Preparation And Performance Regulation Of One-Dimensional Cobalt Oxide Based Acetone Gas Sensing Material

Acetone is a toxic and harmful gas.Excessive inhalation of acetone in the human body can cause various health problems.At the same time,acetone is also a biomarker for diabetic exhaled breath detection.By detecting the concentration of acetone in the exhaled breath,the condition of diabetic patients can be diagnosed.Therefore,there is a huge demand for acetone gas sensors both in environmental monitoring and in the field of diabetes diagnosis.The core of the gas sensor is the sensing material.Experimental results show that the one-dimensional semiconductor cobalt oxide（Co₃O₄）nanomaterial with the advantages of high charge transfer efficiency,large specific surface area and selective catalytic activity for reducing gases,is an ideal acetone-sensitive material.However,direct preparation of one-dimensional Co₃O₄ by solvothermal method will produce agglomeration and dense accumulation,which reduces the effective area of the material and limits its detection of ultra-low concentrations of acetone.To solve this problem,a Co₃O₄ nanorod cluster with three-dimensional radial structure was designed and prepared,which effectively improved the acetone detection limit（LOD）of one-dimensional Co₃O₄.In addition,in view of the poor sensitivity of intrinsic one-dimensional Co₃O₄ to acetone,we proposed using Ce element doping to modify one-dimensional Co₃O₄ and prepared a Ce-doped Co₃O₄ nanotubes.The mechanism of the improved acetone sensitivity of the material after doping was explained.Firstly,layered cobalt hydroxide salt（Co-LHMS）was used as a self-template to prepare three-dimensional radial Co₃O₄ assembled by nanorods via solvothermal method.By adjusting the solvothermal reaction conditions of the precursor Co-LHMS,radial Co₃O₄nanowire clusters with sheet,three-dimensional and dumbbell structure was prepared.Among them,the three-dimensional radial Co₃O₄ nanorod cluster could retain the high specific surface area of one-dimensional materials while reducing the agglomeration phenomenon during the preparation process,changing the stack method of materials,and increasing the transmission channels of gas molecules.By comparing the acetone sensitivity of the three materials,we found that at a relatively low working temperature（200℃）,the response value of the three-dimensional radial Co₃O₄ nanorod cluster to acetone is 4 times that of other structure nanowire clusters.The limit of detection of three-dimensional radial Co₃O₄ nanorod cluster to acetone could reach 100 ppb,which is an excellent performance.Therefore,this work not only provides a possibility for the development of ultra-low concentration acetone sensors,but also provides a new idea for solving similar problems during the synthesis of other one-dimensional materials.Secondly,the electrospinning method was used to prepare PAN/Co（Ac Ac）₂/Ce³⁺precursor fibers,and then by controlling the subsequent calcination process,Ce-doped Co₃O₄nanotubes were successfully prepared.Using this top-down preparation method,we can precisely control the amount of Ce doping in Co₃O₄ nanotubes.After Ce doping,the surface defects of Co₃O₄ nanotubes will be produced,which could promote the adsorption of gas molecules.In addition,after Ce doping,the energy required for the electronic transition of the Co₃O₄ impurity level will be reduced,so the number of carriers will increase at the identical temperature,which further promotes the improvement of its acetone sensitivity.The experimental results show that at a relatively low working temperature（200℃）,the 1 at%Ce doped Co₃O₄ nanotube possess the best acetone sensitivity.The response value to 10 ppm acetone of 1 at%Ce doped Co₃O₄ nanotube could reach 20.3,which is about 3 times higher than that of other Co₃O₄ nanotubes with different Ce doping content.Therefore,this work can not only provide a material with excellent acetone sensitivity,but also provide theoretical guidance for the development of similar materials.