Mechanism of H2O adsorption on ammonium-illite surface based on density functional theory

DU Jia; MIN Fanfei; ZHANG Mingxu; PENG Chenliang; LIU Chunfu

Abstract：To control the hydrophobicity of clay mineral interface and improve the treatment effect of coal slurry which is difficult to sediment,the mechanism of H2O adsorption on the ammonium-illite surfaces was investigated.The adsorption of water on two lattice planes of ammonium-illite,namely the (001) lattice plane in the presence of crystalline substitution and the (00(1)) lattice plane in the absence of crystalline substitution,was simulated using the method of density functional theory.The results show that on the (001) lattice plane,the strongest active site is the position of oxygen atom which interacts with substituted Al.The most stable adsorption is vertically on the Si-O atoms ring in the presence of NH4+.There are two hydrogen bonds between the water molecule and the active atom,with the adsorption energy of -0.67 eV.The NH4+ tends to be pulled away from (001) lattice plane by adsorbed water molecules.By contrast,the most stable adsorption on (00(1)) lattice plane is located above the hollow of Si-O atoms ring,with adsorption energy of-0.41 eV.There are three hydrogen bonds between the water molecule and the surface oxygen atoms.The two most stable adsorptions mentioned are weak electrostatic interactions.In conclusion,choosing the appropriate cationic hydrophobic agent to exchange with NH4+ can cover active sites on (001) lattice plane,and destroy the stable adsorption of H2O,then the hydrophobic regulation of ammonium-illite and its similar clay mineral interface can be achieved in theory.