| Summary: | The adsorption capacity of intrinsic SnS<sub>2</sub> to NH<sub>3</sub>, Cl<sub>2</sub> and C<sub>2</sub>H<sub>2</sub> is very weak. However, non-metallic elements B and N have strong chemical activity, which can significantly improve the conductivity and gas sensitivity of SnS<sub>2</sub>. Based on density functional theory, SnS<sub>2</sub> was modified with B and N atoms to analyze its adsorption mechanism and gas sensitivity for NH<sub>3</sub>, Cl<sub>2</sub> and C<sub>2</sub>H<sub>2</sub> gases. The optimal structure, adsorption energy, state density and frontier molecular orbital theory are analyzed, and the results are in good agreement with the experimental results. The results show that the adsorption of gas molecules is exothermic and spontaneous. Only the adsorption of NH<sub>3</sub> and Cl<sub>2</sub> on B-SnS<sub>2</sub> belongs to chemical adsorption, whereas other gas adsorption systems belong to physical adsorption. Moderate adsorption distance, large adsorption energy, charge transfer and frontier molecular orbital analysis show that gas adsorption leads to the change of the conductivity of the modified SnS<sub>2</sub> system. The adsorption capacity of B-SnS<sub>2</sub> to these gases is Cl<sub>2</sub> > NH<sub>3</sub> > C<sub>2</sub>H<sub>2</sub>. The adsorption capacity of N-SnS<sub>2</sub> is NH<sub>3</sub> > C<sub>2</sub>H<sub>2</sub> > Cl<sub>2</sub>. Therefore, according to different conductivity changes, B-SnS<sub>2</sub> and N-SnS<sub>2</sub> materials can be developed for greenhouse gas detection of gas sensors.
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