• Hajjaji, Mohamed
• Caminade, A.-M.
• Laurent, Regis
• Beraa, Abdellah
• Delavaux-Nicot, Béatrice

Abstract

Nanocomposites of phosphorus-based dendrimers and montmorillonite were prepared and examined using X-ray diffraction, thermal analysis, solid-state nuclear magnetic resonance, and high-resolution transmission electron microscope. The adsorption of chromate by the nanocomposites and the basic clay was studied in the temperature range 298-318 K. For the latter purpose, the kinetics was followed and adsorption isotherms were plotted. The results showed that intercalated nanocomposites (GC1-AT) were formed with the first generation of cationic dendrimers. The use of the second generation of cationic dendrimers resulted in the formation of a mixture of exfoliated and intercalated nanocomposites (GC2-AT). For both dendrimers, adsorption was by cation exchange. The kinetics of the adsorption of chromate on both nanocomposites and Na-saturated montmorillonite (Na-AT) followed the pseudo-second-order equation and the rate constants varied in 0.08-0.19 g/mmol s-1. The rate-limiting steps were discussed on the basis of the results of the external mass transfer and the internal diffusion models. The experimental isotherms fitted will the model of Temkin, and chromate adsorption was an endothermic process and occurred spontaneously (-13 < ΔG° < -6 kJ/mol). The maximum uptake amounts of chromate were in the range 23-38 mg/g. It was shown that as a result of the adsorption of chromate by Na-AT, the adjacent environment of the tetrahedral sheet cation (Si4+) changed. For GC1-AT, the closest environment of the phosphorus atoms of the confined dendrimers was modified, and the interlayer expanded. In the case of GC2-AT, both environments of Si4+ and the inner phosphorus atom of the dendrimers became shielded and the interlayer shrunk.

Topics

• nanocomposite
• x-ray diffraction
• thermal analysis
• dendrimer
• Phosphorus