In this paper, the adsorption behaviors of three gases (H₂, CO, and C₂H₂) decomposed by the transformer oil on Pd-GaSe and Pd₃-GaSe monolayers were calculated by density functional theory. Compared with Pd single-atom doping, Pd₃ cluster doping changed the original structure and charge distribution to a greater extent, and more obviously improved the conductivity. According to the analysis of adsorption energy, charge transfer and deformation charge density, the results show that the two doped structures have better adsorption performance for the three gas molecules (H₂, CO, and C₂H₂) than the intrinsic GaSe monolayer. Compared with Pd-GaSe, Pd₃-GaSe showed stronger adsorption property for the three gases. Analysis of frontier molecular orbitals and recovery characteristics shows that Pd₃-GaSe can be used as an ideal gas sensitive material for H₂ detection because of its good desorption properties and obvious conductivity changes. Pd-GaSe can be used as a disposable resistive sensor for CO. Pd₃-GaSe is a kind of sensing material suitable for disposable resistance sensors for CO and C₂H₂. These two doped structures have great application potential in gas adsorption and detection, and provide indications for further study on gas sensor detection by means of metal-doped GaSe monolayer.

Using the first-principles theory, this study explored the electronic behavior and adsorption effect of SO₂ on an InP₃ monolayer doped with transition metal atoms (Pd, Pt, Au, Fe, Co and Mo). Through calculation and analysis, the optimum doping sites of TM dopants on the InP₃ monolayer were determined, and the adsorption processes of SO₂ by TM-InP₃ monolayers were simulated. In the adsorption process, all TM-InP₃ monolayers and SO₂ molecules were deformed to some extent. All adsorption was characterized as chemical adsorption, and SO₂ acted as an electron acceptor. Comparing E_ad and Q_t, the order of the SO₂ adsorption effect was Mo-InP₃ > Fe-InP₃ > Co-InP₃ > Pt-InP₃ > Pd-InP₃ > Au-InP₃. Except for the Au atom, the other five TM atoms as dopants all enhanced the adsorption effect of InP₃ monolayers for SO₂. Furthermore, the analysis of DCD and DOS further confirmed the above conclusions. Based on frontier orbital theory analysis, it is revealed that the adsorption of SO₂ reduces the conductivity of TM-InP₃ monolayers to different degrees, and it is concluded that Pd-InP₃, Pt-InP₃, Fe-InP₃ and Mo-InP₃ monolayers have great potential in the application of SO₂ resistive gas sensors. This study provides a theoretical basis for further research on TM-InP₃ as a SO₂ sensor.