Synthesis, Characterization And Gas Sensing Properties Of BiOCl Heterostructure Composite

In recent years,people’s living environment is polluted by a variety of harmful gases such as SO₂,NH₃,NO₂,N₂O,H₂S,among which nitrogen dioxide（NO₂）is one of the most harmful gases.Even if the NO₂ level in the air is only ppm,it will cause a variety of respiratory system and human nervous system problems.Examples include sore throats,asthma,cardiac arrest,headaches,pulmonary edema,and sometimes death.Therefore,it is very important to accurately monitor the concentration of NO₂ gas in air.In this paper,BiOCl is selected as the main research object,not only because the preparation process is simple,but also has the advantages of high crystallinity,large specific surface area,and more active sites exposed on the edge of two-dimensional spiral grown layered nanosheets.However,there are few researches in the field of gas sensitivity.In this paper,BiOCl and its composite materials were designed and synthesized to construct a heterogeneous structure to form a fast electron transmission channel between interfaces,accelerate the electron transmission rate,improve the gas sensitivity to NO₂ gas,and reduce the detection limit.In order to solve the problem of low concentration NO₂ gas detection limit of room temperature gas sensor.BiOCl nanosheets were combined with C₃N₄ and ZIF-67 synthesized by hydrothermal method and coprecipitate method to construct C₃N₄/BiOCl（BiC）and ZIF-67/BiOCl（ZBO）composites.By TEM,XRD,FT-IR,BET,TPD and other characterization methods,the structure,morphology and gas-sensitive properties of the composites were studied,and the formation mechanism and gas-sensitive mechanism of the composites in NO₂ atmosphere were discussed.The following research work has been carried out:Firstly,a thin layer of porous C₃N₄ nanosheets was prepared by a one-pot oil bath method and combined with BiOCl nanosheets with a two-dimensional spiral structure.The heterojunction interface between the thin layer of C₃N₄ and BiOCl nanosheets forms a rapid electron transfer channel.In addition,the microstructure of BiOCl nanosheets spirally increases on the porous C₃N₄ thin layer,which can increase the surface area and the gas active site on the surface,thus further improving the gas-sensitive property of BiC composites.The results show that the optimized BiC-2 has a good detection limit and sensitivity to NO₂ at room temperature.The gas sensitive response to 100 ppm NO₂ at room temperature is 53.05（Ra/Rg）,the response time is 3.2 s,and the detection limit is 10 ppb.This study provides theoretical and experimental basis for the application of C₃N₄ and BiOCl composite sensors.Secondly,metal-organic skeletons（MOF）are considered as ideal gas sensing materials due to their high specific surface area,abundant porosity,and advantages in gas adsorption and storage.In this work,we assembled a ZBO gas sensor for NO₂ detection at room temperature by combining 3D structure of ZIF-67 with 2D thin layer of BiOCl nanosheets with oxygen-rich defect structure.The gas sensitive response of the ZBO-2 sensor is 44.81（at 25%relative humidity）,which is 4 times higher than that of the pure ZIF-67 sensor.At room temperature,the ZBO sensor shows a highly sensitive response to low concentration of NO₂:The gas-sensitive response to 5 ppm NO₂ is 10.47,the response time is 16.0 s,and the recovery response time is only 9 s.In addition,the constructed ZBO-2 sensor shows excellent moisture resistance performance:Under the condition of 70%relative humidity,the gas sensitive response to 100 ppm NO₂ is still up to 30.28.The sensor has a broad application prospect in the field of gas sensing.