The Kaolinite Group

Due to the TO structure of the clay, the interlayer H-bonding is very strong. This hinders the intercalation of any molecule or chain into the gallery. Hence, the kaolinite clay cannot be used for nanocomposite preparation. 

FIGURE 2.1 The layered structure of kaolinite clay. (From http /jan.ucc.nau.edu/doetqp/courses/env440/ env440 2/lectures/lecl9/Figl9 3.gif, access date 4.11.06.) 

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An ONIOM study of the adsorption of Sarin on dickite (a 1 1 dioctahedral clay mineral of the kaolinite group)85 was recently published. For the calculations of the studied systems, the two-layered ONIOM method using combinations of quantum-mechanical methods was applied.43,86,87 The investigated systems of... 

The different classes of clay minerals, namely, 1/1,2/1, and so on, have a differenf arrangemenf of tetrahedral and octahedral layers. Structural units of clays, fherefore, consist of either (1) alternating tetrahedral sheets (OT or 1/1 structure e.g., the kaolinite group) (2) a sandwich of one ocfahedral sheet between two tetrahedral sheets (TOT or 2/1 structure e.g., smectite clay minerals, of which fhe mosf common member is monf moril-lonite) or (3) an arrangement in which three TOT units alternate with a brucite layer (2/1/1 structure e.g., chlorite). 

The phyllosilicates in soil clays can be classified into three layer types, distinguished by the numbers of tetrahedral and octahedral sheets combined, and five groups, differentiated by the kinds of isomorphic cation substitutions that occur. The layer types are shown in Fig. 1.3, and the groups are described in Table 1.3. The 1 1 layer type consists of one tetrahedral and one octahedral sheet. In soil clays, it is represented by the kaolinite group, with the unit cell chemical formula [Si4](Al4)Oio(OH)8, where the cation enclosed in brackets is in tetrahedral coordination and that enclosed in parentheses is in octahedral coordination. Normally there is no significant isomorphic substitution for Si(IV) or Al(III) in this group, and, as is common with soil clay minerals, the octahedral sheet has two thirds of its cation sites occupied (dioctahedral phyllosilicate). 

Deeds CT, van Ohphen H, Bradley, WE (1966) Intersalation and Interlayer Hydration of Minerals of the Kaolinite Group. In Proceedings of the Int Clay Conf Pergamon Press Part 2 p 183... 

These minerals are hydrated aluminosilicates which are characterized by a sheetlike structure and can be conveniently divided into three groups (1) the kaolinite group, (2) the mont-morillonite group, and (3) the potash clay (or hydrous mica) group (Table 7.7). In the kaolinite group, all have the same chemical composition and differ only in individual crystal structures. The montmorillonite group can be represented by means of ion substitutions in the general chemical formula. For example, in montmorillonite itself, approximately 16% of the aluminum... 

Two works were devoted to the ab initio cluster calculations of the interactions between minerals of the kaolinite group with thymine (TH) and uracil (U). The key purpose of such studies was to determine (i) the equilibrium adsorption of selected nucleic acids, differing in chemical, molecular structure and functions (DNA, RNA) on specific clay mineral surfaces and (ii) the nature of the interaction between nucleic acids and clay using computational chemistry methods and modeling. An additional objective was to assess the effect of presence of water and sodium cation commonly occurring in soils on the process of adsorption. 

Interactions of Thymine and Uracil with Hydrated Surface of Minerals of the Kaolinite Group... 

Metahalloysite. A clay mineral of the kaolinite group and of the same approximate composition as kaolinite -Al2O3.2SiO2.2H2O. It is formed by the partial dehydration of halloysite (q.v.). 

Nacrite. Al2O3.2SiO2.2H2O. A rare, exceptionally well crystallized, clay mineral of the kaolinite group. 

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