The practical applications of SnO2 materials for NO2 detection in the field of indoor air quality monitoring are strongly plagued by low sensitivity toward ppb-level NO2. Herein, an in situ exsolution strategy was developed to prepare Sn-containing materials with abundant oxygen vacancy defects and Sn/SnO2 heterojunctions (designated as Sn/SnO2-x), which were obtained by annealing mixture of commercial SnO2 and NaBH4 in Ar atmosphere. Compared to commercial SnO2, the optimal Sn/SnO2-x-3 displays the obvious advantages of low operating temperature (110 °C), high sensitivity (response value of 4.65 toward 80 ppb NO2), and low limit of detection (10 ppb NO2 with response value of 1.17). The improvement of NO2 sensing performances is attributed to the synergistic effect of introducing oxygen vacancy defects and constructing Sn/SnO2 heterojunctions. Theoretically, the former leads to increasing the active sites for adsorption of NO2 and the latter reduces the band gap for improvement of carrier concentration. Additionally, this NO2 sensor shows excellent sensing performances for monitoring NO2 concentration in simulated indoor environment. This work not only provides an effective and large-scale approach to prepare novel sensing materials from commercial metal oxides by exsolution method, but also opens the way to fabricate high-performance gas sensors for detection of NO2 with low concentrations.

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