Interlayer structural and confined water effects in kaolinite–alcohol systems via dimethyl sulfoxide intercalation

Methanol- and ethylene glycol-grafted kaolinite were prepared via a stepwise intercalation–grafting strategy using dimethyl sulfoxide-intercalated kaolinite as an intermediate, with the aim of elucidating the structural differences between the two grafted products and clarifying the role of interlayer water. The products were systematically characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), elemental analysis (CHNS) and thermogravimetry–differential scanning calorimetry (TG–DSC). Compared with methoxy-modified kaolinite, the ethylene glycol-grafted kaolinite exhibited enhanced structural ordering, greater organic loading and improved thermal stability. The covalently grafted ethylene glycol molecules adopt a trans configuration in the interlayers of kaolinite, accompanied by a minute fraction of non-bonded ethylene glycol molecules and some amount of interlayer water molecules. Although the confined water in both systems originated from condensation reaction, it probably played opposite roles: it facilitated the ethylene glycol grafting while hindering that for methanol.