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Kaolin-group clay minerals can be modified to form nanotubular and mesoporous structures with interesting catalytic properties, but knowledge of the best methods for preparing these structures is still incomplete. The objective of this study was to investigate intercalation/deintercalation as a method for the delamination and rolling of kaolinite layers in relation to structural order. To prepare nanotubular material, kaolinites of different crystallinities and halloysite (all from Polish deposits) were chosen. The experimental procedure consisted of four stages: (1) preparation of a dimethyl sulfoxide precursor intercalate; (2) interlayer grafting with 1,3-butanediol; (3) hexylamine intercalation; and (4) deintercalation of amine-intercalated minerals using toluene as the solvent. Structural perturbations and changes in the morphology of the minerals were examined by X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and transmission electron microscopy (TEM). The number of rolled kaolinite layers depended heavily on the efficiency of the intercalation steps. An increase in the structural disorder and extensive delamination of the minerals subjected to chemical treatment were recorded. Kaolinite particles which exhibited tubular morphology or showed rolling effects were observed using TEM. The nanotubes formed were ∼30 nm in diameter, with their length depending on the particle sizes of the minerals.

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Cu-doped Al-, Ti-, and Zr-pillared montmorillonites obtained by various procedures have been investigated with the aid of electron spin resonance (ESR). The major species present in pillared montmorillonites exchanged with copper at low pH are physisorbed square planar tetraaquo-complexes [Cu(H2O)4]2+. Only at the surface of uncalcined Al pillars does a chemisorption of copper ions occur, giving an inner-sphere square planar complex [Cu(AlO) n (H2O)4- n] x. Calcination of the samples at 673 K brings about a significant change of the Cu2+ ion environment reflected in the change of ESR parameters. The most characteristic feature is the increased covalency of the Cu–O in-plane σ bonding due to the attachment of copper to lattice oxygens. The spectra show that cupric ions form links with the pillars rather than with the silicate sheet. In the case of Al- and Ti-pillared samples, copper species of different degrees of σ in-plane covalency are obtained depending on the preparative procedure. Catalytic tests with hydroxylation of phenol demonstrate that copper centers of higher covalency show superior catalytic performance. This effect is interpreted in terms of the higher in-plane σ covalency facilitating electron transfer between the donor and the acceptor sites at the catalyst surface. The ESR spectra of almost all copper-exchanged samples show, besides the isolated Cu2+ ions, a component due to the exchange-coupled clustered cupric ions.