The Effect of Mg, Fe(II), and Al Doping on CH(4): Adsorption and Diffusion on the Surface of Na-Kaolinite (001) by Molecular Simulations

Because kaolinite includes a large range of defect elements, the effects of Mg, Fe(II), and Al doping on the CH(4) adsorption and diffusion on the surface of Na-kaolinite (001) were investigated by molecular simulations. The simulation results illustrate that ion doping can significantly reduce the amount of CH(4) adsorbed by kaolinite, but the type of doped ions has little effect on the amount of adsorption. The specific surface area of kaolinite and the interaction energy between CH(4) and the kaolinite’s surface are two key factors that can determine CH(4) adsorption capacity. The first peak value of the radial distribution functions (RDFs) between CH(4) and the pure kaolinite is larger than that between Mg-, Fe(II)-, and Al-doped kaolinite, which indicates that ion doping can reduce the strength of the interactions between CH(4) and the kaolinite’s surface. Besides hydrogen and oxygen atoms, interlayer sodium ions are also strong adsorption sites for CH(4) and lead to a weakened interaction between CH(4) and the kaolinite’s surface, as well as a decrease in CH(4) adsorption. Contrary to the adsorption results, ion doping facilitates the diffusion of CH(4), which is beneficial for actual shale gas extraction.