Research On Room-temperature NH₃ And NO₂ Sensors Based On Three-dimensional Ti₃C₂T_x And Its Composite Sensitive Materials

Sensor is the main means of information acquisition,located in the most front of the information technology chain.As a kind of very important sensor,gas sensor has important applications in aerospace,safety monitoring,environmental monitoring,resource detection,medical diagnosis and treatment,Internet of things,and many other fields.With the rapid development of new communication technology and wearable electronics technology,new requirements are put forward for the sensitivity,selectivity,power consumption,and flexibility of gas sensors.This paper focuses on the development of room-temperature NH₃ and NO₂ sensors based on three-dimensional Ti₃C₂T_x and its composite sensitive materials.By using wet etching technology and ultrasonic spray pyrolysis(USP)technology,novel Ti₃C₂T_x sensitive materials with three-dimensional organ-like and crumpled sphere structure are designed and prepared.The types and proportions of functional groups on the surface of organ-like Ti₃C₂T_x are regulated by alkalization treatment,and a planar room-temperature NH₃sensor based on alkalized three-dimensional organ-like Ti₃C₂T_x is constructed.By further optimizing the microstructure and composite modification of Ti₃C₂T_x sensitive material,room-temperature NO₂ sensor based on three-dimensional Ti₃C₂T_x crumpled sphere,all-MXene degradable NO₂ sensor based on three-dimensional porous Ti₃C₂T_xcrumpled sphere,the planar room-temperature NO₂ sensor based on oxidized three-dimensional Ti₃C₂T_x crumpled sphere,highly-selective room-temperature NO₂ sensor based on three-dimensional Ti₃C₂T_x/r GO crumpled sphere,and highly-sensitive room-temperature flexible NO₂ sensor based on three-dimensional Ti₃C₂T_x/Zn O crumpled sphere have been developed.The specific research contents are as follows:(1)The three-dimensional organ-like Ti₃C₂T_x sensitive material is prepared by HF etching and Na OH solution alkalization method,and the planar room-temperature highly-sensitive NH₃ sensor is constructed.Compared with untreated three-dimensional organ-like Ti₃C₂T_x,The ratio of oxygen to fluorine atoms([O]/[F])on the surface terminal of the three-dimensional organ-like Ti₃C₂T_x sensitive material treated by alkalization is significantly improved,and the sensitivity to NH₃ is also greatly improved.The sensor based on the alkalized three-dimensional organ-like Ti₃C₂T_x have a response of 28.87%to 100 pm NH₃,which is nearly double that of the untreated three-dimensional organ-like Ti₃C₂T_x.The enhancement of NH₃ sensitivity is mainly attributed to the strong adsorption capacity to NH₃ of oxygen-rich terminal three-dimensional organ-like Ti₃C₂T_x obtained by alkalization.(2)In order to increase the specific surface area and active site density of Ti₃C₂T_xsensitive material,and research the effect of microstructure and morphology on the sensing performance,with two-dimensional Ti₃C₂T_x film as the precursor,room-temperature flexible NO₂ sensor based on three-dimensional Ti₃C₂T_x crumpled sphere sensitive material and all-MXene degradable room-temperature NO₂ sensor based on three-dimensional porous Ti₃C₂T_x crumpled sphere sensitive material are respectively constructed by ultrasonic spray pyrolysis technology and drop-coating technology.BET test results show that the specific surface areas of two-dimensional Ti₃C₂T_x film,three-dimensional Ti₃C₂T_x crumpled sphere and three-dimensional porous Ti₃C₂T_x crumpled sphere were 33.56,56.27,and 137.80 m²/g,respectively.The gas-sensitive performance test results show that,compared with the sensor based on two-dimensional Ti₃C₂T_x film sensitive material,the response of the planar room-temperature NO₂ sensor based on three-dimensional Ti₃C₂T_x crumpled sphere to 100 ppm NO₂ is significantly improved,reaching 27.27%,and the selectivity to NO₂ is also significantly improved.The all-MXene degradable room-temperature NO₂ sensor based on three-dimensional porous Ti₃C₂T_x crumpled sphere have a response of 12.11%to 5 ppm NO₂,and the detection limit is as low as 50 ppb.It only takes 6 hours to completely degrade in medical-grade hydrogen peroxide(the concentration of 2%).It is an environmentally friendly and highly sensitive gas sensor.(3)A planar NO₂ sensor at room temperature is constructed based on oxidized three-dimensional Ti₃C₂T_x crumpled sphere sensitive material and polyimide(PI)substrate,and the effect of oxidation defects on gas-sensing mechanism is systematically studied.Three-dimensional Ti₃C₂T_x crumpled sphere sensitive materials without oxidation defects are prepared by ultrasonic spray pyrolysis technology.The oxidized three-dimensional Ti₃C₂T_x crumpled sphere sensitive materials are prepared by heat treatment at 100,150,and 200?in air.Among them,MS-150 sensor has the highest response to 5 ppm NO₂,reaching 26.67%,and has significantly improved the selectivity to NO₂.By comparing the gas-sensing properties of three-dimensional Ti₃C₂T_x/Ti O₂ composite crumlped sphere sensitive materials without oxidation defects,it is confirmed that the enhancement of NO₂-sensing properties of oxidized Ti₃C₂T_x is not caused by the establishment of surface Ti₃C₂T_x/Ti O₂schottky barrier in-situ formed by oxidation.DFT simulation calculation is carried out with the unit cell containing a Ti atomic defect as the model,which further confirms that the improvement of the gas-sensing properties of oxidized Ti₃C₂T_x is mainly due to the great adsorption capacity to NO₂ molecule of surface Ti atom defect caused by oxidation.(4)Room-temperature NO₂ sensors based on three-dimensional Ti₃C₂T_x/r GO composite crumpled sphere and three-dimensional Ti₃C₂T_x/Zn O composite crumpled sphere sensitive material are developed.Firstly,two-dimensional Ti₃C₂T_x films are used as reductants to assist the reduction of graphene oxide(GO),and Ti₃C₂T_x/r GO composite crumpled sphere(MG)sensitive materials are prepared by ultrasonic spray pyrolysis technology.MG-2-1 prepared with the mass ratio of Ti₃C₂T_x to GO of 2:1shows the best NO₂ sensing performance,with the detection limit as low as 10 ppb and the response of 19.854%to 5 ppm NO₂.Moreover,MG-2-1 has extremely outstanding selectivity of NO₂ and low noise level.Secondly,three-dimensional Ti₃C₂T_x/Zn O composite crumpled sphere sensitive materials are prepared by ultrasonic spray pyrolysis technology using zinc acetate and two-dimensional Ti₃C₂T_x film as precursors.The gas-sensing test results show that compared with three-dimensional Ti₃C₂T_x crumpled sphere,the room-temperature flexible NO₂ sensor based on three-dimensional Ti₃C₂T_x/Zn O composite crumpled sphere has a great improvement in NO₂sensitivity,and the response to 100 ppm NO₂ reaches 41.93%,with nearly 100%recovery characteristics and good stability.The response value of the constructed flexible NO₂ sensor attenuated less than 31%in both 0-120°bending and 1000 times consecutive 90°bending,which provides a useful exploration for the construction of flexible wearable gas sensor.