Morphology Regulation And Performance Study Of Bismuth-Based Oxides For Gas Sensitivity

The green,non-toxic metal bismuth（Bi）is becoming increasingly popular due to its safe and non-toxic nature.The properties of bismuth-based oxides are usually improved by modulating their morphology.Three-dimensional（3D）hierarchical structures consisting of nanoparticles,nanorods,nanosheets etc.are often considered to be potentially promising gas-sensitive materials.Three-dimensional materials imply a"hierarchical structure",which is a modulation of the morphology in higher dimensions.Typically,3D materials are micro-or nanostructures consisting of many low-dimensional nanomaterials,such as one-dimensional nanowires/nanorods assembled into 3D sea urchin-like spheres,and three-dimensional flower-like hierarchies consisting of many two-dimensional nanosheets.The hierarchical structure of 3D materials facilitates the contact between the target gas and the surface of the sensor material,and the microscopic accumulation of such 3D structures can provide channels for gas transport and facilitate gas adsorption and desorption,thus enhancing the gas-sensitive performance of the materials.A tart-like Bi₂Sn₂O₇ gas-sensitive material consisting of nanoparticles was prepared by a hydrothermal method.By comparing with the particle-like Bi₂Sn₂O₇ the best working temperature of the tart-like Bi₂Sn₂O₇ sensor was at 210℃,and it showed a sensitivity of 104.4 for 1000 ppm formaldehyde and a very fast response of6 s for 100 ppm formaldehyde in a series of tests at the optimum temperature.The hydrothermal reaction parameters were adjusted to prepare a Cu Bi₂O₄gas-sensitive material consisting of nanorods with a maximum specific surface area of6.0512 m²g^-1,providing more reaction area and reaction sites for gas absorption and electron transport.Its selectivity was tested and found to be excellent for formaldehyde gas,with a sensitivity of 19.1 for formaldehyde at 1000 ppm at the optimum operating temperature.four repeatability experiments were performed on formaldehyde and the curves largely matched with excellent reproducibility.By varying the experimental parameters of the hydrothermal method,flower-like Bi₂WO₆ gas-sensitive materials assembled from nanosheets,with diameters of 1-2μm,were synthesized with significant hierarchical effects.By assembling the Bi₂WO₆gas-sensitive material into the gas sensor,it exhibited a sensitivity of 58.59 for 1000ppm ethanol in tests at optimum temperature,while the flower-like Bi₂WO₆ showed excellent selectivity for 100 ppm methanol,ethanol,acetone,ammonia and formaldehyde gases in selectivity tests.The thesis has 46 figures,4 tables,and 120 references.