Preparation Of Two-Dimensional Metal Oxides And Heterojunctions And Their Performance For Ethanol Gas Detection

The presence of various harmful VOCs gases in the human living environment poses a potential threat to human health.In recent years,the development of sensor technology has become one of the important means to solve the problem of VOCs pollution in the living environment.Two-dimensional metal oxides（2DMOS）have been widely used in the fields of sensing,electronic,magnetic,optical and catalytic materials due to their rich surface chemistry and unique electronic structures.The traditional methods for 2DMOS synthesis are top-down and bottom-up systems,such as mechanical stripping,wet chemical synthesis,chemical vapor deposition and atomic layer deposition.However,these methods are difficult to overcome the strong surface polarizability,resulting in unstable surfaces of the prepared2DMOS and costly and limited yields of the fabrication process.In order to extend the excellent performance of 2DMOS to practical applications,it is crucial to develop an efficient and simple preparation method.To this end,this paper proposes a unique approach to solve this problem by applying it to a gas sensor and improving the sensitivity,response rate,and recovery of the sensor to the gas by means of compounding.In order to investigate the sensing mechanism,this paper investigates the gas adsorption process using first principles computational modeling optimization.Specifically,the paper focuses on the following:（1）The development of 2D semiconductor materials with atomic layer thickness has become a key area for the creation of high-performance electronic devices,but the synthesis of large-area 2D semiconductors remains a major technical challenge.We synthesize ultrathin2D SnO₂ nanosheets using natural oxide layers generated on the surface of liquid metals,which have a thickness of about 6.7 nm and exhibit n-type semiconductor properties with a forbidden band gap width of 3.7 e V.The synthesized two-dimensional SnO₂ nanosheets were subsequently used as sensing materials and showed impressive performance,including a response time of 38 s and a recovery time of 38 s for 10 ppm ethanol vapor at an operating temperature of 300°C.This method of synthesizing nanosheet sensing materials is both simple and scalable,and the resulting sensors exhibit high responsiveness,good selectivity,fast response to ethanol vapor,and excellent reproducibility.（2）To improve the gas adsorption capacity of SnO₂,the response is often improved by compounding multiple oxides as gas-sensitive materials.Three sensors were prepared by synthesizing SnO₂-In₂O₃ heterojunction oxide composite films by liquid metal-assisted exfoliation;AFM characterization of the synthesized composite films revealed that the thickness of the bilayer films was about 3.3 nm.The response time of the Sn-In composite semiconductor oxide at an operating temperature of 300°C to 10 ppm ethanol was 5 s,and the recovery time was 10 s.And the sensor’s response to The response of this sensor to the concentration range of 10-400 ppm ethanol（73.6%-97.99%）was generally higher than that of pure SnO₂ in this concentration range（71.68%-85.34%）.In conclusion,we hope that this study can open up a new avenue for the preparation of various 2D metal oxide based and 2D mixed metal oxide based gas sensors to improve gas detection performance.（3）In order to more fully understand the adsorption process of the gas sensor,we first constructed and optimized the SnO₂（110）model by Material Studio software,and the optimized model showed a dramatic chirality structure and the optimized model cell parameters matched the results of others,and the model was constructed reasonably.The adsorption energy of ethanol adsorption by SnO₂（110）was calculated to be-0.056Ha according to the adsorption energy equation,indicating that the whole adsorption process was spontaneous.The changes in the energy bands of SnO₂（110）before and after the adsorption of ethanol were compared,and it was found that the valence and energy bands of SnO₂became narrower after adsorption,and a small segment of energy band appeared in the forbidden band,which improved the electrical conductivity of SnO₂.A SnO₂-In₂O₃heterojunction adsorption model was constructed to calculate the adsorption energy of-0.0375Ha,indicating that the adsorption process was exothermic and the ethanol molecules underwent spontaneous adsorption.