The non-covalent association is important for many fields of science, including processes in living systems. This work elucidates the mechanism of rhodamine 123 molecular aggregation in dispersions of a layered...

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The molecular aggregation of organic dyes onto clay mineral particles is a very complex phenomenon including dye adsorption, the migration of dye molecules, rearrangement of initially formed aggregates, etc. Some details of this complex process are not yet fully understood. The objective of the present study was to understand the influence of dye surface concentration on the dynamic processes in dye molecular aggregation. A stopped-flow rapid mixing device was used for accurate measurements of the molecular aggregation of the cationic dye rhodamine 123 (R123) in montmorillonite (MntK) colloidal dispersions. The influence of dye surface concentration, which was changed by altering the ratio of the amount of R123 to the mass of MntK (nR123/mMntK), was examined in detail. Chemometric analysis was used to reconstruct the spectral matrix to obtain linearly uncorrelated spectral profiles of the major components and their concentrations at the respective reaction times. The conversion of isolated R123 cations into oblique J-aggregates (head-to-tail molecular assemblies) was observed over time and the existence of a J-dimers intermediate was hypothesized. The reaction kinetics followed a biphasic exponential function. An unexpected effect of dye surface concentration on R123 aggregation was observed: the initial formation of the molecular aggregates increased significantly with dye surface concentration, but an inverse trend was observed after longer reaction times. While dye aggregates were formed slowly at low dye loadings, systems with high R123/MntK ratios (nR123/mMntK) reached spectral stability after the first few seconds of the reaction. After longer reaction times, the greatest degree of dye aggregation was achieved in the dispersion of the lowest dye loading. Such a phenomenon is described for the first time. The results presented here are important for understanding the complex processes occurring in systems based on organic cations and clay minerals, and should be considered in the development of functional hybrid materials of dyes and nanoparticles with a layered structure.

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The present paper gives a brief account of the latest advances in understanding of the mechanism and implications of dye adsorption with a special focus on layered silicate surfaces. It has been clearly demonstrated that the controlled adsorption of novel or already well-known dyes has equally great yet unexplored potential. In principle, the well-engineered surface confinement of the molecules may lead to their aggregation, adsorption, or intercalation-induced fluorescence emission even with conventional dyes, which are not considered as luminophores in solutions or in the solid state. We envision the utilization of silicate-based heterogeneous systems to produce novel polymer blended films or structured liquids, as well as to develop a plethora of other photophysical and biomedical applications.

The current study reflects the demand to mitigate the environmental issues caused by the waste from the agriculture and food industry. The crops that do not meet the supply chain requirements and waste from their processing are overfilling landfills. The mentioned wastes contain cellulose, which is the most abundant carbon precursor. Therefore, one of the possibilities of returning such waste into the life cycle could be preparing the activated carbon through an eco-friendly and simple route. Herein, the carrot pulp from the waste was used. Techniques such as thermogravimetric analysis (TGA), elemental analysis (EA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and x-ray diffraction (XRD) were used to investigate the thermal treatment effect during the carbon material preparation. The development of microstructure, phase formation, and chemical composition of prepared material was evaluated. The obtained carbon material was finally tested for water cleaning from a synthetic pollutant such as rhodamine B and phloxine B. An adsorption mechanism was proposed on the base of positron annihilation lifetime spectroscopy (PALS) results and attributed to the responsible interactions. It was shown that a significant carbon sorbent from the organic waste for water purification was obtained.