Advantage of graphene fluorination instead of oxygenation for restorable adsorption of gaseous ammonia and nitrogen dioxide

An interaction of graphene with gaseous molecules increases substantially with grafting of functional groups to its surface. However, in the efficient sensors, such interaction should not be too strong to provide an easy desorption of molecules. Here, we reveal an influence of fluorine and hydroxyl species on the graphene surface on the restorable adsorption of ammonia and nitrogen dioxide, taken as model gases having a different donor/acceptor property. Conductive films of few-layered fluorinated graphene and oxyfluorinated graphene were produced using a one-step process of the exfoliation and partial reduction of corresponding graphite derivatives. The films showed a similar sensitivity on exposure to NH3 and NO2, while the fluorinated graphene-based sensor had much better recovery after a simple argon purging at room temperature. Density functional theory calculations revealed that NO2 and NH3 molecules are adsorbed on fluorine and oxygen from a hydroxyl group as well as bare carbon atoms located near the functionalized carbon. The strongest adsorption energy was obtained for an oxyfluorinated graphene-NH3 system due to short N⋯H(O) contacts. Our results show that fluorinated graphene is more perspective for gas sensing as compared to oxygenated graphene due to its higher chemical stability and weaker interactions with the adsorbed molecules.

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