H. Ben Rhaiem

Étude par Diffraction X des Modes d'Empilement de la Nacrite Hydratée et Deshydratée

X-ray diffraction based on the comparison of experimental and calculated powder profiles enabled the determination of the structural characteristics of hydrated and dehydrated Tunisian nacrite. Using the concept describing the structure of natural nacrite, the stacking mode of the layers in the hydrated and dehydrated nacrite has been determined. The hydrate is characterized by an 8.42 A basal distance; one water molecule per Si2Al2O5(OH)4 is intercalated in the interlamellar space, located above the vacant octahedral site of the layer at z = 6.5 A and inserted inside the ditrigonal cavity of the tetrahedral sheet of the upper layer. The dehydrated nacrite obtained by heating of the hydrate at 423 K has the same interlayer shift t = −0.35a as the natural nacrite. Coherence domain sizes along c^{\ast} and in the ab plane are the same as those in the hydrate but different from those of the natural mineral. After dehydration, 5% of the layers had an interlayer shift similar to that obtained from the hydrate.

Mineralogy of the <2 μm fraction of three mixed-layer clays from southern and central Tunisia

Abstract Three clay minerals from southern and central Tunisia were characterized. Both XRD quantitative analysis and a chemical method were used to determine the mineralogical and physico-chemical characteristics of the <2 mm clay fractions. The XRD, CEC and specific surface measurement analyses showed that the dominant phase in all samples is illite-smectite with kaolinite and traces of quartz also present. From quantitative XRD, the abundances of the minerals identified are consistent with the measured CEC, specific surface area and TG/DTA properties. Analysis by XRD also showed that the illite-smectite phases are composed of thin stacks (two to a maximum of ten layers per stack) of random illite-smectite and ordered (R1) illite-smectite. There is also some discrete illite.

Evolution structurale de la nacrite en fonction de la nature des molécules organiques intercalees

Nacrite has been intercalated with two polar organic molecules: dimethyl sulfoxide (DMSO) and N-methylacetamide (NMA). The homogeneous nacrite complexes have been studied by X-ray diffraction (XRD) and infrared (IR) spectroscopy. The XRD study is based on a comparison between experimental and calculated patterns. The structures of the intercalated compounds have been determined, including the mutual positions of the layers after intercalation and the positions of the intercalated molecules in the interlayer space. It has been shown that the intercalation process causes not only a swelling of the interlayer space but also a shift in the mutual in-plane positions of the layers. This shift depends on the nature of the intercalated molecules and is related to their shape and the hydrogen bonds which are established with the surrounding surfaces. For a given molecule, the intercalation process is the same for the different polytypes of the kaolinite family. These XRD results are consistent with those of IR spectroscopy.

Étude Structurale d'une Nacrite Tunisienne

X-ray diffraction based on the comparison between the experimental and the calculated (20,11) and (02,31) powder profiles enabled determination of the structural characteristics of a Tunisian nacrite. The nacrite has space group Cc and the stacking mode is 2M. The two-layer periodicity could be described by a rotation of adjacent layers by 60° with the same interlayer shift between all layers (t = −0.35a along the 8.9 A axis). Because the 60° rotated layer can be deduced from the nonrotated one by a mirror plane parallel to the 8.9 A axis, the nacrite can also be described by the stacking of two symmetric layers. This better explains the unique translation between layers and is coherent with the previous description of stacking faults in the other members of the kaolinite family, i.e. kaolinite and dickite.

Study of the structural evolution of the 10 Å unstable hydrate of kaolinite during dehydration by XRD and SAXS

This work deals with understanding the structural evolution of the dehydration of the 10 A unstable hydrate of kaolinite. The method used to characterize this hydrate is based on a comparison between the experimental and the calculated X-ray diffraction profiles. The study was achieved in two steps: (i) the quantitative interpretation of 00l reflections enabled the determination of the number of intercalated water molecules, their positions and the stacking mode of the clay layers along the normal to the (a,b) plane; and (ii) the study of the hkl reflections with h and/or k ¬= 0 enabled the characterization of the structural evolution in the (a,b) plane of the hydrated kaolinite during dehydration. The hydrate is made up of two demixed phases. The first phase is homogenous and corresponds to a 10 A hydrated kaolinite, characterized by two H 2 O molecules per Si 2 Al 2 O 5 (OH) 4 situated at Z = 7.1 A from the surface oxygen. Two adjacent layers are translated with respect to each other, with T 1 = -0.155a + 0.13b + 10n. The abundance of this phase decreases during dehydration. The second phase is made up of 10 A hydrated layers, 8.4 A hydrated layers and 7.2 A dehydrated kaolinite layers, randomly interstratified. The abundance of this second phase increases during dehydration. The corresponding interlayer shifts arc respectively T 21 = -0.155a + 0.13b + 10n for the 10 A hydrated layer, T 22 = -0.355a + 0.35b + 8.4n for the 8.4 A hydrate and T 23 = -0.36a - 0.024b + 7.2n for the natural kaolinite, In addition to these interlayer shifts, some translation defects are introduced, such as -b/3, which exists in the initial kaolinite. The interpretation of the small-angle X-ray scattering (SAXS) patterns showed that the particle thickness remained the same before and after the hydration treatments, whereas X-ray diffraction (XRD) results indicated that the hydration of kaolinite caused a decrease of the mean number of layers in per crystallite from 40 to 20 layers. This decrease is related to the presence of H 2 O molecules situated within the micropores in the kaolinite particles that leave their interlayer space after heating at 573 K. The resulting dehydrated compound is characterized by the same basal distance and mean number of layers m per crystallite as for the natural kaolinite, while the proportion of the defects, such as the -b/3 translation, increases in the completely dehydrated compound (45%) compared with the natural kaolinite (10%).

XRD Study of the Nacrite/CsCl/H2O Intercalation Complex

The intercalation complex of nacrite with an alkali halide (Caesium chloride: CsCl) has been successfully prepared by mixing a CsCl saturated solution with a 8.4Å-hydrated nacrite. The homogeneous nacrite/CsCl complex has been studied by X-ray diffraction (XRD). Using an oriented clay aggregate, 10 basal reflections were obtained. The XRD pattern showed basal spacing of 10.5Å with integral series of 00l reflections indicating an ordered stacking of parallel 1:1 layers. A direct method involving a monodimensional electron density projection, along the normal to the layers, is used to determine the number and the position of intercalated compounds. The best agreement between observed and simulated p(Z) (R = 5%) is obtained by placing one Cl- ion at Z=6.7Å; one Cs+ ion at Z=8.3Å and two H O molecules at 6.3 and 7.4Å.

Selectivity of Na-Montmorillonite versus Concentration of Two Competitive Bivalent Cations (Cu2

The goal of this paper is to examine, by quantitative XRD analysis, the effect of heavy metal cation concentrations (Pb2

Immobilization of LDh enzyme on Layered Double Hydroxides: Structural and morphological modification

This paper presents a study on elaboration and characterization of biohybrides materials LDH-Lactate Dehydrogenase (LDh). The chosen LDHs are (MgAl and ZnAl with R = 2), were synthesized by a coprecipitation method with pH constant. The lactate immobilization in these matrices was obtained by exchange reaction and coprecipitation. A comparative study shows that the coprecipitation method allows a more important rate of immobilization. The structural and morphological modifications are dependent on the preparation methods, showing a loss of crystallinity and an important disorder of LDH structure due to an exfoliation phenomenon of LDH layers for coprecipitation mode. The preservation of the spatial configuration of the enzyme showed that LDHs can be like host matrices for the immobilization of lactate with the objective of developing a lactate biosensor or lactate biofuel cell.