Studies Of Sensing Mechanism Based On Metal-Organic Frameworks-derived Metal Oxides And Perovskite Oxides

As a key component of measuring instruments,sensors play an important role in the field of medical testing and environmental monitoring.This dissertation focuses on the detection of diabetes and blood sugar and the monitoring of automobile exhaust emissions in environmental protection.The following researches are conducted on the sensitivity and selectivity of non-enzymatic glucose detection and the oxygen sensing mechanism of perovskite oxide film.Metal-organic frameworks?MOFs?are a class of crystalline materials self-assembled by metal ions and organic ligands.Recently,metal oxide materials derived from MOFs as precursors have attracted much attention due to their excellent electrochemical performance.However,the structural design and the improvement of glucose sensing performance related to these derived oxides still need to be explored.Hence,the first part of this dissertation is mainly about preparing metal oxide nanomaterials based on new type of MOFs with special crystal structure and morphology.The derived metal oxide nanomaterials are prepared by simple and efficient methods for high-performance transition metal oxide-based glucose sensor.?1?Novel Co-MOF single crystal with layered structure is prepared and used as the precursor to produce a two-dimensional Co₃O₄nanoplate by facile pyrolysis,which has been applied for non-enzymatic glucose detection for the first time.The intrinsic relationship between the crystal structure of Co-MOF and the glucose sensing properties of derived metal oxides is revealed.The Co₃O₄ nanoplates-based glucose sensor has high sensitivity of 917.82?A m M^-1cm^-2,low detection limit of 0.32?M?S/N=3?,with good selectivity in the presence of interfering substances such as L-cysteine,Na Cl,dopamine,ascorbic acid,and uric acid.The two-dimensional structures of Co₃O₄ nanoplates,which are consisted of multilayer nanosheets,increase the interface contact area with the electrolyte and facilitate the rapid transfer of ions.This Co₃O₄ nanoplates-based sensor shows good performance in the detection of glucose without complicated processes,which provides a new approach for the structural design of MOFs-derived oxides and their application in glucose sensing.?2?Cu O nanomaterials with different hierarchical structures are prepared,which are derived from Cu-MOF microrods.The micro/nano structure of the derived metal oxides are tuned by rationally designing the pyrolysis process of MOF.The rod-shaped copper oxide?Cu O-350-NA?composed of porous nanospheres is prepared by pyrolyzing Cu-MOF first under nitrogen atmosphere and then in air,showing excellent glucose sensing performance under alkaline conditions.Compared with Cu O nanoclusters obtained by pyrolysis directly in air,Cu O-350-NA has higher sensitivity(1806.10?A m M^-1 cm^-2)and broader linear range?0.005-6.535 m M?,lower detection limits?0.15?M?,and excellent selectivity.Porous nanospheres Cu O-350-NA have more surface defects and a larger specific surface area,which can effectively promote the diffusion of ions in the electrolyte and the electrochemical reaction,so that its sensing performance is significantly improved.Moreover,Cu O-350-NA-based sensors have shown good sensing performance for the detection of glucose in artificial saliva and actual saliva samples,which shows great potential in the development of a convenient device for non-invasive glucose detection.In addition,Rare-earth cobalt-based perovskite oxides have excellent mixed ion/electron conductive properties,with sensitivity much higher than traditional oxygen-sensitive materials,however,the related mechanisms still need to be explored.The second part of this dissertation is mainly about is mainly based on the perovskite oxide Pr Ba_0.7Ca_0.3Co₂O_5+??PBCC?epitaxial thin film,testing the resistance change of the film in the process of switching between oxidizing atmosphere and reducing atmosphere,understanding the gas-sensitive characteristics of the film,and exploring the hydrogen/oxygen diffusion behavior and mechanism.?1?Ca-doped PBCC thin film is epitaxially grown on?001?strontium titanate?Sr Ti O₃,STO?substrates by pulsed laser deposition technique.We have measured the resistance change of the PBCC/STO film in the temperature range of 350-725 ^oC during switching between the oxidizing atmosphere and the reducing atmosphere,and systematically studied the hydrogen/oxygen diffusion behavior of the film at medium and high temperatures.The resistance change is highly reversible in the temperature range of 350-725 ^oC,indicating that the PBCC/STO film has excellent stability.When the reduced PBCC/STO film is at 450 ^oC,the response time to oxygen is less than 2 s,and its maximum resistance change rate can reach 1.87×10⁶?s^-1.In addition,when the temperature is higher than 600 ^oC,the reduced PBCC/STO film may show a negative resistance response to oxygen.We have proposed the related mechanism for the first time.PBCC/STO films show extremely high oxygen surface transport rate and high surface chemical activity,which is of potential importance for the development of ultra-sensitive oxygen sensors,and the negative resistance response mechanism proposed for the first time is of great significance to study the oxygen diffusion behavior of perovskite oxides.?2?Based on the previous work,to further explore and verify the proposed negative resistance response mechanism,PBCC thin film is epitaxially grown on?001?lanthanum aluminate?La Al O₃,LAO?substrate.We have measured the resistance change of the PBCC/LAO film in the temperature range of 600-700 ^oC during switching between the oxidizing atmosphere and the reducing atmosphere.In this temperature range,the PBCC/LAO thin film undergoes a two-phase transition of semiconductor phase-insulating phase-semiconductor phase either in the oxidizing or reducing atmosphere.Also,the negative resistance responses of PBCC/LAO films occur in the oxidizing gas when temperature is higher than 600 ^oC.The response and recovery time to oxygen of the reduced PBCC/LAO film is very short,indicating that the film is extremely sensitive to oxygen.Moreover,the repeatability of the resistance change is very high,indicating that the PBCC/LAO film has excellent chemical stability in high temperature range,which provides a new choice for the preparation of ultra-sensitive oxygen sensors used in harsh environments.