Size-dependent redox behavior of iron observed by in-situ single nanoparticle spectro-microscopy on well-defined model systems

Abstract

Understanding the chemistry of nanoparticles is crucial in many applications. Their synthesis in a controlled manner and their characterization at the single particle level is essential to gain deeper insight into chemical mechanisms. In this work, single nanoparticle spectro-microscopy with top-down nanofabrication is demonstrated to study individual iron nanoparticles of nine different lateral dimensions from 80 nm down to 6 nm. The particles are probed simultaneously, under same conditions, during in-situ redox reaction using X-ray photoemission electron microscopy elucidating the size effect during the early stage of oxidation, yielding time-dependent evolution of iron oxides and the mechanism for the inter-conversion of oxides in nanoparticles. Fabrication of well-defined system followed by visualization and investigation of singled-out particles eliminates the ambiguities emerging from dispersed nanoparticles and reveals a significant increase in the initial rate of oxidation with decreasing size, but the reactivity per active site basis and the intrinsic chemical properties in the particles remain the same in the scale of interest. This advance of nanopatterning together with spatially-resolved single nanoparticle X-ray absorption spectroscopy will guide future discourse in understanding the impact of confinement of metal nanoparticles and pave way to solve fundamental questions in material science, chemical physics, magnetism, nanomedicine and nanocatalysis.

Coulomb nanoradiator-mediated, site-specific thrombolytic proton treatment with a traversing pristine Bragg peak

“…Fucoidan specifically binds with P-selectin, a molecular determinant of atherothrombotic disease28, in activated platelets. Fucoidan-conjugated IONs29 may improve homogeneous delivery of IONs to the thrombus, which facilitates the identification of the biological effects of redox-active IONs3031 alone by targeting P-selectin, similar to protein disulphide isomerase in gold nanoparticle-mediated radiosensitization3233. The efficacy of targeted delivery of IONs, together with the long-term efficacy and complications of CNR-based thrombolysis, will be studied further in clinical settings.…”

Operando X-Ray Spectroscopic Techniques: A Focus on Hydrogen and Oxygen Evolution Reactions

“…Most of the ex situ characterization techniques study the bulk of the catalysts. However, the bulk structure of a catalyst does not provide any idea regarding the surface composition (Karim et al, 2016). The variation of surface composition during reaction is taken into account to get accurate information regarding the nature of active site, deactivation mechanism, etc., which is essential for optimizing the catalyst design.…”

Catalysis of the Oxygen Evolution Reaction by 4–10 nm Cobalt Nanoparticles

“…Nanoparticle size effects and especially particle size dependent redox behavior has been a recent focus of work in the group of Prof. Gabor Somorjai, in honor of whom it is pleasure to contribute a paper to this issue. It is well known from other types of catalysts that small nanoparticles in general may stabilize higher oxidation states of metals [27], or increase their rate of formation [28]. For cobalt specifically, small particles (less than about 6 nm in diameter) are less active in Fischer-Tropsch type chemistry, where larger Co particles to avoid adsorbate induced restructuring or oxidation of the active metallic Co(0) are needed [29][30][31].…”