Studies On Preparation, Characterization And The Photocatalytic Behaviors Of ZnMn₂O₄ Nanorods

Spinel-type complex metal oxides AB2O4, an important class of inorganic functional semiconducter materials. They have found wide applications in areas such as semiconductor, optoelectronic, magnetic material, sensor, biology, medicine, catalyst and catalyst support, because of their particular structural and physical-chemical properties. Among the spinel materials, ZnMn2O4 have drawn great attention for their various crystal structures and excellent magnetic, optical, electrical and catalytic properties. Properties and the corresponding applications of inorganic semiconductor materials could be affected greatly by their morphologies. Therefore, we could improve optical and catalytic properties of ZnMn2O4 semiconductor material by means of fabricating one-dimention ZnMn2O4 materials with special morphologies. In this present work, ZnMn2O4 nanorods were synthesized, and then a series of characterization and photocatalytic behavior were detected. We respectively took acetone and naphthalene as degradation substrate and used in-situ infrared spectroscopy to study the process of photocatalytic reaction. In this dissertation, the following three aspects investigations were carried out:(1) Usingα-MnO2 nanorods as template, one-dimensional spinel nanomaterials ZnMn2O4 nanorods were successfully prepared. Morphology and structure of ZnMn2O4 nanorods were detected by these means such asⅩ-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental composition on the surface could be measured byⅩ-ray photoelectron spectroscopy (XPS) andⅩ-ray spectroscopy (EDS). And the photoelectric properties were detected through UV-Vis diffuse reflectance spectroscopy (DRS) and surface photovoltage spectroscopy (SPS). The ZnMn2O4 nanorods mainly grew along the (211) crystalline plane with the width in 50-100 nm and the length in 1.5-2μm. As the calcination temperature increased, they presented with much more improved crystallinity and photoelectric response.(2) The in-situ transmission infrared spectroscopy was used to investigate the photocatalytic reaction of acetone on the surface of ZnMn2O4 nanorods and researched the photocatalytic reaction mechanism. Compared with the photocatalytic process of ZnMn2O4 nanorods, the photocatalytic reaction of acetone under UV irradiation was also carried out. In the presence of the catalyst ZnMn2O4 nanorods, acetone reacted with the hydroxyl groups on the catalytic surface and was converted into CO2, H2O, acetate and acetaldehyde. Under UV irradiation only, acetone and was converted into CO2, CO, H2O, formic acid and ether compounds.(3) The in-situ transmission infrared spectroscopy was used to investigate the photocatalytic reaction of the typical PAHs naphthalene on the surface of ZnMn2O4 nanorods and the photocatalytic reaction of naphthalene under UV irradiation was also carried out. Then the reaction mechanisms were speculated. In the presence of the catalyst ZnMn2O4 nanorods, naphthalene reacted with the hydroxyl groups on the catalytic surface and was converted into CO2, H2O, phthalic anhydride, aromatic ester and aromatic ketones. The intermediate products were 1,4-butanediol.1,3-butadiene and 1,4-succinic aldehyde. Under UV irradiation only, naphthalene was converted into CO2, H2O, phthalic anhydride, aromatic ester and aromatic ketones. The intermediate products were 1.4-butanediol,1,4-succinic aldehyde and 1,4-succinate.