RESUMO
The development of a volumetric apparatus (also known as a Sieverts' apparatus) for accurate and reliable hydrogen adsorption measurement is shown. The instrument minimizes the sources of systematic errors which are mainly due to inner volume calibration, stability and uniformity of the temperatures, precise evaluation of the skeletal volume of the measured samples, and thermodynamical properties of the gas species. A series of hardware and software solutions were designed and introduced in the apparatus, which we will indicate as f-PcT, in order to deal with these aspects. The results are represented in terms of an accurate evaluation of the equilibrium and dynamical characteristics of the molecular hydrogen adsorption on two well-known porous media. The contribution of each experimental solution to the error propagation of the adsorbed moles is assessed. The developed volumetric apparatus for gas storage capacity measurements allows an accurate evaluation over a 4 order-of-magnitude pressure range (from 1 kPa to 8 MPa) and in temperatures ranging between 77 K and 470 K. The acquired results are in good agreement with the values reported in the literature.
RESUMO
Rhomboidal and spherical metallic-copper nanostructures were encapsulated within well-formed graphitic shells by using a simple chemical method that involved the catalytic decomposition of acetylene over a copper catalyst that was supported on different smectite clays surfaces by ion-exchange. These metallic-copper nanostructures could be separated from the inorganic support and remained stable for months. The choice of the clay support influenced both the shape and the size of the synthesized Cu nanostructures. The synthesized materials and the supported catalysts from which they were produced were studied in detail by TEM and SEM, powder X-ray diffraction, thermal analysis, as well as by Raman and X-ray photoelectron spectroscopy.
RESUMO
A highly ordered two-dimensional hybrid magnetic nanocomposite has been prepared by synthesizing and intercalating a new cationic aluminum-hydroxy ferric ferrocyanide compound into a cation-adsorbing nanoclay (montmorillonite). Chemical and structural properties were investigated by X-ray diffraction, transmission electron microscopy, thermogravimetric and differential thermal analyses, Fourier transform infrared, X-ray photoemission, and Mössbauer spectroscopies. Elemental analysis was based on proton-induced gamma ray emission and X-ray fluorescence spectroscopy data, N/C elemental ratios, and cation-exchange capacity measurements. Magnetic properties were studied by SQUID magnetometry. The results suggest: (i) that the cationic Prussian blue analog comprises Al-hydroxy cations embedded into a monolayer thick two-dimensional ferric ferrocyanide array; and (ii) that the clay-Prussian blue nanohybrid consists of such arrays stacked between the clay layers. The latter material orders ferromagnetically at approximately 5K showing a hundred times higher remanence than that of the starting material, soluble Prussian blue (ammonium ferric ferrocyanide).
RESUMO
In this work, we describe the insertion of a water-soluble bisadduct fulleropyrrolidine derivative into the interlayer space of three layered smectite clays. The composites were characterized by a combination of powder X-ray diffraction, transmission electron microscopy, X-ray photoemission and FTIR spectroscopies, and laser flash photolysis measurements. The experiments, complemented by computer simulations, give insight into the formation process, structural details, and properties of the fullerene/clay nanocomposites. The reported composite materials constitute a new hybrid system, where C(60) differs from its crystals or its solutions, and open new perspectives for the design and construction of novel C(60)-based organic/clay hybrid materials.
