Zeolites were synthesized from natural Tunisian clay by hydrothermal treatment under high pressure (100 MPa H 2 O pressure) at different gradients of temperature in high pressure autoclaves. The natural clay was first heated at 650 °C (HC-heated clay) and then transformed to an amorphous phase at 650 °C by adding different amount of NaOH. By increasing temperature and NaOH content, low-density frameworks zeolites like faujasite are transformed into more stable zeolites having higher density frameworks like cancrinite due to dissolution and recrystallisation steps. Cancrinite (Na 8 (H 2 0) 2 CO 3 [Al 6 Si 6 O 24 ]) (IZA-code: CAN) was successfully synthesized with a good purity. The synthesized CAN was characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The removal performance of heavy metal ions (Cd 2+ , Pb 2+ ) from solution by pure CAN and clays has been studied. The kinetics of adsorption of Cd 2+ and Pb 2+ are very fast: equilibrium is reached within 2 minutes at 298K. The capacity of adsorption of CAN is higher for Pb 2+ (192 mg/g) than for Cd 2+ (68 mg/g). Adsorption equilibrium of Cd 2+ and Pb 2+ on CAN were well represented by Langmuir equation although the thermodynamic study reveals a more complex mechanism: thermodynamic parameters, such as equilibrium constant, free energy, entropy and enthalpy for adsorption were obtained from the experimental data, including adsorption microcalorimetry.
The stability of small fractal graphene models with two different symmetries and Fe atoms at their mixed edges is addressed by density functional theory (DFT) calculations. Four kinds of edge configurations and Fe atom localizations are determined depending on the model. The edges have mixed configuration, the zig-zag and “intra-zig-zag” in symmetrical structures and armchair and zig-zag type in the architectures with rotational symmetry. The rotational symmetry graphene exhibits slightly higher stability per carbon atom compared to the symmetrical model, while the localization of Fe atoms is more favorable at armchair and “inversed zigzag” than at zigzag type carbon termination. Larger graphene structures with rotational symmetry were observed previously via experimental cutting of graphene with Fe nanoparticles (NPs).
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