Simulation-assisted evidence for the existence of two stable kaolinite/potassium acetate intercalate complexes

Communication: Molecular simulation study of kaolinite intercalation with realistic layer size

Intercalation phenomena of kaolinite in aqueous potassium acetate and in hexyl-amine solutions are studied by large scale molecular dynamics simulations. The simulated kaolinite particle is constructed from ~6.5 × 10(6) atoms, producing a particle size of ~100 nm × 100 nm × 10 nm. The simulation with potassium acetate results in a stable kaolinite-potassium acetate complex, with a basal spacing that is in close agreement with experimental data. The simulation with hexyl-amine shows signs of the experimentally observed delamination of kaolinite (the initial phase of the formation of nanoscrolls from the external layers).

Characterization of kaolinite-ammonium acetate complexes prepared by one-step homogenization method

Although kaolinite-ammonium acetate complexes are of interest in the area of kaolinite nanocomposites, the structures of these complexes have remained largely elusive. Experimental and molecular simulation analysis is used to investigate their structures, revealing that two types of water-containing kaolinite-ammonium acetate complex exist. A cost-efficient one-step homogenization method was used to synthesize these complexes. The effect of the aging time and the amount of reagents on the intercalation were characterized experimentally by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The optimal degree of intercalation was obtained by using two orders of magnitude lower amount of reagents than in the case of the solution method. It was found that the so far less investigated 1.7-nm complex has higher water content than the 1.4-nm one. For both complexes, our molecular simulations predict the double-layered structure of the acetate ions, which is usually assumed in the case of the kaolinite-acetate complexes. For the 1.7-nm complex, however, a quasi-triple-layered structure of water molecules instead of the double-layered one was calculated.

Water-mediated potassium acetate intercalation in kaolinite as revealed by molecular simulation

Molecular simulations are suitable tools to study the adsorption and intercalation of molecules in clays. In this work, a recently proposed thermodynamically consistent force field for inorganic compounds (INTERFACE, Heinz H, Lin TJ, Mishra RK, Emami FS (2013) Langmuir 29:1754-1765), which enables accurate simulations of inorganic-organic interfaces, was tested for a two-sheet type clay mineral. All-atom NpT molecular dynamics simulations were used to describe the characteristics (basal spacing, loading, molecular orientation) of some intercalate complexes of kaolinite with potassium acetate and the results were compared with the available experimental data. The most probable structural configurations of the kaolinite/potassium acetate intercalate complexes were determined from the simulations. Our examinations confirmed some supposed (single- or double-layered) arrangements of guest molecules. The need of interlayer water in the intercalate complex, which can be produced by the basic synthesis procedure in air atmosphere, was verified.