الفهرس 
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Abstract
An Egyptian bentonite clay was subjected to different sort of modifications to create various types of interacting sites. Firstly, Egyptian bentonite clay was modified by nitric acid generating a lot of protonated active sites (e.g. silanols and aluminols) of great tendency to be isomorphic replaced by high-valent cations. Secondly, Egyptian bentonite was modified by EDTA molecules, large molecules enriched by carboxylic and amine groups, affording intercalation of EDTA molecules within the clay lamellar structure. Lastly, Egyptian bentonite clay was modified by DMSO molecules, small molecules enriched with sulfinyl oxygen atoms, resulting in presence of clay exfoliation because of the founded strong interactions of such sulfoxide groups with various active sites in the interlayered structure of clay. The physicochemical characteristics of the three as-prepared modified clay samples were proceeded using XRD, FTIR, ICP, N2-BET and pore size distribution, zeta-potential and particle size, SEM, TEM and AFM analysis. from the discussed characterization results, the following conclusions could be drawn:
(i) from XRD analysis, It can be seen that the d(001) basal spacing increased from 0.7 nm (AT/Clay) to 1.3 nm (EDTA/Clay) linked with lower shifting of the 2θ basal (001) reflection (from 8.75o to 6.67o). This indicates the intercalation of large-sized EDTA molecules inside the interlayer spaces of bentonite clay.
(ii) from FTIR analysis, upon treatment of bentonite clay by EDTA molecules, new peaks characteristic to EDTA molecules demonstrated the ability of the intercalated EDTA molecules to chelate with the exchangeable cations in the clay interlayered spaces via their founded anionic carboxylate groups. On contrary absorption bands belonged to Si-O-Siout-of-plane, Si-O-Al and Al-OH hydroxyls bending vibrations related to the clay sheet structure were shifted to lower frequencies. These findings most probable revealed the capability of EDTA molecule to occupy the clay interlamellar spaces and intimately interact with the clay sheet structure via either their carboxylic or carboxylate ion groups. The paracrystalline Si-O and physically adsorbed water absorption bands were kept unchanged.
(iii) from surface analysis study using low-temperature N2 adsorption isotherms, upon treating with EDTA molecule, uniform aggregates of plate-like particles giving rise to slit-like pores. accompanied with much more discernable hysteresis loop indicating presence of large fractions of mesoporosity.
(iv) from surface zeta-potentials and particle size distribution, The highly recorded negative zeta-potentials by EDTA/Clay when compared to those got by AT/Clay most probable (for example, at pH 4.0). Confirmed the beneficial contributions of carboxylate ions (COO-) of EDTA molecules in bolstering clay by additional negatively charged species.
(v) from microscopic analyses, The SEM images of EDTA/Clay show the deep impact of EDTA molecules in building up a unique edifice of extended highly ordered domains of laminated clay with flattened and smooth surfaces. TEM image of EDTA/Clay demonstrates presence of highly oriented clay platelets with long-range ordered prism-like architecture. Such platelets seem to be well-connected sliding over each other thus points most probable to successful intervening of EDTA molecule within interlamellar structure of clay. By studying AFM, The 3D topographical image of EDTA/Clay demonstrates presence of highly compacted clay sheets that seem to slide over each other customizing mica particles of preeminent heights(Z~1189 nm and P-V~ 446 nm) and substantial flattering surfaces of extended widths (~ 1.25 - 2.5 μm).
The adsorption behavior of the three as-prepared modified clay samples were studied via the removal of Fe3+ ions from aqueous medium. All the adsorption systems were fitted by Freundlich and Langmuir adsorption models, and pseudo-second order and intra-particle diffusion kinetic models. These may give rise to conclude that the adsorption process in all the adsorption systems were affected by the nature of the adsorbate and the presence of sufficient active sites on the adsorbent surfaces. AT/Clay and DMSO/Clay samples fitted Hill and Temkin adsorption model, and recorded lower adsorption activation energy (derived from D-R model), lower Elovich adsorption rate constant and lower heat of adsorption with considerable increased entropic values, compared to EDTA/Clay. The obtained results pointed to the moderated potentials of the adsorption sites belonging to AT/Clay and DMSO/Clay that weaken from adsorbent-adsorbate interaction at the expense of adsorbate-adsorbate interaction. On contrary, the adsorption process ascribing to EDTA/Clay is sought to be chemisorption as the adsorption occurred mainly through strong electrostatic interaction between adsorbents (carboxylate anions of EDTA molecules) and adsorbates. This faith is supported by the high adsorption activation energy from D-R model, the advanced Elovich adsorption rate constant, the high exothermicity of adsorption process, and the highly negative values of the entropyand the spontaneous free energy of adsorption process. Moreover, EDTA/Clay was reused in four-successive adsorption processes for removal of Fe3+ ions from aqueous medium. In this respect, EDTA/Clay sample deserves being a ”special case for study”, where the adsorption active sites are perpetually adapted to electrostatically bound to iron ions from aqueous medium.