Trace ammonia detection realized by mixed Ti-Zr metal-organic-frameworks and its application in exhaled breath sensing at room temperature

The presence of ammonia in exhaled human breath serves as a crucial biomarker for renal diseases. This paper presents a highly sensitive ammonia sensor operable at room temperature, utilizing a Ti/Zr dual metal MOF as its core component, synthesized through a straightforward solvothermal reaction approach. The Ti/Zr-MOF demonstrates excellent responsiveness to ammonia gas, with a detection limit of remarkable sensitivity, reaching as low as 2 ppm. Notably, the sensor exhibits practical insensitivity to similar concentrations of other major interfering breath volatiles, including acetone, ethanol, and saturated moisture. Electron Paramagnetic Resonance (EPR) analysis confirms the presence of oxygen vacancies (Ov) in Ti/Zr-MOF materials, with Ti/Zr-MOF exhibiting stronger Ov signals and the potential for enhanced NH3 adsorption and capture. In-situ FTIR spectrum analysis reveals ammonia-induced -OH (H₂O) moiety formation, indicating a reaction between adsorbed $O_2^{-}$ species and ammonia, resulting in decreased electrical resistance of Ti/Zr-MOF.