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.