Energy-Level Alignment at TiO@NH-MIL-125 Interface for High-Performance Gas Sensing.

Metal oxide (MO)-based chemiresistive sensors have great potential in environmental monitoring, security protection, and disease diagnosis. However, the thermally activated sensing mechanism in pristine MOs leads to high working temperature and poor selectivity, which are the main challenges impeding practical applications. Precise modulation of the band structure at the heterojunction interfaces of MOs offers the opportunity to unlock unique electrical and optical properties, enabling us to overcome these challenges. Metal-organic frameworks (MOFs) with tunable structures are promising materials for aligning the energy levels at the heterojunctions of MOs. Herein, we report the energy-level structural engineering of MO@MOF heterojunctions to optimize chemiresistive sensing performance. The interface was flexibly modulated from a straddling gap to a staggered gap by -NH functionalization of TiO@(NH)-MIL-125, varying x from 0 to 1 and 2, respectively. TiO@(NH)-MIL-125 combines the advantages of MOs and MOFs to synergistically improve gas-sensing properties. As a result, TiO@NH-MIL-125 is the first light-activated material to detect NO at 1 ppb with a response time of < 0.3 min at room temperature. It also exhibited excellent selectivity and long-term stability. Our study underscores the potential of energy band engineering in creating high-performance sensors, offering a strategy to overcome current material limits.