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.