| The organic amines are very important industrial raw materials,and most of them are volatile,flammable and toxic,and need to be determined.Gas sensors can accomplish real-time monitoring and alarm to these target gases.The sensing materials are the cores of gas sensors,in which semiconducting metal oxides account for a large proportion.Mo O3 is one type of transition metal oxide which possesses special quantum size effect and excellent physical and chemical stability,making it begin to be used in gas sensor area.The gas sensors based on Mo O3 nanomaterials are high sensitive to organic amines.Therefore,hierarchical?-Mo O3 constructed by various building unites were designed and prepared here,the morphology and structure were characterized by the modern instrument analysis methods such as scanning electron microscope(SEM),transmission electron microscopy(TEM)and X-ray diffraction(XRD).The as-obtained?-Mo O3 nanomaterial was fabricated into gas sensors to measure the gas-sensing performance to organic amines and other gases.In order to improve the gas sensing performance of?-Mo O3 nanomaterial to organic amine,loading techniques were studied in this thesis.The main contents of the thesis are as follows:(1)The Mo O2 precursor was prepared via solvothermal method by using molybdenyl acetylacetonate,n-butanol and nitric acid as reactants.And flower-like?-Mo O3 with hierarchical nanostructures was obtained after subsequent calcination at400°C in air for 2 h.The diameter of the?-Mo O3 flowers is about 3-5?m consist of microrods with average diameters of 150-200 nm,growing radially from the center of the hierarchical flower-like structure.The optimum reaction conditions were determined by adjusting the concentration of HNO3,reaction temperature and time.The results show that the best experimental conditions are:HNO3 is 6 mol·L-1,the reaction should be carried out at 180°C for 24 h.The flower-like?-Mo O3 nanomaterial has good sensitivity and selectivity to TEA,the response to 100 ppm TEA is 416 and the lowest detection limit is 0.5 ppm.(2)The precursors of Mo O2 hollow spheres were prepared via solvothermal method without any templates and surfactants.And hierarchical?-Mo O3 hollow microspheres were obtained after subsequent calcination at 400°C.The diameter of the?-Mo O3 microspheres is about 400-600 nm which assembled by nanorods with a width of 50 nm.The optimum experimental conditions are:the concentration of molybdenyl acetylacetonate and HNO3 are 0.012 and 6 mol·L-1,respectively,and the reaction should be carried out at 220°C for 12 h.The?-Mo O3 microspheres have good sensitivity and selectivity to triethylamine,the response to 100 ppm TEA is 603 and the lowest detection limit can be up to 0.1 ppm at 217?.(3)The?-Fe2O3/?-Mo O3 microspheres with different Fe/Mo mole ratios were synthesized by one-pot solvothermal method.The?-Fe2O3/?-Mo O3 microspheres are assembled by nanoplates with a width of 30-80 nm,whose diameters are slightly lager than that of the pure ones,which are 400-800 nm.The?-Fe2O3/?-Mo O3 microspheres with the mole ratio of 6 at%have the best sensitivity and selectivity to triethylamine.The optimum working temperature reduces from 217? to 170?,the lowest detection limit decreases from 0.1 ppm to 0.01 ppm and the response time reduces from 6 s to 2.6s when compared to the pure?-Mo O3 microspheres.(4)Au-loaded?-Mo O3 microspheres were prepared by surfactant-modified method,the morphology of the microspheres almost maintained after being loaded by Au.The diameters of the Au/?-Mo O3 microspheres are 400-600 nm,the building unites are still nanorods,and the diameters of the loaded Au nanoparticles are 5-20 nm.The Au/?-Mo O3(1.0 wt%)microspheres have the improved sensitivity and selectivity to aniline but lowered gas-sensing performance to TEA at 330?,comparing with those of pure?-Mo O3 microspheres.The response to 100 ppm aniline can reach 23.7 and the lowest detection limit can be up to 0.5 ppm at 330?.(5)The surface statuses of the?-Mo O3,?-Fe2O3/?-Mo O3 and Au/?-Mo O3microspheres before and after exposure to the gases of organic amines were investigated by XPS.The probable oxidization products of them were analyzed by GC-MS.The gas sensing mechanism of these nanomaterials to organic amines could be interpreted through the following two catalytic oxidation processes:the reaction of organic amines with chemisorbed oxygen are dominant at the relatively low organic amines concentrations,and the lattice oxygen of?-Mo O3 would oxidize the organic amines with the increasing gas concentrations.The oxidation product of triethylamine and aniline are vinylamine and azobenzene,respectively. |
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