ACS Materials Au最新文献

Herein, we present a paper that attempts to bridge the gap between CO oxidation catalytic tests performed in a model stream and a more realistic exhaust gas stream by incorporating characterization methods that allow for active probing of the catalyst surface. The results have shown that it is not just the abundance of a given type of species on the surface that impacts the activity of a system but also the ease of extraction of ions from their surface (time-of-flight secondary ion mass spectrometry) and the response of the support to change in the feed composition (dynamic in situ X-ray diffraction (XRD) with variable atmosphere). The study utilizes the method of doping a catalyst (RuO₂/CZ) with a small amount of alkali-metal (K⁺ or Na⁺) carbonates in order to slightly modify its surface to gain insight into parameters that may cause discrepancies between model stream activity and complex stream activity. The most pronounced difference is that in the model stream, which contains only CO and O₂ in helium, both alkali ions improve the activity of the system at temperatures around 175 °C, whereas in the complex stream, which mimics the exhaust stream from a diesel engine under oxygen lean conditions, the K⁺-doped catalyst is slightly worse than RuO₂ /CZ and RuO₂ + Na⁺/CZ and much worse in propane combustion. The total hydrogen consumption values (temperature-programmed reduction) and the O_ads/O_latt ratios (X-ray photoelectron spectroscopy) both place the RuO₂ + K⁺/CZ system between the other two and hence provided no reason for the unusual behavior of the K⁺-doped catalyst. In contrast, both in situ XRD measurement tests and ToF SIMS results show a pronounced difference between the RuO₂ + K⁺/CZ catalyst and the other two systems, which indicates that the interaction of the surfaces with the reagents might be the cause of the discrepancy. The CO₂-TPD results show that this system retains more CO₂, i.e., the product, at adsorption sites, which might reduce the adsorption of other reagents, i.e., oxygen ions, CO, and propane, hence lowering the overall activity of the system.

Multicore magnetic nanoparticles (MNPs), comprising iron oxide cores embedded in a sugar or starch matrix, are a class of nanomaterials with promising magnetic heating properties. Their internal structure, and particularly the strength of the internal core–core magnetic interactions, are believed to determine the functional properties, but there have been few detailed studies on this to date. We report here on an interlaboratory and multimodality transmission electron microscopy (TEM) and magnetic study of a high-performance MNP material (supplied by Resonant Circuits Limited, RCL) that is currently being used in a clinical study for the treatment of pancreatic cancer. TEM data were collected under a variety of conditions: conventional; high-resolution; scanning; cryogenic; and, for the first time, liquid phase. All the imaging modes showed mostly irregular dextran lamellae of lateral dimensions 30–90 nm, plus ca. 15% n/n of what appeared to be 30–60 nm long “nanorods”, and a multitude of well-dispersed ca. 3.7 nm diameter iron oxide cores. Cryogenic electron tomography indicated that the nanorods were edge-on lamellae, but in dried samples, tomography showed rod- or lath-shaped forms, possibly resulting from the collapse of lamellae during drying. High-resolution TEM (HRTEM) showed the dextran to be crystallized in the low-temperature hydrated dextran polymorph. Magnetic remanence Henkel-plot analysis indicated a weak core–core interaction field of ca. 4.8 kA/m. Theoretical estimates using a point-dipole model associated this field with a core-to-core separation distance of ca. 5 nm, which tallies well with the ca. 4–6 nm range of separation distances observed in liquid-cell TEM data. On this basis, we identify the structure–function link in the RCL nanoparticles to be the unusually well-dispersed multicore structure that leads to their strong heating capability. This insight provides an important design characteristic for the future development of bespoke nanomaterials for this significant clinical application.

Ge_xSi_1–x alloys are gaining renewed interest for many applications in electronics and optics, especially for miniaturized devices showing quantum size effects. Point defects and atomic diffusion play a crucial role in miniaturized and metastable systems. In the present work, Ge self-diffusion in sputter deposited amorphous Ge_xSi_1–x alloys is studied in situ as a function of Ge content x = 0.13, 0.43, 0.8, and 1.0 by neutron reflectometry. The determined Ge self-diffusivities obey the Arrhenius law in the investigated temperature ranges. The higher the Ge content x, the higher the Ge self-diffusivity at the same temperature. The activation enthalpy decreases with x from 4.4 eV for self-diffusion in pure silicon films to about 2 eV self-diffusion in Ge_0.8Si_0.2 and Ge. The decrease of the activation enthalpy for amorphous Ge_xSi_1–x is similar to the case of crystalline Ge_xSi_1–x. Possible explanations are discussed.