Preparation And Sensing Properties Of Two-dimensional Layered Ti₃C₂-MXene

The successful stripping of atomic-thickness graphene won the 2010 Nobel Prize in Physics,which has attracted widespread attention from researchers on two-dimensional carbon materials.At the same time,the new graphene-like transition metal carbides and nitrides MXene were also discovered and rapidly developed in2011 by Yury Gogotsi's group at Drexel University.Ti₃C₂Tx(MXene),as one of the first discovered MXenes materials,has become a research hotspot in two-dimensional layered materials due to its good hydrophilicity,excellent electrical conductivity and excellent mechanical properties.At present,various composite modified materials based on MXenes have been widely used in many fields.This paper systematically studies the application of Ti₃C₂T_x(MXene)in the area of gas and humidity sensors.The main results are listed as follows:1.By using ternary ceramic structure Ti₃Al C₂as raw material,multi-layer and single-layer Ti₃C₂T_xwere prepared by a wet chemical etching method.The effects of etching time(12/24/48h)and etching temperature(25/60°C)on the crystal phase and morphology of the reaction products were studied in detail.Multilayer MXene with accordion-like structure was synthesized by selective etching element Al in the precursor Ti₃Al C₂phase with high concentration of hydrofluoric acid(HF).Then,multilayer MXene was intercalated and ultrasonic stripping to obtain single-layer MXene nanosheets,its stability and specific surface area were tested and analyzed.Subsequently,two morphologies of MXene were employed for gas sensing test,it is found that the multilayer Ti₃C₂T_xis insensitive to gas,while the single-layer Ti₃C₂T_xsensitivity?R/Ra to 100ppm ammonia gas at 75°C can reach 6.5 with good selectivity.2.With potassium stannate as the precursor,urea provides an alkaline environment,the Sn O₂microspheres were synthesized by a facile solvothermal method and multilayer Ti₃C₂T_xwith different proportions were added in situ to prepare the Sn O₂/Ti₃C₂T_xcomposite.Gas sensing results show that the sensitivity value?R/Ra of the SM-5 sensor(Sn O₂/Ti₃C₂T_xmass ratio is 5:1)to 10ppm ethanol is9.5,twice as much as that of pristine Sn O₂at operating temperature of 230°C.Moreover,the composite material also reduces the response and recovery time of the sensor,and has good selectivity and stability.This work also studied the sensitivity mechanism of gas sensor,analyzed and explained how multilayer Ti₃C₂T_ximproves the sensitivity of pristine Sn O₂to ethanol gas.3.The optimized one-step synthesis method was used to prepare the single-layer Ti₃C₂T_xmaterials,the solution obtained by this method has a controllable concentration and uniform dispersion,which can be directly used to prepare devices.According to the rich functional groups and hydrophilic characteristics on the surface of Ti₃C₂Tx during the etching process,a humidity sensor was successfully constructed by combining it with QCM test platform for humidity detection.The morphology and structure of single-layer Ti₃C₂T_xwere characterized by various advanced instruments.The humidity sensitive characteristics of QCM devices with the best coating quality were measured and the test results show that the humidity sensor has high sensitivity,fast response/recovery time,small humidity hysteresis,and good stability and selectivity.In addition,the adsorption enthalpy interaction between Mxene surface functional groups and water molecules was studied by using simulation calculation,and the sensitization mechanism of F ion was explained and verified by experiments.The experiments further confirmed that F ion plays an important role in the sensitization process.