Chemisorption mechanism of crude oil on soil surface.

• Identical bands were observed in the fingerprint region of different infrared spectra. • Chemical shifts of XPS spectra of N1s, O1s and Al2p after adsorption were explained. • DFT calculations were carried out to illustrate the coordination adsorption. One of the main challenges in cleaning crude oil-contaminated soil is the unknown adsorption mechanism between residual oil and soil. Herein, infrared spectrometer (IR) is used to detect the existence of dibutylphthalate (DBP) and pelargonamide on montmorillonite (MMT) surface. In addition, after the adsorption of DBP and pelargonamide on MMT, the bands in fingerprint region of the two IR spectra are almost identical, indicating coordination bonds were formed on the surface of MMT. X-ray photoelectron spectroscopy (XPS) is employed to detect the chemical environment of N, O and Al. The reverse migration of Al2p spectrum and forward migration of N1s and O1s spectra indicate the coordination adsorption of carbonyl and amine groups on MMT surface. Then, density functional theory (DFT) calculations are applied to make a further explanation of the bonding mechanisms of DBP and pelargonamide onto MMT surfaces. The result shows that there are two types of aluminum on the surface of MMT acting as Lewis acid sites in coordination adsorption, namely Al3+/Si4+ isomorphic substitutions and Al3+ adsorbed on MMT by means of electrostatic adsorption. Meanwhile, the oxygenium on the surface of MMT acts as Brønsted bases in hydrogen bonding adsorption. [ABSTRACT FROM AUTHOR]