The packing of spheres is a subject that has drawn the attention of mathematicians and philosophers for centuries, and that currently attracts the interest of the scientific community in several fields. At the nanoscale, the packing of atoms affect the chemical and structural properties of the material, and hence, its potential applications. This report describes the experimental formation of five-fold nanostructures by the packing of interpenetrated icosahedral and decahedral units. These nanowires, formed by the reaction of a mixture of metal salts (Au and Ag) in the presence of oleylamine, are obtained when the chemical composition is specifically Ag/Au=3/1. The experimental images of the icosahedral nanowires have a high likelihood with simulated electron micrographs of structures formed by two or three Boerdijk-Coxeter-Bernal helices roped on a single structure, whereas for the decahedral wires, simulations using a model of adjacent decahedra match the experimental structures. To our knowledge, this is the first report of the synthesis of nanowires formed by the packing of structures with five-fold symmetry. These icosahedral nanowire structures remind those of quasicrystals that can only be formed if at least two atomic species are present and in which icosahedral and decahedral packing has been found for bulk crystals.

In this work we examined MoS2 sheets by aberration-corrected scanning transmission electron microscopy (STEM) at three different energies: 80, 120 and 200 kV. Structural damage of the MoS2 sheets has been controlled at 80 kV according a theoretical calculation based on the inelastic scattering of the electrons involved in the interaction electron-matter. The threshold energy for the MoS2 material has been found and experimentally verified in the microscope. At energies higher than the energy threshold we show surface and edge defects produced by the electron beam irradiation. Quantitative analysis at atomic level in the images obtained at 80 kV has been performed using the experimental images and via STEM simulations using SICSTEM software to determine the exact number of MoS2 layers.

Fe nanoparticles and branched nanostructures of iron oxide were synthesized by chemical reduction in aqueous phase. The mechanism of formation of iron oxides as a function of the amount of surfactant employed during the synthesis process was studied. Specifically Fe, Fe2O3, and Fe3O4nanoparticles were obtained. The oxidation of Fe to Fe3O4and finally to Fe2O3was carried out by oxidative etching process, decreasing the amount of stabilizer agent. The structures obtained were characterized by high resolution (HRTEM) and scanning/transmission (STEM) electron microcopies, energy dispersive spectroscopy (EDS), and optical spectroscopy (UV-Vis and IR).

In the case of the hydrodesulfurization (HDS) processes one of the best catalysts currently available is that based on MoS 2 and WS 2 . A very significant increase in their activity can be achieved by adding Co or Ni as a promoter. In the present report we have used probe aberration corrected STEM (scanning transmission electron microscopy) for the first time to characterize Co doped MoS 2 /WS 2 nanowire catalysts (supported on Al 2 O 3 substrates). The high-resolution imaging reveals clearly the location of Co in the individual catalysts. This has not been possible to date with other experimental techniques because of the insufficient image contrast and/or resolution. On the basis of the HAADF-STEM images, we built two models for the CoÀMoÀS and CoÀWÀS catalysts to illustrate the different morphologies found in the catalysts. With this study it is now possible to better locate, identify, and understand the role of promoters in the design and functioning of catalysts. KEYWORDS: hydrodesulfurization (HDS), MoS 2 and WS 2 based catalysts, Co doped MoS 2 /WS 2 nanowires, probe aberration corrected STEM

This study is aimed at investigating the structural and morphological characterization of natural and modified zeolite obtained from the state of Oaxaca (Mexico). Iron nanoparticles were used for the zeolite modification. The iron nanoparticles were loaded on the zeolite surface by homogeneous nucleation. Adsorption kinetic models of pseudo first and second order were surveyed. The characterization of pristine and modified zeolite was performed by Fourier transform infrared (FTIR), transmission electron microscopy (TEM), and X-ray diffraction (XRD). From the results, three main phases were identified: clinoptilolite, mordenite, and feldspar. We could also determine the adsorption capacity of the zeolites by means of adsorption kinetic models.