Metal-Organic Framework Crystal-Assembled Optical Sensors for Chemical Vapors: Effects of Crystal Sizes and Missing-Linker Defects on Sensing Performances

Microporous metal-organic frameworks (MOFs) are promising candidate materials for chemical sensing, but the reproducible fabrication of MOF-based sensors with optimized and stable performances remains a significant challenge. Here, we report the fabrication of MOF optical sensors with steady but tunable optical properties via assembling UiO-66 crystals with controllable sizes and missing-linker defects. The well-defined but tunable microscopic and mesoscopic structural features of MOF sensing components greatly facilitate the optimization of device performance. The UiO-66 crystal-assembled sensors display fast response (2.00 s) and short recovery (3.00 s) to ethanol vapor (one of the analytes we tested). Our systematical investigation indicates that the mesoporous features of sensing components contribute greatly to the enhanced sensitivity (by similar to 24.6% to the saturated ethanol vapor), response speed (by similar to 42.9%), and recovery speed (by similar to 59.7%) of the crystal-assembled sensors in comparison to their dense counterpart. The building crystal sizes show a slight influence on the response speed but profound effects on the sensitivity and recovery performances of sensors. The missing-linker defects have obvious beneficial effects on the desorption kinetics of analyte and can cause a faster recovery of sensors.