Quantum Chemical Study of Intercalation of Hydrazine Hydrate in Kaolinite

Hydrazine hydrate is now drawn more attention with its alkalinity, adsorption and pollution in clay. In this paper, the cluster model of kaolinite Al6Si6O42H42 was constructed, and the B3LYP/6-31G(d,p), MP2/6-31G(d,p)//B3LYP/6-31G(d,p) and MP2/6-31++G(d,p)//B3LYP/6-31G(d,p) levels were used to explore the intercalation properties ( such as optimal structures, structural parameters, binding energies, charge distributions, vibration spectrum, electrostatic potential, and so on) of hydrazine monohydrate and hydrazine dihydrate in kaolinite. During the optimization, geometries of hydrazine and water molecules and only the innermost part representative of the interaction sites of kaolinite cluster model, including the oxygen atoms on the tetrahedral layer and the hydroxyls on the octahedral layer, have been fully optimized, and the "dangling" valences of the border oxygen atoms were saturated with hydrogen atoms. Results show that the interaction between hydrazine and water molecules after intercalation is different from that before intercalation, when hydrazine monohydrate is intercalated into kaolinite. That is to say, water and hydrazine interact respectively with kaolinite by forming hydrogen bonds, and the interaction between hydrazine molecule and kaolinite is stronger than that between hydrazine and water molecules, and the intercalation points are almost in the active parts of kaolinite. These are the important factors that hydrazine hydrate is easily into the kaolinite layers and difficult to take off. When hydrazine dihydrate is intercalated into kaolinite, the cluster model with different layer spacing was optimized. And the interaction between hydrazine molecule and kaolinite is stronger than that between hydrazine and water molecules with the increase of the layer spacing. When the layer spacing is greater than 1.05 nm, the interaction between hydrazine and water molecules is stronger than that between hydrazine and kaolinite, which also further confirms the feasibility of hydrazine desorption. Specifically, the layer spacing could be increased to weaken the interaction of hydrazine and kaolinite, then the solvent is used to achieve hydrazine desorption.