ABSTRACTThe adsorption of a toxic gas, cyanogen chloride (CNCl) on pristine, Al– and Si–doped BN nanosheet investigated using density functional theory (DFT). The adsorption energies of the most stable complexes of CNCl on pristine, Al– and Si–doped BN nanosheet are –19.96, –95.02 and –176.90 kj/mol, respectively. We found that the CNCl gas has a chemisorption interaction over the Al– and Si–doped BN, with significant change in the structure shape of the CNCl molecule. The value of adsorption interaction energy of Si-boron nitride is very large than that of the Al-boron nitride toward the toxic gas. As a result the Si-boron nitride nanosheet is more reactive to dissociate the gas molecule into safely small fragments. The adsorption of the CNCl molecule can significantly decrease the HOMO–LUMO energy gap of the Al–doped BN by about 14.06%. It is suggested that the Al–doped BN can be considered as a potential nanostructure for sensing the toxic CNCl.