2D/2D Dy 2 O 3 Nanosheet/MoO 3 Nanoflake Heterostructures for Humidity-Independent and Sensitive Ammonia Detection.

Chemiresistive ammonia gas (NH 3 ) sensors have been playing a significant role in the fields of environmental protection, food safety monitoring, and air quality evaluation. Nevertheless, balancing the high sensitivity and humidity tolerance remains challenging. Herein, the two-dimensional (2D) heterostructures of molybdenum trioxide (MoO 3 ) nanoflakes decorated with dysprosium oxide (Dy 2 O 3 ) nanosheets (termed Dy 2 O 3 /MoO 3 ) were synthesized via a facile probe-sonication method. With respect to pristine MoO 3 counterparts, the optimal Dy 2 O 3 /MoO 3 sensors possessed a 4.49-fold larger response at a lower temperature (30.52@328.2 °C vs 6.8@369.7 °C toward 10 ppm of NH 3 ), shorter response/recovery times (11.6/2.9 s vs 26.9/43.4 s), 52.6-fold higher sensitivity (17.35/ppm vs 0.33/ppm), and a lower theoretical detection limit (1.02 vs 32.82 ppb). Besides the nice reversibility, wide detection range (0.45-100 ppm) and robust long-term stability, inspiringly, the Dy 2 O 3 /MoO 3 sensors showed a nearly humidity-independent response. These impressive improvements in the NH 3 -sensing performance were attributed to numerous heterojunctions to strengthen the carrier concentration modulation and the compensation/protection effect of Dy 2 O 3 to mitigate the humidity effect. Moreover, the Dy 2 O 3 /MoO 3 sensors showed preliminary application potential in monitoring pork freshness. This work provides a universal methodology for constructing NH 3 gas sensors with high sensitivity and good humidity resistance and probably extends the application scenarios of MoO 3 -based sensors in the Internet of Things in the future.