Theoretical study of interaction of amide molecules with kaolinite

Abstract

In this paper, we have constructed the cluster models Si6O18H12, Al6O24H30 and Si6Al6O42H42 for SiO, AlO surfaces and isolated kaolinite, respectively. All calculations have been performed at the B3LYP (Becke, three-parameter, Lee–Yang–Parr exchange–correlation functional) level using the 6-31G(d) basis set to investigate the various gas phase properties of interaction of amide (including formamide (FA), acetamide (AA), cis-N-methylformamide (NMFA1), trans-N-methylformamide (NMFA2), cis-N-methylacetamide (NMA1) and trans-N-methylacetamide (NMA2)) with kaolinite, such as optimal structures, structural parameters, interaction energies, charge transfer, vibrational frequencies, electrostatic potential, and so on. Moreover, extra calculations have also been performed at the M052X/6-31G(d) level in order to test the effect of van der Waals interactions on the order of stability of complexes in adsorption or intercalation systems. The results show that hydrogen bonds are formed between amide and the hydroxyl groups of the AlO surface or the basal oxygen atoms of the SiO surface in kaolinite. Moreover, the adsorption between amide and AlO surface of kaolinite is stronger than that of amide and SiO surface of kaolinite, and the intercalation interaction is more stable than the adsorption interaction. As for the order of the stability of intercalated kaolinite complexes, there is a slight difference between the order (K–NMFA2>K–FA>K–AA>K–NMA2>K–NMFA1>K–NMA1) calculated at the level of M052X/6-31G(d) and the order (K–NMFA2>K–FA>K–AA>K–NMFA1>K–NMA2>K–NMA1) calculated at the level of B3LYP/6-31G(d), in which K denotes kaolinite. The order is different from that of adsorbed systems at the same computational level.