Adsorption energy of amide-kaolinite systems using supramolecular method: A study on the basis set effect

Kaolinite is a clay material that has SiO4 tetrahedral and AlO6 octahedral sheets on its surfaces. These surfaces act as flexible platforms for the adsorption of molecules, thus enabling applications in diverse fields, such as in paper industry and the drug delivery. Attention has been brought to us in the case of the adsorption of amide molecules on the Si-O and Al-O surfaces of kaolinite, where the relative strength of the adsorptions of a few of the amide molecules were contradictory. The conundrum maybe due to the factor of the inadequacy of the basis sets and the level of theories used. Hence, we performed theoretical investigations on the relative adsorption energy (E ads) of the amide molecules on the alumina surface with different basis sets, in the frameworks of B3LYP and TPSSTPSS. The purpose is to determine the effects due to the basis sets on E ads. Two amide molecules, acetamide and Nmethylacetamide, were considered in this study. The main conclusion is that it is imperative to test the E ads against the available basis set, even with the basis that is considered large. For the basis sets considered here, excluding 6-31G**, the E abs for the adsorption of the two amide molecules on the alumina sheet of kaolinite are in the range of –0.058 to –0.082 Hartree.