Adsorption mechanism of lignite and water molecules

In order to explore the mechanism of multilayered water molecules adsorbed on lignite, Gaussian 09 software package was used to establish the surface model of lignite molecule.Based on the B3LYP method of density functional theory, nine different adsorption configurations and adsorption energies were calculated by using ORCA program.Using the wave function analysis software Multiwfn and VMD visualized program, the surface electrostatic potential distribution and RDG contours of the adsorbed configuration are obtained, visually reveal the regions and types of weak interaction.Meanwhile, the AIM theory was used to analyze the electronic density topological structure, and the bonding type and stability between atoms were quantitatively analyzed.Results show that the adsorption of water molecules on lignite belongs to physical adsorption.The adsorption is mainly hydrogen bond, and the rest is van der Waals weak interaction.The oxygen-containing functional groups region on lignite surface contains the active site where adsorption takes place.Meanwhile each water molecule provides more active sites for the adsorption of the next layer of water molecules by lignite.The formation and adsorption of dimer water molecules and trimer water molecules greatly alter the structure of lignite.