Adsorption and interactions of methyl green with montmorillonite and sepiolite
The divalent organic cation, methyl green (MG), undergoes a slow transformation (6 h) to a monovalent cation, carbinol (MGOH{sup +}) upon dilution of its solution (10 mM), or in a buffer at neutral pH. Adsorption isotherms of MG on montmorillonite were determined by two procedures, both of which yield a final pH of suspensions between 7 to 7.4. When the amounts of MG in suspension were lower than the cation-exchange capacity (CEC) of the clay (0.8 mol{sub c}/kg clay), no measurable amount of MG remained in solution. The maximal amounts of MGOH{sup +} adsorbed were larger than those of MG{sup 2+}, being 1.15 and 0.75 mol MG/kg clay, respectively, corresponding to 140% of the CEC in the first case. Adsorption of MG on sepiolite (CEC = 0.15 mol{sub c}/kg) further emphasizes the two patterns of its adsorption. The maximal adsorbed amounts of MG{sup 2+} and MGOH{sup +} were 0.09 and 0.30 mol/kg clay, respectively. X-ray diffraction measurements gave lower values for the basal spacings for montmorillonite-MG{sup +} than for MGOH{sup +}, suggesting that MG{sup 2+} binds two clay platelets together, as in the case of other divalent cations. A competition for adsorption between MG and the monovalent organic cation, acriflavin (AF), gave lower adsorbed amounts of AF when competing with MG{sup +}, which is interpreted to be due to the smaller basal spacing in this case, which partially inhibits the entry of AF molecules into the interlammelar space. Spectra of montmorillonite-MG particles in the visible range exhibited significant differences between clay-MG and clay-carbinol.
- Research Organization:
- Hebrew Univ. of Jerusalem, Rehovot (IL)
- OSTI ID:
- 20017489
- Journal Information:
- Journal of Colloid and Interface Science, Vol. 222, Issue 1; Other Information: PBD: 1 Feb 2000; ISSN 0021-9797
- Country of Publication:
- United States
- Language:
- English
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