Tailoring Graphene Functionalization with Organic Residues for Selective Sensing of Nitrogenated Compounds: Structure and Transport Properties via QM Simulations

Graphene bearing organic functional groups chemically tethered to its surface via covalent bonds can find several applications in the sensing of gas, heavy metal ions, and other target species of interest. Herein, we used DFT simulations to study the thermodynamics of graphene functionalization with substituted carbenes, and the use of the resulting adducts to detect gaseous nitrogenated compounds─focusing on ammonia (NH3), methylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA). We find that the modified materials can interact with the amines, selectively also in the presence of other gases such as CO2, SO2, H2S, and CH4. Changes in the electronic properties of the system upon adsorption such as charge density, Löwdin partial charges, and projected density of states (PDOS) were used to analyze the interaction. Expected recovery times suggest that these nanomaterials can be used to detect the nitrogenated compounds here investigated at relatively low temperatures (298 and 373 K). Furthermore, by modeling the conductance of the functionalized graphene bare and in the presence of ammonia, we show that quantum conductance and the integrated currents are sensitive to functionalization and, importantly, to the presence of ammonia under determined conditions, which in principle allows tuning the sensitivity of the resulting device. Our work thus clarifies the principles governing this phenomenon. Carbene-functionalized graphene is concluded to be a potentially good candidate to replace noble-metal-modified graphene for the detection of ammonia/amines in chemoresistance or field-effect transistor-based sensors.