DFT study of CO2 adsorption properties on pristine, vacancy and doped graphenes

Through DFT calculation, the adsorption properties, geometry changes and charge transfer of CO2 molecule on pristine graphene (PG), vacancy defect graphene (VG) and doped graphene (DG) are investigated. The results show that different adsorption forms of CO2 on PG and VG are physisorption through van der Waals force with few charge transfer. On PG, it shows weak physisorption. On VG, it is strong physisorption. Therefore, the appearance of defect can increase adsorption ability for CO2. When CO2 parallel to the H-site of PG and monoatomic vacancy graphene (M-VG), the adsorption structure is the most stable, which is similar with literature. On DG, N-doped can not enhance the adsorption and charge transfer ability, and this result is consistent with codoped system of Cu/N-DG and Ni/N-DG. While Cu or Ni-doped can increase adsorption and charge transfer ability, and decrease the adsorption distance. When CO2 on Cu-DG, Cu/N-DG, Ni-DG and Ni/N-DG, these adsorption processes are chemisorption process in which new chemical bonds are formed. Adding defects and Cu/Ni atoms to graphene can serve as an excellent adsorption material for the preparation of catalysts to activate CO2. Among them, Cu-DG has the best performance. Moreover, through electronic band structures and density of states analysis, we find that vacancy and Cu/Ni-doped can open the band gap, increase the width of the pseudogap, and strengthen the adsorption and activation ability of CO2 gas molecular in heterogeneous catalytic reaction based on graphene support.