The selective detection of harmful gases is of great significance to human health and air quality,trigger-ing 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 com-posite,the holes with high oxidizability in p-type BP could oxidize Sn2+ into Sn4+,thus inhibiting the for-mation 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 pro-moted 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 effi-cient NO2 gas sensors through Lewis acidity modification and interface engineering.