Preparation Of Metal Oxide-based Hydrogen Sulfide And Sensing Materials Performance Study

In recent years,the green development model of sustainable development has been sought after,and more and more attention has been paid to the harm caused by air pollution to the environment and human health.Correspondingly,the detection of polluting gases in the atmosphere is becoming more and more important.In this field,metal oxide gas sensors have attracted much attention due to their small size,low energy consumption,and low cost.However,metal oxides still have some unavoidable defects as gas sensing materials,such as low sensitivity,high detection limit,and poor selectivity.Therefore,it is very necessary to improve the gas-sensing properties of metal oxide materials by modifying them.In this work,the morphology,band structure and surface defects of metal oxides were modified and modified by means of ultrasonic treatment,calcination,hydrothermal treatment and electrospinning.Gas-sensing materials with high sensitivity,low detection limit,low operating temperature,fast response and recovery speed and stable working characteristics are obtained.In this paper,the microstructure,chemical state,and electrical properties of the material were characterized by means of scanning electron microscopy,and its gas-sensing mechanism was analyzed.The main research contents of this paper are as follows:(1)SnO2 multilayer nanosheets were prepared by the synthesis method of ultrasonic treatment and calcination.Its H2S gas sensing performance was tested,and it was found that it has better gas sensing performance compared with pure phase metal oxide gas sensing sensors in previous literatures.At 100℃,the sensitivity to 10 ppm H2S(S=Ra/Rg)is as high as 293,the response time and recovery time are 210 and 178 s,respectively,and the detection limit is as low as 1 ppm.The enhanced gas sensing performance is attributed to the effective surface area brought by its excellent hole structure,which provides sufficient active sites for oxygen adsorption,and the gap and hole structure between the sheets also allow the gas to diffuse freely,further enhancing the gas-sensing performance.(2)Ni0.9Zn0.1O/ZnO nanosheet-coated fibers were prepared by a combination of electrospinning and hydrothermal method to improve the sensing performance of ZnO materials for H2S.The composite fibers are about 2 μm in diameter and are densely and vertically covered by irregularly shaped nanosheets with a thickness of about 20 nm.When the operating temperature is 100℃,the maximum response of the Ni0.9Zn0.1O/ZnO sample to 5 ppm H2S is about 450,which is 15 times that of the pure ZnO nanofiber gas sensor(～30).In addition,the Ni0.9Zn0.1O/ZnO-based gas sensor exhibits good selectivity and stability for H2S,and can also effectively detect hydrogen sulfide at concentrations as low as 10 ppb.The p-n heterojunction existing between Ni0.9Zn0.1O and ZnO nanoparticles is considered to be the main reason for its excellent gas sensing performance.(3)WO3 nanoparticle materials were synthesized by calcining paratungstic acid in a muffle furnace.Dicyandiamine was added to the raw materials,mixed uniformly and then calcined,which could safely and effectively obtain Ov-WO3 containing surface oxygen vacancies.The number of surface oxygen vacancies can be directionally controlled by changing the calcination temperature.The gas-sensing properties of WO3 and Ov-WO3 were tested,and Ov-WO3-600 obtained by mixing with dicyandiamine at 600℃ showed the best performance.At 100℃,the sensitivity to 5 ppm H2S reached 2777,and the response time was only 2 s,and the recovery time was also short(178 s).WO3 and Ov-WO3 materials have little response to other gases and can work stably for a long time.The mechanism of oxygen vacancies enhancing gas sensing performance is mainly attributed to the nature of their donor defects.A moderate amount of oxygen vacancies can provide additional free electrons into the conduction band of the material,thereby increasing the resistance change before and after the gas sensing reaction.Surface oxygen vacancies can also make more material surfaces adsorb more oxygen anions.However,with the further loss of oxygen atoms on the surface of the material,the lattice mismatch intensifies,and the interfacial barrier during the electron migration process increases,which hinders the further improvement of the sensitivity of the material.