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

Abstract

Abstract:Layer charge is one of the key parameters used for the characterisation of expandable clay minerals, smectites. It determines most significant properties of the material which are important from the industrial application point of view. This work is related to a novel method introduced to characterize the layer charge of smectites, based on using cationic organic dyes as molecular sensors. One xanthene and four phenothiazine cationic dyes were tested using reduced charge montmorillonites (RCMs) and compared with methylene blue, which has been used most frequently. The characterization of the charge was based on the formation of molecular assemblies (H-and J-aggregates) composed by dye cations, which were easily detectable using absorption spectroscopy in the UV/VIS spectrum. More detailed characterization of the spectra required calculations of second-derivative curves. For all of the reaction systems tested in this work, the molecular aggregation increased with the layer charge of RCMs. Slight to moderate differences in the formation of dye assemblies related to the differences in the molecular structures of the individual dye cations. For example, the molecular asymmetry of azure A brought about the formation of coexistent species of similar structures. The structure of the heteroaromatic skeleton affected the extent of the aggregation and spectral changes with time. The presence of reactive, non-substituted amino groups in thionine cations probably partially decomposed in the clay mineral colloids based on high-charge RCMs. Any of the tested dyes could be used as molecular sensors for empirical characterization of the layer charge of clays taking into account the differences mentioned above.© Versita Warsaw and Springer-Verlag Berlin Heidelberg.

The molecular aggregation of pyronin Y in natural bentonite clay suspension

“…3. It can be concluded by these results that the amount of H-type aggregation can partially be controlled not only by changing CEC% but also with the fresh or aged suspensions as well as the charge density on clay layers [38]. An isosbestic point was observed at 540 nm for the absorption spectra of PyY in the clay suspension that implies the presence of at least two different species, monomers and aggregates.…”

“…J-aggregates were mostly observed at low surface charge when intense surface charge of clay mineral promotes H-aggregate formation [49]. Czimerova et al [38] reported that the reduced charge density of clay mineral caused an increase in amount of PyY monomers whereas the H-aggregate of PyY in aqueous clay dispersion was favored at high charge density. Although molecular aggregation in water is observed at high dye concentrations, in the case of clay suspensions, this phenomenon occurs in a very low dye concentration [47].…”

“…Such an observation was reported by Bergman and O'Konski [47] that cationic dyes are exposed molecular aggregation in clay suspension at low concentrations. Additionally, the charge density of clay particles is a significant factor on the molecular aggregation type and degree [12,38]. In the present work, the charge density of the clay minerals was assumed to be maximum because no heat treatment was performed on the clay mineral at which the thermal treatment decreases the surface charge density [38].…”

“…Additionally, the charge density of clay particles is a significant factor on the molecular aggregation type and degree [12,38]. In the present work, the charge density of the clay minerals was assumed to be maximum because no heat treatment was performed on the clay mineral at which the thermal treatment decreases the surface charge density [38]. It was reported that the aggregate states (H-aggregate or J-aggregate) of Oxazine 4 dyes were changed by decreasing the charge density of clay mineral.…”

“…However, the number of studies on the interactions between pyronin dyes and clay minerals in an aqueous suspension are limited. Czimerova et al [38] studied the interaction of montmorillonite with PyY in aqueous media by UV-vis absorption spectroscopy. They explained that the optical properties and aggregate sites of PyY in the suspension were controlled by the interaction time and the charge density of clay minerals.…”