Atomic Plasma Grafting: Precise Control of Functional Groups on TiCT 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 TiCT 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 TiCT MXene. For performance assessment and sensing mechanism elucidation, we synthesize few-layered TiCT MXene through liquid exfoliation and then graft functional groups via in situ plasma treatment. Functionalized TiCT MXene with large amounts of -O functional groups shows NO 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 adsorption energy, thereby enhancing charge transport. The -O functionalized TiCT sensor shows a record-breaking response of 13.8% toward 10 ppm NO, 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.