High-resolution Transmission Electron Microscopy Measurements Research Articles

Nanostructuring Iridium Complexes into Crystalline Phosphorescent Nanoparticles: Structural Characterization, Photophysics, and Biological Applications.

One of the key challenges in materials science is to control the properties of a material by directing its supramolecular arrangement. Here we show that iridium complexes, such as FIrpic, Ir-PPY, and Ir-MDQ, can be organized into crystalline and phosphorescent nanoparticles through the nanoprecipitation method, which allows thorough modification of their functional properties. Moreover, we found that it is possible to combine different iridium complexes into a single multicomponent nanostructure, thus creating nanoparticles whose photonic properties derive from the close spatial proximity of the electronic excited states of the different Ir complexes. The morphology of all nanoparticles was fully characterized by microscopic and spectroscopic techniques, and their ordered arrangement was assessed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) measurements. We demonstrate that the nanostructuring of the complexes influences their optical and redox properties-by promoting a fine-tuning of emission, photoluminescence quantum yield, excited state lifetime, HOMO/LUMO energy levels, and energy-transfer processes-as well as their interaction with living cells. Investigations on glioblastoma U-251 MG cells demonstrate that nanostructuring represents an effective tool to regulate the efficiency of cell loading, cell viability, colocalization, and penetration in 3D spheroids.

Isolating contiguous Pt atoms and forming Pt-Zn intermetallic nanoparticles to regulate selectivity in 4-nitrophenylacetylene hydrogenation

Noble metals play a momentous role in heterogeneous catalysis but still face a huge challenge in selectivity control. Herein, we report isolating contiguous Pt atoms and forming Pt-Zn intermetallic nanoparticles as an effective strategy to optimize the selectivity of Pt catalysts. Contiguous Pt atoms are isolated into single atoms and Pt-Zn intermetallic nanoparticles are formed which are supported on hollow nitrogen-doped carbon nanotubes (PtZn/HNCNT), as confirmed by aberration-corrected high-resolution transmission electron microscopy and X-ray absorption spectrometry measurements. Interestingly, this PtZn/HNCNT catalyst promotes the hydrogenation of 4-nitrophenylacetylene to 4-aminophenylacetylene with a much higher conversion ( > 99%) and selectivity (99%) than the comparison samples with Pt isolated-single-atomic-sites (Pt/HNCNT) and Pt nanoparticles (Pt/CN). Further density functional theory (DFT) calculations disclose that the positive Zn atoms assist the adsorption of nitro group and Pt-Zn intermetallic nanoparticles facilitate the hydrogenation on nitro group kinetically.

Nanocomposite films with silver nanoparticles synthesized in situ: Effect of corn starch content

The aim of this work was to analyze the effect of native corn starch content (1, 3 and 5% w/v) on the development of nanocomposite films with 143 ppm silver nanoparticles (AgNPs) synthesized in situ. The tested concentrations allowed synthesizing AgNPs in situ and suspensions maintained their filmogenic capacity, regardless the starch content. The characteristics of AgNPs were studied by spectrophotometric techniques, high-resolution transmission electron microscopy (HR-TEM) and zeta potential measurement, finding they are spherical with diameters between 19.9 and 13.4 nm and negatively charged. Films containing 1% starch, were difficult to handle coinciding with the mechanical profile obtained, which corresponds to a slightly ductile material. Nanocomposite films with 5% starch showed improved mechanical and barrier properties due to the increase of starch content, but they did not evidence a matrix reinforcement by the AgNPs incorporation. Furthermore, films containing 3% starch show the optimal mechanical and barrier properties, attributed to the reinforcement of AgNPs. Regarding the antimicrobial capacity, all nanocomposite films inhibited microorganisms’ growth. Thus, considering the obtained results nanocomposite films formulated with 3% starch were selected as the most suitable option for their application as food packaging.

Role of hole confinement in the recombination properties of InGaN quantum structures

We study the isolated contribution of hole localization for well-known charge carrier recombination properties observed in conventional, polar InGaN quantum wells (QWs). This involves the interplay of charge carrier localization and non-radiative transitions, a non-exponential decay of the emission and a specific temperature dependence of the emission, denoted as “s-shape”. We investigate two dimensional In0.25Ga0.75N QWs of single monolayer (ML) thickness, stacked in a superlattice with GaN barriers of 6, 12, 25 and 50 MLs. Our results are based on scanning and high-resolution transmission electron microscopy (STEM and HR-TEM), continuous-wave (CW) and time-resolved photoluminescence (TRPL) measurements as well as density functional theory (DFT) calculations. We show that the recombination processes in our structures are not affected by polarization fields and electron localization. Nevertheless, we observe all the aforementioned recombination properties typically found in standard polar InGaN quantum wells. Via decreasing the GaN barrier width to 6 MLs and below, the localization of holes in our QWs is strongly reduced. This enhances the influence of non-radiative recombination, resulting in a decreased lifetime of the emission, a weaker spectral dependence of the decay time and a reduced s-shape of the emission peak. These findings suggest that single exponential decay observed in non-polar QWs might be related to an increasing influence of non-radiative transitions.

Structure dependence of ferroelectricity in high quality BiMnO3 epitaxial films

Epitaxial ${\mathrm{BiMnO}}_{3}$ (BMO) thin films were prepared on (001)-oriented ${\mathrm{SrTiO}}_{3}$ substrates with a ${\mathrm{SrRuO}}_{3}$ buffer layer using pulsed laser deposition. The correlation between ferroelectric and structural properties of BMO has been investigated in detail. By high-resolution transmission electron microscopy measurement, we observed a structural transition from pseudocubic to monoclinic structure with increasing thickness of BMO films, which can be ascribed to the intermediate layer and small composition fluctuation, i.e., Bi deficiency. The ferroelectricity of the BMO films has been characterized by piezoresponse force microscope, demonstrating that pseudocubic BMO thin films show intrinsic ferroelectricity, while the ferroelectricity is absent or very weak in the monoclinic BMO thin films at room temperature. The results of density-functional theory calculations also support the experimental results.

A Combined a-SAXS and XAS Study of the Operando Compositional and Morphological Changes Undergone By High Surface Area IrO2 Oxygen Evolution Electrocatalysts

Sluggish kinetics of the anodic process in polymer electrolyte water electrolyzers (PEWEs) - oxygen evolution reaction (OER) - is the main contributor to the efficiency losses.1 Iridium oxide is the state-of-the-art OER catalyst, however its high price and low abundance2 require minimizing its content in the anode while keeping high OER activity. This can be achieved by maximizing the mass specific surface area (SA) of IrO2, e.g. by synthesizing small IrO2 particles.3 On the other hand, high-SA IrO2 catalysts tend to degrade when operating under the dynamic conditions typical for PEWE’s coupled with intermittent renewable energy source such as wind or solar, and the mechanisms causing this instability remain poorly understood.4 In order to study the degradation mechanisms in detail, we used a modified, chlorine-free Adams fusion method to produce a high-SA IrO2 catalyst3 (referred as ‘IrO2-AS’ in what follows) that displayed a SA of 350 m2∙g-1 based on N2 adsorption / desorption measurements. A fraction of this as-synthetized catalyst was heat treated for 1 h at 400 °C in air to yield a second sample (‘IrO2-HT’) with a SA of 250 m2∙g-1. These two samples were electrochemically tested in 0.1 M HClO4 electrolyte measuring the polarization curve and applying an accelerated stress test (AST) in which the potential is cycled 500 times between 1.0 and 1.6 V vs. the reversible hydrogen electrode (RHE) holding the potential for 10 s at each value, thus simulating the dynamic operation conditions discussed above. The polarization curve measurement indicate an initial activity of 1.490 V and 1.509 V (at i= 10 A∙gox -1) for IrO2-AS and IrO2-HT, respectively. While, the latter AST led to the loss of 50 % vs. 30 % of the initial OER-activity displayed by IrO2-AS vs. IrO2-HT, respectively. To shed light on the reasons for this difference in stability, both catalysts were characterized using a novel setup available at the SuperXAS beamline of the Swiss Light Source and that allows to study the morphological and compositional properties of an (electro)catalyst by combining anomalous small angle X-ray scattering (A-SAXS) and X-ray absorption spectroscopy (XAS), respectively.5 Base on the X-ray absorption fine structure (XANES) and the Extended X-ray absorption fine structure analysis the operando XAS measurements (at 1.0 V vs. RHE) proved that neither of the catalysts suffered from significant changes in their chemical composition in the course of the AST. Complementarily, the A-SAXS curves of the IrO2-AS sample did change during the AST (see Fig. 1a), and were successfully fitted using a model that implies particles with a disk shape assembled in a 2D-agglomerated structure. The model suggests that during the AST the disks’ diameter grew and their thickness became thinner (see Figs. 1c and 1d, respectively), while the 2D-agglomerated structure remained stable. This allowed us determining the variation of SA and corresponding iridium mass, leading to the conclusion that the sample’s loss of OER-performance mainly stems from Ir-dissolution. On the contrary, for IrO2-HT the A-SAXS curves did not change during the AST (cf. Fig. 1b), thus proving that this catalyst displays a stable morphology that is consistent with its enhanced stability in the AST. Chiefly, these A-SAXS-derived conclusions were validated through high-resolution transmission electron microscopy measurements of the initial and post-mortem materials. In conclusion, the combined use of A-SAXS and XAS unveiled the reasons for the different stability behavior of pristine and calcined iridium oxides. Specifically, while XAS showed that the two samples did not change composition in the course of the AST, the A-SAXS results obtained for IrO2-AS indicated the changes in its disk morphology driven by Ir-dissolution. Comparatively, the enhanced stability displayed by IrO2-HT can be attributed to the preliminary agglomeration of its oxide particles caused by the heat-treatment step, which prevents drastic shape variation and limits the loss of Ir during the AST. M. Bernt and H. A. Gasteiger, J. Electrochem. Soc., 163, 3179–3189 (2016).P. C. K. Vesborg and T. F. Jaramillo, RCS Adv., 2, 7933–7947 (2012).D. F. Abbott et al., Chem. Mater., 28, 6591–6604 (2016).C. Rakousky et al., J. Power Sources, 326, 120–128 (2016).M. Povia et al., ACS Catal., 8, 7000–7015 (2018). Figure 1

One-pot synthesis of peony-like Bi2S3/BiVO4(040) with high photocatalytic activity for glyphosate degradation under visible light irradiation

In this work, samples consisting of BiVO4 with exposed (040) facets coupled with Bi2S3 (Bi2S3/BiVO4) were prepared through a one-pot hydrothermal method, using ethylenediaminetetraacetic acid as directing agent and L-cysteine as sulfur source and soft template. X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmission electron microscopy measurements indicated that the Bi2S3 content had a significant influence on the growth of (040) and (121) facets as well as on the morphology of the Bi2S3/BiVO4 samples. When the Bi2S3 content reached 1 mmol, the Bi2S3/BiVO4 samples exhibited a peony-like morphology. The results of transient photocurrent tests and electrochemical impedance spectroscopy measurements confirmed that a more effective charge separation and a faster interfacial charge transfer occurred in Bi2S3/BiVO4 than BiVO4. The enhanced photocatalytic activity of the Bi2S3/BiVO4 samples could be attributed to the improved absorption capability in the visible light region and the enhanced electron-hole pair separation efficiency due to the formation of the Bi2S3/BiVO4 heterostructure. In addition, the Bi2S3/BiVO4 samples showed relative stability and reusability. The simple method presented in this work could be used to fabricate composite photocatalysts with high activity for different applications, such as photocatalytic degradation of organic pollutants, photocatalytic splitting of water, and photocatalytic reduction of carbon dioxide.

Chiral Plasmons: Au Nanoparticle Assemblies on Thermoresponsive Organic Templates.

Template-assisted strategies are widely used to fabricate nanostructured materials. By taking these strategies a step forward, herein we report the design of two chiral plasmonic nanostructures based on Au nanoparticle (NP) assemblies organized in clockwise and anticlockwise directions, having opposite response to circularly polarized light. The chiral plasmonic nanostructures are obtained by growing Au NPs on chiral templates based on d- and l-forms of alanine functionalized phenyleneethynylenes. Interestingly, Au NP assemblies show mirror symmetrical electronic circular dichroism (ECD) bands at their surface plasmon frequency originating through their asymmetric organization. Upon increasing the temperature, the chiral templates dissociate as evident from the disappearance of their ECD signal. The profound advantage of the thermoresponsive nature of the templates is employed to obtain free-standing chiral plasmonic nanostructures. The tilt angle high-resolution transmission electron microscopic measurements indicate that the NP assemblies, grown on a template based on the d-isomer, organize in clockwise direction ( P-form) and on l-isomer in anticlockwise direction ( M-form). The inherent chirality prevailing on the surface of the template drives the helical growth of the Au NPs in opposite directions. Experimental results are rationalized by a model which accounts for the large polarizability of Au NPs. The large polarizability leads to large oscillating dipole moments whose effects become prominent when interparticle distances are comparable to the particle size.

In Situ Study of Molecular Structure of Water and Ice Entrapped in Graphene Nanovessels.

Water is ubiquitous in natural systems, ranging from the vast oceans to the nanocapillaries in the earth crust or cellular organelles. In bulk or in intimate contact with solid surfaces, water molecules arrange themselves according to their hydrogen (H) bonding, which critically affects their short- and long-range molecular structures. Formation of H-bonds among water molecules designates the energy levels of certain nonbonding molecular orbitals of water, which are quantifiable by spectroscopic techniques. While the molecular architecture of water in nanoenclosures is of particular interest to both science and industry, it requires fine spectroscopic probes with nanometer spatial resolution and sub-eV energy sensitivity. Graphene liquid cells (GLCs), which feature opposing closely spaced sheets of hydrophobic graphene, facilitate high-resolution transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) measurements of attoliter water volumes encapsulated tightly in the GLC nanovessels. We perform in situ TEM and EELS analysis of water encased in thin GLCs exposed to room and cryogenic temperatures to examine the nanoscale arrangement of the contained water molecules. Simultaneous quantification of GLC thickness leads to the conclusion that H-bonding strengthens under increased water confinement. The present results demonstrate the feasibility of nanoscale chemical characterization of aqueous fluids trapped in GLC nanovessels and offer insights on water molecule arrangement under high-confinement conditions.

Nucleation Enhancement and Area-Selective Atomic Layer Deposition of Ruthenium Using RuO4 and H2 Gas

Inherent substrate selectivity is reported for the thermal RuO4 (ToRuS)/H2 gas atomic layer deposition (ALD) process on H-terminated Si (Si–H) versus SiO2. In situ spectroscopic ellipsometry (SE) detected Ru growth from the first cycle on blanket Si–H, whereas on blanket SiO2, 60 cycles were needed to detect growth. Area-selective growth was evaluated on a patterned substrate with 1–10 μm wide Si–H lines separated by 10 μm wide SiO2 regions. Ex situ planar scanning electron microscopy and cross-sectional high-resolution transmission electron microscopy measurements showed that a smooth, continuous Ru film of 4.5 nm could be deposited on Si–H, with no Ru detected on SiO2. The proposed mechanism behind the inherent substrate selectivity is the oxidation of the Si–H surface by RuO4, which was confirmed by in vacuo X-ray photoelectron spectroscopy (XPS) experiments. A methodology to enhance the nucleation of the RuO4/H2 gas process on oxide substrates is also reported. In situ SE and in vacuo XPS experiments ...

Photonic upconversion in solution-processed Gd-based thin films for delayed quantum efficiency roll-off in a-Si flat panel image detectors

ABSTRACTAmorphous Si (a-Si) is used for fabrication of commercial low-cost flat panel image detectors for radiographic applications such as computed tomography (CT) imaging. a-Si photodiodes are known to exhibit a rapid decrease in quantum efficiency near 750nm. While crystalline Si does not suffer from such an early decline, the large-area and low-cost constraints of medical imagers make it challenging and costly to use crystalline Si for such devices. In this work, we report on the development of a sensitive layer for upconversion from 785 nm to green region of the spectrum, which nearly matches the peak quantum efficiency of a-Si detectors. Various host materials have been extensively studied in literature with rare earth ions such as Er3+(emission: green+red), Tm3+(emission: blue), Ho3+(emission: red+green) along with Yb3+ as a sensitizer for upconversion to the visible regime at high incident optical power (∼100 mW) for colloidal solutions. We carried out a thermal decomposition synthesis of NaYF4:Yb(18%),Er(2%),Gd(15%) at moderate temperature (∼320°C), resulting in a nearly pure hexagonal phase material. This is confirmed by powder X-ray diffraction (PXRD) of the unannealed sample with a lattice constant (∼5.17 Å). High-resolution transmission electron microscopy (HRTEM) measurements reveal the formation of nearly spherical nanoparticles. The observed plane ([100]) inferred from lattice fringes in TEM data with a visibly estimated interplanar distance (4.4±1.6 Å) is in reasonable agreement with standard data (∼5.17 Å) for comparable NaYF4-based materials. Excitation (785 nm) of the deposited thin films of Gd-doped unannealed material at relatively low incident power (∼0.4 mW) exhibits a PL response in green (539 nm) and red (665 nm) region of the spectrum. Gd-based upconversion material based thin films are thus a feasible photonic material for potential effective extension of high quantum efficiency range in a-Si for flat panel image detectors.

Aqueous synthesis and antibacterial activity of Silver nanoparticles against pseudomonas putida

Aqueous synthesis of silver nanoparticles (NPs) is gaining importance as their biocompatibility and eco-friendly nature. However, in this work, we have reported aqueous synthesis of silver NPs through a chemical route and studied its bio compatibility with pseudomonas putida. The prepared nanostructures have been analyzed by using high resolution transmission electron microscope (HRTEM), selected-area electron diffraction (SAED), Energy-dispersive spectra (EDS), UV-visible spectrophotometer and photoluminescence (PL) spectroflourimeter. It is found that the synthesized materials exhibit an absorption peak at ∼ 420 nm and it is the characteristic surface plasmon resonance peak in silver NPs. It is found from HRTEM measurement that the synthesized NPs are spherical in shape and the average particle size is 2.5 nm. The synthesized samples show strong PL emission in the UV region below 400 nm. Antimicrobial effect of silver NPs for Pseudomonas putida is investigated by using disk diffusion method. The prepared silver NPs exhibit strong antimicrobial activity against Pseudomonas putida at concentrations ranging between 90µg/ml to 170µg/ml for 24 hours. Thus it may be concluded that silver NPs can be used as effective antimicrobial control systems upto 130 µg/ml

Synthesis and characterizations of CoCr2O4/C composite using high energy ball-milling technique as novel anode materials for Li-ion batteries

Abstract In this study, we successfully synthesize CoCr2O4/C composite (CCO/CB) as novel anode materials for Li-ion batteries by using hydrothermal reaction and high energy ball milling technique. The crystal structure and surface morphologies of as-prepared samples are carried out by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The electrochemical results showed that the initial reversible capacity of CoCr2O4 and CCO/CB-7:3 samples are 582 mAh/g and 1189 mAh/g at a current density of 0.1 A/g, respectively. After cycling for 50 cycles at 0.2 A/g, CCO/CB-7:3 reach reversible capacity of as high as 1058 mAh/g. Bare CoCr2O4, however, deliver reversible capacity of only 699 mAh/g. Furthermore, CCO/CB-7:3 also exhibits superior rate capability that of CCO at different current densities from 0.1 to 5 A/g. In addition, the reaction mechanism of CoCr2O4 during charge and discharge process are identified by ex-situ XRD and HRTEM measurements. These results indicate that CCO/CB-7:3 is a novel and potential candidate as an anode material for Li-ion batteries.

Functionalization of the support material based on N-doped carbon-reduced graphene oxide and its influence on the non-enzymatic detection of glucose

Herein CoO-Co-N-doped carbon nanoparticles decorated on reduced graphene oxide (CoO-Co-NC-rGO) has been successfully synthesized by using zeolitic imidazolate framework-67 loaded on graphene oxide (ZIF-67-GO) as precursor. The ZIF-67 could be in-situ prepared on GO through a simple wet-chemical method. Subsequently, an annealing treatment towards ZIF-67-GO has been utilized to obtain CoO-Co-NC-rGO. On the one hand, ZIF-67 could be pyrolyzed to form CoO-Co-N-doped carbon nanoparticles. On the other hand, GO could be reduced to form rGO in the annealing treatment. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) measurements showed CoO-Co-NC-rGO with two-dimensional nanosheets. Owing to the structural and compositional advantages of NC and rGO, the CoO-Co-NC-rGO exhibited excellent electro-catalytic activity for the oxidation of glucose. The established non-enzymatic glucose sensor based on CoO-Co-NC-rGO showed the linear detection range from 0.5 to 10.0 μM, the detection limit of 0.34 μM at a signal-to-noise ratio of 3, and the sensitivity of 3172 μA mM−1 cm−2.

Chemical Vapor-Deposited Vanadium Pentoxide Nanosheets with Highly Stable and Low Switching Voltages for Effective Selector Devices.

Recently, attempts to overcome the physical limits of memory devices have led to the development of promising materials and architectures for next-generation memory technology. The selector device is one of the essential ingredients of high-density stacked memory systems. However, complicated constituent deposition conditions and thermal degradation are problematic, even with effective selector device materials. Herein, we demonstrate the highly stable and low-threshold voltages of vanadium pentoxide (V2O5) nanosheets synthesized by facile chemical vapor deposition, which have not been previously reported on the threshold switching (TS) properties. The electrons occupying trap sites in poly-crystalline V2O5 nanosheet contribute to the perfectly symmetric TS feature at the bias polarity and low-threshold voltages in V2O5, confirmed by high-resolution transmission electron microscopy measurements. Furthermore, we find an additional PdO interlayer in V2O5 nanodevices connected with a Pd/Au electrode after thermal annealing treatment. The PdO interlayer decreases the threshold voltages, and the Ion/ Ioff ratio increases because of the increased trap density of V2O5. These studies provide insights into V2O5 switching characteristics, which can support low power consumption in nonvolatile memory devices.

Au Nanoparticles Deposited on Magnetic Carbon Nanofibers as the Ultrahigh Sensitive Substrate for Surface-Enhanced Raman Scattering: Detections of Rhodamine 6G and Aromatic Amino Acids.

Surface-enhanced Raman scattering (SERS) is a unique spectroscopy that can offer high-sensitive detection for many molecules. Herein, the Au particles deposited on carbon nanofiber-encapsulated magnetic Ni nanoparticles (NPs) (Ni@CNFs@Au) have been successfully synthesized for SERS measurements. The Ni@CNFs@Au substrates have the advantages of a high SERS sensitivity and good magnetic response. The Ni@CNFs could be directly obtained from CO2 hydrogenation on a Ni catalyst, which has been characterized as having rich carboxylic acid groups, graphitic structures, and a high surface area. The Ni@CNFs surface could effectively increase the density of hotspots during Au NP aggregation and influence the morphology of the Au nanostructures. The spherical shape, oval shape, and coral-like Au nanostructures were prepared on Ni@CNFs with various Au concentrations. Brunauer-Emmett-Teller, zeta potential, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements were used to characterize the Ni@CNFs@Au samples. The Au NPs deposited on the Ni@CNFs presented a suitable oval shape, and an average size of ∼30-40 nm. The size allowed surprisingly ultrasensitive SERS detection of rhodamine 6G (R6G) with a resolution of approximately a single molecule under an excitation wavelength of 532 nm. Using 785 nm excitation, a low R6G concentration of ∼1 × 10-14 M was detected. Moreover, the Ni@CNFs@Au substrates could be rapidly magnetically separated after adsorption. Phenylalanine and tyrosine amino acids, which are associated with the liver disease, were examined using SERS with the Ni@CNFs@Au substrate. Ultralow concentrations of ∼1 × 10-11 M for phenylalanine and ∼1 × 10-13 M for tyrosine were clearly measured. The Ni@CNFs@Au substrates exhibited applicability as excellent SERS detection platforms that combine high-sensitivity and rapid magnetic separation for various adsorption molecules.

One-step hydrogen extraction and storage in plasma generated palladium nanoparticles

This study demonstrates a novel way of hydrogen extraction from toluene and direct storage in plasma generated palladium (Pd) nanoparticles in one-step. Monodispersed Pd nanoparticles with a narrow particle-size distribution have been successfully synthesized, for the first time, by a plasma discharge between Pd electrodes in the cavitation field of toluene. The resulting well-dispersed Pd nanoparticles embedded in carbon are stabilized against agglomeration. The effect of experiment time on the particle size and the expansion of lattice spacing due to hydrogen are investigated by experimental and computational studies using density functional theory (DFT). Using X-ray diffraction and high-resolution transmission electron microscopy measurements, it was found that particle size and lattice expansion increases with experiment time. Pd nanoparticle synthesis for in situ hydrogen storage in one step using plasma discharge in an appropriate solvent emphasizes the importance of adopting this methodology which offers several advantages. These include rapid reaction rate, ability to form very small nanoparticles with narrow size distribution and hydrogen extraction from the solvent for direct storage in the Pd nanoparticle lattice.

Oxygen reduction reaction and hydrogen evolution reaction catalyzed by carbon-supported molybdenum-coated palladium nanocubes

Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are two important processes for electrochemical energy storage and conversion. Herein, we describe the preparation of carbon-supported Pd nanocubes@Mo core@shell nanostructures as efficient dual catalysts for both ORR and HER. The core@shell structure was manifested by high-resolution transmission electron microscopy measurements, including high angle-angular dark field-scanning transmission electron microscopy and elemental mapping analysis. Further structural insights were obtained in X-ray diffraction and X-ray photoelectron spectroscopy measurements. The nanostructures exhibited apparent electrocatalytic activity toward both ORR and HER, and the performances were markedly higher than those without the deposition of a Mo overlayer. In ORR, the activity was even better than that of commercial Pt/C within the context of onset potential, specific and mass activities; whereas in HER, the performance of Pd nanocubes@Mo core@shell nanostructures remained subpar as compared to that of Pt/C in terms of the overpotential to reach the current density of 10 mA cm−2, the Tafel slope was comparable and the stability was excellent. The excellent electrocatalytic performance can be attributed to the Pd-Mo synergistic effects imparted from the core-shell structure.

SO3 decomposition over CuO–CeO2 based catalysts in the sulfur–iodine cycle for hydrogen production

The effect of several catalyst supports with large specific surface area (such as SiC, Al2O3, SiC–Al2O3–ball, and SiC–Al2O3) on catalytic activity was evaluated in this study. CuO–CeO2 supported on SiC–Al2O3 exhibited high stability and activity, which was considerably close to the thermodynamic equilibrium curve at 625 °C during the stability test for 50 h. The SO3 decomposition temperature decreased from 750 °C to 625 °C. SiC–Al2O3contained numerous micropores and mesopores and had a large specific area, indicating strong adsorption, as determined by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and nitrogen adsorption measurement. X-ray photoelectron spectroscopy (XPS) revealed that the surface of SiC–Al2O3consisted of Al2O3, SiC, and SiO2 and that the cerium oxide surface had the largest number of defects. Temperature-programmed reduction (H2-TPR) results indicated that the cerium–copper oxides on the surface of powdered SiC–Al2O3 had the strongest redox potential and that CuO had the lowest reduction temperature.

Catalytic Application of Oxygen Vacancies Induced by Bi3+ Incorporation in ThO2 Samples Obtained by Solution Combustion Synthesis

Recognizing immense advantages of solution-based combustion synthesis, its applicability to determine the extent of dissolution of Bi3+ in fluorite-structured thoria has been examined to generate high-surface-area samples with massive defects. Up to 50 mol % of thorium could be substituted with bismuth retaining fluorite structure beyond which phase separation occurred. The lattice parameters from Le-Bail refinements of their powder X-ray diffraction patterns showed marginal increase with increase in bismuth content, suggesting the competing effect between the size of the cation and the oxygen vacancy concentration. Energy-dispersive X-ray spectrometry analysis and high-resolution transmission electron microscopy measurements have also confirmed the composition and structure of the limiting composition. With progressive bismuth content, the band due to the fluorite (at 460 cm–1) diffused and a defect band in the region 570–600 cm–1 emerged in the Raman spectra. From these changes, the oxygen vacancy concentrations in these samples have been determined, which increased with increase in bismuth content. Absorbance in the visible region was noticed for bismuth-containing samples, and band gap values determined from the Kubelka–Munk function were in the range 2.34–3.24 eV. In addition to the blue emission from oxygen vacancies, 3P1 → 1S0 transition of Bi3+ was noticed in the photoluminescence spectrum. From Brunauer–Emmett–Teller measurements, the surface area of Th0.50Bi0.50O2−δ obtained by solution combustion synthesis was measured to be 265.74 m2 g–1, higher than the value (39.00 m2 g–1) for the sample prepared by solid-state synthesis. All of these factors combined with oxygen vacancies as defect centers have been found to play critical control over their use as catalyst for the reductive transformation of nitroaromatics and oxidative decolorization of organic dye molecules (methyl orange and xylenol orange). A nice correlation between oxygen vacancy concentration and pseudo first-order rate constants of these catalytic conversions has been arrived. The catalyst was found to retain its efficiency up to four cycles without undergoing any structural change during these experiments.