Abstract
Tin oxide is widely studied for ethanol sensing because of its high sensitivity and environmental benignity; yet its operating temperatures generally exceed 200 °C to achieve an acceptable overall sensing performance. In this study, we report a layered mesoporous aggregate of SnO2 nanocrystals 3–5 nm in size, which is synthesized by oxidizing metallic tin particles in a mixed aqueous solution of HNO3 and H2O2 at 80 °C. The aggregate calcinated at 300 °C possesses a high specific surface area of 135 m2 g−1, and 0.182 cm3 g−1 mesopores ca. 2.5 nm in size. At an operating temperature of 180 °C, the SnO2 aggregate exhibits a response of 110 towards 100 ppm ethanol in air. At an even lower working temperature of 140 °C, an ideal overall sensing performance is achieved: a response of 37, a response/recovery time of 26/21 s, together with high selectivity and stability. The layered mesoporous architecture with a high specific surface area contributes to the high response at low operating temperatures. Besides, with increasing operating temperatures from below to beyond 150 °C, it takes much a longer time to achieve a total recovery in resistance. The ethanol sensing mechanism is thus believed to change accordingly from the direct adsorption one to the oxygen ionosorption model.
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