A. Ben Haj Amara

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.

X-ray diffraction, infrared and TGA/DTG analysis of hydrated nacrite

Abstract An homogenous 8.4 Å hydrate was obtained after washing intercalated KAc-nacrite. X-ray diffraction analysis based on comparison of the experimental and calculated profiles enabled the amount of water (one molecule per Si2Al2O5(OH)4) and the z coordinate along c* (6.5 Å) to be determined. The hydration state was accompanied by a decrease in the coherent domain along c* in the order nacrite > KAc-nacrite > H2O-nacrite. The IR spectrum of the hydrated nacrite showed an evolution of the structure with a shift of v(OH) from 3702, 3649 and 3630 cm-1 to 3690, 3641 and 3620 cm-1, respectively for the nacrite hydroxyls. The v(OH) stretching bands of the interlayer water appeared at 3602 and 3545 cm-1 and their bending band at 1655 cm-1. The TGA/DTG analysis of the air-dry hydrated nacrite showed a loss of water at 245°C, the weight loss (1 molecule per Si2Al2O5(OH)4) corresponding to the interlamellar water, in agreement with that determined by XRD.

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.

Sepiolite nanoplatform for the simultaneous assembly of magnetite and zinc oxide nanoparticles as photocatalyst for improving removal of organic pollutants

Novel ternary ZnO/Fe3O4-sepiolite nanostructured materials were developed in a two-step procedure based on the incorporation of ZnO nanoparticles on a substrate composed by magnetite nanoparticles previously assembled to the sepiolite fibrous silicate (Fe3O4-sepiolite). The structural and morphological characterization shows that both, ZnO and Fe3O4 nanoparticles, were homogeneously dispersed on the surface of sepiolite. Therefore, the resulting material is characterized as a multifunctional nanoplatform simultaneously providing magnetic and photoactive properties. ZnO/Fe3O4-sepiolite materials exhibit superparamagnetic properties at room temperature, which is one of the sought properties in view to facilitate their recovery from the reaction medium after application as heterogeneous catalysts. ZnO/Fe3O4-sepiolite materials were tested as photocatalysts using methylene blue dye in water as model of a pollutant molecule, showing full decolorization after 2h of UV irradiation. Moreover, the photocatalytic activity of this nanoplataform may be maintained after reuse in several consecutive cycles of treatment. Remarkably, the ZnO/magnetite-sepiolite nanostructured material displays a similar activity as ZnO/sepiolite materials, but shows the additional advantage of easier recovery by means of a magnet which facilitates its reuse.

Etude structurale par diffraction des RX et spectroscopie IR des hydrates 10 et 8.4 Å de kaolinite

Two hydrated kaolinites, characterized by 10 and 8.4 A basal distances, were synthesized by treating the kaolinite KGa-1 with dimethyl sulfoxide (DMSO) and ammonium fluoride (NH4F). The X-ray diffraction study was based on a comparison between the experimental and calculated profiles. This study was conducted in two steps: firstly, the study of the 00l reflections enabled the determination of the stacking mode along c*, the number of water molecules and their positions along the normal to the plane of the sheet structure; secondly, the study of the hk bands, with h and/or k ≠ 0, enabled the determination of the stacking mode and the positions of the water molecules in the (a,b) plane. The 10 A hydrated kaolinite is characterized by two water molecules per Al2Si2O5(OH)4 unit, situated at 3 and 3.4 A from the hydroxyl surface, over the octahedral sites. Two adjacent layers are translated with respect to each other, with T11 = −0.38a − 0.37b + 10n. The 8.4 A hydrated kaolinite is characterized by one water molecule per Al2Si2O5(OH)4 unit, situated at 2.4 A from the hydroxyl surface and inserted between the vacant octahedral site and the ditrigonal cavity of the tetrahedral sheet. The corresponding interlayer shift is T11 = −0.355a + 0.35b + 8.4n.

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.

Etude structurale d'un hydrate 10 Å instable de kaolinite

The treatment of KGa-1 kaolinite with dimethyl sulfoxide and ammonium fluoride heated at 383 K provides an unstable hydrated phase characterized by a 10 A basal distance. When air-dried, this hydrate gives a dehydrated phase at 7.15 A. The aim of this work is to determine the structural characteristics of this hydrate. The method used to characterize this hydrate is based on the comparison between experimental and calculated X-ray diffraction profiles. This study is achieved in two steps: the study of 00l reflections enabled the determination of the number of intercalated water molecules, their positions and the stacking mode along the normal to the (a, b) plane; and the study of the hkl reflections with h and/or k ≠ 0 enabled the determination of the stacking mode and the positions of water molecules in the (a, b) plane. The unstable hydrate is characterized by two water molecules per Al2Si2O5(OH)4 unit situated at z1 = z2 = 7.57 A. Two adjacent layers are translated with respect to each other with TI = −0.155a + 0.13b + 10n.

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.