Exfoliation of layered silicates through immobilization of imidazolium groups

Layered octosilicate immobilized covalently with butylimidazolium groups was fully exfoliated into monolayer nanosheets in water. The thickness of the nanosheets was 1.9 nm (atomic force microscopy (AFM)). The colloidal aggregates of the nanosheets did not show X-ray diffraction (XRD) peaks at lower angles, suggesting the absence of layer stacking. After drying of the colloidal aggregates, a sharp peak at 1.9 nm was observed. This d-value agreed well with the thickness observed by AFM. The in-plane crystal structure of octosilicate was retained after exfoliation because of the presence of the XRD peak at 0.19 nm assignable to the (400) plane of octosilicate. The interlayer surface of Bim-Oct immobilized with butylimidazolium groups is suggested to be easily hydrated, which leads to the swelling and the following exfoliation into nanosheets. The significant change of the silicate surface by the immobilization is novel, which reflects the unique property of butylimidazolium groups. A transparent and colorless film was successfully obtained by spin-coating the colloidal aggregates of nanosheets on a glass substrate. An anionic dye of Orange II was intercalated into the interlayer of restacked nanosheets in the film. The immobilization of imidazolium groups on layered silicates is innovative for the preparation of nanosheets which are designable for various applications.