Gas-sensing Properties Of Two-dimensional MXene/Metal Oxide Heterostructures

Sensors,as one of the important ways for information acquisition,can convert information into electrical signals.Among them,gas sensors act as the"electronic nose"and are widely used in environmental monitoring,detection of toxic gases,security surveillance,medical diagnosis,and other fields.Currently,the existing gas sensors still have limitations such as limited ability to identify multi-component gases,low integration,and short lifespan,which cannot meet the application requirements in complex environmental changes.Two-dimensional layered transition metal carbides,nitrides,or carbonitrides,known as MXene materials,possess excellent electrical properties,mechanical strength,and ultra-high electrical conductivity,making them demonstrate tremendous advantages in gas sensing applications.However,single-material MXene based gas sensors often have low sensitivity due to their immense specific surface area and ultra-high reactivity,resulting in poor selectivity typically associated with MXene based gas sensors,which restricts their application in multi-scene gas detection.Metal oxide semiconductor gas sensor materials have been developed into a mature class of gas-sensitive materials due to their low cost,great stability,and excellent sensitivity.Therefore,this paper constructs heterostructures by combining two-dimensional layered MXene materials with different metal oxide materials,designing gas sensors to address multi-scene gas detection.This not only enhances the response values of gas sensors to target gases but also reduces the detection limit of the sensor,improves the operating temperature,realizing the room temperature gas detection.Additionally,the sensors achieve the recognition of multi-component gases,laying the foundation for gas detection in response to complex environmental changes.1.Through solvent thermal method,the In₂O₃-TiO₂-MXene heterostructure was constructed.Using polyol solvent to regulate grain growth,cubic phase In₂O₃nanoparticles were loaded onto Ti₃C₂T_x MXene multilayered nanosheet derived Ti₃C₂T_x@TiO₂.Gas sensing test results indicated that the ITM-30 based gas sensor exhibited excellent response to triethylamine.At 110℃,the response of triethylamine gas at 100 ppm reached 32,which was 4.5 times higher than that of pure In₂O₃ based sensor.This sensor also showed fast response（2 s）,good selectivity,and long-term stability.The coupling of p-n type heterojunction and n-n type heterojunction is the main reason for enhancing the gas sensor performance.The functional groups on the Ti₃C₂T_x MXene surface provide abundant active sites for gas adsorption,enabling the rapid detection of triethylamine gas.2.Using hydrothermal method,Fe₂O₃ nanoparticles are loaded onto few-layer Ti₃C₂T_x MXene nanosheets to construct Fe₂O₃/MXene heterostructure.Gas sensing test results showed that Fe₂O₃/MXene-1%based sensor could detect real-time concentrations of ppb-level n-butanol gas,with a response value of 1.31 to 70 ppb n-butanol.Fe₂O₃/MXene-1%based sensor also exhibited an excellent response value of83.7 to 100 ppm n-butanol at 150°C,which is over 22 times higher than that of the pure Fe₂O₃ based sensor.This sensor also demonstrated excellent selectivity,stability,and fast response time（3 s）.The formation of Schotty heterojunction structure promoted carrier migration,and effectively improved gas sensing performance.In addition,the size effect of sensing materials,as well as the excellent conductivity and low thermal noise of Ti₃C₂T_x MXene provide a transport channel for electrons in the material,increasing the electron transfer rate within the composite material,enabling the detection of low concentrations for n-butanol gas.3.Constructing NiO/MXene heterostructure through in-situ precipitation method.The electrostatic interaction between Ni²⁺and the electronegative MXene allows for the in-situ growth of NiO nanoparticles on single-layer Ti₃C₂T_x MXene nanosheets.The gas sensitivity test showed that the NiO/MXene based sensor showed 98%to 500ppm xylene at room temperature and 11.4 to 100 ppm formaldehyde at 170°C,which was 5.36 times higher than the pure NiO based sensor.The differences in gas molecule bond energy and an increase in temperature lead to the generation of more electron-hole pairs in the depletion region of heterojunction.Temperature modulation affects the activity of surface redox reactions and the types of adsorbed oxygen species,which is the reason behind achieving dual gas detection.4.By using electrostatic adsorption method,ZnO nanoparticles are uniformly dispersed on few-layer Ti₃C₂T_x MXene nanosheets to form ZnO-MXene heterostructure.The gas sensitive test results showed that under the UV LED light irradiation at a wavelength of 450 nm,the baseline resistance of the ZnO-MXene based sensor was reduced,achieving the detection of formaldehyde gas at room temperature.The response value for 100 ppm formaldehyde gas was 5.2,and the response value for 100 ppm triethylamine at 160°C was 28.2,which is 5.4 times that of the pure ZnO based sensor.The light-emitting carriers generated by the LED’s radiation on a heterogeneous structure alter the material’s electrical conductivity,enhance the separation efficiency of electrons and holes and improve the gas-sensing performance.Temperature plays a key role in the selective catalytic action of both gases,which is the key factor for achieving dual gas detection of formaldehyde and triethylamine.