Design,preparation And Gas-sensing Performance Of Metal Oxide Based Heterostructures

With the advantages of low cost,easy of preparation,portability and fit for mass production,metal oxide semiconductor（MOS）based resistive gas sensor has attracted the attention of researchers all over the world.However,most MOS gas sensors suffer from low response,slow response/recovery speed,poor selectivity,etc.Heterojunction is a very promising structure in gas sensing fields because it can make use of the advantages of different pure phase materials as well as generate more unique synergestic effects.The goal of this research is to improve the gas sensing properties of MOS materials via heterojunction construction and heterostructure design and to probe into the sensing mechanisms of heterostructure materials in detail.The main contents are as follows:（1）By choosing Co₃O₄,a good catalyst toward ethanol,as a main sensing material and Zn O as an additive material,Zn O-decorated Co₃O₄ hollow polyhedrons heterostructure is synthesized via thermal decomposition of ZIF（zeolitic imidazolate frameworks）as self-sacrificial templates.Experimental results reveal that 2 mol%Zn O-Co₃O₄ heterostructure presents the best gas sensing performance,which is attributed to the formation of p-n heterojunction between Co₃O₄ and Zn O as well as the large specific surface area of Zn O-Co₃O₄.（2）Co-MOF-74（metal orgainc frameworks）derived Co₃O₄/graphene nanoscrolls（Co₃O₄/GNS）heterostructure is designed.The uniform arrangement of large amounts of Co-MOF-74 nanoparticles on the interlayer galleries of graphene nanoscrolls gives rise to a large heterojunction interface.Meanwhile,GNS with hollow structure and big interlayer distance can act as high-speed gas transport channels.As a result,appreciable response together with rapid response/recovery speed toward ppb-level acetone is obtained.（3）Traditional heterostructure synthesis methods involve various raw materials,complicated synthetic process and suffer from potential contaminant.WO₃-W₁₈O₄₉heterostructure is synthesized via a novel one-step approach using just one oxide precursor.When applied in 500 ppm NH₃detection,the response of WO₃-W₁₈O₄₉heterostructure with loose nanowire bundle-like morphology is 5.63 times higher compared with compact spindle-shaped W₁₈O₄₉nanomaterial.（4）So far almost all resistive CO₂ sensors are utilized in atmospheric environment.However,in some fields,gas sensors should be operated in oxygen-free environment.The effect of background oxygen content ambient on the CO₂gas sensing performances of La OCl-doped Sn O₂ holow nanofibers are comprehensively investigated.It is found that in low oxygen concentration（0-500 ppm O₂）background,the amount of V_Ο⁺⁺is a decisive factor for CO₂ gas-sensing properties.16 at.%La OCl-Sn O₂contains the highest amount of V_Ο⁺⁺,thus exhibiting maximum response.In high oxygen concentration（500 ppm-100%O₂）background,the adsorption extent of CO₂ is the key to evaluate the gas-sensing performance.8 at.%La OCl-Sn O₂holds the highest amount of carbonates,giving rise to the best gas sensing properties.This work systemically investigate the relationship between composition/structure and gas sensor performance of the heterostructure nanomaterials through the above four parts and proposes the principles of heterojunction construction and heterostructure design,providing some new thoughts for the choose of proper gas sensing materials and novel heterostructure design.