Acetone Gas Sensing with Quartz Crystal Microbalance and Adsorption Characteristics for UiO-66 Metal-Organic Frameworks

University of Oslo 66 (UiO-66) is a metal-organic framework (MOF) with a high acetone gas adsorption capacity and selectivity. However, the sensor characteristics remain unclear mainly because conventional solvothermal synthesis leads to UiO-66 particle aggregation, impeding stable sensor signal acquisitions. To counter the agglomeration of UiO-66 particles, particle conditioning by solvothermal synthesis using acetic acid and dispersion solution by ultrasonic application were used for uniform particle deposition. This process successfully formed a uniform particle film on quartz crystal microbalance (QCM) sensors via the electrostatic spray method. Using the QCM measuring method, the fabricated UiO-66 sensors exhibited a reversible and stable signal response to acetone gas concentrations spanning several hundred parts per billion to parts per million, whereas the conventional zeolitic imidazolate framework (ZIF)-based sensor did not show a stable sensor signal. Additionally, the UiO-66 sensor sensitivity was positively correlated with the amount of UiO-66 particle coating, confirming that UiO-66 directly affects acetone gas adsorption and desorption. During the adsorption evaluation using UiO-66 particles, acetone gas desorption at 25 +/- 3 degrees C became more pronounced upon reaching adsorption saturation, indicating its characteristics as a sensor material. To evaluate the adsorption strength of UiO-66, we performed density functional theory calculations. The estimated adsorption enthalpy between UiO-66 and acetone molecules was lower than those of ZIF-based MOFs with proven acetone sensor characteristics, thereby confirming the high acetone adsorption performance of UiO-66. Such a lower adsorption energy of UiO-66 suggests that superior sensor sensitivity may have been obtained owing to the high adsorption characteristic of UiO-66 on acetone molecules. These findings indicate that UiO-66 can be used as an adsorbent and sensor material for acetone gas, indicating its potential for various applications.