706 research outputs found

    Size control of Au nanoparticles from the scalable and solvent-free matrix assembly cluster source

    Get PDF
    Nanostructured gold is an intriguing system for heterogeneous catalysis at low temperature. Its activity is related to choice of support selection, particle-support interaction, and especially the particle size. Here, we investigate the possibility of controlling the size of Au clusters (nanoparticles) in the novel Matrix Assembly Cluster Source (MACS), a solvent-free nanoparticle source with potential for scale-up to the gram level. The novelty of the MACS is the idea of making clusters by sputtering a pre-condensed matrix of metal atoms embedded in a condensed non-reactive gas, e.g., Ar. This concept, introduced in 2016, has already proved deposition rates several orders of magnitude higher than conventional cluster beam routes. Such scale-up in the cluster production rate is crucial for industrial research on nanocatalysis under realistic reaction condition. Here, we report a systematic study of how Au metal loading in the matrix affects the size distribution of clusters generated. Furthermore, the obtained dependence of cluster size on deposition time provides clear confirmation of cluster formation inside the matrix by ion irradiation, rather than by aggregation of atoms on the TEM support after deposition

    Low pressure bottom-up synthesis of metal@oxide and oxide nanoparticles: control of structure and functional properties

    Get PDF
    Experimental activity on core@shell, metal@oxide, and oxide nanoparticles (NPs) grown with physical synthesis, and more specifically by low pressure gas aggregation sources (LPGAS) is reviewed, through a selection of examples encompassing some potential applications in nanotechnology. After an introduction to the applications of NPs, a brief description of the main characteristics of the growth process of clusters and NPs in LPGAS is given. Thereafter, some relevant case studies are reported: Formation of native oxide shells around the metal cores in core@shell NPs. Experimental efforts to obtain magnetic stabilization in magnetic core@shell NPs by controlling their structure and morphology. Recent advancements in NP source design and new techniques of co-deposition, with relevant results in the realization of NPs with a greater variety of functionalities. Recent results on reducible oxide NPs, with potentialities in nanocatalysis, energy storage, and other applications. Although this list is far from being exhaustive, the aim of the authors is to provide the reader a descriptive glimpse into the physics behind the growth and studies of low pressure gas-phase synthesized NPs, with their ever-growing potentialities for the rational design of new functional materials

    Electrocatalytic Behavior of PtCu Clusters Produced by Nanoparticle Beam Deposition

    Get PDF
    State-of-the-art electrocatalysts for electrolyzer and fuel cell applications currently rely on platinum group metals, which are costly and subject to supply risks. In recent years, a vast collection of research has explored the possibility of reducing the Pt content in such catalysts by alloying with earth-abundant and cheap metals, enabling co-optimization of cost and activity. Here, using nanoparticle beam deposition, we explore the electrocatalytic performance of PtCu alloy clusters in the hydrogen evolution reaction (HER). Elemental compositions of the produced bimetallic clusters were shown by X-ray photoelectron spectroscopy (XPS) to range from 2 at. % to 38 at. % Pt, while high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) combined with energy dispersive X-ray (EDX) spectroscopy indicated that the predominant cluster morphologies could be characterized as either a fully mixed alloy or as a mixed core with a Cu-rich shell. In contrast with previous studies, a monotonic decrease in HER activity with increasing Cu content was observed over the composition range studied, with the current density measured at -0.3 V (vs reversible hydrogen electrode) scaling approximately linearly with Pt at. %. This trend opens up the possibility that PtCu could be used as a reference system for comparing the composition-dependent activity of other bimetallic catalysts

    A brief tutorial for the STEM-CELL software

    Get PDF
    TEM and STEM analytical studies are going in toward a stronger involvement of computing for the image interpretation. Geometric Phase Analysis [1], for example, has proved to be a useful tool to evaluate the strain in different structures. TEM Image simulations are another very important tool to be compared with complicated structures to obtain quantitative interpretation of the contrast

    Use of Cold Atmospheric Plasma to Detoxify Hazelnuts from Aflatoxins

    Get PDF
    Aflatoxins, produced by Aspergillus flavus and A. parasiticus, can contaminate different foodstuffs, such as nuts. Cold atmospheric pressure plasma has the potential to be used for mycotoxin detoxification. In this study, the operating parameters of cold atmospheric pressure plasma were optimized to reduce the presence of aflatoxins on dehulled hazelnuts. First, the effect of different gases was tested (N2, 0.1% O2 and 1% O2, 21% O2), then power (400, 700, 1000, 1150 W) and exposure time (1, 2, 4, and 12 min) were optimized. In preliminary tests on aflatoxin standard solutions, this method allowed to obtain a complete detoxification using a high power for a few minutes. On hazelnuts, in similar conditions (1000 W, 12 min), a reduction in the concentration of total aflatoxins and AFB1 of over 70% was obtained. Aflatoxins B1 and G1 were more sensitive to plasma treatments compared to aflatoxins B2 and G2, respectively. Under plasma treatment, aflatoxin B1 was more sensitive compared to aflatoxin G1. At the highest power, and for the longest time, the maximum temperature increment was 28.9 °C. Cold atmospheric plasma has the potential to be a promising method for aflatoxin detoxification on food, because it is effective and it could help to maintain the organoleptic characteristics

    Hydrothermal Fabrication of Carbon-Supported Oxide-Derived Copper Heterostructures : A Robust Catalyst System for Enhanced Electro-Reduction of CO2 to C2H4

    Get PDF
    Anthropogenic CO can be converted to alternative fuels and value-added products by electrocatalytic routes. Copper-based catalysts are found to be the star materials for obtaining longer-chain carbon compounds beyond 2e products. Herein, we report a facile hydrothermal fabrication of a highly robust electrocatalyst: in-situ grown heterostructures of plate-like CuO−CuO on carbon black. Simultaneous synthesis of copper-carbon catalysts with varied amounts of copper was conducted to determine the optimum blend. It is observed that the optimum ratio and structure have aided in achieving the state of art faradaic efficiency for ethylene >45 % at −1.6 V vs. RHE at industrially relevant high current densities over 160 to 200 mA ⋅ cm. It is understood that the in-situ modification of CuO to CuO during the electrolysis is the driving force for the highly selective conversion of CO to ethylene through the *CO intermediates at the onset potentials followed by C−C coupling. The excellent distribution of Cu-based platelets on the carbon structure enables rapid electron transfer and enhanced catalytic efficiency. It is inferred that choosing the right composition of the catalyst by tuning the catalyst layer over the gas diffusion electrode can substantially affect the product selectivity and promote reaching the potential industrial scale

    Enhancing thermoelectric performance of Solution-Processed polycrystalline SnSe with PbSe nanocrystals

    Get PDF
    There is a growing interest in cost-effective polycrystalline SnSe-based thermoelectric (TE) materials, which are able to replace the high performance but mechanically fragile and costly single-crystalline SnSe. In this study, we present a low-temperature solution-based approach to produce SnSe-PbSe nanocomposites with outstanding TE performance. Our method involves combining surfactant-free SnSe particles with oleate-capped PbSe nanocrystals in specific ratios, followed by thermal annealing and consolidation using spark plasma sintering. These nanocomposites are characterized by distinct compositional and structural properties that significantly impact their transport properties. In particular, the addition of oleate-capped PbSe nanocrystals results in: i) a reduction in the electrostatically adsorbed Na at the surface of the SnSe particles; ii) a reduction of Sn vacancies due to alloying with Pb; iii) an increase in grain boundary density; and iv) the formation of PbSnSe secondary phases. Notably, the SnSe-2.5 %PbSe nanocomposites demonstrate a 30 % decrease in thermal conductivity compared to that of the SnSe matrix. This reduction contributes to a maximum figure of merit (zT) of 1.75 at 788 K with a high average zT value of ca. 1.2 in the medium temperature range of 573-773 K. These values represent one of the highest reported in polycrystalline SnSe materials, showcasing the potential of our fabricated SnSe-PbSe nanocomposites for cost-effective TE applications

    Influence of defect distribution on the reducibility of CeO2-x nanoparticles

    Get PDF
    Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution- and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties
    • …
    corecore