Challenges in Determining the Size Distribution of Nanoparticles in Consumer Products by Asymmetric Flow Field-Flow Fractionation Coupled to Inductively Coupled Plasma-Mass Spectrometry: The Example of Al₂O₃, TiO₂, and SiO₂ Nanoparticles in Toothpaste

According to the current European regulation on cosmetics, any ingredient present as a nanomaterial should be indicated in the ingredient list. There is a need for analytical methods capable of determining the size of the relevant ingredients and thus assessing if these are nanomaterials or not. An analytical method based on asymmetric flow field-flow fractionation (AF4) and inductively coupled plasma-mass spectrometry (ICP-MS) was developed to determine the size of particles present in a commercial toothpaste. Multi-angle light scattering (MALS) was used for on-line size determination. The number-based particle size distributions (PSDs) of the particles were retrieved upon mathematical conversion of the mass-based PSDs recovered from the AF4-ICP-MS fractograms. AF4-ICP-MS allowed to separate and detect Al2O3 and TiO2 particles in the toothpaste and to retrieve a correct TiO2 number-based PSD. The potential presence of particles in the lower size range of the Al2O3 mass-based PSD had a strong impact on sizing and nanomaterial classification upon conversion. AF4 coupled with ICP-MS and MALS was found to be a powerful approach for characterization of different particles in a multiple-particle system such as toothpaste. Confirmation of particle size by a secondary method such as single particle ICP-MS or hydrodynamic chromatography was crucial

Tunable CHA/AEI Zeolite Intergrowths with A Priori Biselective Organic Structure-Directing Agents: Controlling Enrichment and Implications for Selective Catalytic Reduction of NOx

[EN] A novel ab initio methodology based on high-throughput simulations has permitted designing unique biselective organic structure-directing agents (OSDAs) that allow the efficient synthesis of CHA/AEI zeolite intergrowth materials with controlled phase compositions. Distinctive local crystallographic ordering of the CHA/AEI intergrowths was revealed at the nanoscale level using integrated differential phase contrast scanning transmission electron microscopy (iDPC STEM). These novel CHA/AEI materials have been tested for the selective catalytic reduction (SCR) of NOx, presenting an outstanding catalytic performance and hydrothermal stability, even surpassing the performance of the well-established commercial CHA-type catalyst. This methodology opens the possibility for synthetizing new zeolite intergrowths with more complex structures and unique catalytic properties.E.B.-J., C.P., M.M. and A.C. acknowledge financial support by the Spanish Government [Grant RTI2018-101033-B-I00 (MCIU/AEI/FEDER, UE)], and by CSIC [I-link+ Program (LINKA20381)]. D.S.-K. and R.G.-B. acknowledge the Energy Initiative (MITEI) and MIT International Science and Technology Initiatives (MISTI) Seed Funds. D.S.-K. was additionally funded by the MIT Energy Fellowship. Y.R.-L acknowledges support by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-SC0016214. E.B.-J. acknowledges the Spanish Government for an FPI scholarship (PRE2019-088360). T.W. acknowledges financial support by the Swedish Research Council (Grant No. 2019-05465). T.W. and T.U. acknowledge funding from the Swedish Strategic Res. Foundation (project nr. ITM17-0301). The Electron Microscopy Service of the UPV is also acknowledged for their help in sample characterization. Computer calculations were executed at the Massachusetts Green High-Performance Computing Center with support from MIT Research Computing, and at the Extreme Sci. and Eng. Discovery Environment (XSEDE)[33] Expanse through allocation TG-DMR200068.Bello-Jurado, E.; Schwalbe-Koda, D.; Nero, M.; Paris, C.; Uusimäki, T.; Román-Leshkov, Y.; Corma Canós, A.... (2022). Tunable CHA/AEI Zeolite Intergrowths with A Priori Biselective Organic Structure-Directing Agents: Controlling Enrichment and Implications for Selective Catalytic Reduction of NOx. Angewandte Chemie International Edition. 61(28):1-6. https://doi.org/10.1002/anie.20220183716612

Three dimensional quantitative characterization of magnetite nanoparticles embedded in mesoporous silicon: local curvature, demagnetizing factors and magnetic Monte Carlo simulations

Magnetite nanoparticles embedded within the pores of a mesoporous silicon template have been characterized using electron tomography. Linear least squares optimization was used to fit an arbitrary ellipsoid to each segmented particle from the three dimensional reconstruction. It was then possible to calculate the demagnetizing factors and the direction of the shape anisotropy easy axis for every particle. The demagnetizing factors, along with the knowledge of spatial and volume distribution of the superparamagnetic nanoparticles, were used as a model for magnetic Monte Carlo simulations, yielding zero field cooling/field cooling and magnetic hysteresis curves, which were compared to the measured ones. Additionally, the local curvature of the magnetite particles' docking site within the mesoporous silicon's surface was obtained in two different ways and a comparison will be given. A new iterative semi-automatic image alignment program was written and the importance of image segmentation for a truly objective analysis is also addressed

Infiltration of Fe3O4-nanoparticles into porous silicon with respect to magnetic interactions (Nanostructured Thin Films IV)

Mesoporous silicon (PS) is used as matrix for infiltration of Fe3O4 nanoparticles (5 and 8 nm). The structure and magnetic behaviour of such composites are investigated and a correlation between the morphology of the nanocomposite (structure of the matrices, size and distribution of Fe3O4 particles) and the magnetic properties of the system is figured out. This system shows a superparamagnetic (SPM) behaviour at room temperature and becomes ferromagnetic (FM) at lower temperatures. The transition temperature between SPM and a blocked state depends on the particle size, their coating and on their magnetic interactions. Dipolar coupling between the particles can be influenced by varying the PS morphology as well as by the filling factor. The blocking temperature (TB) of the composite is tuneable and changes due to the variation of dipolar coupling of the Fe3O4-particles (distance between particles). Results gained from electron microscopy and tomography, respectively such as size and spatial distribution of the particles together with the magnetic data lead to a more detailed knowledge of the Fe3O4/silicon nanocomposite system

Elucidating the lithiation process in Fe3–δO4 nanoparticles by correlating magnetic and structural properties

Due to their high potential energy storage magnetite (Fe3O4) nanoparticles have become appealing for anode materials in lithium-ion batteries. However, the details of the lithiation process are still not completely understood. Here, we investigate chem- ical lithiation in 70 nm cubic shaped magnetite nanoparticles with varying degree of lithiation x = 0, 0.5, 1, 1.5. The induced changes on the structural and magnetic properties were investigated by using X-ray techniques along with electron microscopy and magnetic measurements. The results indicate that a structural transformation from spinel to rock salt phase occurs above a critical limit for the lithium concentra- tion (xc), which is determined to be between 0.5< xc≤1 for Fe3–δO4. Magnetization measurements clearly shows the formation of the LiFeO2 phase with its distinct anti- ferromagnetic behaviour below its Need temperature. Upon lithiation, magnetization measurements reveal exchange bias in the hysteresis loops with an asymmetry, which can be attributed to the formation of mosaic-like LiFeO2 subdomains. The combined characterization techniques enabled us to unambiguously identify the phases and their distribution involved in the lithiation process. Correlating magnetic and structural properties opens the path to increase the understanding of the processes involved in a variety of non-magnetic applications of magnetic materials