Based　on　first-principles　computations　and　global　search　method,　we　identify　a　new　two-dimensional　K3Cl2　nanosheet　with　unique　structural　and　electrical　properties.　Formation　energy　and　phonon　spectrum　calculations　and　ab　initio　molecular　dynamics　(AIMD)　simulations　confirm　the　stability　of　this　predicted　structure.　The　metallic　character　of　the　K3Cl2　can　be　maintained　under　tensile　uniaxial　and　biaxial　strains.　The　calculation　demonstrates　that　K3Cl2　nanosheet　can　effectively　detect　NO2　molecules　from　the　mixture　of　H2,　H2O,　NH3,　CO,　NO,　NO2　and　CO2.　The　reason　of　the　conversion　from　metal　to　semiconductor　of　K3Cl2　adsorbing　different　number　of　NO2　molecules　might　lie　in　the　change　of　bonding/antibonding　state　of　K-N,　K-O　and　N[sbnd]O　bonds.　Our　calculated　results　show　that　K3Cl2　nanosheet　is　a　promising　NO2　gas　sensor　and　capturer　with　high　selectivity　and　sensitivity.　©　2022　Elsevier　B.V.