Dual-MOF-Layered Films via Solution Shearing Approach: A Versatile Platform for Tunable Chemiresistive Sensors

Metal-organic frameworks (MOFs) are ideal for gas sensing due to their high porosity and chemical diversity. However, their low electrical conductivity has traditionally limited their application in chemiresistive-type sensors. The recent development of electrically conductive MOFs (cMOFs) has addressed this limitation. However, directly designing cMOFs with specific sensing properties remains challenging due to the limited understanding of their structure-property relationships. At this stage, the synergistic integration of cMOFs with conventional insulating MOFs has emerged as a viable solution, enabling diverse gas interactions and the rational design of sensing properties. Despite this potential, exploration of the diverse roles of MOFs in such composites remains underutilized. Herein, we develop a series of MOF-on-cMOF sensors and demonstrate their tunable sensing properties. A two-step solution-shearing-based film fabrication method enables facile integration of cMOFs with a wide range of conventional MOFs in layered structures. On cMOF thin film as a primary sensing layer, secondary MOF layers with different pore structures and adsorption properties were strategically selected and deposited. These layered film sensors exhibited tunable sensing properties, including enhanced sensitivity, selectivity, response speed, and recovery for analytes such as NH₃, H₂S, and NO₂. These improvements cannot be achieved solely through the conventional role of MOFs as sieving layers. Furthermore, computational analyses elucidated the structure-property relationships underlying these improvements, offering key insights into the rational design of MOF-based gas sensors.