Tunable Synthesis of 2D Bismuth Oxyhydroxide and Oxysulfide from Solid–Liquid Interfacial Reaction for High Performance Optoelectronic Gas Sensing

Abstract The self‐limiting Cabrera–Mott oxidation reaction on metal surfaces provides an effective pathway for synthesizing atomically thin 2D metal oxide. Inspired by this reaction, it is proposed that solid bismuth metals can react with dissolved oxygen and water molecules in an aqueous environment, forming an ultrathin oxyhydroxide layer on their surfaces. The lattice mismatch between the surface oxyhydroxide layer and the underlying pure metal enables the mechanical exfoliation of detached 2D oxyhydroxide nanosheets. Moreover, the sulfurization interaction between the oxyhydroxide and dissolved H₂S expands the applicability of solid–liquid interfacial reactions for realizing 2D bismuth oxysulfide, effectively tuning their electronic bandgap energy, work function, and band position. Given its good photoresponse from blue to UV light, the optoelectronic gas sensing performances of bismuth oxysulfide are investigated. Under purple light irradiation, the Bi₂O_1.12S_1.88‐based gas sensor exhibits an excellent optoelectronic response factor of 48.5% toward 10 ppb NO₂, which is the lowest detection limit for reported bismuth compounds‐based gas sensor so far. This work provides a novel and facile synthesis approach for 2D metal oxyhydroxide and oxysulfide and simultaneously demonstrates the substantial potential of bismuth oxysulfide in high‐performance optoelectronic gas sensing.