Study On Gas Sensing Properties Of Nanostructured Zinc Oxide Prepared By Hydrothermal Method

With the rapid development of industry and the continuous improvement of human living standards,it also brings serious pollution problems to the atmospheric environment on which human beings depend.It is urgent to detect the pollutants in the atmosphere in real time and accurately.The research in the field of gas sensors has attracted great interest of scientists.There are many kinds of gas sensors,involving a wide range of scientific fields,and the semiconductor metal oxide gas sensor has become a research hotspot in the field of gas sensors because of its unique advantages such as high sensitivity,good repeatability and easy preparation.Among many semiconductor metal oxides,zinc oxide?ZnO?has become one of the hot research materials in the field of gas sensors due to its large band gap,high exciton binding energy and excellent chemical and physical stability.However,for pure ZnO materials,there are many disadvantages,such as low sensitivity,high temperature,high detection limit and poor selectivity.Researchers have done a lot of modified sensitization work on nanostructured ZnO gas sensors,and made a breakthrough progress.In order to further improve the performance of ZnO based gas sensors,in this paper,ZnO nano materials were synthesized by hydrothermal method,and the micro morphology of ZnO was properly controlled by changing the reaction conditions.The modification and sensitization of ZnO gas sensors were further realized by noble metal modification and heterogeneous recombination.The specific research contents are as follows:Ag modified ZnO nanorod composite was prepared by one-step hydrothermal method,and the relationship between Ag content and sensor performance was explored.The analysis of material characterization shows that the modification of Ag does not change the micro morphology of ZnO,and the metal Ag is located on the outside of ZnO nanorods.Compared with the pure ZnO sensor,the response of all Ag-ZnO sensors to C₂H₂ is significantly enhanced.The response of 3at%Ag-ZnO sensor to100ppm C₂H₂ at 175?is 539,which is the highest value in all sensors,33 times higher than that of the pure ZnO sensor.Ag-ZnO sensors have the advantages of fast response,low operating temperature and high selectivity.Compared with pure ZnO sensor,the improvement of gas sensing performance of Ag-ZnO sensor is mainly due to the combination of chemical sensitization and electronic sensitization of Ag.Due to the modification of Ag,the content of oxygen adsorbed on the surface of the material increases and the activity of the material increases,and Schottky junction is formed at the interface of Ag and ZnO,which improves the response of the sensor.Under the guidance of Ostwald ripening mechanism,Crystalline mesoporous ZnO/ZnCo₂O₄ microspheres were synthesized by one-step hydrothermal method.The as-prepared materials are monodispersed nanoparticle aggregates,and the mesopores are formed by connected intraparticle voids.The analysis of material characterization shows that nanoparticle sizes which make up the microspheres are enlarged with increasing thermal treatment temperatures?400-800??while keeping the holistic size of the microsphere basically unchanged,which result in the change of surface pore density.Benefits from their structural advantages,when evaluated as a sensing material for the detection of hazardous gases,ZnO/ZnCo₂O₄ composite calcined at 500?exhibited enhanced sensitivity and selectivity compared to those of other calcined temperatures to H₂S gas and the detection limit is 500 ppb.The sensing mechanism might be attributed to its porous structure and the large specific surface area,which can promote the diffusion of gas molecules and their adsorption on the surface of the sensing material.This work not only represents a new example of Ostwald ripening mechanism-based formation of inorganic hollow structures in the template-free aqueous solution,but also provides a brand new and efficient sensing material for detection of H₂S gas.