Moisés Cabo

Synthesis of compositionally graded nanocast NiO/NiCo2O4/Co3O4 mesoporous composites with tunable magnetic properties

A series of mesoporous NiO/NiCo2O4/Co3O4 composites has been synthesized by nanocasting using SBA-15 silica as a hard template. The evaporation method was used as the impregnation step. Nickel and cobalt nitrates in different Ni(II) : Co(II) molar ratios were dissolved in ethanol and used as precursors. The composites show variable degrees of order, from randomly organized nanorods to highly ordered hexagonally-packed nanowires as the Ni(II) : Co(II) molar ratio decreases. The materials exhibit moderately large surface areas in the 60–80 m2 g−1 range. Their magnetic properties, saturation magnetization (MS) and coercivity (HC), can be easily tuned given the ferrimagnetic (NiCo2O4) and antiferromagnetic (NiO and Co3O4) character of the constituents. Moreover, the NiCo2O4 rich materials are magnetic at room temperature and consequently can be easily manipulated by small magnets. Owing to their appealing combination of properties, the nanocomposites are expected to be attractive for myriad applications.

EEL spectroscopic tomography: Towards a new dimension in nanomaterials analysis

Electron tomography is a widely spread technique for recovering the three dimensional (3D) shape of nanostructured materials. Using a spectroscopic signal to achieve a reconstruction adds a fourth chemical dimension to the 3D structure. Up to date, energy filtering of the images in the transmission electron microscope (EFTEM) is the usual spectroscopic method even if most of the information in the spectrum is lost. Unlike EFTEM tomography, the use of electron energy-loss spectroscopy (EELS) spectrum images (SI) for tomographic reconstruction retains all chemical information, and the possibilities of this new approach still remain to be fully exploited. In this article we prove the feasibility of EEL spectroscopic tomography at low voltages (80 kV) and short acquisition times from data acquired using an aberration corrected instrument and data treatment by Multivariate Analysis (MVA), applied to Fe(x)Co((3-x))O(4)@Co(3)O(4) mesoporous materials. This approach provides a new scope into materials; the recovery of full EELS signal in 3D.

Two Different Structures of Crystalline Mesoporous Indium Oxide Obtained by Nanocasting Process

Crystalline mesoporous metal oxides with narrow pore size distributions and controllable morphologies are interesting in a wide range of applications such as gas sensing, optics or catalysis. The synthesis pathway known as nanocasting is based in the growth of metal and semi-conductor nanoparticles within the pores of a regular mesoporous material. The use of the regular channels of ordered mesoporous silica as matrices for the controlled growth of nanoparticles and nanorods has been widely reported. In this method, the three-dimensional pore system of the matrix is filled with a suitable metal oxide precursor, which is then converted to the oxide during the calcination process. The structure matrix is finally removed, yielding the metal oxide as its negative replica. This nanocasting method has allowed the synthesis of numerous mesoporous metal oxides, many of which were formerly unavailable by the conventional synthesis method of supramolecular structure direction.