The Effect of Mg, Fe(II), and Al Doping on CH₄: Adsorption and Diffusion on the Surface of Na-Kaolinite (001) by...

Because kaolinite includes a large range of defect elements, the effects of Mg, Fe(II), and Al doping on the CH₄ 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 CH₄ 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 CH₄ and the kaolinite's surface are two key factors that can determine CH₄ adsorption capacity. The first peak value of the radial distribution functions (RDFs) between CH₄ 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 CH₄ and the kaolinite's surface. Besides hydrogen and oxygen atoms, interlayer sodium ions are also strong adsorption sites for CH₄ and lead to a weakened interaction between CH₄ and the kaolinite's surface, as well as a decrease in CH₄ adsorption. Contrary to the adsorption results, ion doping facilitates the diffusion of CH₄, which is beneficial for actual shale gas extraction.