29Si AND 27Al CPMAS NMR QUALITATIVE AND QUANTITATIVE ANALYSIS OF KAOLINITE AND DICKITE IN KOS ISLAND KAOLINS, GREECE

Η μέθοδος του Πυρηνικού Μαγνητικού Συντονισμού (NMR) και οι τεχνικές 7ΑΙ και 9Si CPMAS NMR εφαρμόστηκαν στην έρευνα επιλεγμένων δειγμάτων υδροθερμικά εξαλλοιωμένων ρυολίθων της νήσου Κω. Επιλέχθηκαν δείγματα πλούσια σε καολινίτη και δικίτη που είχαν ήδη αναλυθεί και με τη χρήση της Περιθλασιμετρίας Ακτινών Χ και σημειακών χημικών αναλύσεων (που ελήφθησαν από το HL·κτpovικό Μικροσκόπιο). Ο καολινίτης και ο δικίτης μπορούν να ανιχνευτούν βάση των φασμάτων του τετραεδρικού Πυριτίου και του οκταεδρικού Αργιλίου (με τις τεχνικές 27ΑΙ και 29Si CPMAS NMR). Βρέθηκε ότι η αλληλεπίδραση των ανακλάσεων υποβαθμίζεται και το σχήμα των ανακλάσεων γίνεται οξύληκτο όταν ο χρόνος αποφόρτισης (pulse recycling delay) είναι υψηλός (10 δευτεpόL·πτa). Ο λόγος οκταεδρικό Αργίλιο / τετραεδρικό Πυρίτιο των ορυκτών της ομάδας του καολινίτη όπως μετρήθηκε από τις τεχνικές του Πυρηνικού Μαγνητικού Συντονισμού βρέθηκε παρόμοιος με αυτόν που προέκυψε από τις σημειακές χημικές αναλύσεις. Σε αυτήν την εργασία παρουσιάζεται για πρώτη φορά μια προσέγγιση που κάνει εφικτή τη λήψη οξύληκτων ανακλάσεων Πυρηνικού Μαγνητικού Συντονισμού σε στερεά δείγματα (27Al and 29Si CPMAS NMR). Το οξύληκτο σχήμα των ανακλάσεων μεγιστοποιεί την ακρίβεια των μετρήσεων της θέσεων των ανακλάσεων και του λόγου οκταεδρικό Αργίλιο / τετραεδρικό Πυρίτιο.The application of 27Al and 29Si CPMAS NMR spectroscopy to the investigation of selected /caolinite and dickite bearing samples from hydrothermally altered rhyolites of Kos island is tested using also XRD and analytical SEM-EDS data. Kaolinite and dickite, can be detected by both their tetrahedral Si and octahedral Al CPMAS NMR spectra. It was found that the interference of the peaks become less significant and the shape of the peaL· narrow when the pulse recycling delay is high (up to 10s). The octahedral Al / tetrahedral Si ratios of kaolinite group mineral forms from samples showing various degrees of alteration, calculated from the NMR spectra, were found to be very similar to these derived from the structural formulae of SEM-EDS microanalyses. In this work it is presented for the first time an approach to provide narrow CPMAS NMR peaks. The narrow shape of the peaks provides accurate measurements of the exact position of the peaL· and the octahedral Al / tetrahedral Si ratios

Nanocrystalline TiO2 and halloysite clay mineral composite films prepared by sol-gel method:Synergistic effect and the case of silver modification to the photocatalytic degradation of basic blue- 41 azo dye in water

Tubular halloysite clay mineral and nanocrystalline TiO2 were incorporated in the preparation of nanocomposite films on glass substrates via sol-gel method at 450 °C. The synthesis involves a simple chemical method employing nonionic surfactant molecule as pore directing agent along with the acetic acid-based sol-gel route without addition of water molecules. Drying and thermal treatment of composite films ensure elimination of organic material and lead to the formation of TiO2 nanoparticles homogeneously distributed on the surface of the halloysite. Nanocomposite films without cracks of active anatase crystal phase and small crystallite size on halloysite nanotubes are characterized by microscopy techniques and porosimetry methods in order to examine their structural properties. The composite halloysite-TiO2 films with variable quantities of halloysite were examined as photocatalysts to the discoloration of Basic Blue 41 azo dye in water. These nanocomposite films proved to be very promising photocatalysts and highly effective to dye's discoloration in spite of small amount of halloysite/TiO2 catalyst immobilized onto glass substrates. It also has been shown that the efficiency of the halloysite/TiO2 films could be further improved when silver particles were deposited on their surface after successful adsorption from an aqueous solution of a silver salt and UV reduction of the adsorbed ions

HEAVY METALS IN STREAM SEDIMENTS AFFECTED BY A LANDFILL AND ASSOCIATED IMPACT ON GROUNDWATER QUALITY

Sanitary landfill facilities are essential to modern societies as repositories for municipal solid wastes. However, they always entrain a certain risk of environmental impact. For this reason monitoring is essential to their operation. In the present work, the environmental impact of such a landfill is studied. Soil samples were collected in and around the landfill and their mineralogy was studied. Top layers of stream sediments were collected to examine possible dispersion of pollutants in the environment. Chemical analyses showed enrichment in As, Cu, Zn, and Pb in the stream sediments compared to uncontaminated samples. The presence of anions such as chloride, sulphate and phosphate adsorbed on clay minerals suggest the interaction of stream sediments with run-off water from the landfill. The groundwater near the landfill site was characterised as not potable and not suitable for irrigation purposes, because some parameters such as NO3 - and Cl- were close or exceeded the permissible limits given by EE, EPA and WHO

Identification of network modules by optimization of ratio association

We introduce a novel method for identifying the modular structures of a network based on the maximization of an objective function: the ratio association. This cost function arises when the communities detection problem is described in the probabilistic autoencoder frame. An analogy with kernel k-means methods allows to develop an efficient optimization algorithm, based on the deterministic annealing scheme. The performance of the proposed method is shown on a real data set and on simulated networks

Transport Properties of Carbon Nanotube C60_{60} Peapods

We measure the conductance of carbon nanotube peapods from room temperature down to 250mK. Our devices show both metallic and semiconducting behavior at room temperature. At the lowest temperatures, we observe single electron effects. Our results suggest that the encapsulated C$_{60}$ molecules do not introduce substantial backscattering for electrons near the Fermi level. This is remarkable given that previous tunneling spectroscopy measurements show that encapsulated C$_{60}$ strongly modifies the electronic structure of a nanotube away from the Fermi level.Comment: 9 pages, 4 figures. This is one of two manuscripts replacing the one orginally submitted as arXiv:cond-mat/0606258. The other one is arXiv:0704.3641 [cond-mat