42 Search Results

Supported alloy nanoparticles are prevailing alternative low-cost catalysts for both heterogeneous and electrochemical catalytic processes. Selective interaction of an alloy component with a specific reactant induces a dynamic structural change of alloy nanoparticles under reaction conditions and largely controls their catalytic properties. However, such a multi-component dynamic-interaction-controlled evolution, both structural and chemical, remains far from clear. Herein, by using state-of-the-art environmental TEM, we directly visualize, in-situ at the atomic scale, the evolution of an AuCu alloy nanoparticle supported on CeO2 during CO oxidation. We find that gas molecules can “free” metal atoms on the {001} surface and form highly mobile atom clusters. Remarkably, we discover that CO exposure induces Au segregation and activation on nanoparticle surface, while O2 exposure leads to the segregation and oxidation of Cu on the particle surface. The as-formed Cu2O/AuCu interface may facilitate CO-O interaction corroborated by DFT calculations. These findings provide insights into the atomistic mechanisms on alloy nanoparticles during catalytic CO oxidation reaction, and to a broad scope of rational design of alloy nanoparticle catalysts.

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Empowered by an ultrawide bandgap (E_g = 4.5–4.9 eV), beta gallium oxide (β-Ga₂O₃) crystal is an ideal material for solar-blind ultraviolet (SBUV, λ < 280 nm) detection. Here, we report on the first demonstration of dual-modality SBUV light sensing integrated in the same device enabled by multi-physics coupling across photo-electrical and photo-thermo-mechanical domains. The specially designed suspended β-Ga₂O₃ nanoelectromechanical systems (NEMS) transducer reveals dual-modality responses, with a photocurrent responsivity of 4 mA/W and a frequency shift responsivity of 250 Hz/nW, upon SBUV light exposure. An additional demonstration of a β-Ga₂O₃ photo-field-effect transistor exhibits a boosted responsivity of 63 A/W. Analysis on the device suggests that reducing the thickness and length of the transducer could further improve the SBUV light sensing responsivities for both modalities. The demonstration could pave the way for future realization of SBUV detectors with dual modalities for enhanced detection fidelity, or respectively optimized for different sensing scenarios.

As a more environmentally friendly and energy-efficient route, the sulfation roasting–water leaching technique has been developed for highly effective extraction of non-ferrous metals from nickel sulfide concentrate in the presence of a Na{sub 2}SO{sub 4} additive. The effects of several important roasting parameters—the roasting temperature, the addition of Na{sub 2}SO{sub 4}, the holding time, and the heating rate in particular—have been investigated. The results suggest that about 90 pct Ni, 92 pct Co, 95 pct Cu, and < 1 pct Fe can be leached from the calcine roasted under the optimum conditions. Furthermore, the behavior and mechanism of the Na{sub 2}SO{sub 4} additive in the roasting process have been well addressed by detailed characterization of the roasted product and leaching residue using quantitative phase analysis (QPA) and energy dispersive spectroscopy (EDS) mapping. The Na{sub 2}SO{sub 4} additive was observed to play a noticeable role in promoting the sulfation degree of valuable metals by forming liquid phases [Na{sub 2}Me(SO{sub 4}){sub 2}] at the outermost layer, which can create a suitable dynamic environment for sulfation. Thus, addition of Na{sub 2}SO{sub 4} might be conducive to an alternative metallurgical process involving complex sulfide ores.

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Abstract Single‐atom catalysts (SACs) feature the maximum atom economy and superior performance for various catalysis fields, attracting tremendous attention in materials science. However, conventional synthesis of SACs involves high energy consumption at high temperature, complicated procedures, a massive waste of metal species, and poor yields, greatly impeding their development. Herein, a facile dangling bond trapping strategy to construct SACs under ambient conditions from easily accessible bulk metals (such as Fe, Co, Ni, and Cu) is presented. When mixing graphene oxide (GO) slurry with metal foam and drying in ambient conditions, the M ⁰ would transfer electrons to the dangling oxygen groups on GO, obtaining M ^δ+ (0 < δ < 3) species. Meanwhile, M ^δ+ coordinates with the surface oxygen dangling bonds of GO to form MO bonds. Subsequently, the metal atoms are pulled out of the metal foam by the MO bonds under the assistance of sonication to give M SAs/GO materials. This synthesis at room temperature from bulk metals provides a versatile platform for facile and low‐cost fabrication of SACs, crucial for their mass production and practical application in diverse industrial reactions.

Ti{sub 5}Si{sub 3}, Ti{sub 5}Si{sub 3}/TiC, and Ti{sub 5}Si{sub 3}/Ti{sub 3}SiC{sub 2} have been electrochemically synthesized from the Ti-bearing blast furnace slag/TiO{sub 2} and/or C mixture precursors at a cell voltage of 3.8 V and 1223 K to 1273 K (950 °C to 1000 °C) in molten CaCl{sub 2}. The pressed porous mixture pellets were used as the cathode, and a solid oxide oxygen-ion-conducting membrane (SOM)-based anode was used as the anode. The phase composition and morphologies of the cathodic products were systematically characterized. The final products possess a porous nodular microstructure due to the interconnection of particles. The variations of impurity elements, i.e., Ca, Mg, and Al, have been analyzed, and the result shows that Ca and Mg can be almost completely removed; however, Al cannot be easily removed from the pellet due to the formation of Ti-Al alloys during the electroreduction process. The electroreduction process has also been investigated by the layer-depended phase composition analysis of the dipped/partially reduced pellets to understand the detailed reaction process. The results indicate that the electroreduction process of the Ti-bearing blast furnace slag/TiO{sub 2} and/or C mixture precursors can be typically divided into four periods, i.e., (i) the decomposition of initial Ca(Mg,Al)(Si,Al){sub 2}O{sub 6}, (ii) the reduction of Ti/Si-containing intermediate phases, (iii) the removal of impurity elements, and (iv) the formation of Ti{sub 5}Si{sub 3}, TiC, and Ti{sub 3}SiC{sub 2}. It is suggested that the SOM-based anode process has great potential to be used for the direct and facile preparation of Ti alloys and composites from cheap Ti-containing ores.

Atomic layers of hexagonal boron nitride (h-BN) crystal are excellent candidates for structural materials as enabling ultrathin, two-dimensional (2D) nanoelectromechanical systems (NEMS) due to the outstanding mechanical properties and very wide bandgap (5.9 eV) of h-BN. In this work, we report the experimental demonstration of h-BN 2D nanomechanical resonators vibrating at high and very high frequencies (from ~ 5 to ~ 70 MHz), and investigations of the elastic properties of h-BN by measuring the multimode resonant behavior of these devices. First, we demonstrate a dry-transferred doubly clamped h-BN membrane with ~ 6.7 nm thickness, the thinnest h-BN resonator known to date. In addition, we fabricate circular drumhead h-BN resonators with thicknesses ranging from ~ 9 to 292 nm, from which we measure up to eight resonance modes in the range of ~ 18 to 35 MHz. Combining measurements and modeling of the rich multimode resonances, we resolve h-BN’s elastic behavior, including the transition from membrane to disk regime, with built-in tension ranging from 0.02 to 2 N m^-1. The Young’s modulus of h-BN is determined to be EY≈392 GPa from the measured resonances. The ultrasensitive measurements further reveal subtle structural characteristics and mechanical properties of the suspended h-BN diaphragms, including anisotropic built-in tension and bulging, thus suggesting guidelines on how these effects can be exploited for engineering multimode resonant functions in 2D NEMS transducers.

Many regulators have been identified to participate in the cross-talk between muscle and bone, however, most previous studies focus on secreting proteins. In this study, we demonstrated that exosomes from myoblasts C2C12 can promote pre-osteoblasts MC3T3-E1 differentiation to osteoblasts. We revealed that the effect of C2C12 exosomes depended on its miR-27a-3p component, they can increase miR-27a-3p level in the recipient cells, and decrease its direct target adenomatous polyposis coli (APC) expression, thus activating β-catenin pathway. Furthermore, C2C12 exosomes failed to exert above effects when miR-27a-3p was deprived. These findings indicates exosomal microRNAs can be regarded as a novel type of “myokines” with osteogenesis promoting potential, which would broad our understanding of the muscle-bone interaction under physiological and pathological conditions.

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