The Introduction of Defects in Ti3C2Tx and Ti3C2Tx‐Assisted Reduction of Graphene Oxide for Highly Selective Detection of ppb‐Level NO2

Abstract At present, the main gas‐sensing mechanism of oxidized MXene (Ti 3 C 2 T x ) is commonly regarded as Schottky barrier modulation, but the influence of surface defects generated by oxidation is ignored and ambiguous. Herein, oxidized Ti 3 C 2 T 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 Ti 3 C 2 T x /TiO 2 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 Ti 3 C 2 T x /TiO 2 heterojunction in‐situ generated by oxidation. First‐principles density functional theory calculations show that Ti atom vacancy can greatly improve the adsorption ability of Ti 3 C 2 T x to gases (especially for NO 2 ). Subsequently, with the facile oxidability, Ti 3 C 2 T x is utilized as a reductant to assist the reduction of graphene oxide, and Ti 3 C 2 T x /TiO 2 /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 NO 2 (10 ppb), great NO 2 selectivity, and high NO 2 response. The clarification of the gas‐sensing mechanism of oxidized Ti 3 C 2 T x and the utilization of oxidation of Ti 3 C 2 T x provide a new idea for the application of MXenes.