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Graphene has been widely used as a nanofiller in advanced electronic devices and nanocomposite materials to achieve enhanced electronic, mechanical, and barrier properties. Adequate polymers play the role of the composite matrix and can assist in the liquid-phase exfoliation of pristine graphene without any heavy chemical modification and the detriment of the properties of graphene. This stabilization mechanism is generally attributed to the steric forces formed between the polymer-adsorbed adsorbent. However, the key influence of the polymer concentration on the maximum graphene content in the colloidal solutions is still unclear. In this study, three different molar weights of water-soluble polyvinyl alcohol (PVA) were used for graphene dispersion. The influence of the PVA concentration on the graphene dispersion was systematically studied. Based on Flory’s theory, we first proposed a model to describe the polymer adsorption process in the graphene/PVA/water ternary system in the “dilute” regime and simulated the adsorption-free energy changes during this transformation. This model is in good agreement with the experimental results and explains the critical polymer concentration, Cc, allowing the optimization of the graphene/polymer ratio. This fundamental understanding of polymer physisorption on 2D materials provides a simple method for producing nanocomposites with controlled nanosheet/polymer ratios and structures, which are of great interest for energy devices and biomaterials.

Optical spectroscopy techniques represent a powerful tool to study the vibrational modes of nano-objects and address both their intrinsic properties (related to nanoparticle morphology, crystallinity, and local environment) and their interaction with light, which plays a key role in nanophotonics and optomechanics applications. In this paper, we report low-frequency inelastic light scattering measurements on single gold nanocrystals, combined with detailed characterizations of their morphology and environment using transmission electron microscopy and tomography and numerical simulations of their optical and vibrational responses. Our studies confirm the conclusions of previous ensemble measurements regarding the large impact of the nanoparticle crystallinity on inelastic scattering spectra. Moreover, their single-particle character allows us to address subtle shape and environment effects. We show that slight nanoparticle shape anisotropies induce further splitting of Raman-active modes. We also demonstrate that local environment anisotropies lead to richer inelastic light scattering spectra and allow the detection of vibrational modes predicted to be Raman-inactive by usual Raman selection rules, which are based on the (here invalid) assumption of a symmetric internal electric field.

Electrochemical studies of nanomaterial-based electrodes have been widely developed for catalyst and energy-harvesting applications. The evolution of these electrodes over time and their efficiency have been extensively studied and analyzed in order to optimize their performance. However, the electrochemical responses of electrodes are rarely studied in terms of the position of the active species within these electrodes. In this paper, we highlight that the spatial location of silver nanoparticles (NPs) embedded inside semiconductive porous films, TiO2or Fe2O3, is crucial for the electrochemical response. In fact, by using cycling voltammetry and electron tomography experiments, we show the existence of an “electroactive area”, corresponding to a reduced thickness of the sample in close vicinity to a fluorine-doped tin oxide substrate where most of the electrochemical responses originate. Our results demonstrate that, for a film thickness of several hundred nanometers, only less than 30 nm close to the substrate responds electrochemically. However, cyclic voltammetry empties the electroactive area of silver NPs. Therefore, application of chronoamperometry coupled to irradiation allowed regeneration of this area thanks to an increased diffusion of silver species. In this paper, we also show the significant diffusion of silver species within the film during electrochemical experiments, a phenomenon even increased by irradiation. These results are therefore an important step that shows the importance of the localization of active species within a porous film and help in understanding and increasing the durability of nanomaterial-based electrodes.

Plasmonic Au nanoparticles (AuNPs) embedded into a TiO2dielectric matrix were analyzed by combining two-dimensional and three-dimensional electron microscopy techniques. The preparation method was reactive magnetron sputtering, followed by thermal annealing treatments at 400 and 600 °C. The goal was to assess the nanostructural characteristics and correlate them with the optical properties of the AuNPs, particularly the localized surface plasmon resonance (LSPR) behavior. High-angle annular dark field-scanning transmission electron microscopy results showed the presence of small-sized AuNPs (quantum size regime) in the as-deposited Au–TiO2film, resulting in a negligible LSPR response. The in-vacuum thermal annealing at 400 °C induced the formation of intermediate-sized nanoparticles (NPs), in the range of 10–40 nm, which led to the appearance of a well-defined LSPR band, positioned at 636 nm. Electron tomography revealed that most of the NPs are small-sized and are embedded into the TiO2matrix, whereas the larger NPs are located at the surface. Annealing at 600 °C promotes a bimodal size distribution with intermediate-sized NPs embedded in the matrix and big-sized NPs, up to 100 nm, appearing at the surface. The latter are responsible for a broadening and a redshift, to 645 nm, in the LSPR band because of increase of scattering-to-absorption ratio. Beyond differentiating and quantifying the surface and embedded NPs, electron tomography also provided the identification of “hot-spots”. The presence of NPs at the surface, individual or in dimers, permits adsorption sites for LSPR sensing and for surface-enhanced spectroscopies, such as surface-enhanced Raman scattering.

Bimetallic systems present new opportunities to tailor the optical properties of nanoparticles. Morphology, structural, and optical properties of gold and of gold–silver nanoparticles have been studied by three-dimensional (3D) scanning transmission electron microscopy (STEM), STEM imaging, and monochromated subnanometer electron beams. The 3D morphology of these nanoparticles consists of bipyramidal prisms with well-defined facets. Furthermore, in the case of the core–shell nanoparticles, from these tomographical studies, we have determined the silver (shell) distribution and their atomic arrangement. Multipolar localized surface plasmon resonances (LSPR) have been studied, at subnanometer level and at high-energy resolution, as a function of their shape, their size (aspect ratio), and the surrounding environment. These results have been interpreted in the framework of the discrete dipole approximation (DDA) simulations. The effect of the silver outer-shell has been elucidated. We observed a significant damping of plasmon excitations due to the difference of dielectric function of these two metals. In addition, we have shown that the combination of the tomographical and plasmonic (experiments and simulations) studies with such high spatial resolution constitutes a very powerful and fundamental tool for understanding and optimizing the photonics properties of nanomaterials.

We present here a series of experiments performed by electron tomography with the main goal to investigate the 3D porous characteristics that can be encountered in the course of preparing micro‐ and mesoporous materials. The examples are chosen in order to illustrate the ability of this technique to furnish direct information of various natures: morphological, concerning the accessibility to a internal surface of a porous sample, as well as on the shape and 3D ordering of the cavities in a porous network. All these parameters are of prime importance in the catalysis field, since they govern the catalytic performances of the sample. The results underline the uniqueness and the benefits of this technique to provide relevant information on different types of porosities on a nanometer scale

Silicon carbide (SiC) is a ceramic material that has received intensive consideration during the past decade owing to its attractive properties and the diversity of its applications, ranging from microelectronics to catalysis. In particular, new β-SiC materials with high specific surface area are of great interest to the area of industrial catalysis. The aim of the present article is to report the direct visualization of the porous network of β-SiC in a nanometer range using the ability of electron tomography (ET) but also to determine the precise localization of active phases with respect to the porosity of this support. Focus is set on the use of ET to get more insight about the filling mode during sample preparation and, finally, the dispersion and accessibility of the active phase. Thus, an intensive study of the impact of the impregnation solvents on the active phase localization has also been carried out and selective deposition of the active phase within the porous network of SiC is evidenced. In addition, the catalytic activity and selectivity of the synthesized samples were compared toward the liquid phase hydrogenation of cinnamaldehyde.

Are you in?Bimetallic PtRu nanoparticles have been selectively confined inside or deposited outside carbon nanotubes see picture. The confined nanoparticles display significantly higher selectivity and catalytic activity in hydrogenation reactions.

Drinnen oder draußen?PtRuDimetallnanopartikel wurden selektiv in Kohlenstoffnanoröhren eingeschlossen oder auf ihrer äußeren Oberfläche abgeschieden siehe Bild. Die eingeschlossenen Nanopartikel sind wesentlich selektivere und aktivere Hydrierungskatalysatoren.