First principles study on the functionalization of graphene with Fe catalyst for the detection of CO₂: Effect of catalyst clustering

The surface functionalization of graphene plays an important role in the development of graphene-based sensors for gas detection and removal. Here, we report the effect of decoration of graphene with Fe catalyst, as either scattered adatoms (Fe_adatoms@G) or clustered (Fe_cluster@G) on the detection of CO₂ gas molecule and its influence on the structural, adsorption, electronic and magnetic properties of graphene using the spin-polarized density functional theory (DFT). The results show that the adsorption of scattered Fe-adatoms and Fe₄-cluster on graphene would break the degeneracy of spin-up and spin-down states, resulting in ferromagnetic adsorption-bed for the detection of CO₂ molecules. The magnetic moment of Fe_adatoms@G remains the same for all concentration of CO₂, while the magnetic moment of Fe_cluster@G decreases from 10.03 µ_B to 4 µ_B by increasing the concentration of CO₂ from one to four molecules. It is found that the scattered Fe-adatoms on graphene have the higher tendency to adsorb more CO₂ molecules than that of the cluster with the same number of Fe atoms, whereas Fe₄-cluster on graphene detects CO₂ molecules using magnetism. Our results have indeed a direct application to fabricate solid-state and magnetic-based gas sensors using graphene to detect CO₂ gas molecules.