Covalent grafting of pyridine-2-methanol into kaolinite layers

A novel hybrid organic-clay material was prepared by grafting of pyridine-2-methanol in the interlayer space of kaolinite by using a kaolinite/methanol compound as an intermediate. A kaolinite/methanol compound was obtained by guest displacement process of a kaolinite/N-methylformamide pre-intercalation complex with methanol. The structural, morphological and thermal properties of the hybrid material and intermediate species were examined by using X-ray powder diffraction, Fourier transform infrared, thermal analysis, scanning electron microscopy and surface area measurement techniques. The X-ray powder diffraction patterns showed that the penetration of pyridine-2-methanol between the kaolinite/methanol layers caused the emergence of a new peak at 6.51(2θ) with the distance of 13.57 Å. The pyridine-2-methanol species present in the kaolinite interlayers led to appreciable decreases in the intensities of the peaks at 3696, 3667, 3650 and 938 cm−1 which originate from inner-surface hydroxyl groups of pure kaolinite and the new vibrational peaks belonging to the guest molecule were appeared. The thermal analysis data confirmed that the removal of intercalated species occurred in the temperature range 100–180 °C, whereas the grafted pyridine-2-methanol molecules remained stable up to 350 °C which may be explained by grafting of the pyridine-2-methanol molecules onto the inner-surface hydroxyls on the interlayer surfaces of kaolinite through Al–O–C covalent bond formations. The organic molecules located in the interlayer spaces caused significant alterations in the morphology of the pure kaolinite. The specific surface areas of the kaolinite–methanol and kaolinite-N-methylformamide compounds increased whereas that of kaolinite/pyridine-2-methanol hybrid material decreased with respect to that of pure kaolinite.

► Pyridine-2-methanol molecules were grafted onto kaolinite by means of Al–O–C covalent bonds.
► The grafted species thermally more stable than intercalated molecules.
► Pyridine-2-methanol molecules were located as a monolayer arrangement.
► The textural properties of kaolinite are changed by the insertion of the quest molecules.