Modeling of experimental X-ray diffraction (XRD) patterns represents the optimum approach to the structure determination of mixed-layer structures (MLSs) that are commonly found in natural clay-rich samples. This approach allows for a detailed structural characterization of both pure and mixed-layer clay phases and for a semi-quantitative phase analysis in complex mixtures. The two informations are essential to gain new insight into the actual nature of reactions taking place in geological environments. Significant new findings obtained at different scales (from that of the particle to that of the elementary layer) on the actual structure of MLSs by modeling XRD profiles are reported.

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The advent of modern transmission electron microscopes has revolutionized the classic field of clay mineralogy. Its application to the study of dioctahedral phyllosilicates, illite-smectite in particular, in the past two decades has contributed much of our understanding of the crystal chemical relations and the smectite to illite reaction mechanisms. These contributions are summarized in the following five areas. first, there are only 3 discrete clay minerals in a prograde sequence from smectite to regularly interstratified R1 I-S to illite with increasing diagenetic/metamorphic grade. These observations are in contrast to the conventionally accepted continuous sequence as determined by X-ray diffraction. Reasons for such a contrast are discussed. Second, the 1M polytype is not an intermediate between 1M_d for smectite-rich I-S and 2M₁ for mature illite of diagenetic/metamorphic grade. Rather, the 1M polytype has a different composition than either 1M_d or 2M₁, i.e., it is Mg rich as compared to 1M_d or 2M₁ polytypes. Third, smectite, interstratified I-S, and illite may form from fluids at the same time over a temperature (depth)-composition gradient, without one being necessarily preceded by another. Fourth, the smectite to illite reaction mechanism is via dissolution of reactants, transport of dissolved chemical ions, and crystallization of products. Different mechanisms, such as layer-by-layer replacement (or sometimes called solid-state transformation), may be different variations of the same mechanism, e.g., the layer-by-layer replacement mechanism may operate at the atomic scale, whereas dissolution-crystallization may be over dimensions of pore space or greater. finally, TEM data have made important contributions in providing evidence that are inconsistent with the fundamental particle theory, suggesting that natural, interstratified I-S sequences are not accumulations of fundamental particles.

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Illite-smectite (I-S) mixed-layer minerals (MLMs) are ubiquitous in low-temperature geological environments: weathering, diagenesis, low-grade metamorphism, hydrothermal alteration, and even contact metamorphism. We have studied I-S MLMs in hydrothermally altered volcanic rocks at Kakkonda, and the integration of the results provides a clue to longstanding controversy about the crystal chemical nature of the component layers, the formation mechanism, and the controlling factors. The Kakkonda I-S MLMs consist of basically the two component layers with few vermiculite layers. Changes in the I/5 ratio and the Reichweite (R) parameter occur with a continuous manner as a function of temperature from 150-200°C. The actual stacking of layers in each I-S crystallite is represented by stacking of Mn sub-units rather than individual I and S layers, where Mn denotes a sub-unit that is composed of central illitic interlayers with the number of n sandwiched by two half smectitic interlayers at the outermost surface. The number of n increases with temperature in turn from n=0 for pure smectite, n=1 for R1 I-S, to n>2 for R3 I-S. According to the present model, the formation of I-S resulted from the precipitation of various types of Mn without the precursor smectite, and it is neither the layer-by-layer transformation nor the dissolution-crystallization. The chemistry of reacting fl uid affected the composition of product I-S and resultantly the formation temperature under the conditions of constant composition of precursor rocks and constant water/rock ratio.

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This article describes the nematic-like orientational order of exfoliated platelets in concentrated smectite clay gels. At concentrations larger than a few percent (w/w), clay gels are strongly birefringent, which is usually associated with nematic liquid-crystalline ordering. This means that the clay platelets tend to align parallel to each other in a cooperative way. Indeed, very oriented samples can easily be prepared and their SAXS patterns are strongly anisotropic, resulting in nematic order parameters of S-0.55 quite comparable to those of common organic liquid crystals used for display applications. Even though the sol/gel transition occurs at concentrations lower than the isotropic/nematic one, nematic ordering appears in concentrated clay gels and it must be considered in most practical situations.

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Unilamellar two-dimensional crystallites of transition metal oxides, T1_0.910₂, Ca₂Nb₃O₁₀ and Mn0₂, have been derived by delaminating layered host precursors via intercalation of quaternary ammonium ions. The nanosheets are characterized by their high two-dimensional anisotropy with a molecular thickness, and this structural feature yields novel physicochemical properties. A range of useful nanostructured materials can be fabricated by organizing these nanosheets as a building block through various wet processes. Flocculation induced by the addition of appropriate cationic species can produce restacked lamellar aggregates, through which functional materials, e.g. porous or fluorescent materials, can be designed by the selection of the nanosheets and combined flocculating agents. The sequential adsorption procedure via electrostatic self-assembly can be employed to deposit the nanosheets layer-by-layer with polycations, which can lead to multilayer ultrathin films and hollow nanospheres.

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The adsorption properties of clay particles in aqueous suspension can be characterized by UV/Vis absorption and fluorescence spectroscopies of dyes adsorbed on the clay surfaces. Rhodamine laser dyes are adequate molecular probes for this purpose since their photophysical properties depend on several factors such as the molecular structure, the dye aggregation, the polarity and acidity of the environment, H-bonding interactions, etc. The displacement of the absorption and/or fluorescence bands of the rhodamine monomer adsorbed at clay surfaces can give information about the polarity and acidity of both the interlayer space and the water/clay interface. These physicochemical properties can be correlated with the type and extent of the isomorphic substitution of the clay. Furthermore, monomers, dimers and higher-order aggregates of rhodamines can be spectroscopically identified in both external surface and the interlayer space of smectite-type clays in aqueous suspensions. The presence or predominance of these species is governed by the relative dye/clay concentration, the aging of the samples, the hydrophobic character of the dye, the nature of the clay, etc. The evolution of these species with the aging time can be used not only to characterize the clay surfaces but also to analyze dynamic aspects of the adsorption mechanisms.

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This paper reports on the modifications of the interlamellar surfaces of kaolinite by the direct grafting of two difierent alditols, namely, D-mannitol and dulcitol, from the melt. Several starting materials were used among which the kaolinite-DMSO intercalate was the most efiective. The results of the XRD, FTIR and TGA analyses confirmed the grafting of the polyol molecules on the aluminol surface of kaolinite. ¹³C CP and DD/MAS spectra indicated the complete displacement of the guest molecules of the starting materials by the polyols and the rigidity of the latter in the interlamellar space. ²⁹Si and ²⁷M NMR spectra of the starting materials and the products are also discussed. It is plausible that oligomeric forms of the alditols are grafted on the aluminol surfaces of kaolinite at more than one point, in a bridging manner.

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Protonated 11-cis retinal Schiff base (RSB) is a chromophore molecule in our visual rhodopsins. Protonated RSB of the all-trans form is a chromophore of bacterial rhodopsins thatact for bacterial ion-pump or light-sensor. It is well known that rhodopsins are excellent light-sensor molecules in terms of (i) color tuning, (ii) photoisomerization, and (iii) functional expression. Protein environment of rhodopsins regulates visible absorption of a unique chromophore, so that we can distinguish so many colors. Photoisomerization of the rhodopsin chromophore is highly selective and efficient, which causes the molecular basis of high sensitivity of our vision. In fact, our ultrafast spectroscopy revealed that photoisomerization is an event occurring in femtoseconds. Photoisomerization in protein also takes place even at 77 K, where the environment of the chromophore is freezed. Relaxation of the photoisomerized chromophore leads tc various functional expressions of rhodopsins, such as visual excitation, bacterial phototaxis, and ion-pumping to create biological energy. Thus, rhodopsins are the goal for artificial light-sensors.
Although it has been difficult to mimic the properties of rhodopsins in other materials, it was found that clay acts as a novel model matrix to mimic visible absorption spectra of protonated RSB in rhodopsins. Montmorillonite (MONT) interlayers were modified by dimethyloctadecylamine (DOA) in benzene solution, and the appearance of a large spectral red shift (λ_mas at 530 nm) indicated that RSB was successfully intercalated into these layers. Absorption spectra of RSB at> 500 nm have been achieved only in the system other than in proteins. A proton is probably supplied from DOA to RSB, forming a protonated RSB in clay. We also found that illumination of RSB in clay at 77 K results in formation of a bathochromic product, which is reverted to the original state by light in a manner similar to what is observed in rhodopsins. Infrared spectral changes suggested that RSB is protonated in clay, and that trans-cis isomerization occurs at 77 K The clay interlayer thus works to not only regulate color, but also to mimic the primary photochemical reaction of RSB in rhodopsins.

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Nanohybridization of various biomolecules with layered double hydroxides and hydroxy double salts has been explored for the advanced applications, especially, safe and controlled delivery of pharmaceutical, cosmetic, and agrochemical ingredients. This review deals with LDH and HDS nanohybrids for cosmetic applications along with a brief introduction of their pharmaceutical applications. LDH and HDS nanohybrids have been synthesized by coprecipitation and ion exchange routes those which lead to stabilization of the biomolecules within the interlayer space of those lamellar materials. The intercalated biomolecules are released mainly by ion-exchange and difffusion-facilitated processes. Bioactivities of the nanohybrids are remarkably improved compared to those of the free biomolecules. This review strongly supports that nanohybridization of biomolecules with layered metal hydroxides leads to the enhanced efficiency as well as the protected and release-controlled delivery of various biomolecules, especially unstable ones.

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High-resolution in-situ X-ray reflectivity measurements were used to characterize the sorption of K, Cs, Ca, and Ba from chloride solutions, Zn from chloride, nitrate, and trifluorosulfonate (triflate) solutions, and fulvic acid in the presence and absence of BaC1₂ onto the basal surface of muscovite. X-ray reflectivity data were collected through the specular reflection condition and converted to electron density profiles perpendicular to the interface by applying atomistic structural models that included surface relaxation, sorbate concentration and position, water structure, and surface roughness. Interpretations of the electron density profiles indicated that cations were attached to the basal surface dominantly in the first and second adsorbed layers, anions did not cosorb in large amounts with divalent cations, and fulvic acid sorbed as approximately 8-Å thick layers. All derived profiles imply that no separate water layer exists between the sorbates and mineral surface. Water layering above the sorbed cation layers and minimal relaxation of the bulk muscovite were observed.

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The natural speciation of Mn (0.19g/kg), Ni (46mg/kg) and Zn (42mg/kg) in the clayey horizon (120cm depth, pH=5.6) of a paddy soil in northern Taiwan was studied by X-ray microfluorescence, microdiffraction, and micro and polarized EXAFS spectroscopy. In Mn-rich aggregates and mottles, Ni and Zn are taken up by lithiophorite, but by a different structural mechanism: Ni (r=0.70 Å) substitutes for Mn (r (Mn⁴⁺)=0.54 Å, r (Mn³⁺)=0.65 Å) in the manganese layer, whereas Zn (r=0.74 Å) fills vacant sites in the gibbsitic layer, similarly to lithium (r=0.74 Å). In contrast with nickel, which is detected only where there is lithiophorite, the Zn-lithiophorite association observed in Mn-rich areas of the soil matrix is not representative of the bulk soil. Powder and polarized EXAFS spectroscopy, complemented by X-ray diffraction, revealed that Zn is predominantly bound to hydroxy-Al interlayers sandwiched between 2: 1 vermiculite layers in the fine soil matrix. The incorporation of Zn in the gibbsitic layer of both lithiophorite and vermiculite increases the stability of these minerals by providing positive charge to balance the negative charge from the 2: 1 phyllosilicate layer and the manganese layer of lithiophorite. This binding environment for zinc is probably the dominant mechanism by which zinc is sequestered in acidic to near-neutral aluminium-rich clayey soils.

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In this paper we present our recent results with respect to the crystal structures of two trioctahedral sodium micas, aspidolite and wonesite, and discuss the nature of the interlayer structure in sodium micas. High-resolution transmission electron microscopy (HRTEM) and electron diffraction analyses of these micas indicate the existence of a large layer offset, i.e., lateral shift between the two tetrahedral sheets across the sodium-bearing interlayer region. The amounts of the layer offset are about 0.9Å(aspidolite) and 1.25 Å(wonesite), and their direction is one of [100], [110] and [110]. These directions are occasionally disordered. By combination of the intralayer shift in the 2: 1 layer and the layer offset, ordered aspidolite has monoclinic ([100] layer offset, C2/m) and triclinic ([110] or [110] layer offset, C1) cells with one-layer periodicity. Both structures were identified in powder X-ray diffraction patterns and probably the triclinic structure is more common. This is the first report that structural variations are generated in micas by the combination of the intralayer shift and layer offset. The layer offset in wonesite is close to [110] and the structure is one-layer triclinic (C1).
These results give us an insight that sodium micas (preiswerkite, paragonite, aspidolite, wonesite, etc.) can possess various amounts of the layer offset, depending on the cavity space in the tetrahedral sheet that is primarily determined by the ditrigonal rotation angle. Therefore the composition in the 2: 1 layer can drastically change the crystallography (e.g., powder diffraction patterns) of the sodium micas. In conclusion, sodium micas are not the simple analogue of potassium micas but belong to a group with a very unique character.

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The interactions of clay minerals with humic substances and synthetic organic polymers have beeninvestigated for more than five decades. More recently, the focus of attention hasshifted to the synthesis and development of clay-polymer ‘nanocomposites’. Since the nanometer-thick silicatelayers are more or less uniformly dispersed in the polymer matrix, these novel hybrid materials display superior mechanical, optical, thermal, andgas barrierproperties. Here we utline the principles and practice of the clay-humic and clay-polymer interaction, with particular reference to work done in our laboratory. Because of space limitations only the important findings and concl usions will be presented. As far as is possible, we will also refer to key papers and reviews, rather than citeindi vidual authors.

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Epoxy/Clay nanocomposites have been prepared by exfoliating the modified clays, which are intercalated with the amine functional group, in an epoxy resin. Exfoliation of the clay within the cross-linked epoxy matrix was verified by using X-ray diffraction and transmission electron microscopy. The Epoxy/Clay nanocomposites are applied to prepare epoxy copper-clad laminar, relatively higher thermal stability, lower coefficient of thermal expansion, and water absorption were observed when they compared with FR-4 laminar without clay existed.

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Excellent properties of organic polymer/clay minelal hybrids, such as mechanical property, gas barrier effect and anti-flamability, have attracted many attentions. This paper reviewed the preparation of the hybrid materials and their properties, from view points of a driving force for swelling, structure in nanometer scale and organic-inorganic interactions. The swelling, exfoliate and dispersing behaviour were understand by an balance of an interlayer attractive forces to the interaction between guest molecule and host layers, polymerization energy and mechanical energy. The properties of the composites are attributable to the hybrid structure around the silicate layers within the nanometer distance. A weak hydrophobic interaction in nanometer scale should be studied to develop the nano-hybrid materials.

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