In this study, the adsorption performances of graphene before and after modification to H₂S and CH₄ molecules were studied using first principles with the density functional theory (DFT) method. The most stable adsorption configuration, the adsorption energy, the density of states, and the charge transfer are discussed to research the adsorption properties of intrinsic graphene (IG), Ni-doped graphene (Ni–G), vacancy defect graphene (DG), and graphene oxide (G–OH) for H₂S and CH₄. The weak adsorption and charge transfer of IG achieved different degrees of promotion by doping the Ni atom, setting a single vacancy defect, and adding oxygen-containing functional groups. It can be found that a single vacancy defect significantly enhances the strength of interaction between graphene and adsorbed molecules. DG peculiarly shows excellent adsorption performance for H₂S, which is of great significance for the study of a promising sensor for H₂S gas.

In this study, we reported a successful synthesis of a nanocomposite based on SnO₂ nanoneedles anchored to NiO microsphere by a simple two-step hydrothermal route. The results show that the SnO₂/NiO nanocomposite-based sensor exhibits more prominent performances than the pristine NiO microsphere to NO₂ such as larger responses and more outstanding repeatability. The improved properties are mainly attributed to the p–n heterojunctions formed at the SnO₂–NiO interface, leading to the change of potential barrier height and the enlargement of the depletion layer. Besides, the novel and unique nanostructure provides large and effective areas for the surface reaction. In addition, a plausible growth mechanism and the enhanced sensing mechanism were proposed to further discuss the special nanostructure which will benefit the exploration of high-performance sensors.