Synthesis And Ethanol Sensing Properties Of Lavered Bi³⁺/Ⅵ（Ⅶ） Nanocomposites

Layered materials possess unique physical and chemical properties owing to the anisotropy,thus providing people with a promising application prospect.As a member of layered material,bismuth-based compound has become a star material in materials,physics and chemistry due to their low toxicity and stability.In recent years,the application of bismuth-based in the fields of thermoelectricity,photocatalysiss,and gas sensing and so on has become a focus of attention of scientific researchers.However,there are still relatively few studies on bismuth-based nanomaterials in the field of sensors.In this paper,bismuth-based nanomaterials and their corresponding heterostructures are studied,aiming at using a simple in-situ preparation method to obtain a target sample with a uniform size and regular size,and use it as a sensitive material to investigate the relationship between the composition and structure of the gas sensor and the gas sensing performance.The main research contents of this paper are as follows:1.The crystalline Bi₂S₃ nanowires were synthesized by a simple one-step hydrothermal method,and their growth mechanism was explained preliminarily.For the first time,we explored the sensitivity of Bi₂S₃nanowires to ethanol gas by means of the non-contact surface photovoltage.It was found that the response of Bi₂S₃ nanowires to ethanol gas is stronger than that of conventional powders at room temperature.Even in a low concentration of ethanol atmosphere,the surface photovoltage sensor based on Bi₂S₃ nanowires still has high response and good selectivity.2.In Chapter 2,we know that one-dimensional nanomaterials can achieve good response performance.In order to further improve the response performance and reduce the power consumption of the sensor.This chapter aims to obtain sensitive materials with large specific surface area and more active sites by constructing n-n junctions.Simultaneously with the advantages of resistance-type gas sensors,a quantitative and excellent ethanol gas sensor is constructed.First,we synthesize hierarchical Bi₂WO₆microspheres,and then use a simple one-step in-situ ion exchange method to synthesize Bi₂S₃/Bi₂WO₆heterojunctions.Then,gas sensors with different compositions of Bi₂S₃/Bi₂WO₆ composites were prepared,and the response of gas sensors based on Bi₂S₃/Bi₂WO₆ composites was first investigated.According to the research,the gas sensor based on Bi₂S₃/Bi₂WO₆ composite material has good selectivity to ethanol gas.Compared with the reported results,the optimal working temperature of Bi₂S₃/Bi₂WO₆ heterojunction gas sensor synthesized by us is 210°C,which has a significant decrease trend.Among them,the product obtained under the condition that the molar ratio of Bi₂WO₆ to TAA is 2:10 is the best component.In the same conditions,the optimal response to 50 ppm ethanol is 15.The response-recovery time is 6 s and 8 s,respectively,and good linear correlation at low concentrations can be used for quantitative detection.3.Since p-n is the basis for building many devices,this chapter aims to obtain sensitive materials with a large specific surface area and bulk resistance by constructing p-n junctions.At the same time,the advantages of resistance-type gas sensors are used to construct an ethanol gas sensor with excellent performance.We used BiOI as precursors to synthesize Bi₂WO₆/BiOI composites with different composition ratios by in-situ ion exchange method,and then tested their gas sensitivity properties for the first time.According to the research,the gas sensor based on Bi₂WO₆/BiOI composite material has good selectivity to ethanol gas.The research shows that gas sensors based on Bi₂WO₆/BiOI composites also have good selectivity for ethanol gas.However,different gas sensors have different optimum working temperatures and sensitivities.Among them,the gas sensor based on 70%Bi₂WO₆/BiOI complex has the highest sensitivity to 50 ppm ethanol,with a response of 13.9.Although the best working temperature（290℃）of the gas sensor has not been reduced compared to the reported Bi₂WO₆ gas sensor,the performance of the sensor（such as sensitivity and selectivity）has been improved.At the same time,we explain the mechanism of gas-sensing response and response enhancement.