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Molecular orientation of methylene blue cations adsorbed on clay surfaces

J. BUJDÁK^1,*,, N. IYI¹, Y. KANEKO¹ and R. SASAI²

¹ National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, and ² Research Center for Advanced Waste and Emission Management (ResCWE), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan

^* E-mail: uachjuro{at}savba.sk

(Received 2 February 2003; revised 30 July 2003)

Cationic dye, methylene blue (MB), was intercalated into films of expandable clay minerals with low, moderate and high layer charges (saponite, montmorillonite and synthetic expandable mica-fluorohectorite, respectively) . Tilted orientation of the dye cations on the silicate surface was observed by polarized ultraviolet-visible (UV-Vis) transmission spectroscopy. The tilting angle of the dye cations increased with the formation of high-order H-aggregates that absorb light at 525 nm. These dye species were formed only on the surface of fluorohectorite, which has the highest layer charge, and exhibited dichroism. Models for the orientation of MB cations on a clay surface were proposed based on MB orientation models previously reported, and compared with the basal spacings determined by X-ray diffraction.

KEYWORDS: clay mineral, H-aggregates, methylene blue, molecular aggregation, molecular orientation, polarized spectroscopy