Acid-engineered sulfated zirconium oxide for highly sensitive and selective NH₃ gas sensing

Ammonia gas (NH₃), a toxic gas, demands precise detection for environmental and health safety, necessitating highly sensitive sensors. Sulfated metal oxides exhibit unique advantages in gas sensing due to their abundant acid sites, which facilitate gas adsorption and activation. Herein, Zr₃SO₉ was synthesized via the hydrothermal method and modified by acid treatment to enhance NH₃-sensing performance. Results showed that 2 M HCl-treated Zr₃SO₉ (2 M HCl-Zr₃SO₉) exhibited superior NH₃-sensing properties. Its response value to 50 ppm NH₃ reaches 33.5, representing a sixfold increase over pristine Zr₃SO₉. The detection limit is as low as 0.26 ppm, while maintaining excellent selectivity and repeatability. Mechanistically, acid treatment enhanced surface acidity and optimized acidity distribution. The improved performance stems from synergistic adsorption across acidic sites with varying acidity coupled with Zr⁴⁺/Zr³⁺ redox-driven electron transfer, which collectively promote NH₃ adsorption and conversion. This work highlights acid site engineering as a key strategy for developing highly efficient metal oxide semiconductor sensors.