Preparation And Properties Of Cobalt Based Metal Oxide Gas Sensitive Materials

In recent years,metal oxide based nanomaterials have attracted much attention.Due to their excellent electrochemical properties and low synthesis costs,metal oxide based nano-materials have shown promising applications in such fields as supercapacitors,sensors,and electrochemical fields.Among them,in the detection of toxic and harmful gases,has been widely studied.Traditional monomeric metal oxide based gas sensors generally have the disad-vantages of high operating temperature,long response/recovery time and poor stability.In order to further improve the gas sensitivity of the material,a series of experiments on composite materials are designed in this paper.Three kinds of multi-element metal oxide composite ma-terials such asα-Fe₂O₃/Co₃O₄,double-shell Co₃O₄ and Pt/Co₃O₄ are synthesized by a two-step method combined with high temperature annealing process.The main contents are as follows:Co₃O₄ nanoparticle-decorated hierarchical flower-likeα-Fe₂O₃ microspheres by a simple two-step method and high temperature annealing.The uniformly dispersed flower-likeα-Fe2O3microspheres with a diameter of 1.1-1.2μm were self-assembled by petal nanosheets with a thickness of 50 nm.A large amount of Co3O4 nanoparticles were modified on the surface ofα-Fe₂O₃ nanosheets.The results of gas-sensing test showed that the sensitivity ofα-Fe₂O₃/Co₃O₄composite sensor to volumetric concentration of 100×10^-6 ethanol was 16.1 at operating tem-perature of 170°C,which was twice that of pureα-Fe2O3 microspheres sensor.In addition,its response/recovery time is 3.3 s/5.4 s,which is significantly lower than the response/recovery time of pureα-Fe2O3 sensors.The increase of gas sensitivity ofα-Fe2O3/Co3O4 composites is mainly attributed to the large specific surface area with large number of reactive sites of the flower-likeα-Fe₂O₃ microspheres,the porous structure of the nanosheets facilitates gas diffu-sion,and synergistic effect between n-typeα-Fe₂O₃ and p-type Co₃O₄.The double-shell Co3O4 hollow nanocages were synthesized by the two-step reaction and calcination of cobalt-based metal organic framework ZIF-67.The morphology and microstruc-ture of the sample were characterized by SEM and TEM,the product has a double hollow do-decahedral morphology with a diameter of about 450 nm.The obtained double-shell Co3O4hollow nanocage is used for gas sensor.Compared with single-layer Co3O4 nanocage,the dou-ble-shell Co3O4 hollow nanocage has excellent gas sensitivity to acetone,the gas response reached 41.9 at the optimum operating temperature of 160oC.The improvement in gas sensing properties is attributed to its excellent hierarchical double-shell hollow structure:large specific surface area and regular arrangement of nanopore channels,as well as the presence of oxygen vacancy defects.The double-shell Co₃O₄ hollow nanocages proved to be an excellent candidate for constructing high-performance acetone sensor for various applications.Preparation of Pt nanoparticle functionalized double-shell Co3O4 nanocages by impregna-tion method.The performance of gas sensor composed of Pt modified Co3O4 nanocage was studied and compared with the pure double-shell Co3O4 nanocage sensors.The results of gas-sensing showed that the response of 2%wtPt nanoparticle modified double-shell Co3O4nanocage composites sensor to acetone was higher than that of double-shell Co3O4 nanocage.The sensor showed good reproducibility and excellent selectivity for acetone gas,the optimum operating temperature is as low as 140oC and the response time is 1.35 s.The excellent gas sensitivity is attributed to the spillover effect and catalytic effect of the Pt nanoparticle,hierar-chical hollow structure of Co₃O₄ nanocages.