. Among the various water pollutants, non-biodegradable heavy metal ions are the most prevalent. Thus, trace-level detection of these metal ions using a simple technique is essential. To address this issue, we have developed a fluorescent probe of Au/C nanodots (GCNDs-gold carbon nanodots) using an eco-friendly method based on an extract from waste onion leaves (Allium cepa-red onions). The leaves are rich in many flavonoids, playing a vital role in the formation of GCNDs. Transmission electron microscopy (TEM) and Scanning transmission electron microscopy-Energy-dispersive X-ray spectroscopy (STEM-EDS) elemental mapping clearly indicated that the newly synthesized materials are approximately 2 nm in size. The resulting GCNDs exhibited a strong orange fluorescence with excitation at 380 nm and emission at 610 nm. The GCNDs were applied as a fluorescent probe for the detection of Hg2+ ions. They can detect ultra-trace concentrations of Hg2+ with a detection limit of 1.3 nM. The X-ray photoelectron spectroscopy results facilitated the identification of a clear detection mechanism. We also used the new probe on a real river water sample. The newly developed sensor is highly stable with a strong fluorescent property and can be used for various applications such as in catalysis and biomedicine.

Mesoporous SiO2/BiVO4/CuOx nanospheres for Z-scheme, visible light aerobic C–N coupling and dehydrogenation

In light of the growing demand to use renewable energy, we have synthesized a mesoporous bismuth vanadate-copper oxide-silica photocatalyst (SiO2/BiVO4/CuOx) to act as a chromophore in a Z-scheme system. These photocatalysts are intended for effective light harvesting and charge separation in the synthesis of solar chemicals, using air as an environmentally benign oxidant. Full characterization of the SiO2/BiVO4/CuOx was conducted, including X-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS), and scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), which confirm the presence of CuOx at the heterojunction of the nanostructures. The other characterization methods that were employed included powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), elemental mapping, UV–vis diffuse reflectance spectroscopy (UV–vis DRS), N2 sorption experiments, photoluminescence spectroscopy (PL), electrochemical impedance spectroscopy (EIS), and photocurrent measurements. Notably, the SiO2/BiVO4/CuOx nanospheres perform seven times faster than bulk BiVO4 and provide higher yields for the oxidative coupling of amines to imines, which are valuable precursors for agrochemicals and active pharmaceutical ingredients. The superior photocatalysis of SiO2/BiVO4/CuOx is attributed to the surface CuOx nanoparticles that increase the average PL lifetime from 2.3 to 4.5ns, which improved the charge separation and decreased the unproductive recombinations of electron–hole pairs. In addition, the photocurrent density of the SiO2/BiVO4/CuOx electrode was about 3.5 times higher than that of SiO2/BiVO4, while lower charge transfer resistance was observed by EIS. Meanwhile, chemical scavenging experiments revealed that holes and superoxide radicals were the main reactive oxygen species in the photocatalytic reaction. The nanospheres also show broad functional group tolerance, good recyclability with high conversions, and high to moderate yields for the oxidatively coupled imine products after eight runs. Thus, we demonstrate that an effective and green approach in artificial photosynthesis is applicable for organic synthesis as well.

Cation Redistribution along the Spiral of Ni-Doped Phyllosilicate Nanoscrolls: Energy Modelling and STEM/EDS Study.

Here, we study the stress-induced self-organization of Mg2+ and Ni2+ cations in the crystal structure of multiwalled (Mg1-x ,Nix )3 Si2 O5 (OH)4 phyllosilicate nanoscrolls. The phyllosilicate layer strives to compensate size and surface energy difference between the metal oxide and silica sheets by curling. But as soon as the layer grows, the scrolling mechanism becomes a spent force. An energy model proposes secondary compensation of strain: two cations distribute along the nanoscroll spiral in accordance with preferable radii of curvature. To reveal this, we study synthetic (Mg1-x ,Nix )3 Si2 O5 (OH)4 nanoscrolls by the scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDS) technique. For a number of scrolls, we have found indeed a change of Ni concentration with increase in distance from the nanoscroll central axis. The concentration gradient, according to our estimates, can reach 50 at.% over 25 nm of the wall thickness.

Phase stability of single phase Al0.12CrNiFeCo high entropy alloy upon irradiation

Phase stability of NiCoFeCr and Al0.12NiCoFeCr single phase high entropy alloys (HEAs) was studied under 3 MeV Ni2+ irradiation at 500 °C to a fluence of 1 × 1017/cm2 reaching a peak dose of ~100 displacements per atom (dpa). Transmission electron microscopy (TEM) diffraction pattern and scanning transmission electron microscopy-energy dispersive X-Ray spectroscopy (STEM-EDS) were utilized to detect any second phases that formed in the irradiated regions of the specimens. While the single phase of NiCoFeCr alloy has remained stable under the irradiation, the phase in Al0.12NiCoFeCr alloy decomposed into FCC matrix phase, and Ni3Al type nanoprecipitates with L12 ordered structure. On the other hand, in Al0.12NiCoFeCr alloy, the non-irradiated region of the TEM specimen (annealed for 10 h at 500 °C) and the as-cast alloy annealed for 490 h at 500 °C exhibited no such precipitates similar to those observed in the irradiated region. Based upon the thermodynamic stability of these alloys, we propose that radiation-enhanced diffusion under the irradiation accelerated the formation of the Ni3Al type equilibrium phase. Our study clearly demonstrates that the phase stability of HEAs under irradiation should be considered as one of the deciding factors in the materials design and selection for nuclear applications.

Ruthenium stabilized on transition metal-on-transition metal oxide nanoparticles for naphthalene hydrogenation

The multi-metallic nanocatalysts of ruthenium nanoclusters-on-transition metal/transition metal oxide nanoparticles (TM/TMO NPs) then supported on carbon (Ru/Ni/NiO/C or Ru/Co/Co3O4/C) were designed and synthesized. The Ni/NiO or Co/Co3O4 NPs strongly stabalized the ruthenium nanoclusters by the interfacial interaction among them. These catalysts exhibited high catalytic activity and 100% selectivity to decalin for naphthalene hydrogenation due to the synergy effect of multiple catalytic sites, where naphthalene was absorbed and activated at the TMO sites (NiO or Co3O4), H2 was activated at the Ru sites and it produced the activated H* species, H* was transferred to the surface of NiO or Co3O4 by the hydrogen spillover effect of TM (Ni or Co), reacting with the activated naphthalene and forming decalin. The nanostructures and synergetic effect of the Ru/Ni/NiO/C and Ru/Co/Co3O4/C catalysts were revealed by a series of techniques, such as high-resolution transmission electron microscope (HRTEM), temperature-programmed reduction (TPR), scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) mapping, high-sensitivity low-energy ion scattering (HS-LEIS) and X-ray absorption spectroscopy (XAS). It is promising that the hydrogen storage can proceed at room temperature via catalyzing naphthalene hydrogenation over the Ru/Ni/NiO/C or Ru/Co/Co3O4/C catalyst.