Interaction of molecules with chemically modified surface of graphene


A.V.Okotrub, V.I. Sysoev, L.G. Bulusheva


Nikolaev Institute of Inorganic Chemistry SB RAS



Abstract:

Graphene is a remarkable material with the best surface to volume ratio because of its 2D nature, which implies that every atom can be considered as a surface one. These features make graphene attractive for use as a sensing material; however, the limiting factor is the chemical inertness of pristine graphene. 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. We propose a method to create reactive centers by removal of fluorine atoms from the outer surface of fluorinated graphene while preserving the backside fluorination. The reduction degree of the material and its electrical response revealed upon ammonia exposure were controlled by measuring the surface conductivity. The sensing properties depend on the reduction degree and found the correlation of the adsorption energy of ammonia with the number of residual fluorine atoms by the use of quantum-chemical calculations [1]. 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 like fluorine and oxygen from a hydroxyl group as well as bare carbon atoms located near the functionalized carbon. The highest adsorption energy was obtained for an oxyfluorinated graphene–NH3 system due to short 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. [1] M. V. Katkov, V. I. Sysoev, A. V. Gusel’nikov, I. P. Asanov, L. G. Bulusheva, “A backside fluorine-functionalized graphene layer for ammonia detection” // Phys. Chem. Chem. Phys., 17, 444 (2015). [2] V. I. Sysoev, L. G. Bulusheva, I. P. Asanov, Yu. V. Shubin and A. V. Okotrub “Thermally exfoliated fluorinated graphite for NO2 gas sensing” Physica Status Solidi (B) Basic Research, 253, 2492-2498 (2016). [3] V.I. Sysoev, A.V. Okotrub, I.P. Asanov, P.N. Gevko, L.G. Bulusheva “Advantage of graphene fluorination instead of oxygenation for restorable adsorption of gaseous ammonia and nitrogen dioxide” // Carbon, 118, 225-232 (2017).