1H MAS NMR spectra of kaolinite/formamide intercalation compound

The high spinning speed 1H magic angle spinning nuclear magnetic resonance (1H MAS NMR) technique was employed to distinguish the two groups of surface hydroxyls of kaolinite and investigate the intercalation mechanism of kaolinite/formamide compound. The proton chemical shifts of the inner hydroxyl and inner surface hydroxyl of kaolinte are in the range of δ 1.3– 0.9 and δ 2.4–3.0 respectively. After formamide intercalation three proton peaks were detected. The proton peak of the inner surface hydroxyls of the intercalation compound shifts to high-field with δ 2.3–2.7, which is assigned to the formation of the hydrogen bond between the inner surface hydroxyl and formamide carbonyl group. Whereas, the proton peak of the inner hydroxyl shifts to δ 0.3 toward low-field, that is attributed to van der Waal’s effect between the inner hydroxyl proton and the amino group proton of the formamide which may be keyed into the ditrigonal hole of the kaolinite. The third peak, additional proton peak, is in the range of δ5.4–5.6, that is ascribed to the hydrogen bond formation between the amino group proton of formimide and SiO4 tetrahedral oxygen of the kaolinite.