Tesi di Dottorato

This thesis was carried out at the laboratory of the Surface Nanoscience in the Department of Physics of University of Calabria, and at the Institute of Membrane Technology (ITM) of CNR, dealing the study of nanostructured systems with low dimensionality. The first part of the work consisted in the synthesis and characterization of graphite oxide (GO), obtained by chemical oxidation and sonication of natural graphite. We used an innovative oxidation process with respect to those present in the literature, and the resulting material was studied by means of UV-visible and Infrared absorption spectroscopy, Raman and XPS spectroscopies, and by TEM and SEM microscopies. The sonicated graphite oxide (sGO) was tested for adsorption of dyes, with the aim to contribute to research in the field of the reduction of pollutants in the liquid phase. We used Methylene Blue, Acridine Orange and Cresyl Violet dyes, whose kinetics of adsorption on sGO was been meticulously studied by the UV-visible absorption spectroscopy. The results showed that the graphite oxide effectively absorbs the three dyes, and the chemical nature of the adsorption process was evidenced by means the kinetic simulations adopting different models. The second part of the work relates to the synthesis of carbon-based nanostructures of the type "nano-onions" (CNOs), similar to multi-layer fullerenes, of great scientific and technological interest. The CNOs can be obtained by means of arc discharge between carbon electrodes immersed in deionized water. This method was used in this thesis work, and the produced carbonaceous nanomaterials have been characterized by Raman spectroscopy and TEM microscopy. Particular attention has been paid to those nanomaterials that contain a high percentage of CNO, since the arc discharge method also generates carbon nanotubes (CNT) and amorphous carbon. The main finding of the research was the identification of a solid agglomerate on the cathode, consisting almost exclusively of polyhedral CNOs and turbostratic graphite. The genesis of such CNOs is not attributable to a crystallization process of the carbon ions expelled from the plasma zone towards the surrounding water. The evidence of the fact that during the discharge the cathode remains at a temperature certainly lower respect to the anode, has permitted to hypothesize the CNOs training process, in which the carbon ions crystallize in the presence of a temperature gradient in the immediate vicinity of the cathode surface. In the last part of this research activity, I investigated a crystal of Indium Selenium (InSe) by means of different electron spectroscopies, in ultra-high vacuum conditions. Through electron energy loss spectroscopy (EELS) the electronic properties of InSe and its reactivity towards oxygen and air have been studied. The results have allowed to identify the most relevant transitions between electronic states in good agreement with existing theoretical calculations of the electronic structure and density of states. Experimental observations have also shown that the material is very stable with respect to possible oxidizing agents.

The present thesis is focused on the development of novel nancomposite membranes, prepared by the incorporation of two-dimensional inorganic layered structures such as (i) smectite clays (synthetic and natural), (ii) graphene oxide (GO), and (iii) layered double hydroxides (LDHs) with different compositions into the polymer matrix of Nafion, for use as electrolytes in Proton Exchange Membrane fuel cells. The characteristics of the membranes were studied mainly, in terms of transport properties by NMR spectroscopy, in order to study the water dynamics inside the electrolyte membranes. For this purpose the Pulse-Field-Gradient Spin-Echo NMR (PFGSENMR) method was employed to obtain a direct measurement of water self-diffusion coefficients on the water-swelled membranes in a wide temperature range (25-140 °C). This technique together with the 1H-NMR spectral analysis and NMR spin-lattice relaxation times (T1) conducted under variable temperature. Furthermore, both pristine materials (fillers and Nafion) as well as the resulted nanocomposite membranes were characterized by a combination of X-ray diffraction, FTIR spectroscopy, thermal analysis (DTA/TGA), Raman spectroscopies and scanning electronic microscopy (SEM).

Tesi di Dottorato

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