Beidellite/montmorillonite-Phosphorus-based dendrimer organoclays :Structural features and chromate  interaction analysis

Organoclays are promising materials for pollutant retention, medicinal applications, and catalysis, making them an intriguing research topic. In this study, beidellite/montmorillonite and phosphorus-based dendrimer organoclays were prepared, and their microstructure was examined using X-ray diffraction, thermal analysis, Fourier-transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, and high-resolution transmission electron microscopy. The study also investigated the dynamic and equilibrium adsorption of chromate onto these organoclays within a temperature range of 298-318°C. It was found that the formation of organoclays involved the substitution of Na+ ions with dendrimers, and the structural configuration depended on the dendrimer size. Additionally, chromate retention by the organoclays occurred rapidly, with the kinetics data fitting well to the pseudo-second-order equation, suggesting chemisorption as the primary adsorption mechanism. The adsorption kinetics were controlled by intragranular diffusion (diffusion coefficient ranging from 0.007 to 0.018 mmol.g⁻¹) and external diffusion (diffusion coefficient ranging from 0.011 to 0.06 min⁻¹). Thermodynamic data and adsorption isotherms modeling showed that chromate adsorption was spontaneous and endothermic, and the isotherms fitted well to the Temkin model. Chromate binding to the organoclay involved protonated amino groups of the dendrimer (first-generation), with an adsorption capacity of 15 mg of chromate per gram, slightly exceeding that of some other organoclays.