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Gammoudi S.,Center National des Recherches en science des Materiaux | Frini-Srasra N.,Tunis el Manar University | Srasra E.,Center National des Recherches en science des Materiaux
Engineering Geology | Year: 2012

The use of organoclays as adsorbents in the remediation of polluted water has been the subject of many recent studies. In this present work, a Tunisian smectite modified by two cationic surfactants was used as a sorbent for the investigation of the adsorption kinetics, isotherms and thermodynamic parameters of nitrate ions at various contact time, initial concentrations and temperatures. Two simplified kinetic models, first-order and second-order, were used to predict the adsorption constants. It was found that the adsorption kinetics of nitrate was best described by the second-order model. Adsorption isotherms and equilibrium adsorption capacities were determined by the fittings of the experimental data to two well-known isotherm models including Langmuir and Freundlich. The results showed that Langmuir model appears to fit the adsorption better than Freundlich model. The equilibrium constants were used to calculate thermodynamic parameters, such as the change of free energy, enthalpy and entropy. © 2011 Elsevier B.V.


Gammoudi S.,Center National des Recherches en science des Materiaux | Frini-Srasra N.,Center National des Recherches en science des Materiaux | Srasra E.,Tunis el Manar University
International Journal of Mineral Processing | Year: 2013

Organically modified clays ('organoclays') have attracted a great deal of interest because of their wide applications in industry and environmental protection. In this work, organoclays were prepared with Tunisian smectite samples using two cationic surfactants (HDPy and HDTMA). The aim was to prepare fluoride adsorbing materials. A full microstructural characterization of the organoclays by XRD, FTIR and DSC was performed. Different configurations of surfactants within smectite interlayer are proposed. The DSC analyses show that the intercalation of the surfactant cations was governed by different processes. These organoclays showed high removal capacities for fluoride ions. The adsorption kinetics and adsorption isotherms of fluoride ions from aqueous solution were investigated. Two simplified kinetic models, pseudo-first-order and pseudo-second-order, were used to predict the adsorption rate constants. Adsorption isotherms and equilibrium adsorption capacities were determined by the fittings of the experimental data to two well-known isotherm models including Langmuir and Freundlich. © 2013 Published by Elsevier B.V.


Mnasri S.,Center National des Recherches en science des Materiaux | Frini-Srasra N.,Center National des Recherches en science des Materiaux
Clay Minerals | Year: 2012

The exchange reaction of Na-bentonite with zirconium pillars gives products which suffer from a loss of crystallinity, with basal spacing about 18 Å and surface area of 200 m2 g-1. Aluminium introduced in different amounts in the zirconium intercalated solution leads to an improvement in the stability and crystallinity of zirconia-pillared clays (Zr-PILCs) and creates pillared clays with new properties. Adding a small amount of Al (10 molar %) leads to an increase of d001 from 18 Å to 20.5 Å and an increase of the percentage of introduced zirconium from 16.71 to 21, expressed as ZrO2 wt.%, accompanied by an increase of the Brösted and Lewis acidic sites. The acetalization of acetone with ethylene glycol was studied in order to compare the activity of PILCs. The results show that the yield of the aforementioned reaction depends strongly of the composition and acidity of the catalyst. © 2012 The Mineralogical Society.


Mnasri-Ghnimi S.,Center National des Recherches en science des Materiaux | Frini-Srasra N.,Center National des Recherches en science des Materiaux
Applied Clay Science | Year: 2014

A series of pillared interlayered clays (PILCs) including Al-, Zr- and Al-Zr-PILC have been prepared and characterized by X-ray diffraction, elemental analyses, N2 adsorption, cationic exchange capacity and IR measurements after n-butylamine adsorption. Cerium introduced in the Zr4+ and/or Al3+ intercalated solution allows for an improvement of the stability and crystallinity of PILC and creates pillared clays with new properties. The resulting materials were used for the synthesis of 1,3-dioxolane. The addition of cerium has a major influence in this reaction. © 2013 The Authors.


Hamdi N.,Center National des Recherches en Science des Materiaux | Srasra E.,Center National des Recherches en Science des Materiaux
Applied Clay Science | Year: 2014

Surfactant modified smectite was prepared using hexadecyltrimethylammonium bromide (HDTMAB) at three CEC levels (0.5, 1 and 2 CEC). Potentiometric titration behavior of Na-smectite and organosmectites was investigated and interpreted according to surface complexation theory. The point of zero charge (PZC) was determined by both the methods potentiometric and mass titrations. The PZC of Na-smectite is about 6.2 and that of the organosmectites (H0.5, H1 and H2) is 6.8, 7.7 and 8, respectively. The titration data was modulated using the ProtoFit program in order to determine the PZC and the equilibrium constants (pKas). The results give a good agreement between the experimental and modeling study. © 2014 Elsevier B.V.


Mnasri S.,Center National des Recherches en science des Materiaux | Frini-Srasra N.,Center National des Recherches en science des Materiaux
Infrared Physics and Technology | Year: 2013

The surface acidity of different pillared clay, zirconium-, aluminium- and mixed zirconium-aluminium-pillared bentonite was determined by Fourier transform infrared spectroscopy technique using N-butylamine as probe molecule. The spectra obtained showed well resolved absorption bands for Lewis and Brönsted acid sites in the clay catalysts. In order to understand the role of acid sites present on clay catalysts, synthesis of 2,2-dimethyl-1,3-dioxolane by acetalyzation of acetone with ethylene glycol under autogenous pressure and without solvent has been studied. The Brönsted and Lewis acidity data obtained by FT-IR study for modified bentonite correlated well with the catalytic activity in the synthesis of 2,2-dimethyl-1,3-dioxolane reaction. Among the modified clay catalysts, Zr90-Al10-PILC bentonite catalysts showed good activity and aluminium rich PILC showed negligible activity in the acetalyzation reaction. This inactivity is attributed to the absence of Brönsted acidity. © 2013 Elsevier Ltd. All rights reserved.


Ferhi M.,Center National des Recherches en science des Materiaux | Horchani-Naifer K.,Center National des Recherches en science des Materiaux | Ferid M.,Center National des Recherches en science des Materiaux
Optical Materials | Year: 2011

KLa(PO3)4 (KLP) and LiLa(PO3)4 (LLP) doped with different concentrations of Eu3+ are grown by solid state reaction. The obtained powders are identified by X-ray diffraction, Raman and FT-IR spectroscopies. These polyphosphates KLa(PO3)4 and LiLa(PO3)4 crystallize in the monoclinic system but with different space groups respectively P21 and C2/c. The evolution of crystal lattice parameters as function of Eu3+ concentration in these host lattices was studied. Spectroscopic properties of the Eu 3+-doped KLa(PO3)4 and LiLa(PO 3)4 at room temperature (RT) are presented. The excitation spectra of the Eu3+ ion in condensed polyphosphates along the UV-Visible domain are registered. They show that the position of the charge transfer band (CTB) depends on the host lattices. The effect of structural characteristics of condensed polyphosphates on their optical and colorimetric properties was investigated for the first time. Colorimetric parameters of the Eu3+ ions red emission in KLP and LLP are determined and compared with other host matrices. Evolution of colorimetric properties as function of Eu3+concentration was discussed. © 2011 Elsevier B.V. All rights reserved.


Hamdi N.,Center National des Recherches en Science des Materiaux | Srasra E.,Center National des Recherches en Science des Materiaux
Waste Management | Year: 2013

Three natural clayey soils from Tunisia were studied to assess their suitability for use as a liner for an acid waste disposal site. An investigation of the effect of the mineral composition and mechanical compaction on the hydraulic conductivity and fluoride and phosphate removal of three different soils is presented. The hydraulic conductivity of these three natural soils are 8.5×10-10, 2.08×10-9 and 6.8×10-10m/s for soil-1, soil-2 and soil-3, respectively. Soil specimens were compacted under various compaction strains in order to obtain three wet densities (1850, 1950 and 2050kg/m3). In this condition, the hydraulic conductivity (k) was reduced with increasing density of sample for all soils. The test results of hydraulic conductivity at long-term (>200days) using acidic waste solution (pH=2.7, charged with fluoride and phosphate ions) shows a decrease in k with time only for natural soil-1 and soil-2. However, the specimens of soil-2 compressed to the two highest densities (1950 and 2050kg/m3) are cracked after 60 and 20days, respectively, of hydraulic conductivity testing. This damage is the result of a continued increase in the internal stress due to the swelling and to the effect of aggressive wastewater. The analysis of anions shows that the retention of fluoride is higher compared to phosphate and soil-1 has the highest sorption capacity. © 2012.


Mbarki R.,Center National des Recherches en science des Materiaux | Mnif A.,Center National des Recherches en science des Materiaux | Hamzaoui A.H.,Center National des Recherches en science des Materiaux
Materials Science in Semiconductor Processing | Year: 2015

Magnesium oxide powders (MgO) were synthesized via a sol-gel process (SG). The crystalline structure, particle size, and roughness weight loss were investigated through X-ray diffraction, atomic force microscopy, Differential Thermal Analysis (DTA) and Thermal Gravimetric Analysis (TGA). X-ray diffraction patterns revealed that MgO powders obtained were crystallized. The crystallite size of the obtained MgO powders is equal to 79.8 nm. The morphology is displayed as granular and porous. The RMS value is determined as 0.3158 nm whereas the weight loss is around 0.70%. Complex impedance spectroscopy was used to examine electrical properties. The dielectric phenomena and electrical conductivity properties of MgO powders were studied to improve the conductivity. The activation energy of the MgO powders in the temperature study was found to be 0.178 eV. © 2014 Elsevier Ltd. All rights reserved.


Mnasri S.,Center National des Recherches en science des Materiaux | Frini-Srasra N.,Center National des Recherches en science des Materiaux
Surface Engineering and Applied Electrochemistry | Year: 2013

The aim of this work is to study the solids obtained by pillaring Tunisian bentonite with zirconium polycations from the hydrolysis of zirconium tetrachloride. For comparative purposes, the pillaring of Wyoming montmorillonite, a reference clay, is also studied. Variations in the dialysis number, concentration of Zr solution, pH, temperature in the synthesis procedure as well as the pillaring method, affect the structure and properties of the pillared clay obtained. It has been verified that the structure of the pillared clays strongly depends on the method of preparation and the pH Zr solution in some cases, well ordered pillared clays (with basal spacings between 15 and 18.2 A) have been obtained, while in several others noncrystalline solids yielded. Delamination of the clays seems to take place both when the intercalation solutions obtained from zirconium tetrachloride have pH > 2.8 and when they are subjected to a reflux treatment. Best results were obtained at pH = 2.8 [Zr4+] = 0.1 M, at room temperature, and when using five dialysis, the direct method. The specific total surface area and micropore volume of the solids have reached the values up to 200 m2 g-1 and 0.06 cm3 g-1, respectively. Potentiometric titration and mass titration data suggest that pillared materials produce a shift of the point zero charge toward the point zero charge of the zirconium oxide. The amount of ZrO2 fixed have varied between 6 and 30% of the weight of the pillared samples. The activity of the zirconium pillared clay for 1,3-dioxolane synthesis has been investigated. The method of intercalation has been found to be the most suitable for this reaction. © 2013 Allerton Press, Inc.

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