| Ammonia gas?NH3?is a kind of great harmful gas to human beings in air pollution.NH3can seriously irritate the airways of humans,causing vomiting,headaches,pulmonary edema and even death.Therefore,it is urgent to develop a gas sensor which can quickly and accurately detect trace amount of NH3.The traditional metal oxide NH3 sensor could't be widely used because of requiring high working temperature.In recent years,tin disulfide?Sn S2?has become a hot research material in the field of NH3 sensing due to its graphene-like structure,higher electronegativity,narrow band gap and many other excellent properties.However,lamellar Sn S2 is easy to stack because of van der Waals forces,which greatly limits its performance.Constructing highly dispersed flower-shaped Sn S2 is the way to expand the practical application of Sn S2.In order to further activate the inactive basal plane with a large proportion in Sn S2,a large number of S vacancies should be constructed which can obtain more active adsorption sites,so as to improve the adsorption capacity of the material.Because of the pure Sn S2 is still not ideal for NH3 sensing performance,it is needed to be further optimized.Hence,the research work of improving the NH3 gas sensitivity of Sn S2 was carried out in turn by three parts:preparation methods,defects control and structural composites.The main work is as follows:?1?Through one-step solvothermal method with thiourea or thioacetamide?TAA?as the source of sulfur respectively,the flower-shaped Sn S2 nanometerials were synthesized successfully with different morphology.Through various characterization analysises,it was determined that the types of Sn S2 synthesized are all n-type semiconductors.Moreover,compared with the group of thiourea,the XRD peaks of Sn S2 which synthesized with TAA increase by about 69%,and the peaks of Raman increase by about 37%.EDS results show that the atomic molar ratio of S and Sn are 2.03:1,which prove that the purity and crystallinity of the material are better than the group of thiourea.Through simple gas sensitivity test,it was found that the response value of Sn S2 to NH3 in TAA group is 2 times higher than thiourea group.?2?There are only a limited number of active sites on the edge structure after all,so the fast argon?Ar?plasma treatment was used to improve the adsorption of NH3 to the inactive basal plane with a large proportion in Sn S2.Moreover,to regulate the number of sulfur vacancy defects on the basal plane of Sn S2,the plasma time was controlled in groups to determine the optimal regulation time.Through various characterization analysises,the XRD peaks of Sn S2after 4s argon plasma increases by about 69%,and the peaks of Raman increases by about 37%.EDS results show that the atomic molar ratio of S and Sn are 1.81:1,which prove that the purity and crystallinity of the material are better and a large number of sulfur vacancy defects are produced.BET analysis shows that the specific surface area increases by 30%and the pore diameter increases by 3%,which provides favorable conditions for the absorption of NH3 gas molecules.It was found that when testing at the concentration of 20ppm of NH3 in 125?,the response value is as high as 7.4 of the Sn S2 after 4s Ar plasma,and the material has excellent selectivity to NH3.Both the response value and selectivity are improved twice as much as the pure Sn S2.The response and recovery time are 137s/176s,respectively.On this basis,the density functional theory was used to calculate the partial density of states,band structure,the differential charge density and gases adsorption energy.And explains in detail why the Sn S2with S vacancy defects has better gas sensitivity.?3?In order to further improve the gas sensitivity of Sn S2 to NH3,three heterogeneous structure of Sn S2/Mo S2/GO was constructed by two-step solvothermal method.The morphology and structure of Sn S2/Mo S2/GO was analyzed according to the characterization and gas sensitivity test.The results show that the heterogeneous structure of Sn S2/Mo S2/GO eliminates the possibility of collision with impurities during electron migration by dispersing impurities and electrons.This special structure can significantly improve the conductivity and the charge mobility of materials.Therefore,the Sn S2/Mo S2/GO heterogeneous structure can significantly reduce the resistance value and the response/recovery time of the gas sensor.The response and recovery time can reach 40s/47s,which is about 4 times better than pure Sn S2.Moreover,it also has a good selectivity for NH3 gas,and the selectivity is improved by 2 times compared with pure Sn S2.By constructing heterogeneous structure,more new ideas have been opened up for the design of LMDs semiconductor sensing materials with high speed response recovery characteristics. |
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