Visible Spectroscopy of Methylene Blue on Hectorite, Laponite B, and Barasym in Aqueous Suspension

The absorption spectra of methylene blue ion exchanged on hectorite, Laponite B, Barasym, or sepiolite in dilute aqueous suspensions show the presence of the monomer, the protonated monomer, the dimer, and the trimer. Due to conformational differences, the absorption band maximum of the monomer with respect to its maximum in aqueous solution is red shifted when it is adsorbed on the external surface and blue shifted when it is adsorbed on the interlamellar surface. The availability of the interlamellar surface for methylene blue as a function of the type of clay and/or the counterion present thereby can be probed. The results indicate that 0.6–0.7% of the cation-exchange capacity of Barasym consists of acid sites capable of protonating methylene blue. Counterions of low hydration energy were found to induce a small number of similar sites in hectorite and Laponite B; hence, these sites must be situated on the external surface. Dimers formed on external surfaces show one absorption band. Dimers formed on the interlamellar surface of hectorite yield spectra having two absorption bands. The trimer was formed only at the external surface. With increasing loading of the clays, the spectra of methylene blue showed metachromasy. The metachromatic behavior can be fully explained by dye aggregation, which is the result of its concentration on the surface. No π-electron interaction with the surface oxygens need be invoked.

[1]  G. Lewis,et al.  Methylene Blue and Other Indicators in General Acids. The Acidity Function , 1943 .

[2]  S. Yariv,et al.  Metachromasy in Clay Minerals. Part I. Sorption of Methylene‐Blue by Montmorillonite , 1971 .

[3]  C. T. O'konski,et al.  A SPECTROSCOPIC STUDY OF METHYLENE BLUE MONOMER, DIMER, AND COMPLEXES WITH MONTMORILLONITE , 1963 .

[4]  I. B. Berlman.  Empirical correlation between nuclear conformation and certain fluorescence and absorption characteristics of aromatic compounds , 1970 .

[5]  D. Avnir,et al.  Adsorption characteristics of rhodamine 6G on montmorillonite and laponite, elucidated from electronic absorption and emission spectra , 1984 .

[6]  J. K. Thomas.  The chemistry of excitation at interfaces , 1984 .

[7]  Pham Till Hang,et al.  Methylene Blue Absorption by Clay Minerals. Determination of Surface Areas and Cation Exchange Capacities (Clay-Organic Studies XVIII) , 1970 .

[8]  William W. West,et al.  The Dimeric State of Cyanine Dyes , 1965 .

[9]  R. Schoonheydt,et al.  Spectroscopic Study of the Surface Chemistry of Proflavine on Clay Minerals , 1987 .

[10]  W. T. Granquist,et al.  Catalysis by layer lattice silicates. I. The structure and thermal modification of a synthetic ammonium dioctahedral clay , 1972 .

[11]  J. Murrell.  The theory of the electronic spectra of organic molecules , 1963 .

[12]  R. Schoonheydt,et al.  Spectroscopy of proflavine adsorbed on clays , 1986 .

[13]  A. Maes,et al.  Heterogeneity of Charge Density Distribution in Montmorillonite as Inferred from Cobalt Adsorption , 1975 .

[14]  A. Álvarez.  Sepiolite: Properties and Uses , 1984 .

[15]  R. Schoonheydt,et al.  Study of the adsorption on clay particles by means of a fluorescent probe , 1987 .

[16]  V. Cofman.  Biophysical chemistry. Part II , 1929 .

[17]  G. Kortuem,et al.  Reflectance Spectroscopy: Principles, Methods, Applications , 1969 .

[18]  J. Ramsay,et al.  Colloidal properties of synthetic hectorite clay dispersions: I. Rheology , 1986 .

[19]  P. Levitz,et al.  Interaction of water with clay surfaces , 1984, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[20]  E. Braswell.  Evidence for trimerization in aqueous solutions of methylene blue , 1968 .

[21]  J. K. Thomas.  Characterization of surfaces by excited states , 1987 .

[22]  S. L. Fornili,et al.  Solvent isotope effect in the monomer–dimer equilibrium of methylene blue , 1981 .

[23]  P. Hang.  Methylene Blue Adsorption by Clay Minerals, Determination of Surface Areas and Cation Exchange Capacities , 1970 .

[24]  J. Serratosa,et al.  Reactions of clays with organic substances. , 1987 .

[25]  M. Schubert,et al.  A Qualitative Theory of Metachromasy in Solution1 , 1955 .

[26]  L. Michaelis,et al.  Metachromasy of Basic Dyestuffs , 1945 .

[27]  J. Uytterhoeven,et al.  Spectroscopy of bis(ethylenediamine)copper(2+) on clay surfaces. Surface and charge-density effects , 1980 .

[28]  S. Yariv,et al.  Metachromasy in clay minerals. Sorption of acridine orange by montmorillonite , 1984 .

[29]  R. Schoonheydt,et al.  Luminescence of tris(2,2'-bipyridine)ruthenium(II) in aqueous clay minerals suspensions , 1984 .

[30]  M. Nakagaki,et al.  The Location and Microenvironment of Dimerizing Cationic Dyes in Lipid Membranes as Studied by Means of Their Absorption Spectra , 1983 .