Ni-doped UiO-66 defect engineering enhanced quartz crystal microbalance sensors for ppb-level ammonia detection

The development of highly selective trace ammonia (NH 3 ) detection technology based on metal-organic frameworks (MOFs) is of critical significance for the precise monitoring of ammonia in industrial and agricultural production environments. In this study, a series of UiO-66 materials doped with different metal ions (X-UiO-66, X = nickel, copper, iron, and aluminum) were synthesized. Through comparative analysis, the Ni-UiO-66 based QCM sensor exhibited superior sensing performance for trace NH 3 at room temperature: A detection limit as low as 50 ppb, high sensitivity (frequency response of 1766 Hz to 25 ppm NH 3 ), fast response/recovery times (10 s/13 s), as well as good selectivity, long-term stability, and reliable detection capability in high-humidity environments. The doping of Ni 2 + creates defects in the framework, increases the specific surface area, and provides more abundant active adsorption sites, thereby significantly enhancing the sensitivity to NH 3 . Furthermore, adsorption tests, Gaussian simulations, and in-situ infrared spectroscopy revealed a significantly optimized reversible weak chemical adsorption interaction between Ni-UiO-66 and NH 3 , which endowed the material with enhanced selectivity compared to pristine UiO-66 toward NH 3 . This work provides a reliable strategy for designing MOF-based sensing materials that combine structural stability and high activity.