Study On Oxygen Vacancy Self-doped ZnO_1-x Room Temperature NO₂ Gas Sensor

The NO2 emission caused by the development of industrialization is one of the main causes of air pollution.NO2 can damage the human respiratory tract and cause respiratory inflammation.Many studies have shown that nitrogen dioxide pollution is positively correlated with human mortality.At the same time,NO2 is also the main ingredient that causes acid rain,which poses a great threat to agricultural production and construction safety.Due to the huge volume,high cost and complicated operation of the current NO2 monitoring equipment,it is difficult to realize the networked and distributed monitoring.Therefore,metal oxide semiconductor sensors with small size,low cost,easy networking,and maintenance-free have become an important monitoring method.However,due to material characteristics,current metal oxide semiconductor sensors need to work under high temperature or ultraviolet light,resulting in high power consumption of the sensor,short life span,and even a fire hazard.It is necessary to find a way to narrow the metal oxide semiconductor bandgap so that it can work under room temperature and visible light.This article explores the method of narrowing the bandgap of ZnO by introducing oxygen vacancies in ZnO to establish donor defect energy level.Atmospheric plasma spraying method,hydrogen heat treatment reduction method and peroxide-thermal decomposition method were used to make ZnO stoichiometric ratio unbalanced and complete oxygen vacancy self-doping.The morphology,structure,oxygen vacancy characterization and gas sensing test of the prepared ZnO1-x material were carried out,and the gas sensing mechanism was analyzed.The specific research content is as follows:(1)Preparing oxygen vacancy self-doped ZnO1-x gas-sensitive material by atmospheric plasma spraying method.The first point is to use the reducibility of hydrogen to partially reduce ZnO to form oxygen vacancies.The second point is to use the characteristics of atmospheric plasma spraying to make Zn and O atoms escape at extremely high temperatures.Due to the different escape rates of Zn and O,the stoichiometric ratio of ZnO becomes unbalanced,and this unbalanced stoichiometric ratio is retained after rapid cooling to form oxygen vacancies.The gas-sensing results show that the sensor has the best gas-sensing performance when the hydrogen flow rate is 7L/min,and its response to 500 ppb NO2 under blue light irradiation is 3.32.(2)Preparing oxygen vacancy self-doped ZnO1-x gas-sensitive material by hydrogen heat treatment reduction method.Following the first point of the principle of using atmospheric plasma spraying to produce oxygen vacancies,ZnO is partially reduced at 500? to complete the self-doping of oxygen vacancies using the reducibility of hydrogen directly.The gas sensitivity test results show that the H-1 sample with a hydrogen heat treatment time of 1 h exhibits the best gas sensitivity under blue light irradiation,and its response to lppm NO2 can reach 7.(2)Preparing oxygen vacancy self-doped ZnO1-x gas-sensitive material by peroxide-thermal decomposition method.According to the second point of the principle of atmospheric plasma spraying to create oxygen vacancies,make atoms escape at a lower temperature to achieve self-doping of oxygen vacancies.Hydrogen peroxide is used to over-oxidize ZnO to obtain chemically unstable ZnO2,which is then heat-treated under the protection of argon at 600? to complete the self-doping of oxygen vacancies.The experimental results show that the longer the peroxide treatment time,the better the gas sensitivity of the material.After 4 hours of peroxidation treatment,the response value of the sensor under green light irradiation was 26.9,the response time was 14.5 min,and the recovery time was 33.9 min.Its response value under blue light irradiation has been reduced,but it can still reach 9.2,but the response time has been shortened by 53%,and the recovery time has been shortened by 68%.