Preparation Co₃O₄ Composites With P-n Heterojunction By Template Method And Their Enhanced Gas Sensing Properties

With the expanding of science and technology,people pay more attention to the problem of environmental pollution and personal safety.As one of the most hazardous pollutants and carcinogenic organic volatile compounds,formaldehyde can be released from buildings and interior decoration materials.Therefore,it is urgent to develop a rapid detection of low concentration of formaldehyde.Different from the n-type semiconductor,the sensitivity of the p-type semiconductor Co3O4 is lower,but it can selectively oxidize different gases because of its special surface reaction.Structural optimization and construction of p-n heterojunction can greatly improve the sensitivity of Co3O4 based sensors and retain their superior selectivity,long-term stability and other advantages.In this paper,Co3O4/ZnO composites with high surface area and high porosity have been prepared by template method,which is aimed to expand the application of Co3O4 in gas sensing.Specific contents are as follows:1.The hollow Co3O4 spheres were prepared by using SiO2 as a hard template followed by NaOH etching.The prepared hollow spheres have a large specific surface area and outstanding gas sensing properties.On this basis,ZnO was introduced into the system by precipitation method,and the effects of ZnO addition on the gas sensing properties of the composites were investigated.The test results exhibits when the molar ratio of Co:Zn is 2 in the complex,the gas sensitive response of the complex at 160 ? to 10 ppm formaldehyde is about 4 times that of pure Co3O4,which is about five times higher that of sole ZnO,and has a particularly rapid response and recovery.The gas sensing mechanism of ZnO enhanced C03O4 is attributed to the formation of p-n heterojunction and the hollow structure of the material itself.2.The Co3O4/ZnO composites were synthesized by calcination of bimetallic metal-organic framework containing different ratios of Co and Zn as sacrificial templates.The effects of calcination temperature on the morphology and structure of the material were discussed in detail.The composite prepared by the method still maintains the morphology of MOFs and has high porosity.The test results shows that the response of Co3O4/ZnO composite to 10 ppm HCHO was reached maximum at 120 ?,and the detection limit was calculated that lowed to 600 ppb when the molar ratio of Co:Zn is 4.The ehanced properties are attributed to the excellent structure and formation of p-n heterojunction.The method can be extended to the direct synthesis of high porosity and large surface of other complexes to detect environmental toxic and harmful gases.