The Preparation Of Layered Cobalt Hierarchical Strucure Precursors And Its Gas Sensing Properties

With the development of economy and industrialization,the environmental pollution is becoming increasingly serious.Air pollution is mainly from the burning of fossil fuels,the emissions of industrial production andvehicle exhausts,causing a series of environmental problems,such as haze,acid rain and the destruction of the ozone layer,which cause great threat to the human life.Semiconductor based gas sensors have attracted considerable attention because of their high portability,simplicity of use and low cost,whicn can be used to realize real-time monitoring of toxic and harmful gases.The semiconductor gas sensing materials are the key factors to build gas sensors.It is meaningful for us to carry out the research and prepare the semiconductor gas sensing materials with excellent performance to realize the detection of toxic and harmful gasesAs a typical p-type semiconductor material,Co3O4 has the properties of high catalytic activity,good stability,excellent electrochemical and magnetic properties,which is widely used in many research fields.However,thegas sensing property of Co3O4 is relatively weak,the low response value?poor selectivity?high response temperature and other shortcomings limits its application in gas sensing.In the recent years,a lot of researchs has been carried out on improving the gas sensing performance of Co3O4 semiconductor materials.The construction of p-n hetrejunction semiconductor and the construction of graphene oxide composites are the focus of present researches.1.A series of CoTi-HTLcs materials with different cobalt-titanium ratios were prepared by coprecipitation method,following with calcination procedure to construct Co3O4-TiO2 hetrejunction semiconductor materials.A series of analytical tests were used to test the morphology and crystal structure of semiconductor materials to characterize the formation of Co3O4-TiO2 hetrejunction.Gassensing property tests showed that the gas sensing properties of Co3O4-TiO2 hetrejunction semiconductor materials shows significantly improvement compared with Co3O4.The sample of CoTiO-4-350 shows the best gassensing performance,the gas sensing response to 50 ppm xylene reached 116 at the operating temperature of 115?,which is 3.5 times higher than Co3O4-350,and the response and recovery time are 130 s and 150 s.What's more,the Co3O4-TiO2 hetrejunction semiconductor materials have the advantages of low detection limit,good selectivity,repeatability and stability.Therefore,forming p-n hetrejunction semiconductor materials is an effective way to enhance the gas sensing performance of Co₃O₄.2.The modified Hummers method was used to prepare the graphite oxide.Co-HTLcs/rGO composites were prepared by co-precipitation method,and following with calcination under nitrogen atmosphere to prepare Co₃O₄/rGO composites.To verify the formation of graphene-based composites,the morphologies and crystal structures of the composites were characterized by a series of analytical tests.From the gas sensing tests of graphene composites,the graphene loading can significantly improve the gassensing properties of Co3O4 semiconductor materials.When the graphene loading is 20%and the calcination temperature is 300 ?,the Co3O4/rGO composite reaches a maximum response value of 82 to 50 ppm xylene at 115 ?,while the responseand recovery time are 140 s and 160 s.What's more,the Co3O4/rGO composites show other excellent gas sensing properties,such as low detection limit,good response and recovery curves and excellent selectivity.