Adsorption of small gas molecules on pure and Al-doped graphene sheet: a quantum mechanical study

The interaction of small gas molecules ( $$\hbox {CCl}₄$$ , $$\hbox {CH}₄$$ , $$\hbox {NH}₃$$ , $$\hbox {CO}₂$$ , $$\hbox {N}₂$$ , CO, $$\hbox {NO}₂, \hbox {CCl}₂\hbox {F}₂$$ , $$\hbox {SO}₂$$ , $$\hbox {CF}₄$$ , $$\hbox {H}₂$$ ) on pure and aluminium-doped graphene were investigated by using the density functional theory to explore their potential applications as sensors. It has been found that all gas molecules show much stronger adsorption on the Al-doped graphene than that of pure graphene (PG). The Al-doped graphene shows the highest adsorption energy with $$\hbox {NO}₂$$ , $$\hbox {NH}₃$$ and $$\hbox {CO}₂$$ molecules, whereas the PG binds strongly with $$\hbox {NO}₂$$ . Therefore, the strong interactions between the adsorbed gas molecules and the Al-doped graphene induce dramatic changes to graphene’s electronic properties. These results reveal that the sensitivity of graphene-based gas sensor could be drastically improved by introducing the appropriate dopant or defect. It also carried out the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap of the complex molecular structure that has been explored by M06/6-31++G** method. These results indicate that the energy gap fine tuning of the pure and Al-doped graphene can be affected through the binding of small gas molecules.