Anion exchangeable layered silicates modified with ionic liquids on the interlayer surface

Novel layered materials with two-dimensionally arranged anion exchangeable sites in the interlayer space were prepared by immobilization of imidazolium chloride salts (1-butyl (or 1-octyl)-3-(3-triethoxysilylpropyl)-4,5- dihydroimidazolium chloride, abbreviated as BimSi(OEt)₃Cl or OimSi(OEt)₃Cl, respectively) containing terminal triethoxysilyl groups onto layered octosilicate via silylation. More than 80% of SiOH/SiO ^- groups on the silicate layers were silylated and they are denoted as Bim-Oct and Oim-Oct. The cation exchangeable sites on octosilicate were stoichiometrically converted to anion exchangeable sites. The confronting arrangement of SiOH/SiO^- groups on octosilicate is essential for this stoichiometric conversion because the silylation reagents ideally react with the surface SiOH/SiO^- groups to form bidentate immobilization on octosilicate. The anion exchangeable capacity of the silylated materials is around 2 mmol g^-1. The affinity of these materials for Cl ^-, Br^-, I^-, and NO₃^- is quite different from those of conventional anion exchangeable layered double hydroxides (LDHs). Bim-Oct is stable at pH 1.0, which is in clear contrast to the behavior of LDHs. Bim-Oct exhibits a high capacity for sorption of sulfasalazine, a bulky prodrug. The release behavior of the accommodated sulfasalazine is largely dependent on the pH values of simulated gastric and intestinal fluids, suggesting that these novel layered anion exchangers are potentially applicable to drug delivery systems.