Lucian Roiban

An Efficient Strategy to Drive Nanoparticles into Carbon Nanotubes and the Remarkable Effect of Confinement on Their Catalytic Performance

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.

Mapping the 3D distribution of CdSe nanocrystals in highly oriented and nanostructured hybrid P3HT–CdSe films grown by directional epitaxial crystallization

Highly oriented and nanostructured hybrid thin films made of regioregular poly(3-hexylthiophene) and colloidal CdSe nanocrystals are prepared by a zone melting method using epitaxial growth on 1,3,5-trichlorobenzene oriented crystals. The structure of the films has been analyzed by X-ray diffraction using synchrotron radiation, electron diffraction and 3D electron tomography to afford a multi-scale structural and morphological description of the highly structured hybrid films. A quantitative analysis of the reconstructed volumes based on electron tomography is used to establish a 3D map of the distribution of the CdSe nanocrystals in the bulk of the films. In particular, the influence of the P3HT-CdSe ratio on the 3D structure of the hybrid layers has been analyzed. In all cases, a bi-layer structure was observed. It is made of a first layer of pure oriented semi-crystalline P3HT grown epitaxially on the TCB substrate and a second P3HT layer containing CdSe nanocrystals uniformly distributed in the amorphous interlamellar zones of the polymer. The thickness of the P3HT layer containing CdSe nanoparticles increases gradually with increasing content of NCs in the films. A growth model is proposed to explain this original transversal organization of CdSe NCs in the oriented matrix of P3HT.

Three-dimensional chemistry of multiphase nanomaterials by energy-filtered transmission electron microscopy tomography.

A three-dimensional (3D) study of multiphase nanostructures by chemically selective electron tomography combining tomographic approach and energy-filtered imaging is reported. The implementation of this technique at the nanometer scale requires careful procedures for data acquisition, computing, and analysis. Based on the performances of modern transmission electron microscopy equipment and on developments in data processing, electron tomography in the energy-filtered imaging mode is shown to be a very appropriate analysis tool to provide 3D chemical maps at the nanoscale. Two examples highlight the usefulness of analytical electron tomography to investigate inhomogeneous 3D nanostructures, such as multiphase specimens or core-shell nanoparticles. The capability of discerning in a silica-alumina porous particle the two different components is illustrated. A quantitative analysis in the whole specimen and toward the pore surface is reported. This tool is shown to open new perspectives in catalysis by providing a way to characterize precisely 3D nanostructures from a chemical point of view.

The core contribution of transmission electron microscopy to functional nanomaterials engineering

Research on nanomaterials and nanostructured materials is burgeoning because their numerous and versatile applications contribute to solve societal needs in the domain of medicine, energy, environment and STICs. Optimizing their properties requires in-depth analysis of their structural, morphological and chemical features at the nanoscale. In a transmission electron microscope (TEM), combining tomography with electron energy loss spectroscopy and high-magnification imaging in high-angle annular dark-field mode provides access to all features of the same object. Today, TEM experiments in three dimensions are paramount to solve tough structural problems associated with nanoscale matter. This approach allowed a thorough morphological description of silica fibers. Moreover, quantitative analysis of the mesoporous network of binary metal oxide prepared by template-assisted spray-drying was performed, and the homogeneity of amino functionalized metal-organic frameworks was assessed. Besides, the morphology and internal structure of metal phosphide nanoparticles was deciphered, providing a milestone for understanding phase segregation at the nanoscale. By extrapolating to larger classes of materials, from soft matter to hard metals and/or ceramics, this approach allows probing small volumes and uncovering materials characteristics and properties at two or three dimensions. Altogether, this feature article aims at providing (nano)materials scientists with a representative set of examples that illustrates the capabilities of modern TEM and tomography, which can be transposed to their own research.

3 D Chemical Distribution of Titania–Alumina Catalyst Supports Prepared by the Swing-pH Method

Analytical electron tomography combined with more classical techniques such as X‐ray fluorescence and X‐ray photoelectron spectroscopy were performed with a series of titania–alumina catalyst supports prepared by using the swing‐pH method. The bulk proportion of titania and alumina was varied along the sample series. It was observed that, independently of this bulk proportion, only 30u2009% of the surface of the grains of the resulting catalysts was titania covered. It was also shown that the porosity of the material was driven by alumina, and for low titania contents, alumina formed a layer close the surface of the grains. At concentrations higher than 30u2009% titania, the layer was broken and aggregates covered by alumina were formed, which may have an impact on catalysis if these materials are used as supports for an active phase.

Rapid Tomography in Environmental TEM: How Fast Can We Go to Follow the 3D Evolution of Nanomaterials in situ?

Environmental Transmission Electron Microscopy (ETEM) in a dedicated instrument has been the subject of recent considerable developments allowing to follow chemical reactions in situ under environmental, e.g. gas and temperature conditions even at atomic resolution. A typical domain of applications concerns catalysis, where supported nanoparticles (NPs) are followed during calcination, oxidation or reduction in the presence of various gases. Whereas numerous works have now been published in conventional imaging, that is, 2D projection, little work is reported on 3D investigations performed in situ. It is easy to understand why such an approach is difficult: since TEM tomography consists in reconstructing numerically a tilt series of projections over a wide angular range, the time to acquire these data is generally too important as compared to the speed of the sample evolution, or the kinetics of the studied chemical reaction. The duration of the conventional acquisition step is typically one hour, or a fraction of one hour, making it impossible to get tilting sequences where the object does not experience any significant shape change which obviously hampers 3D reconstruction. This trivial statement leads to the conclusion that speeding up the acquisition procedure is the key of Environmental Tomography. This contribution summarizes where we are in developing Fast Tomography in Bright Field (E)TEM at the minute and even second level mainly for applications on nano-catalysts. Experiments are performed in a FEI Titan ETEM and using a Wildfire heating holder from DENS Solutions allowing ±70° tilt with S5-type MEMS-based SiNx chips.

Obtaining 3D Chemical Maps by Energy Filtered Transmission Electron Microscopy Tomography

Energy filtered transmission electron microscopy tomography (EFTEM tomography) can provide three-dimensional (3D) chemical maps of materials at a nanometric scale. EFTEM tomography can separate chemical elements that are very difficult to distinguish using other imaging techniques. The experimental protocol described here shows how to create 3D chemical maps to understand the chemical distribution and morphology of a material. Sample preparation steps for data segmentation are presented. This protocol permits the 3D distribution analysis of chemical elements in a nanometric sample. However, it should be noted that currently, the 3D chemical maps can only be generated for samples that are not beam sensitive, since the recording of filtered images requires long exposure times to an intense electron beam. The protocol was applied to quantify the chemical distribution of the components of two different heterogeneous catalyst supports. In the first study, the chemical distribution of aluminum and titanium in titania-alumina supports was analyzed. The samples were prepared using the swing-pH method. In the second, the chemical distribution of aluminum and silicon in silica-alumina supports that were prepared using the sol-powder and mechanical mixture methods was examined.

Three-Dimensional Analytical Surface Quantification of Heterogeneous Silica-Alumina Catalyst Supports

The ability of energy‐filtered transmission electron microscopy (EFTEM) tomography to provide 3u2009D chemical maps at the nanoscale opens a new way to analyse heterogeneous materials quantitatively. In association with other techniques, EFTEM tomography has been employed in the study of amorphous silica‐alumina catalyst supports. Two types of samples prepared either by mechanical mixing (MM) or by the precipitation of silica on boehmite (PSB) that have similar proportions of silica and alumina were analysed. The sample synthesised by the PSB method shows a smaller degree of heterogeneity than the sample obtained by MM. For both types of samples, a higher concentration of alumina was found at the surface, whereas silica mostly constituted the core of the sample. A thermal treatment in a humid atmosphere was shown to redistribute the silica inside the sample as well as on its surface, which decreased the specific surface area at the same time. The acid sites localisation was defined as a specific curve at the interface between the two components upon reaching the surface of the support. The length of this curve, the “alumina–silica boundary line”, was estimated by using EFTEM tomography and discussed qualitatively with the chemical inter‐mixing information deduced from additional techniques such as FTIR and NMR spectroscopy.