Most studies on the synthesis of nanoparticles are currently focused on the controlled synthesis of new morphologies, including core-shell structures, which are expected to exhibit new magnetic properties for uses in spintronics and recording media applications. In this study, the structure, morphology, and composition of cubic-shaped nanoparticles are carefully investigated and compared to those of spherically shaped nanoparticles through the use of a combination of techniques: X-ray diffraction (XRD) and transmission electronic microscopy (TEM) combined with more sensitive techniques such as scanning transmission electron microscopy-high-angle annular dark field (STEM-HAADF) imaging, electron tomography, and holography. While spherically shaped nanoparticles (NPs) crystallize with the spinel structure, cubic-shaped NPs can be described as a cubic core of w€ ustite surrounded by a spinel shell. Stresses are observed at the core-shell interface and within the spinel shell due to the epitaxial growth and oxidation mechanisms of the w€ ustite phase. Furthermore, magnetic measurements displayed an exchange bias coupling between the antiferromagnetic (AFM) core and the ferrimagnetic (FIM) shell structure of cubic-shaped nanoparticles. It is shown that the magnetic properties are influenced by stresses generated by the oxidation of w€ ustite and, also exhibit variations depending upon the evolution of this core-shell structure as a function of the oxidation time.

The growth of colloidal nanoparticles is simultaneously driven by kinetic and thermodynamic effects that are difficult to distinguish. We have exploited in situ scanning transmission electron microscopy in liquid to study the growth of Au nanoplates by radiolysis and unravel the mechanisms influencing their formation and shape. The electron dose provides a straightforward control of the growth rate that allows quantifying the kinetic effects on the planar nanoparticles formation. Indeed, we demonstrate that the surface-reaction rate per unit area has the same dose-rate dependent behavior than the concentration of reducing agents in the liquid cell. Interestingly, we also determine a critical supply rate of gold monomers for nanoparticle faceting, corresponding to three layers per second, above which the formation of nanoplates is not possible because the growth is then dominated by kinetic effects. At lower electron dose, the growth is driven by thermodynamic and the formation and shape of nanoplates are directly related to the twin-planes formed during the growth.

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Plasmonic nanoparticles, particularly gold nanoparticles (GNPs) hold a great potential as structural and functional building blocks for three-dimensional (3D) nanoarchitectures with specific optical applications. However, a rational control of their assembly into nanoscale superstructures with defined positioning and overall arrangement still remains challenging. Herein, we propose a solution to this challenge by using as building blocks: (1) nanometric silica helices with tunable handedness and sizes as a matrix and (2) GNPs with diameter varying from 4 to 10 nm to prepare a collection of helical GNPs superstructures (called Goldhelices hereafter). These nanomaterials exhibit well-defined arrangement of GNPs following the helicity of the silica template. Strong chiroptical activity is evidenced by circular dichroism (CD) spectroscopy at the wavelength of the surface plasmon resonance (SPR) of the GNPs with a anisotropy factor (g-factor) of the order of 1 × 10, i.e., 10-fold larger than what is typically reported in the literature. Such CD signals were simulated using a coupled dipole method which fit very well the experimental data. The measured signals are 1-2 orders of magnitude lower than the simulated signals, which is explained by the disordered GNPs grafting, the polydispersity of the GNPs, and the dimension of the nanohelices. These Goldhelices based on inorganic templates are much more robust than previously reported organic-based chiroptical nanostructures, making them good candidates for complex hierarchical organization, providing a promising approach for light management and benefits in applications such as circular polarizers, chiral metamaterials, or chiral sensing in the visible range.

Gold nanoparticles are used in an expanding spectrum of biomedical applications. However, little is known about their long-term fate in the organism as it is generally admitted that the inertness of gold nanoparticles prevents their biodegradation. In this work, the biotransformations of gold nanoparticles captured by primary fibroblasts were monitored during up to 6 mo. The combination of electron microscopy imaging and transcriptomics study reveals an unexpected 2-step process of biotransformation. First, there is the degradation of gold nanoparticles, with faster disappearance of the smallest size. This degradation is mediated by NADPH oxidase that produces highly oxidizing reactive oxygen species in the lysosome combined with a cell-protective expression of the nuclear factor, erythroid 2. Second, a gold recrystallization process generates biomineralized nanostructures consisting of 2.5-nm crystalline particles self-assembled into nanoleaves. Metallothioneins are strongly suspected to participate in buildings blocks biomineralization that self-assembles in a process that could be affected by a chelating agent. These degradation products are similar to aurosomes structures revealed 50 y ago in vivo after gold salt therapy. Overall, we bring to light steps in the lifecycle of gold nanoparticles in which cellular pathways are partially shared with ionic gold, revealing a common gold metabolism.

Zeolites are widely used in industrial processes, mostly as catalysts or adsorbents. Increasing their micropore volume could further improve their already exceptional catalytic and separation performances. We report a tunable extraction of zeolite framework cations (Si, Al) on a faujasite-type zeolite, the archetype of molecular sieves with cages and the most widely used as a catalyst and sorbent; this results in ca. 10% higher micropore volume with limited impact on its thermal stability. This increased micropore volume results from the opening of some of the small (sodalite) cages, otherwise inaccessible to most molecules. As more active sites become accessible, the catalytic performances for these modified zeolites are substantially improved. The method, based on etching with NHF, is also applicable to other cage-containing microporous molecular sieves, where some of the most industrially relevant zeolites are found.

A general method is described for the deposition of metal nanoparticles selectively either inside or outside of carbon nanotubes (CNTs). The method is based on the difference in the interface energies of organic and aqueous solutions with the CNT surface. Because of their lipophilic character, the organic solvent better wets the surface of the nanotubes compared to water and penetrates into the inner volume. The precise control of the volume of each phase allows filling the CNT with the organic phase and covering its outer surface with the aqueous one. Hence, metal nanoparticles can be put with high selectivity either inside or outside the CNT, just by choosing in which solvent the metal precursor is dissolved. SEM, TEM, and 3D-TEM investigations show that a selectivity in localization close to 75% can be reached by this technique. The nanoparticles are homogeneously dispersed and present a narrow size distribution, centered on 5 nm. In this way, one can decorate either the inner or the outer surface of open CNTs, without the need of discriminating the diameter of the opening and without any further step of functionalization than a treatment with nitric acid.

Unveiling the mechanism of electrocatalytic processes is fundamental for the search of more efficient and stable electrode materials for clean energy conversion devices. Although several in situ techniques are now available to track structural changes during electrocatalysis, especially of water oxidation, a direct observation, in real space, of morphological changes of nanostructured electrocatalysts is missing. Herein, we implement an in situ electrochemical Transmission Electron Microscopy (in situ EC-TEM) methodology for studying electrocatalysts of the oxygen evolution reaction (OER) during operation, by using model cobalt oxide Co3O4 nanoparticles. The observation conditions were optimized to mimic standard electrochemistry experiments in a regular electrochemical cell, allowing to perform cyclic voltammetry and chronopotentiometry in similar conditions in situ and ex situ. This in situ EC-TEM method enables us to observe the chemical, morphological and structural evolutions occurring in the initial nanoparticle-based electrode exposed to different aqueous electrolytes and under OER conditions. The results show that surface amorphization occurs, yielding a nanometric cobalt (oxyhydr)oxide-like phase during OER. This process is irreversible and occurs to an extent that has not been described before. Furthermore, we show that the pH and counter-ions of the electrolytes impact this restructuration, shedding light on the materials properties in neutral phosphate electrolytes. In addition to the structural changes followed in situ during the electrochemical measurements, this study demonstrates that it is possible to rely on in situ electrochemical TEM to reveal processes in electrocatalysts while preserving a good correlation with ex situ regular electrochemistry.