Molecular orientation of methylene blue cations adsorbed on clay surfaces

Abstract

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.

Structural characterization of hexadecyltrimethylammonium-smectite composites and their potentiometric electrode applications

“…The CEC value of Na-S was determined as 79 mequiv./100 g clay by methylene blue adsorption techniques [73]. This method is complicated by the dimerization of methylene blue when the concentration exceeds about 7 × 10 −6 mol L −1 [74][75][76]. The present experiments were conducted at lower concentration than this limit value in only the presence of monomers.…”

Mechanism of methylene blue removal from water by swelling clays

“…The plane of the dye heteroaromatic system was not arranged in a parallel fashion as assumed in earlier studies [14], but rather in a tilted or perpendicular fashion [30]. Although the dye molecular plane is perpendicular with respect to the clay surface plane, the longest axis of a MB cation may remain rather parallel or tilted at low angles with respect to the clay surface plane [41].…”

Spectral properties of tetraanionic porphyrin in formamide colloids of layered double hydroxides

“…A similar feature was observed for the systems based on cationic dyes and layered materials with negative charge. The H-aggregates of methylene blue (MB) were formed in colloidal dispersions of various clay minerals [15], whereby the molecular aggregation in solid films based on the same components was limited to the small amounts of H-type dimers [21].…”