Methylene Blue Interactions with Reduced-Charge Smectites

Abstract

Abstract--The objective of this work was to prepare series of reduced-charge materials from different parent Li-saturated dioctahedral smectites, to investigate the effects of temperature, chemical composition and charge location in smectites on the charge reduction and to characterize reduced-charge smectites (RCSs) using methylene blue (MB) adsorption. The layer charge decrease, induced by Li fixation, is correlated with the trends in the spectra of MB-RCS dispersions in the visible region (VIS) spectra. Distribution of the negative surface charge of the clay minerals controls the distance between the adsorbed MB cations and thus affects the formation of MB dimers and higher agglomerates. Because each form of MB (monomer, dimer, higher agglomerate, J-aggregates) absorbs light at a different wavelength, the VIS spectra of MB depend sensitively on the charge density at the clay surface. Both cation exchange capacity (CEC) values and spectra of MB-clay dispersions clearly detect extensive reduction of the layercharge density in reduced-charge montmorillonites (RCMs) upon Li-thermal treatment. The extent of charge reduction depends on the temperature of the thermal treatment, as well as on the octahedral charge of the montmorillonite. Reduction of the layer charge proceeds to a much lesser extent for smectites with mainly tetrahedral charge and high Fe content (Fe-rich beidellite and ferruginous smectite). Both CEC data and MB spectra detect only a slight decrease of the layer charge density, which relates to the low octahedral charge of these minerals. Following heating at higher temperatures (120-160~ slightly higher Li fixation is indicated by CEC values; however, no charge reduction is confirmed by MB spectra. Release of protons accompanying Li + fixation in Fe-rich smectites heated at 180 or 200~ was detected in the spectra of MB-clay dispersions and confirmed by potentiometric titrations.

Interaction of montmorillonite with phenothiazine dyes and pyronin in aqueous dispersions: A visible spectroscopy study

“…2a. The basic trends in the MB spectra for colloids of RCMs and the changes of the spectra with time are in agreement with the results obtained with similar reaction systems, which have been studied previously [10,11,13,19]. The spectral changes with layer charge are in accordance with the theory of layer charge influence on the MB molecular aggregation [11].…”

“…If the layer charge density of clay minerals is sufficiently high, the distances between neighbouring adsorbed dye cations are smaller and H-aggregates are preferentially formed. Less densely packed J-aggregates resulting from a head-to-tail coupling [12] occur less frequently under specific conditions on the surfaces of clay minerals of medium to low charge densities [13].…”

“…Due to the sensitivity of methylene blue (MB) aggregation to layer charge density of clay minerals, MB has been studied in numerous works where it has served as a sensitive probe for fast qualitative characterisation of layer charge distribution of smectites [5,11,13,14]. Besides MB, there are several structurally similar cationic dyes, which exhibit metachromatic behaviour, which has not been described for dye/clay mineral system yet.…”

Effect of pH Solution on the Optical Properties of Cationic Dyes in Dye/Maghnia Montmorillonite Suspensions

“…At high alkaline medium (pH>9) the colorless carbinol base is formed. Such an effect was observed for the similar malachite green [20], methyl green [21], and crystal violet [22].…”

Fluorescence tuning of 2D montmorillonite optically active layers with beta-cyclodextrine/dye supramolecular complexes

“…Clearly, the adsorption of organic cationic species is an experimentally straightforward task (Janek and Lagaly, 2003;Bujdák and Iyi, 2008). Nevertheless, the high local charge density distribution, including domain areas existing on the clay mineral surface, is the greatest obstacle to control formation of desired dye aggregates for 2D surface functionalization (Lagaly and Weiss, 1975;Ogawa et al, 1996;Janek et al, 1997;Bujdák et al, 2001). One of the ways to overcome this obstacle was proposed by Takagi et al (2013) called size matching approach using synthetic layered silicates with defined negative layer charge density and using dye molecules having defined inter-molecular distance of positively charged functional groups.…”