Controllable Syntheses And Research Of Gas Sensing Properties Of Silver Phosphate And Porous Zinc Oxide Nanomaterials

With the rapidly development of social industry,people's living space fill with the toxic and harmful gases,which directly threatens people's lives and property.Thus,real-time online monitoring of toxic and harmful gases is necessary.The semiconductor gas sensor has the advantages of simple structure,easy miniaturization,low price,long working life,etc.,and has been widely applied to real-time online monitoring of toxic and harmful gases.However,the semiconductor gas sensors have some problems such as high operating temperature,poor selectivity,and insufficient sensitivity,which limit the further expansion of their application fields.In recent years,in order to improve the gas sensing performance of semiconductor gas sensors,researchers have studied gas sensing materials in depth from two aspects:1)improving the gas-sensitive properties of traditional metal oxide gas sensing materials.It mainly improves the sensitivity,selectivity and working temperature and other gas-sensitive properties of metal oxides by regulating surface defects,particle size and morphology;2)developing new non-metal oxide semiconductor gas sensing materials.It is mainly based on the special chemical adsorption properties of gas molecules on the surface of certain semiconductor materials?such as carbon nanotubes,graphene,etc.?to study new semiconductor gas sensing materials.Based on the excellent catalytic properties of Ag₃PO₄,the gas-sensitive properties of Ag₃PO₄ nanoparticles,a novel gas-sensitive material,were systematically studied.Furthermore,this thesis takes the traditional metal oxide gas sensing material ZnO as the research object.The synthesis strategy of porous nanomaterials by calcining precursor MOFs is used to improve the gas sensitivity of ZnO to H₂S through the morphology control of porous ZnO nanomaterials.The main research contents are as follows:?1?Preparation and gas sensing properties of Ag₃PO₄ nanoparticlesStudying gas sensing properties of novel semiconductor materials with unique gas chemisorption characteristics is great significance for the development of new semiconductor gas sensing materials and high performance gas sensors.Based on the special electronic structure and superior catalytic activity of Ag₃PO₄,the gas sensing properties of Ag₃PO₄ semiconductor materials were systematically studied for the first time.The Ag₃PO₄ nanoparticles were synthesized by simple solid-phase grinding method.The morphology,crystal structure and surface element chemical state of Ag₃PO₄ nanomaterials were analyzed by SEM,XRD and XPS.The gas sensing properties of Ag₃PO₄nanoparticles were systematically studied by intelligent gas sensing test system.In addition,the gas sensing mechanism was explained by in-situ FT-IR characterization combined with theoretical calculation.The results show that the sensitivity of Ag₃PO₄ nanoparticles to NH₃ is up to 52%at an operating temperature of near room temperature 50°C,and the sensitivity decreases with increasing operating temperature?from 50°C to 100°C?,indicating that Ag₃PO₄ has excellent low temperature gas sensitivity reaction to NH₃.Moreover,Ag₃PO₄ nanoparticles exhibit very high gas selectivity to NH₃ at operating temperature of 50°C and negligible response to other gases including H₂,CO,ethanol,acetone,NO₂ and SO₂.The in situ FT-IR characterization and theoretical calculations show that the lone pair of NH₃ coordinates with the empty orbital of the silver atom on the surface of Ag₃PO₄ accompanied with higher adsorption energy,more charge transfer amount and more thermodynamic advantage for the coordination reaction of NH₃,which explains the reasons of high gas sensitivity to NH₃.?2?Morphology control of porous ZnO nanomaterialsThe gas sensing material morphology mainly regulates the gas sensing performance by regulating the utilization rate of the gas sensing material in the gas sensing process,and the gas sensing material utilization rate is closely related to the gas diffusion in the material,mainly including the diffusion of gas in the material nanostructure in the gas sensitive membrane.The preparation of porous nanomaterials can improve the diffusion efficiency of gases in the nanostructures of materials,while the morphology of porous nanomaterials determines the diffusion efficiency of gases in gas sensitive membranes.In this paper,ZnO was used as the research object.The synthesis strategy of porous ZnO nanomaterials by calcining precursors Zn-BTC MOFs and adjusting the morphology of Zn-BTC MOFs were used to synthesize porous ZnO nanomaterials with different morphologies.In this paper,ZnO nanomaterial was served as the source of Zn²⁺,H₃BTC was the organic ligand,ethanol/water was the mixed solvent,and ultrasonic was the synthesis method to prepare Zn-BTC MOFs.The effects of ultrasonic time,H₃BTC concentration and ethanol/water ratio on the morphology of Zn-BTC MOFs were systematically studied.The obtained Zn-BTC MOFs were characterized by SEM,TEM and XRD.The results show that ultrasonic time,H₃BTC concentration and ethanol/water ratio all have an effect on the morphology of Zn-BTC MOFs.By regulating these parameters,the morphology of Zn-BTC MOFs can be controlled to obtain one-dimensional?nanorod?and two-dimensional?nanosheets?and three-dimensional?nanoparticle?Zn-BTC MOFs.Based on the obtained morphologies of Zn-BTC MOFs,porous ZnO nanomaterials with the same morphology can be obtained by simple high-temperature calcination.?3?Preparation and gas sensing properties of porous ZnO nanorodsGas-sensitive membranes with one-dimensional porous nanomaterials have excellent gas diffusion efficiency,and high-performance gas sensing devices can be obtained.Based on the previous research results,the porous ZnO nanorods were prepared by simple calcination treatment of the obtained one-dimensional Zn-BTC MOFs.In this paper,the crystal structure and morphology of the nanomaterial were characterized by XRD,SAED,SEM and TEM.The gas sensing performance was systematically tested by gas sensing system.The mechanism of gas sensitivity enhancement was studied by BET,EPR,XPS and PL etc.The results show that Zn²⁺is oxidized during high temperature calcination to form ZnO nanomaterial with uniform particle size,and the decomposition of organic ligands in Zn-BTC MOFs produces a rich pore structure at the same time.The gas-sensitivity studies show that the H₂S gas sensitivity of porous ZnO nanorods is significantly improved compared to commercial ZnO nanoparticles with similar particle sizes.In addition to improving the utilization of gas sensing materials,the BET,EPR,XPS,and PL spectra show that porous ZnO nanorods also have more surface defects than commercial ZnO nanoparticles,explaining the reason for the improvement of gas sensitivity.