Hazardous gas adsorption of Janus HfSeTe monolayer adjusted by surface vacancy defect: A DFT study

Janus transitional metal dichalcogenides (TMDCs) have raised wide attraction because of its unique physical and chemical properties. This work focuses on the effect of single surface vacancy (Se and Te vacancy) on adsorption and sensing properties of Janus HfSeTe monolayer to several hazardous gases (CO, H2S, NH3, NO, NO2, and SO2). The adsorption structures, adsorption energy, charge transfer, electronic properties and work function are calculated using density functional theory. It is found that different surface vacancy (Se or Te vacancy) brings different adsorption behavior, and the introduction of vacancy significantly enhances the chemical interactions between Janus HfSeTe monolayer and adsorbed gases. The adsorption energy and charge transfer obviously increase for all these molecules compared to the adsorption on pristine HfSeTe monolayer. More notably, the adsorption of CO, NO, NO2 and SO2 brings new chemical bond formation, and the atomic density of states (DOS) suggests that there exist states overlapping between dangling Hf atom and atom in molecule. In addition, H2S and NH3 adsorptions make the work function decrease while other adsorptions lead to the risen of work function. Based on the distinguished adsorption properties and different degree of work function variation, Janus HfSeTe is a potential candidate in hazardous gas scavenger and sensing material.