Polydopamine functionalized MXene for chemiresistive gas sensing: partial oxidation and optimized chemical state pinning

Two-dimensional MXene has been receiving attention for its outstanding properties of intrinsic metallic con-ductivity, high specific surface area and abundant surface terminations, showing great potential in gas sensing. However, it suffers from low sensing response and poor chemical stability. To address these issues, we propose a series of surface treatment to anchor interaction sites onto MXene, and to pin its optimized chemical state. Interaction sites including -OH, -NH2, and -O- were functionalized through self-polymerization of dopamine and controlled oxidation of the MXene base. These functionalized groups can interact with gas molecules through hydrogen bonding; besides, multiple Schottky barriers are generated within the sensing layer, thus improving formaldehyde sensing response by over 16-fold in comparison with pristine MXene. This optimized sensing state was further pinned through a hydrophobic treatment, and the composite obtained demonstrated a long-term stability (larger than 25 days) as well as a high sensitivity.