Effect of Open Metal Sites in Cobalt-Based Bimetallic Metal–Organic Framework Nanoparticles-Coated Quartz Crystal Microbalance (QCM) for Humidity Detection

As one of the most important environmental parameters, humidity always affects people’s life. It is still a challenge in attaining precise humidity sensors with a rapid and convenient method. Herein, cobalt-based bimetallic zeolitic imidazolate frameworks (ZIFs) nanomaterials were obtained by a facile solution precipitation method and applied for quartz crystal microbalance (QCM) sensors to measure relative humidity (RH) at room temperature. The characterization and sensing results show that ZIF-67 and ZIF-CoX (X = Ni, Cu, Zn) samples possess well-defined polyhedron, and the sensor based on ZIF-CoNi exhibits satisfactory sensitivity (6.10 Hz/%RH, at 97% RH), short response/recovery time (3/3 s, at 97% RH), and narrow hysteresis in the range 11%–97% RH compared with that of ZIF-67, while ZIF-CoCu and ZIF-CoZn have poor sensitivity. Finally, the humidity sensing mechanism was explored by wetting behaviors and FT-IR. Such a comprehensive research provides valuable information for the fast detection of humidity.