Suppression of Sn2+ and Lewis acidity in SnS2/black phosphorus heterostructure for ppb-level room temperature NO2 gas sensor

The selective detection of harmful gases is of great significance to human health and air quality, triggering the need for special customizations of sensing material structure. In this study, we prepared a novel SnS2/black phosphorus (BP) two-dimensional (2D)-2D heterostructure via the in situ hydrothermal growth of SnS2 nanosheets on exfoliated BP lamellae for NO2 sensing applications. In the SnS2/BP composite, the holes with high oxidizability in p-type BP could oxidize Sn2+ into Sn4+, thus inhibiting the formation of Lewis acidic S vacancies. This Sn2+/Lewis acidity suppression of the composite was further confirmed by X-ray photoelectron spectroscopy and acidic double-layer capacitance analyses, and promoted the adsorption and detection of acidic NO2. Owing to its valence and Lewis acidity engineering, the SnS2/BP heterostructure sensor could detect trace levels of NO2 as low as 100 ppb (parts per billion) with high response, fast response/recovery, good stability, and selectivity at room temperature. The high absorption energy of NO2 (-0.74 eV), as indicated by the density functional theory calculations, suggests that NO2 was chemically adsorbed on the SnS2/BP surface, which was also evidenced by the in situ Raman spectroscopy results. This work opens up interesting opportunities for the rational design of highly efficient NO2 gas sensors through Lewis acidity modification and interface engineering.