Preparation Of Cu₂O/Fe₂O₃ Hollow Nanostructures And Study On Its Gas Sensing Properties

Gas sensors based on semiconductor metal oxides have the advantages of small size,all solid-state,and stable performance,so they are widely used in the detection and monitoring of harmful gases.They can effectively solve problems such as air pollution,leakage of volatile harmful gases,and other threats to people’s physical and mental health and property safety.The commonly used metal oxide gas sensing materials are limited by high activation energy of gas sensing reactions,easy aggregation of basic structural units,and difficulty in gas diffusion,resulting in their actual gas sensing performance far lower than theoretical expectations.In view of the key problems of the current metal oxides in gas sensing applications,such as slow response,poor selectivity,high detection limit,etc.,this paper designed and constructed a technical scheme of heterogeneous multilayer hollow micro/nano-structure to regulate the structure unit configuration,shell layer number and porous structure of heterogeneous multilayer structure,in order to increase the active site,inhibit agglomeration,adjust the interface reaction barrier,and ultimately achieve the purpose of improving gas sensing performance.This paper through controlled synthesis of the typical p-type semiconductor Cu₂O,n-type semiconductor Fe₂O₃,and Cu₂O@Fe₂O₃ composite gas sensing materials with micro/nano-structures,exploring the assembly process and formation mechanism of hollow micro/nano-structures with high specific surface area,comparing and testing the gas sensing performance of Cu₂O,Fe₂O₃,and Cu₂O@Fe₂O₃ materials,and discussing the reasons for the improvement of gas sensing performance in pure phase structure and heterojunction composite structure,aiming to provide new ideas for the development of metal oxide gas sensing materials.The main research content and conclusions are as follows:（1）Cu₂O single-layer（Cu₂O SHS）and double-layer（Cu₂O DHS）hierarchical hollow structures were prepared by solvothermal method.The single-layer/double-layer structures were self-assembled by zero-dimensional nanoparticles and two-dimensional nanosheets,respectively.The size of Cu₂O two-layer structure was about 4μm,and the specific surface area was 27.38 m²g^-1.This hierarchical structure effectively prevents the agglomeration of basic units.It was found that glutamic acid acted as the reducing agent of Cu²⁺,and the formation of Cu₂O was consistent with Ostwald ripening mechanism.（2）Short rod,long rod,solid and hollowα-Fe₂O₃ structures were obtained though hydrothermal method by controlling the amount of Na₂SO₄.The solid and hollow Fe₂O₃ structures are like sea urchins with the size of about 3μm.The spheres are hierarchical structures composed of single crystal nanorods with several hundred nanords.The presence of SO₄^2-in the precursor solution is the key to the self-assembly ofα-Fe₂O₃ to form the urchin-like structure.The specific surface areas of solid（Fe₂O₃ SSs）and hollow（Fe₂O₃ HSs）structures are about 91.6 and109.4 m²g^-1,respectively.In addition,based on the Cu₂O bilayer hollow structure,the Cu₂O@Fe₂O₃ heterogeneous three-layer hollow structure formed by the heterogeneous Fe₂O₃ nanorods array has a specific surface area of 123.26 m²g^-1 and an average pore size of 13.6 nm,which has excellent mesoporous pore size and higher specific surface area.（3）Fe₂O₃ SSs and Fe₂O₃ HSs sensors have the highest selectivity for toluene gas.At the optimum operating temperature of 270℃,the sensitivity and response/recovery time of Fe₂O₃ HSs sensor to 50 ppm toluene gas are 13.8 and1.4/10 s,respectively,which is about 1.8 times of Fe₂O₃ SSs sensitivity（7.6）.Cu₂O and Cu₂O@Fe₂O₃ sensors are selective to xylene gas,and the best operating temperature is 240℃and 270℃,respectively.At their respective optimum operating temperatures,the Cu₂O@Fe₂O₃ sensor has a sensitivity of 4.62,1.8 times that of the Cu₂O DHS sensor（2.6）and 2.4 times that of the Cu₂O SHS sensor（1.94）.The reasons for the enhancement of gas-sensitive properties of heterojunction recombination are as follows:reasonable hollow porous structure,catalytic activity of Fe₂O₃ and the presence of numerous p-n heterojunctions at Cu₂O/Fe₂O₃heterointerface.The gas-sensitive mechanism can be explained by the crystal boundary barrier model.In summary,this paper designed and synthesized Cu₂O/Fe₂O₃ hollow porous structure,constructed Cu₂O@Fe₂O₃ p-n heterojunction,and applied in the gas sensitive field,improve the sensitivity of oxide sensor to the detection of volatile organic compounds such as toluene and xylene gas.