| Diabetes is a common chronic disease that seriously threatens human life and health,and its early diagnosis is essential.Clinical studies have found that acetone in exhaled air can be used as a biomarker of diabetes:the acetone concentration of a healthy individual ranges from 0.3 to 0.9 ppm（parts per million）,while its concentration of a diabetic is above 1.8 ppm.Based on the difference in acetone concentration of exhaled air,early screening for diabetes with acetone sensors can be achieved quickly,inexpensively,and conveniently.Spinel-type Co3O4,as a typical p-type metal oxide semiconductor with good conductivity and catalytic ability,is considered as one of the ideal gas-sensing materials for acetone detection.However,Co3O4-based acetone sensors have some disadvantages,such as high operating temperature,poor sensitivity at low concentration and poor selectivity.Therefore,it is critical and urgent to develop and design acetone-sensing materials with low operation temperature,high response at low concentration and good selectivity.In this thesis,we have developed the hierarchical nanostructures of Co3O4 and two-dimensional nanomaterials to improve the gas-sensing performance of Co3O4-based nanomaterials by taking the advantages of graphene oxide and MXene,such as high surface areas,abundant surface functional groups and excellent electrical conductivity;and the acetone-sensing performance of Co3O4/rGO can be further improved by modifying their surfaces with Ag nanoparticles.Combined with the systematic characterization and gas-sensitive behavior evaluation of the Co3O4-based nanocomposites obtained,the effects of GO,Ag and Ti3C2Tx MXene on their microstructures and properties were comparatively analyzed,and the physical and chemical mechanisms of the spinel Co3O4 nanocomposites to improve the acetone gas-sensitive performance were deeply understood.The main research contents of the thesis are summarized as following:（1）Synthesis of Co3O4/rGO and Ag@Co3O4/rGO nanocomposites and their acetone-sensing performance.Firstly,Co3O4/rGO nanocomposites were prepared by the microwave method,and two-dimensional GO with a large specific surface area was used as the growing platform for Co3O4 nanoparticles,to form a sunflower-like morphology with a porous structure assembled by nanosheets and nanoparticles.The microstructure and phase composition of the as-obtained samples were analyzed by different characterization methods,and their gas-sensing properties were systematically tested.The results showed that the response of the resulting sample of Co3O4/rGO-1,with a GO addition of 1 wt.%,reached 18.9 for 50 ppm acetone at160℃,2.6 times higher than that of the pure Co3O4 sensor,and the operation temperature was reduced significantly by adding some GO.Further,based on Co3O4/rGO-1,the sample Ag@Co3O4/rGO-1 was prepared by anchoring Ag nanoparticles on the surface of Co3O4/rGO-1.Ag modified samples significantly improved their gas-sensitive performance,and the resulting sample of Ag1@Co3O4/rGO-1 with 1 wt.%Ag,exhibited a high response of 12 for 1.8 ppm acetone at 160℃and up to 79.2 for 50 ppm acetone,6 times higher than that of the Co3O4/rGO-1 sensor.The above Ag1@Co3O4/rGO-1 sensor could detect a low-concentration acetone at ppb levels,with a typical response of 2.4 for 100 ppb acetone.In addition,the response-recovery times were also substantially shortened,with a response/recovery times of 26/11 s for a 1.8 ppm acetone,respectively.（2）Synthesis of Co3O4/Ti3C2Tx nanocomposites and their acetone-sensing performance.The suspension of Ti3C2Tx nanosheets was firstly produced by etching and exfoliating the Ti3Al C2 MAX phase with HCl and Li F aq.solutions;subsequently,a Co2+solution was added to the above Ti3C2Tx nanosheets,and the Co3O4/Ti3C2Tx nanocomposites with a porous sheet-like three-dimensional network structure were synthesized by a microwave method and annealing process.The microstructures and phase compositions of the obtained samples were analyzed using different characterization methods,and their gas-sensing properties were systematically tested.The results showed that the typical sample of Co3O4/Ti3C2Tx-6%with 6 wt.%of Ti3C2Tx exhibited an optimal operating temperature 160℃,much lower than that（200℃）of the pure Co3O4,and its response to 50 ppm acetone was up to 90.2,12 times higher than that of the Co3O4 sensor.Typically,the Co3O4/Ti3C2Tx-6%exhibited a response of 18.8 to 1.8 ppm acetone,suggesting an excellent acetone-sensing performance.The Co3O4/Ti3C2Tx-6%sensor also performed an outstanding acetone detection at ppb level,with a response of 3.2 for a100 ppb acetone;especially,the sensor had an ultra-fast detection capability,with a response and recovery times of 13 and 8 s for 50 ppm acetone,respectively.The Co3O4/Ti3C2Tx-6%sensor was of highly selective detection and long-term stability for acetone sensing application.The abundant pores and three-dimensional network structure resulted in a high specific surface area,which provides more adsorption sites and reactive ones for gas molecules,and the good conductivity of Ti3C2Tx is also helpful to enhance its acetone-sensing performance. |
