Adsorption of rubidium on raw and MTZ- and MBI-imogolite hybrid surfaces: An evidence of the chelate effect

Imogolite is an important paracrystalline hydrous aluminosilicate with a unique nanofiber structure. The synthetic imogolite sample was used for organofunctionalization process with 2-mercaptothiazoline and 2-mercaptobenzimidazole. Due to the increment of basic centers attached to the pendant chains, the metal adsorption capability of the final chelating materials, was found to be higher than is precursor. The ability of these materials to remove rubidium from aqueous solution was followed by a series of adsorption isotherms at room temperature and pH 4.0, in batch adsorption experiments in order to explain the adsorption mechanism. The maximum number of moles adsorbed was determined to be 17.89 × 10−2, 29.89 × 10−2, and 30.55 × 10−2 mmol g−1 for IMO, IMOMBI, and IMOMTZ, respectively. In order to evaluate the aluminosilicate samples as adsorbents in dynamic system, a glass column was fulfilled with aluminosilicate samples (1.0 g) and it was fed with 1.9 × 10−3 mol dm−3 rubidium at pH 4.0. The energetic effects caused by metal cations adsorption were determined through calorimetric titrations. The enthalpic and entropic values indicated the existence of favorable reaction between rubidium-nitrogen and sulfur center atoms on pendant chain covalent bonded to the inorganic backbone.

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► Number of moles adsorbed was determined to be 30.5 × 10−2 mmol g−1 for IMOMTZ.
► Adsorption reached the equilibrium before 15 min for IMOMTZ.
► The adsorption can be related directly to the available N and S atoms.
► The aluminosilicate samples present a high degree of crystallinity.
► The spontaneity of these systems, reflected in the negative Gibbs free energies.