A low temperature gas sensor based on Pd-functionalized mesoporous SnO2 fibers for detecting trace formaldehyde

Abstract

The permissible limitation of formaldehyde (HCHO) is 80 ppb in an indoor environment. Hence, the rapid real-time monitoring of trace HCHO is urgent and faced as a great challenge by gas sensors based on semiconducting metal oxides. To enhance the HCHO sensing performance of gas sensors, mesoporous SnO₂ fibers are used to fabricate a bare SnO₂ sensor and then the sensor is functionalized with Pd nanodots by a facile dipping–annealing process. The obtained Pd-functionalized SnO₂ sensor exhibits a very high response to HCHO, ultralow detection limit (50 ppb), excellent sensor selectivity over other reducing gases, and short response and recovery time to 100 ppb HCHO (53 s and 103 s, respectively) at a low working temperature of 190 °C. Herein, the Pd nanodots loaded onto SnO₂ fibers serve as sensitizers or promoters, increasing the amount of adsorbates as well as molecule–ion conversion rate and simultaneously providing a new catalytic oxidization pathway of HCHO (HCHO → [CH₂O]_n (POM) → HCOOH → CO₂ + H₂O) accompanied with a promotion in the electron transfer rate, and thus improving HCHO sensing performance. The combination of the SnO₂ mesoporous structure and catalytic activity of the Pd nanodots loaded could give us a very attractive sensing behavior for applications as real-time monitoring gas sensors with rapid response speed.