The Introduction of Defects in Ti₃C₂T_x and Ti₃C₂T_x‐Assisted Reduction of Graphene Oxide for Highly Selective Detection of ppb‐Level NO₂

Abstract At present, the main gas‐sensing mechanism of oxidized MXene (Ti₃C₂T_x) is commonly regarded as Schottky barrier modulation, but the influence of surface defects generated by oxidation is ignored and ambiguous. Herein, oxidized Ti₃C₂T_x crumpled spheres (MS) are obtained, accompanying numerous surface defects through thermal oxidation of MS synthesized by ultrasonic spray pyrolysis technology and gas‐sensing properties of oxidized MS with Ti₃C₂T_x/TiO₂ crumpled spheres (MT‐10‐1) without new surface defects are compared. It is demonstrated that the significant improvement of the gas‐sensing properties of oxidized MS is due to the introduction of Ti atom defects rather than Ti₃C₂T_x/TiO₂ heterojunction in‐situ generated by oxidation. First‐principles density functional theory calculations show that Ti atom vacancy can greatly improve the adsorption ability of Ti₃C₂T_x to gases (especially for NO₂). Subsequently, with the facile oxidability, Ti₃C₂T_x is utilized as a reductant to assist the reduction of graphene oxide, and Ti₃C₂T_x/TiO₂/rGO crumpled spheres are subtly designed and successfully synthesized for further enhancing the gas‐sensing performance. The MG‐2‐1 sensor achieves a low detection limit of NO₂ (10 ppb), great NO₂ selectivity, and high NO₂ response. The clarification of the gas‐sensing mechanism of oxidized Ti₃C₂T_x and the utilization of oxidation of Ti₃C₂T_x provide a new idea for the application of MXenes.