Structural and electronic analysis of Li/Al layered double hydroxides and their adsorption for CO2

The most stable structures and electronic properties of different Li/Al layered double hydroxides models (i.e., Li/Al-X, X = F−, Cl−, Br−, OH−, NO3−, CO32−, SO42−) and their hydrates, the adsorption of CO2 on Li/Al-X (X = Cl−, NO3−, CO32−) were ascertained by means of density functional theory. Results revealed that the planes of NO3− and CO32− are parallel with the layers in dehydrated state, although the plane of NO3− becomes vertical with the layers upon the introduction of water molecules. Electronic density analysis suggested that SO42− and CO32− significantly strengthens the reducibility of the Li/Al layered double hydroxides. The distribution of the frontier orbitals indicated the high reactivity of the anions and hydroxyl groups of the layers. The orders of the predicted stability are F− > Cl− > Br− > NO3− for the monovalent anions and SO42− > CO32− for the divalent anions. The calculated adsorption energies of CO2 in Li/Al-X (X = Cl−, NO3−, CO3−) supported the experimental observation that Li/Al-CO3 exhibits higher CO2 capture capacity than Li/Al-NO3 and Li/Al-Cl. Non-covalent interaction analysis indicated that the interactions among mineral surfaces, anions, water and CO2 are dominated by H-bonds, electrostatic interactions, and van der Waals forces. In addition, radial distribution functions were applied to provide insight for the interaction of water or CO2 with carbonate ion and hydroxyl layers.