Detection of Methanol or Hydrogen Based on Modifying the Composition of Sensors of ZIFs on V₂CT_<i>x</i> Mxene

The safe use of methanol-reforming hydrogen fuel cells requires the accurate identification and detection of the gases involved in methanol and hydrogen. To address this issue, we construct unique gas sensors by uniformly growing zeolitic imidazolate framework (ZIF) (ZIF-67 and ZIF-8) particles on the surface of functionalized V2CTx (F-V2CTx), which are prealkalized and then grafted with (3-aminopropyl) triethoxysilane (APTES). In the achieved composite of F-V2CTx/ZIFs, V2CTx provides a fast electron transport channel, and ZIFs provide adsorption sites for specific gases. Thus, with different ZIF modifications, the V2CTx/ZIF-based sensors are modulated to realize the selective detection of methanol or hydrogen. This reveals that the F-V2CTx/ZIF-8 and F-V2CTx/ZIF-67 sensors exhibit fast response/recovery to hydrogen (5/4 s to 500 ppm H2) and methanol (3/12 s to 10 ppm methanol), respectively. The F-V2CTx/ZIF-67 sensor exhibits the capability of detecting sub ppm methanol, with a theoretical detection limit of 72 ppb, while the F-V2CTx/ZIF-8 sensor shows good selectivity to hydrogen at room temperature. The mechanisms for the gas-sensing enhancement and gas-selectivity modulation of V2CTx/ZIF sensors are clarified based on the heterojunction effect and first-principles calculations, respectively. This work expands the application of nanocomposites composed of V2CTx and ZIFs in the field of gas sensors and proposes an effective strategy for gas selectivity modulation by different ZIF modifications.