Organic-inorganic hybrid layer-by-layer electrostatic self-assembled film of cationic dye Methylene Blue and a clay mineral: Spectroscopic and Atomic Force microscopic investigations

Abstract

The metachromic cationic dye Methylene Blue (MB) belongs to the thiazine class of organic dye. This dye cation can interact electrostatically with inorganic clay mineral Montmorillonite (MMT) to form organic-inorganic hybrid layer-by-layer (LbL) self-assembled film onto a poly(allylamine hydrochloride) coated quartz substrate. The degree of dye aggregations in LbL films was found to depend on concentrations of both MMT clay and MB in LbL self-assembled films as evidenced by UV–vis absorption spectroscopic technique. The adsorption of dye molecules to the LbL films was found to a two-step exponential process: first step was very fast and the later process had a much delay period. Also the assembling behavior and organizations of MB molecules in the host clay matrix in LbL films significantly depend on pH of dye solution from which LbL film was fabricated. For MMT/MB mixed solution the π-π* transition of absorption bands of MB shifted to lower wavelength due to the formation of large number of H-aggregates in their mixed aqueous solution. Fourier Transform infrared (in ATR mode) spectroscopic method was employed to explore the electrostatic interaction between clay MMT and MB in LbL films. Atomic Force microscopic image of hybrid LbL films revealed the surface morphology and roughness profile of the organic-inorganic hybrid molecular assemblies onto the solid substrate.