Systematic exploration of the interactions between Fe-doped kaolinite and coal based on DFT calculations

Abstract

In order to explore the interactions between Fe-doped kaolinite and coal, the lattice substitution of different valence Fe in kaolinite crystal was analyzed by Mössbauer spectrometer and density functional theory (DFT) calculations. The results show that there are three lattice substitution forms of Fe with different valence states in kaolinite, are mainly six-coordinate Fe2+, four-coordinate Fe3+ and six-coordinated Fe3+, and the difficult and easy level of lattice substitution from easy to difficult is six-coordinate Fe2+ > four-coordinate Fe3+ > six-coordinated Fe3+. According to the results of Mössbauer spectrum analysis and DFT calculation, the best calculation model of Fe-doped kaolinite was determined, and the interactions between Fe-doped kaolinite and coal were investigated in this study through DFT calculations. The results show that the interaction mechanism between Fe-doped kaolinite and coal is the result of hydrogen-bond interaction and the strong electrostatic attraction between benzene rings and Fe-doped kaolinite surfaces, and the interactions between Fe-doped kaolinite and coal are stronger than that between perfect kaolinite and coal. The lattice substitution of Fe mainly enhances the reactivity of kaolinite (0 0 1) surface, and the equilibrium cation Na+ has a certain influence on the reactivity of kaolinite (0 0 1) and (001¯) surface. The results can provide a theoretical basis for further study of the true adsorption state of kaolinite surface in coal slurry water.