Preparation And Gas Sensing Properties Of MnO₂/Ti₃C₂T_x MXene Composite

As a type of volatile organic compound(VOC),ethanol can cause eye and skin irritation and severe poisoning reactions if exposed to it for a long time.Its inherent volatility and flammability make it a risk of burning and explosion when exposed to high temperature and open flame.In order to protect the safety of personnel and the environment,prevent fires and explosions,and meet the environmental concentration requirements of food,medicine,and chemical industries,real-time and accurate monitoring of ethanol gas is required.The semiconductor metal oxide manganese dioxide MnO2 is easy to prepare,low in cost,and high in stability.It is an ideal choice for detecting VOC gases.The new type of two-dimensional material Ti3C2Tx MXene also has good gas sensing performance for VOC gases.It has the advantages of high conductivity,numerous active sites and abundant terminal functional groups,which can promote the adsorption of gas molecules.In this thesis,MnO2 and Ti3C2Tx MXene were combined to construct a heterostructure.The ethanol gas sensing performance of the composite was studied.The specific work and research results are as follows:1.The MnO2 nanowires were prepared by hydrothermal method and high temperature annealing process.The Single few-layer Ti3C2Tx MXene was prepared by top-down selective etching and ultrasonic stripping.The Polydiallyldimethylammonium chloride solution(PDDA)was used as surfactant to modify the surface of MnO2 nanowires,and the uniformly dispersed MnO2/Ti3C2Tx MXene composites were prepared by electrostatic self-assembly method.2.The properties of MnO2,Ti3C2Tx MXene and MnO2/Ti3C2Tx MXene composites were characterized and analyzed by XRD,SEM,TEM,EDS,AFM,PL,physical adsorption testing and other characterization methods.The research results showed that the composite of single few-layer Ti3C2Tx MXene and MnO2 nanowires could be tightly wrapped by MnO2 nanowires,dispersed evenly.Its size was mainly around 5-10 μm.The MnO2/Ti3C2Tx MXene composite had stable properties and a large specific surface area of 36.65 m2/g.It was a good chemical resistance material for gas sensors.3.The MnO2/Ti3C2Tx MXene composite gas sensor device was prepared by using semiconductor micro-nano technology,and their gas sensing performance was tested.The research results showed that the optimal operating temperature of the MnO2/Ti3C2Tx MXene composite sensor was 450℃,and the gas response to 200 ppm ethanol reached 199.5%,which was 187.5%higher than that of pure MnO2 nanowire devices.The p-p heterojunction formed at the contact interface between MnO2 and Ti3C2Tx MXene could better separate and transport carriers;The fluffy heterostructure could also enhance the diffusion velocity of ethanol gas molecules,thus improving the gas sensing performance of MnO2/Ti3C2Tx MXene composites.The study found that the MnO2/Ti3C2Tx MXene composite gas sensor had good selectivity and repeatability to ethanol.Its minimum detection limit reached 1 ppm.