Preparation Of Zinc-Based Composite Metal Oxides And Their Ammonia Sensing Performance

Gas sensors are widely used in industry,environmental monitoring,civil and other aspects,detection and alarm ammonia,hydrogen sulfide,mercaptan and other toxic gases.Metal oxide semiconductor（MOS）is a kind of important solid state sensor materials,but,traditional single metal oxides have the disadvantages of high working temperature and high detection limit tradition.In recent years,researchers have used recombination,doping,surface modification,morphology regulation and other methods to increase the sensing active sites of metal oxides and accelerate their electron transport capacity.The research and development of high-performance metal oxide gas sensor materials is still the focus of this field.Based on the unique structural characteristics of laminate elements with adjustable and uniform distribution based on hydrotalcite（LDHs）like materials.In this paper,zinc-based hydrotalcite（Zn-LDHs）was used as the precursor,two kinds of composite metal oxide gas sensing materials were prepared by control:ZnO/ZnCr₂O₄and Ru O₂/ZnO/ZnCr₂O₄.The morphology,composition and structure of the samples were characterized and analyzed,and the formation mechanism of the composite metal oxide materials was speculated,the ammonia sensing properties of the samples were tested and the structure-activity relationship was investigated.The main findings are as follows:（1）ZnO/ZnCr₂O₄ heterostructure composite oxides were prepared by air calcination using ZnCr-LDHs as precursor,the calcination temperature obviously affects the composition and morphology of the catalyst.Researches show that the formation of ZnO/ZnCr₂O₄ can be divided into four steps:Firstly,the ZnCr-LDHs laminate structure is destroyed by calcination,forming amorphous Zinc-Chromium metal oxides,while retaining part of the laminate structure.Then,as the calcination temperature rises,the structure of hydrotalcite completely collapses and ZnO crystal phase appears,in which Cr³⁺is doped.The third step is ZnCr₂O₄ nucleation and ZnO crystal phase growth.Finally,ZnO and ZnCr₂O₄ crystal phases continue to grow to form ZnO/ZnCr₂O₄composite metal oxides.The two crystal phases are in close contact to form a crystal interface.NH₃ gas sensitivity test results show that ZnO/ZnCr₂O₄prepared at 500°C calcination has good sensor performance,working temperature as low as room temperature,NH₃ concentration reduced by 10times to 3.75 ppm and excellent NH₃ stability.This is mainly attributed to the synergy between ZnO and ZnCr₂O₄ components.It is speculated that the interface between the two crystal phases improves the election transfer ability of the material,and the active sites on the crystal surface are more than that of single oxide,thus improving the gas sensing performance.（2）Firstly,Ru³⁺was loaded onto ZnCr-LDHs laminates by photodeposition,and Ru/ZnCr-LDHs samples were prepared,Ru O₂/ZnO/ZnCr₂O₄ composite metal oxides were obtained by air calcination.It was found that the samples prepared by calcination at 500°C had the best sensing performance,low NH₃ concentration to 1 ppm and shorter response and recovery time.This may be because the addition Ru O₂increases the number of active sites on the composite meta oxides,thus greatly improving the sensing performance.