The orientation of rhodamine 6G (R6G) in the 22-Å basal-spaced complex with Li-fluor-taeniolite has been studied using X-raypowder diffraction, 1-dimensional Fourier analysis, polarized infrared (IR) spectroscopy, carbon analysis and thermal analysis. The R6G was adsorbed by cation exchange in aqueous solution. In the range of 0.086 to 0.46 molar ratio of R6G to taeniolite, the basal spacings of the complex were nearly constant at 21.7 to 22.2 Å. From X-raydiffraction (XRD) data, it was confirmed that R6G in the complex orients with its longest xanthene ring axis perpendicular to the ab plane of the host. The pleochroism of IR absorption bands at 1331, 1517, 1537 and 1621 cm−1 supports the vertical orientation. The wide stability range of the vertical configuration is consistent with the strong coulombic force between the highly negatively charged silicate layer of the host [cation exchange capacity (CEC) = 157 ± 9 meq/100 g] and the positively charged nitrogen bonded to both sides of the R6G xanthene ring.

The organization of organic species on the ordered structures of clays and clay minerals is one way to produce inorganic-organic hybrids with controlled microstructures and properties. The reactions of the adsorbed species and their arrangement on the clay surfaces can be guided by the choice of clay and of adsorbed species. The purpose of the present study was to intercalate alkylammonium ions into a Thai bentonite and to study the effect on dye-adsorption efficiency. A series of alkylammonium ions, CnH2n+1NH3+ (n = 8, 10, 12, or 18), was incorporated into the interlayer spaces of a natural bentonite by mixing an aqueous dispersion of bentonite with an aqueous solution of protonated alkylamines at room temperature. The basal spacings of the intercalation compounds varied depending on the alkyl chain lengths and the amount of alkylammonium ions. The alkylammonium ions adsorbed formed lateral monolayer, bilayer, pseudo-trimolecular layer, paraffin-type monolayer, and/or paraffin-type bilayer structures. The adsorption efficiency of alkylammonium-bentonites was determined using batch adsorption experiments of rhodamine 6G from a water-ethanol solution; the greatest efficiency was 87% while that of the bare bentonite was 47%. The loading amount and the arrangement of the intercalated alkylammonium ions in the interlayer spaces, as well as the specific surface area and pore volume, played important roles in the adsorption efficiency of alkylammonium-bentonite. The adsorption equilibrium data for rhodamine 6G on the best adsorbent were interpreted using the Langmuir isotherm model and a pseudo-second order kinetics model. The adsorption efficiency of the adsorbent decreased by only 17% after five runs.

Interactions between smectite clay minerals and various organic dyes have been studied extensively, but little information has accumulated from dye interactions with mixed-layer illite-smectite (I-S) minerals, especially regarding relationships with clay layer expandability, layer charge, particle size/shape, and molecular aggregation of organic dye molecules. The purpose of this study was to investigate the surface interactions of a set of mixed-layer illite-smectites from different geological environments with Rhodamine 6G dye. The samples used have different amounts of expandable smectite interlayers, different particle size and/or shape, and different layer-charge density at the surface. Five smectites with differences in layer charge and some non-expandable layer silicates were also tested. The interactions detected by UV-vis spectroscopy show no reaction between R6G and non-expandable minerals (kaolinite, mica), and intense reactions forming H-aggregates and monomers with smectites and illite-smectites. The intensity of H-aggregate formation increases with increase in the layer charge of smectites. Mixed-layer illite-smectites interact with R6G more intensely than do smectites. H-aggregate and monomer formation increases with the illitization process for randomly ordered illite-smectites (R = 0) and decreases in the course of illitization for the ordered illite-smectites (R > 0).