Interaction of nitrogen mustard agents and their simulant with zinc oxide surfaces: a density functional theory study

The interaction of hazardous chemical warfare agents (CWAs) with metal oxide surfaces is relevant for understanding their detection by chemiresistive sensors. In this work, the adsorption behaviour of a nitrogen mustard (HN2) and its simulant, dipropylene glycol monomethyl ether (DPGME), on stoichiometric and oxygen-enriched ZnO surfaces is investigated using density functional theory-based methods, complemented by higher-level calculations on the isolated molecules. Both molecules adsorb via coordination to exposed Zn sites and exhibit comparable adsorption energies across all surface models. Despite their distinct molecular structures, HN2 and DPGME induce closely similar modifications in the electronic structure of ZnO, as evidenced by charge transfer analysis, density of states, and work function variations. Oxygen enrichment significantly alters the electronic properties of the surface, leading to a transition from an n-type to a p-type character, which is reversed upon molecular adsorption. Multiple analyses consistently support adsorption-induced electronic redistribution. These results provide atomistic insight into the relationship between adsorption geometry, charge redistribution, and electronic response at oxide surfaces, and rationalize the similar behaviour of structurally different molecules at the ZnO interface.