Sulfonation of the interlayer surface of kaolinite

Abstract

The interlayer surface of kaolinite was functionalized with sulfonic acid groups through the grafting of propane sultone. The presence of the modifier was confirmed by the increase of the d001-value from 7.1 Å (starting kaolinite) to 12.3 Å. The formation of stable Al-O-C bond following the ring-opening reaction of the cyclic sultone was confirmed both by the 13C NMR and FTIR characterizations. After a full washing of the modified material with water, the clay mineral appears as functionalized flat particles with thicknesses not exceeding 0.02 μm. This was the consequence of the delamination, due to the ionization of the grafted sulfonic acid groups in water, followed by a substantial decrease of the interlayer cohesive force. The nanohybrid material with structural formula determined from the thermo gravimetric analysis, Al2Si2O5(OH)3.77(O(CH2)3SO3H)0.23, was tested as adsorbent for methylene blue, a cationic dye. The amount adsorbed was at least two times higher compared to pristine kaolinite (76.8 μmol g−1 instead of 32.9 μmol g−1). This performance was less important than expected because the dye was adsorbed as trimer (according to the UV–Vis analysis of the aqueous suspension of the modified clay in dye solution), a too bulky configuration to fit in the interlayer space of the modified kaolinite.