Trivacancy and Stone-Wales defected silicene for adsorption of small gas molecules

The adsorption characteristics of small gas molecules (CO₂, CO, H₂O, N₂, NO, NH₃, NO₂ and O₂) on trivacancy and Stone-Wales defected silicene were investigated by density functional theory calculations. The results reveal that CO, H₂O and N₂ are absorbed on trivacancy silicene in a physical way via van der Waals forces, whereas CO₂, NO, NH₃, NO₂ and O₂ are chemisorbed on trivancancy silicene via strong covalent (SisbndN or SisbndO) bonds. For Stone-Wales defected silicene, N₂, H₂O and CO₂ are physisorbed whereas CO, O₂, NO, NH₃, and NO₂ are chemisorbed. The chemisorption of gas molecules on trivancancy and Stone-Wales defected silicene widens the band gap. In particular, the NO₂ chemisorption on trivacancy or Stone-Wales defective silicene shows significant hole doping. Additionally, O₂ is found to be readily decomposed into two O atoms on trivacancy silicene due to the small energy barrier and large exothermic reaction heat. Our work offers a possible method to regulate the electronic properties of silicene for applications at the nanoscale.