Atomic Plasma Grafting: Precise Control of Functional Groups on Ti 3 C 2 T x MXene for Room Temperature Gas Sensors.

Gas sensing properties of two-dimensional (2D) materials are derived from charge transfer between the analyte and surface functional groups. However, for sensing films consisting of 2D Ti 3 C 2 T x MXene nanosheets, the precise control of surface functional groups for achieving optimal gas sensing performance and the associate mechanism are still far from well understood. Herein, we present a functional group engineering strategy based on plasma exposure for optimizing the gas sensing performance of Ti 3 C 2 T x MXene. For performance assessment and sensing mechanism elucidation, we synthesize few-layered Ti 3 C 2 T x MXene through liquid exfoliation and then graft functional groups via in situ plasma treatment. Functionalized Ti 3 C 2 T x MXene with large amounts of -O functional groups shows NO 2 sensing properties that are unprecedented among MXene-based gas sensors. Density functional theory (DFT) calculations reveal that -O functional groups are associated with increased NO 2 adsorption energy, thereby enhancing charge transport. The -O functionalized Ti 3 C 2 T x sensor shows a record-breaking response of 13.8% toward 10 ppm NO 2 , good selectivity, and long-term stability at room temperature. The proposed technique is also capable of improving selectivity, a well-known challenge in chemoresistive gas sensing. This work paves the way to the possibility of using plasma grafting for precise functionalization of MXene surfaces toward practical realization of electronic devices.