Novel Methodology To Control the Adsorption Structure of Cationic Porphyrins on the Clay Surface Using the “Size-Matching Rule”

Saponite-type clays that have different cation exchange capacities were successfully synthesized by hydrothermal synthesis. The structure and properties were analyzed by X-ray diffraction, X-ray fluorescence, 27Al NMR, FT-IR, thermogravimetric and differential thermal analysis, atomic force microscopy, and cation exchange capacity measurement. The intercharge distances on the synthetic saponite (SS) surfaces were calculated to be 0.8–1.9 nm on the basis of a hexagonal array. The complex formation behavior between SS and cationic porphyrins was examined. It turns out that the average intermolecular distance between porphyrin molecules on the SS surface can be controlled, depending on the charge density of the SS. In the case of tetrakis(1-methylpyridinium-4-yl)porphyrin (H2TMPyP4+), the average intermolecular distances on the SS surface can be controlled from 2.3 to 3.0 nm on the basis of a hexagonal array. It was also found that absorption maxima of porphyrins depend on the charge density of the SS. The a...