Alkalized SnS Nanoflakes with Enhanced Sensing Properties towards Methanol Vapor

Two-dimensional (2D) group-Ⅳ monochalcogenides MX (M = Ge, Sn; X = S, Se) are isoelectronic and isostructural analogues to phosphorene. Due to superior oxidation resistance relative to black phosphorus, MX are recently explored to be potentialsubstitute of phosphorene for highly sensitive gas sensor applications. In this work, nanoflakes of tin monosulfide (SnS) was synthesized by a one-step solvothermal method and then employed for methanol-sensing at room temperature. The as-synthesized SnS shows nanoflower-like hierarchical architecture assembled by 2D nanoflakes. To achieve satisfactory gas response magnitude, a KOH alkalization process for post-treatment of the synthesized SnS was developed further. It is proved that appropriate alkalization could induce the ultrathin nanoflakes and introduce additional –O function terminals on the surface, which are favorable for methanol adsorption and response. The resultant alkalized SnS sensor displays a ∼3.2-fold enhancement in gas response to 5 ppm methanol. And it is capable of sensing rarefied methanol vapor as low as 100 ppb. The response enhancement could attribute to the alkalization-induced ultrathin geometry of SnS nanoflakes, introduction of lattice defects and –O functional terminals available for active adsorption of gas molecules. Further first-principles calculations clarify the crucial contribution and underlying mechanism of attached –O terminal on methanol adsorption and reaction clearly.