Adsorption behavior of fluorides on Ag(1 1 1) and its doped surfaces: A first-principles calculation

Abstract

Based on density functional theory, the first-principles calculation was adopted to investigate the adsorption behavior of fluoride molecules on pure, Co-doped and Pd-doped Ag(111) surfaces. Calculation models of gas molecules adsorbed at different sites were established and the important adsorption parameters like adsorption energy, bond length, bond angle, Mulliken charge population and charge density difference were analyzed. Calculation results show that pure, Co-doped and Pd-doped Ag(111) surfaces show different adsorption behaviors due to the different lattice change and charge transfer caused by doping. Judged from the comparison of adsorption energy, the gas adsorption sequence for Ag(111) surface is CCl2F2 > SF6 > C2F4 > CF4, and the optimal adsorption site is Cl-Ag site. The adsorption energies of Co doping system are all negative, which indicates that the adsorption process can be spontaneous under thermodynamic conditions. Except for the systems of CF4, C2F4 and CCl2F2 respectively adsorbed on Co-doped Ag(111) surface, the adsorption processes of other systems are chemisorption. The gas adsorption sequence for Co-doped Ag(111) surface is SF6 > CCl2F2 > C2F4 > CF4, and the optimal adsorption site is F-Co site. Compared with Co doping, Pd doping makes the adsorption energy of the adsorption system smaller. Meanwhile, the covalent bonds formed between Pd and Ag atoms are stronger, which makes the adsorption process easier. The gas adsorption sequence for Pd-doped Ag(111) surface is CCl2F2 > CF4 > C2F4 > SF6, and the optimal adsorption site is Cl-Pd site. Therefore, the research of this work provides a feasible theoretical guidance for the design of efficient gas pollutant adsorption surfaces.