| Methane(CH4)is a colorless,tasteless,flammable and explosive gas.It is not only the main raw material of many synthetic gas and chemical products,but also the main component of natural gas and mashgas.It is also one of the main gases that cause greenhouse effect.Therefore,it is very important to develop a reliable CH4 Sensor to detect CH4 leakage in real time for safe storage,transportation and use.SnO2 is a typical n-type metal oxide semiconductor,which is one of the earliest developed and most widely used gas sensing materials.The biggest advantage is that SnO2 is sensitive to a variety of gases.In this paper,SnO2 nanomaterials were modified by other metal oxide semiconductors and noble metals to improve their gas sensitivity(response value,working temperature,stability,etc.)to CH4.The sensitization mechanism of SnO2nanomaterials to CH4 was studied.At the same time,through the first principle calculation based on the density functional theory,the doping model of Pt and the adsorption model of CH4 under the two modes of surface deposition and doping are established respectively,At the same time,through the first principle calculation based on the density functional theory,the doping model of Pt and the adsorption model of CH4 under the two modes of surface deposition and doping are established respectively,and the doping formation energy and adsorption energy of the model are calculated,which provides a theoretical basis for the study of improving the CH4 sensitivity of SnO2 by doping noble metals.1.Nanoflower-like SnO2 with uniform particle size and good dispersibility was successfully synthesized by hydrothermal method using SnCl4?5H2O as the Sn source.Then,the WO3 nanosheets synthesized by the hydrothermal method were supported on the surface of the flower-like SnO2 sample by the impregnation-calcination method to improve the gas sensitivity of SnO2 to CH4 gas.When the loading amount of WO3nanosheet reaches 25 wt%,the specific surface area of SnO2 nanoflower increases from4.37 m2g-1 to 6.49 m2g-1.The results of gas sensing performance test show that the the optimal working temperature of SnO2 sensor is reduced from 120 oC to 110 oC and the sensitivity to CH4 is improved by the modification of WO3.2.Using HAuCl4·4H2O as the Au source,the noble metal Au with different content was successfully deposited on the nanoflower-like SnO2 surface to form the Au-SnO2nanoflower like gas sensitive material with high sensitivity to CH4.When the deposition amount of Au nanoparticles reached 1.5 wt%,the specific surface area and the content of chemisorption oxygen were improved compared with the pure SnO2 samples.And,the gas sensitivity test results show that the 1.5-Au/SnO2 gas sensor achieves the best gas sensitivity performance for CH4,sensitivity and selectivity have been greatly improved.3.Pt-SnO2 nanoflower-like gas-sensitive composites with both noble metal doping and surface deposition were successfully synthesized by thermal reduction-calcination using H2Pt Cl6?6H2O as the Pt source.When the doping amount of Pt was 2.5 wt%,the specific surface area of Sn O2 increased greatly from 4.37 m2g-1 to 21.47 m2g-1.The doping of Pt increases the content of defect oxygen and chemisorption oxygen of SnO2nanomaterials.The results of gas sensing performance test show that the gas sensing performance of 2.5-Pt/SnO2 gas sensor is the best,the best working temperature is reduced from 120 oC to 100 oC,and the sensitivity and stability are greatly improved.4.Based on first-principles calculations of density functional theory,the models of Pt surface deposition,doping on SnO2(110)surface and CH4 adsorption on SnO2(110)surface were established.After optimization calculation,it is concluded that:1)The doping formation energy of Pt at Sn6c site is the lowest,indicating that Pt is easier to be doped to Sn6c site.2)For the two types of models of Pt,the crystal energy model of Pt doped on SnO2(110)surface has lower adsorption energy for CH4 molecules.3)In each adsorption model,CH4 molecules are most easily adsorbed on theO2C vacancy of the top layer of the model,and the adsorption system is the most stable.The gas-sensitivity mechanism of sensitive materials was further verified by comparing the adsorption capacity of two modified models for CH4 molecules and the charge population analysis before and after adsorption.It also provides a possible effective method for improving the gas sensing performance. |
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