Engineered Ce ₂ Sn ₂ O ₇ /TiO ₂ Heterojunctions for High‐Performance MEMS Ammonia Gas Sensor

ABSTRACT Pyrochlore‐based metal oxide nanocomposites offer an attractive pathway for developing next‐generation gas sensors by exploiting interfacial charge transfer and band engineering. Here, we report for the first time the use of Ce 2 Sn 2 O 7 /TiO 2 nanocomposites for ultra‐trace NH 3 detection at room temperature. The materials are synthesized via a facile hydrothermal route and systematically evaluated against common volatile organic compounds, including ethanol, acetone, methanol, n‐butanol, isopropanol, and triethanolamine. The Ce 2 Sn 2 O 7 /TiO 2 heterojunction demonstrated outstanding selectivity toward NH 3 , with the optimized CeTi2 sensor delivering an ultrahigh response of 83.8% to 100 ppm, a rapid response time of 12 and 5 s, and an exceptionally low detection limit of 2 ppb under ambient conditions (25°C). At 100°C, the prepared CeTi2 sensor displays a gas sensing response of 82.1% towards 100 ppm of NH 3 . Beyond sensitivity, the device exhibited excellent repeatability and long‐term stability, and ensured reliable operation under realistic environments. Mechanistic analysis revealed that the Ce 2 Sn 2 O 7 /TiO 2 interface induces strong surface band bending and remarkably accelerates charge transport and reversible adsorption–desorption dynamics. This work establishes Ce 2 Sn 2 O 7 /TiO 2 as a pioneering platform for ppt‐level NH 3 detection, offering a powerful combination of selectivity, stability, and energy‐efficient operation for environmental monitoring and industrial safety.