Synthesis And Gas Sensing Properties Of ZnFe₂O₄ Based Ags Sensing Materials

With the rapid development of industry and economy,it also brings all kinds of toxic,harmful,flammable and explosive gases,such as hydrogen sulfide(H₂S),volatile organic compounds(VOCs),nitrogen oxides(NO_x),sulfur oxides(SO_x),etc.,which pose a major and continuous threat to environmental safety and human health.Therefore,it is particularly necessary to analyze,monitor,detect and warn the gas.Zinc ferrite(Zn Fe₂O₄)is an important n-type metal oxide semiconductor and its band gap is 1.9 e V.It has high conductivity and catalytic activity,and has become an important part of the field of gas sensors.However,at present,from the preparation and properties of Zn Fe₂O₄,the synthesis of Zn Fe₂O₄ material is still complex and the working temperature is high;From the point of composite and doping,the gas sensing performance enhancement mechanism of Zn Fe₂O₄ materials has not been clearly explained.Therefore,it is of great theoretical significance and application value to further study the preparation,modification methods,gas sensing characteristics and gas sensing performance enhancement mechanism of Zn Fe₂O₄ gas sensing materials.In this paper,we synthesized Zn Fe₂O₄ material by simple hydrothermal method,modified Zn Fe₂O₄ material through different strategies,evaluated the gas sensing characteristics of the material,and studied the possible mechanism of its sensing performance enhancement,which increased the possibility for the development of practical applications of new high-performance gas sensors.The details are as follows:(1)Porous Zn Fe₂O₄ nanospheres were synthesized by a simple one-step hydrothermal method,and the gas sensing properties of Zn Fe₂O₄ materials were comprehensively studied.The results show that the response of Zn Fe₂O₄ to 30 ppm acetone at low operating temperature(150?)is 65.74,and the response-recovery time is(150 s,59 s).At the same time,it has good repeatability and stability.The spherical Zn Fe₂O₄ with rough and porous surface is loosely stacked and dispersed,which can provide rich active sites and convenient adsorption-desorption channels for the target gas,thereby promoting the diffusion of acetone molecules and surface redox reaction.(2)The Ca Fe₂O₄/Zn Fe₂O₄ materials with different proportions were synthesized by two-step hydrothermal method.The results show that the gas sensing performance of Zn Fe₂O₄ can be improved by compounding appropriate amount of Ca Fe₂O₄.Compared with Ca Fe₂O₄,Zn Fe₂O₄ and other ratios of Ca Fe₂O₄/Zn Fe₂O₄,the composite named Ca Fe₂O₄/Zn Fe₂O₄-2 shows the best gas sensing performance for isoprene.The response of the sensor based on Ca Fe₂O₄/Zn Fe₂O₄-2 to 30 ppm isoprene is 19.50,which is 6.3 and2.9 times higher than that of Ca Fe₂O₄ and Zn Fe₂O₄ respectively.In addition,it has long-term stability,good moisture resistance,fast response and recovery time(72 s,35 s).The excellent gas sensing performance of Ca Fe₂O₄/Zn Fe₂O₄-2 may be due to its improved electron hole separation rate,high oxygen vacancy content,large specific surface area,narrow band gap and the formation of p-n heterojunction.Therefore,proper complexing of Ca Fe₂O₄ with Zn Fe₂O₄ is an effective strategy to enhance the isoprene sensing performance.(3)The Pd@g-C₃N₄/Zn Fe₂O₄ material was prepared through a simple one-step hydrothermal method.The Zn Fe₂O₄ modified by flake g-C₃N₄ and noble metal Pd can generate abundant active species,form homojunctions and Schottky junctions,and have synergistic effects,which makes the Pd@g-C₃N₄/Zn Fe₂O₄ composite have high electron-hole separation rate,charge transfer ability,and oxygen vacancy defect.The results show that,compared with pure Zn Fe₂O₄ and g-C₃N₄/Zn Fe₂O₄,the Pd@g-C₃N₄/Zn Fe₂O₄exhibits the best gas sensing performance for triethylamine.The response(S)of the sensor based on Pd@g-C₃N₄/Zn Fe₂O₄ to 30 ppm triethylamine is as high as 85,about 4.7times higher than Zn Fe₂O₄(S=18)and about 2.5 times higher than g-C₃N₄/Zn Fe₂O₄(S=34).Meanwhile the Pd@g-C₃N₄/Zn Fe₂O₄ has good recoverability,long-term stability,selectivity,rapid response-recovery time(39 s,28 s).Therefore,the modification of Zn Fe₂O₄ with flake g-C₃N₄ and noble metal Pd nanoparticles is an effective strategy to enhance the gas sensing performance.