Investigation On Acetone Gas Sensing Performance Of Functionalized WO₃

Chemiresistive gas sensors based on metal oxide semiconductor have always received extensive attention due to their integration,low cost,simple structure,and high sensitivity.But it usually needs to work at a relatively high temperature,which will cause high power consumption and certain security risks and limit its application in the Internet of Things.In order to meet the more accurate and demanding gas detection requirements,the development of gas sensors with high sensitivity,high selectivity,fast response and recovery time,and low power consumption and low cost is still a research that requires continuous breakthroughs.Acetone gas is a harmful gas that exists widely in people's production and life,and it is also a biomarker in the exhaled breath of diabetic patients.The detection of acetone in the exhaled breath of humans is of great significance in the non-invasive diagnosis of diabetes.Tungsten oxide(WO₃)is a very common N-type oxide semiconductor material with a band gap of 2.4-2.8 e V at room temperature.It has been widely used in many fields such as photocatalysis,electrocatalysis,solar cells and supercapacitors.In the field of gas sensors,WO₃ is a very good gas-sensitive material that can be used for acetone detection.Nowadays,the research directions of high-performance gas sensors mainly include the development of new gas-sensitive sensing materials,the optimization of micro-nano structures,the modification of materials,and the optimal design of device structures,etc.Among them,the specific strategies of material modification include element doping,noble metal modification,heterostructure fabrication,defect engineering,and control of crystal planes and interfaces,etc.It is one of the effective strategies to improve the sensing performance of materials.In this paper,around the development of high-performance acetone gas sensors,we have carried out comparative systematic research work on the preparation,structure optimization and material modification of WO₃,and studied the sensing characteristics of WO₃ sensors for acetone gas.The main research work carried out and the main research results obtained include:1?The preparation process and growth principle of urchin-like WO₃ hollow spheres are studied.In the past research reports,a large number of urchin-like WO₃ have been discovered,and their morphology is represented by a large number of upright nanorods extending from the center of the sphere,and hollow urchin spherical appearances are rarely reported.The urchin-like WO₃ spheres in this study is made up of a large number of slender nanowires entangled in the shell.Through a comparison of several controlled variable experiment,it is found that ethylene glycol as a soft template is the key to inducing the formation of hollow structures.The gas sensitivity test results show that the WO₃ structure with high specific surface area has a higher response to acetone.In addition,we also studied the effect of annealing temperature on the sensing properties of the material.The results show that WO₃ annealed at 450?has the best response to acetone.2?The sensing properties and sensing mechanism of Cr-doped urchin-like WO₃hollow spheres to acetone gas were studied.It was found that Cr-doped WO₃ did not induce the formation of?-WO₃ with ferroelectric properties.Comparing the synthesized Cr-WO₃ with different doping ratios in detail,all synthesized WO₃ are?-WO₃,and the Cr element is successfully incorporated into the lattice of WO₃.The gas sensitivity test results show that when the doping amount of the chromium source is 100 mg,the response of the Cr-WO₃ sensor is about 3.5 times higher than that of the pure WO₃ sensor,and its response to 100 ppm acetone gas reaches 71.52.The electron microscope observation found that compared with pure WO₃,the nanowires in Cr-WO₃ urchin spheres have a smaller diameter,which resulted in a larger specific surface area of the material and enhanced gas sensitivity.In addition,Cr will introduce a large number of oxygen vacancies in the WO₃ lattice and modulate the energy band structure,resulting in enhanced gas sensitivity.3?For the first time,a highly active defective WO₃ was prepared by introducing fluoride ions into the WO₃ hydrothermal precursor solution and applied it to high-performance sensing of acetone.The comparison of the introduction of two fluorine sources,ammonium fluoride and hydrofluoric acid,proved that fluoride ions are the main cause of WO₃ activation,and the amount of fluoride ions introduced during the synthesis of highly active WO₃ needs to be moderate.The analysis and characterization of the material structure,molecular bonds and element chemical state proved that,When F?is introduced in the synthesis process of WO₃,it will lead to the formation of h-WO₃ with(002)active surface as the main exposed surface and the increase of defects such as oxygen vacancies and unsaturated coordination atoms.Under the same conditions,we analyzed and compared their differences in response to acetone gas.The results show that the defective WO₃ has a much higher response to acetone.It can reach a response value of 3.3 to 0.5 ppm acetone at 200?,which can be used for non-invasive diagnosis of diabetes.