The study describes the chemical-mineralogical characterization of Barremian sand deposits. These Sidi Aich sands were collected in central Tunisia. The collected raw silica sand from the Jebel Meloussi (central Tunisia) was characterised by different techniques, such as X-ray diffraction (XRD), X-ray uorescence (XRF) and scanning electron microscopy (SEM). X-ray diffraction showed a predominance of quartz and potassic feldspars and lower amounts of kaolinite and calcite. The obtained silica gels had pore diameters over 20 Å and speci c surface areas up to 183 m 2 /g, close to those reported for commercial silica gel materials. The N 2 adsorption isotherms have shown that new materials synthesised from Tunisian silica sands are mesoporous materials with high chemi-physical adsorption capabilities.
In this paper, we use Tunisian clay materials as alternative low-cost adsorbents, as well as substrates to immobilise TiO 2 for the decolouration of methylene blue (MB) dye solutions. The collected raw clay from the mine of Tamra was characterised by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence (XRF). XRD patterns of the raw clay showed halloysite as the main phase (61%), with a lower content of kaolinite (39%). For MB adsorption, the experimental data were fitted by Langmuir and Freundlich adsorption equations. It was found that the studied clays alone were not very efficient at adsorbing MB dye molecules. The decolouration of MB was improved by adding a photocatalytic function to the clay, by adding various amounts of TiO 2 nanopowder (20-80 wt%) to the clay, imbuing it with photocatalytic capabilities. These combined effects of the phenomena of adsorption and photocatalysis for MB removal by the TiO 2 -doped clay resulted in a very satisfactory performance, even with the relatively low quantity of 20 wt% added TiO 2 photocatalyst. This gave 48.6% removal after only 30-min adsorption in the dark, increasing to 84.1% removal after a further 3 h under UV light, through combined chemo-physical adsorption and photocatalytic decolouration phenomena.
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