Sandwich‐Structured ZnO/MXene Heterojunction for Sensitive and Stable Room‐Temperature Ammonia Sensing

2D metal carbides/nitrides (MXenes) have attracted considerable interests in NH3 sensing due to their high electrical conductivity and abundant terminal groups. However, the strong interlayer interactions between MXene nanosheets result in challenges related to sensor recovery and rapid response decay in MXene-based sensors. Here, A one-step hydrothermal strategy is developed that anchors Zn atoms and grows ZnO polycrystals on the Ti vacancies of Ti3C2Tx layers, forming a sandwich-structured ZnO/Ti3C2Tx heterojunction. At room temperature, the NH3 sensitivity of ZnO/Ti3C2Tx is a remarkable 45-fold higher than that of Ti3C2Tx, with a low detection limit of 138 ppb and a rapid recovery time of 39 s. Furthermore, the heterojunction exhibits exceptional long-term stability, maintaining a consistent response over 21 days. The results confirm that in situ intercalation of the ZnO polycrystals effectively solves the recovery problem in MXene substrates by completely exfoliating the Ti3C2Tx nanosheets. Meanwhile, the room-temperature sensing performance and recovery speed of the sandwich-structured ZnO/Ti3C2Tx is enhanced by rapid electron conduction. This straightforward and effective route for in situ exfoliation and intercalation of MXene layers promises the broader use of 2Dmaterial heterojunctions in sensing applications.