The Construction Of Three-dimensional Mxene Composites And The Sensing Performance

With the rapid progress and development of society,the increasing concerns about human health monitoring are motivating the research on smart wearable devices,especially flexible and wearable sensors.Piezoresistive sensor is an important type of flexible and wearable sensor.Because of the rigidity of the sensing material and the viscoelasticity of the flexible substrate,piezoresistive sensors often have defects in deformation ability,sensitivity and sensing range,which limits their application in flexible and wearable devices.At present,the research focus is how to prepare sensors with high sensitivity and wide working range.Through effective methods,reasonable and ingenious design,adjusting the contact resistance between the flexible substrate and the sensing material,it can easily achieve the purpose of improving the working range and sensitivity of the sensor.Therefore,new materials and reasonable structure are the key to solve this problem.Therefore,we choose to use the recently developed two-dimensional sheet transition metal carbide(Ti3C2TxMXene)with excellent hydrophilic ability and metal like conductivity to construct a reasonable three-dimensional microstructure,and to prepare composite materials cleverly combined with flexible substrate.Through common templates and simple preparation methods,flexible and wearable sensors with stable and reliable performance,excellent sensitivity and multifunctional property are prepared.The main research contents of this thesis are as follows:(1)Two dimensional nano-sheet transition metal carbide was successfully prepared by etching the transition metal carbide precursor(MAX)with hydrochloric acid/lithium fluoride.There are many problems in the preparation of monolithic MXene.In this chapter,we use hydrochloric acid and lithium fluoride as etchants to generate hydrofluoric acid in situ to etch the transition metal carbide precursor Ti3AlC2 MAX phase.On the one hand,we effectively avoid the danger of direct use of hydrofluoric acid,and the preparation process is more environmentally friendly;on the other hand,the lithium ion contained in the etching solution can play a role of intercalation.By controlling the etching temperature and etching time,we have prepared a monolithic MXene nano-sheets with complete lamellae,stable performance and high conductivity.(2)MXene-PDMS composite with hollow structure was prepared,and its sensing performance was studied:the preparation of stable output signal and the use of reliable hollow structure bendable pressure sensor make the current research hotspot.In this experiment,we use nickel foam as the sacrifical substrate,by impregnating different times of MXene aqueous dispersion,then pouring polymethyl two siloxane(PDMS),removing the nickel substrate with hydrochloric acid,obtaining hollow-structure MXene-PDMS composites,and forming a pressure sensor with high bending,stable performance and high sensitivity.The sensor can realize the effective detection of 0-1800 wide range bending angle and stable detection for different frequencies of 0.05-2 Hz.The minimum detection limit is 10 mg,and the response speed is 20 ms.And it can realize the detection of bending movement of various parts of human body and stereo sound.It can also monitor the ultrasonic peeling state of graphene oxide and other power material in the solvent in real time.(3)MXene-wood sponge with layered structure was prepared for self-energy storage sensor:In this experiment,wood sponge with layered structure was selected as the substrate to prepare layered MXene-wood sponge sensor.The natural wood was treated with sodium hydroxide and sodium chlorite in two steps,and the wood sponge with excellent resilience was obtained.Then MXene nano-sheets were loaded on the three-dimensional skeleton of wood sponge to obtain MXene-wood sponge sensor.The sensor can achieve very stable detection under 0-50%strain,and it is also stable for different frequency detection.It can also work normally at a low temperature of-196?.It can also be used in super capacitor self-energy storage to detect human physiological signals.And it has excellent air permeability and tailorability,which is very suitable for wearable pressure sensor.