Exohedral and endohedral adsorption of alkaline earth cations in BN nanocluster.

Adsorption of three alkaline earth cations inside and outside of a B(12)N(12) nano-cage in aqueous medium was investigated using density functional theory. The results obtained are discussed in terms of thermodynamic, geometric, and electronic properties. Based on the calculation of enthalpy changes at 298 K and 1 atm, the adsorption of the considered cations was found to be exothermic outside the cluster while it is endothermic inside. It was also found that the exohedral adsorption favorability of the cluster increases in the series: Ca(2+) < Mg(2+) << Be(2+) with Gibbs free energy changes in the range of -0.08 to -1.53 eV at B3LYP/6-31G (d) level of theory. Overall, interaction of the cations with the cluster influences the electronic properties of the cluster through stabilizing the HOMO and LUMO as well as reducing the energy gap between them. However, the electronic properties changed much more in the case of endohedral adsorption in comparison with the exohedral adsorption.