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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.

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.

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.

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 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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