Adsorption behaviour of Si anchored on g-C₃N₄/graphene van der Waals heterostructure for selective sensing of toxic gases: Insights from a first-principles study

Monitoring the levels of toxic gas molecules could efficiently ensure the safety of human health and the environment. Herein, the adsorption behaviour, geometries, energies and electronic properties of H₂S, CO, NO₂, NH₃ and CO₂ gas molecules on the Si-doped g-C₃N₄/graphene surface were systematically investigated using density functional theory calculations. Based on the study of adsorption and desorption behaviour, we indicate that Si-doped g-C₃N₄/graphene was a suitable sensing material for H₂S, CO and CO₂, while being a disposable gas sensor for the detection of NH₃ and NO₂ due to their greater adsorption energy. The electronic properties of Si-doped g-C₃N₄/graphene heterostructure showed strong hybridisation between the adsorbate orbitals and interacting surfaces, as well as the remarkable presence of NH₃ and NO₂ orbitals around the Fermi level. The Si-doped g-C₃N₄/graphene were potentially good H₂S, CO and CO₂ sensors because of the short recovery time, shift in electrical conductivity, apparent charge transfer and reasonable adsorption energies. To sum up, the results obtained in this study could provide details about the process of gas sensing mechanism.