First Principles Study Of Adsorption Behavior Of Three Organic Hazardous Gases On The Surface Of SnO₂-based Gas Sensing Materials

As the most studied and widely used metal oxide gas-sensitive material,SnO₂ has been used in the detection of hazardous gases at home and abroad.The gas-sensitivity mechanism is still controversial,so it is necessary to continue to develop research work of this area.In this paper,the Dmol3 module in Materials Studio is used to simulate the adsorption process of three organic volatile gases,acetonitrile,tetrachloroethylene and acrylonitrile,on the surface of SnO₂-based gas-sensitive materials,with adsorption energy,charge transfer,and electronic state density being calculated.The following main conclusions were reached:（1）When the three gases are adsorbed on the surface of the SnO₂-based gas sensitive material,the adsorption process is an exothermic process.The system releases energy to outside to promotes the stability of the entire system.At the same time,the gas molecules will transfer charges to the surface,which will increase the surface charge and make it more stable,leading to the decreasing of surface resistance.After the adsorption process finished,the surface electronic structure changed with a new energy band appearing between the forbidden bands of SnO₂,which enhanced the electronic transition ability of SnO₂.（2）For pure SnO₂,an intrinsic SnO₂（110）crystal plane is constructed in this paper.Of the four gases,tetrachloroethylene cannot be directly adsorbed on the SnO₂（110）crystal plane,and will be far away from the SnO₂（110）crystal plane during the adsorption process.The other two gases can be directly adsorbed on the Sn_5C atoms of the surface and N atom of the gases being connected to the Sn_5C atoms of the surface with the formation of a Sn-N key.（3）When SnO₂ is exposed to the air,it actively absorbs O₂,and the surface with oxygen vacancy defects can absorb O^2-after O₂ ionizes to obtain O^2-.In this case,a pre-adsorbed oxygen SnO₂（110）surface is constructed in this paper.All three gases can be directly adsorbed on the surface of pre-adsorbed oxygen.When perchloroethylene is adsorbed on the surface,O=O bond of the pre-adsorption surface is broken to generate new bonds.Compared with the intrinsic surface,the adsorption performance is enhanced;The adsorption situation of the other gases are similar to that of the intrinsic surface,and the corresponding adsorption parameters change a little,which means the adsorption performance are not enhanced.（4）When Perchlorethylene（PCE）gas molecules are adsorbed on the SnO₂/rGO heterocrystalline surface,they also keep away from the surface.However,under the same conditions,when the PCE gas molecules are adsorbed on the SnO₂/rGO heterocrystalline surface,the values of adsorption energy and charge transfer amount become larger.Therefore,the gas sensing performance of PCE gas molecules on the surface of SnO₂/rGO composite gas sensing material is improved.