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Defects can significantly alter the properties of 2D material surfaces, thereby affecting the application results. In this work, the adsorption behaviors of H 2 S, SO 2 , NH 3 , and NO 2 gas molecules on rationally defective diboron dinitride (n -BN) monolayers in the presence and absence of an external electric field and moisture condition are studied by the first-principles calculation approach. The results demonstrate that the boron and nitrogen defects are more likely to be generated and both defective monolayers have strong absorption effects on SO 2 and NO 2 gas molecules with absolute values of adsorption energy above 2.5 eV. And the conductivity change after adsorption of NO 2 molecule is particularly pronounced in nitrogen defect monolayer, thus greatly increasing the sensitivity to the gas molecule. Based on the high sensitivity, the defective monolayer could be an ideal one-time scavenger for SO 2 and NO 2 gas molecules. While the H 2 S and NH 3 molecules could obtain the appropriate adsorption energy and the adjustable recovery time on the defective monolayer under the dry or existent external electric field environment. These results make it possible to design a useable gas device with good gas sensing and capturing characteristics on the defective n -BN monolayer. [Display omitted] • The gas sensing and capturing properties on defective n -BN are studied by DFT method. • Defects can improve the sensitivity of the n -BN monolayer to H 2 S, NH 3 , SO 2 and NO 2 gas molecules. • Electrical conductivity, recovery time, electrical field and humidity are all considered. • Defective n -BN monolayer can be expect to be an ideal scavenger for SO 2 and NO 2 gas molecules. [ABSTRACT FROM AUTHOR]