Design And Experimental Study Of MOF-derived ZnO Gas Sensor

With the booming development of IOT technology,gas sensors play an important role in industrial production,environmental protection and medical fields.Due to the late start of domestic research on gas sensors,the high-end development technology of gas sensors is still in the hands of foreign manufacturers.The development of high performance gas sensors for specific hazardous gases is of great importance.In this paper,we developed a ZnO gas sensor and detection system based on ZnO nanocluster material for the hazardous volatile organic compound trimethylamine（TMA）gas.Firstly,metal-organic framework（MOF）precursors and ZnO nanocluster gas-sensitive materials were prepared,and structural morphological characterization and defect studies were carried out.In addition to the original Zn-MOF precursors obtained by ligating terephthalic acid or 1,3,5-homophthalic tricarboxylic acid with Zn²⁺ions alone,defect engineered（DE）Zn-MOF precursors with unsaturated coordination sites were also prepared by competing the ligands of two organic ligands with Zn²⁺ions in different proportions based on the defect growth mechanism.Further,the MOF precursors were annealed to obtain ZnO nanocluster materials,and possible growth mechanisms of DE Zn-MOF precursors and ZnO nanocluster materials were proposed.The distribution and species of oxygen vacancies in ZnO nanoclusters have been investigated by the techniques of x-ray photoelectron spectroscopy（XPS）,ultraviolet-visible（UV-vis）spectroscopy,photoluminescence（PL）spectroscopy and electron paramagnetic resonance（EPR）spectroscopy,and the formation mechanism of abundant double positively charged oxygen vacancies(Vo²⁺)defects in DE Zn-MOF derived ZnO nanoclusters has been proposed.Secondly,the performance of the ZnO gas sensor was tested including optimal operating temperature,selectivity,repeatability and response to different concentrations of TMA gas.The results showed that the gas-sensitive performance of the DE Zn-MOF derived DL2 and DL4 sensors was significantly improved compared to the original Zn-MOF derived SL1 gas sensor.The response values of the first two sensors reached105.72 and 270.1 for 20 ppm TMA gas at 140°C,which were 2.55 and 8.62 times higher than those of the SL1 sensor,respectively,and also had the advantages of fast response and low lower detection limit（0.5 ppm）.Further,based on density functional theory（DFT）,the ideal surface and defective（oxygen vacancy）surface adsorption models of ZnO（101）crystalline surfaces were developed,and the adsorption energy and differential charge density of TMA molecules on the two surfaces were calculated.The calculated results show that the surface oxygen vacancies promote the adsorption of TMA molecules on the ZnO surface and can facilitate the charge transfer between the two.Finally,based on the electronic depletion layer（EDL）theory and DFT calculation results,the performance enhancement mechanism of DE Zn-MOF derived ZnO gas sensor is proposed.In order to verify the accuracy of the above experimental method and theory,the DE Cu-BTC derived Cu O gas sensor was also prepared.The performance test results demonstrated that the gas-sensitive performance of the metal oxide gas sensor could be effectively enhanced by the DE MOF template method.Finally,the design and experimental study of the detection system of ZnO gas sensor was carried out using ZnO gas sensor as the core sensing element.The detection system consists of a lower computer part:peripheral circuit module,voltage module,signal measurement module and microcontroller core module to ensure the normal operation of the sensor and accurate signal transmission to the upper computer;the upper computer part:data processing software based on Labview software development,including data display and saving,image saving,concentration alarm and switch control functions.In addition,the electric-thermal coupling simulation of the sensor gas-sensitive element was carried out by COMSOL 6.0 software,and the working parameters of the detection system were determined by combining with the analysis of the detection system performance index.The performance test results show that the ZnO gas sensor detection system has good selectivity and repeatability for TMA gas,with a response value of 54.4 for 20 ppm TMA,response time and response time of 6 s and 36 s.In addition,the detection system has the ability to resist interference for low concentration（16.7%）of triethylamine gas,which has certain practicality.