Preparation And Photocatalytic Property Of Bi-doped Nanostructured MnO₂/Ti Materials

In this paper, one-dimensional Bi2O3-MnO2/Ti materials are prepared successfully in normal temperature and pressure; and the main research contents have three parts:①ZnO/Ti nanorod template was synthesized by galvanostatic electrodeposition method. The morphology and structure of ZnO/Ti nanorod were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of the Zn2+, NO32-concentration and the deposition current on the morphology of the ZnO nanorod arrays were investigated. The photocatalytic properties of ZnO nanorod template were discussed;②One-dimensional MnO2/Ti nanoelectrode was synthesized by anodic electrodeposition method using ZnO/Ti nanorod template. The morphology and structure of One-dimensional MnO2/Ti were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of the deposition time on the morphology of the one-dimensional MnO2were investigated. The preparation mechanism and photocatalytic properties of one-dimensional MnO2were discussed;③Bi2O3/Ti and Bi203-Mn02/Ti were prepared using dip-decomposition method. The morphology and structure of Bi2O3/Ti, Bi2O3-MnO2/Ti were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy spectrum analysis (EDS). The photocatalytic properties of Bi2O3/Ti, Bi2O3-MnO2/Ti were discussed; and the reason of enhanced photocatalytic activity of Bi-doped MnO2/Ti was discussed; ④the electronic structure of Bi-doped MnO2/Ti was calculated using density functional theory. The main results are as follows:1. Through the SEM images we knew that the Zn(NO3)2concentration was0.01mol·L-1and the deposition current was0.5mA·cm-2, the uniform and consistent ZnO nanorods array were prepared successfully; the average diameter was about100nm. Through the XRD analysis we knew that its structure was hexagonal wurtzite. The photodegradation rate of ZnO/Ti nanorod electrode was83.3%in the degradation of methyl orange under2.5hours of irradiation of UV lamp, which showed good photocatalytic activities; and without UV lamp, the photodegradation rate was only7%. The photocatalytic activity is derived from produced ZnO(hVB+) and ZnO(eCB-) under the light; however, ZnO(hVB+) and ZnO(eCB-) can also produce O0-·, HO2·, H2O2, OH·through a series of reactions. Through the series of oxidation process, the methyl orange is finally oxidized to CO2and H2O.2. Through the SEM images we knew the deposition time had obvious influences on the morphology of the MnO2. When the deposition time was3h, the MnO2had the columnar shape, the average diameter was about50nm; When the deposition time was between1.5h and2.Oh, it had the honeycomb shape. Through the XRD analysis we knew its crystal structure was a-MnO2. The photodegradation rate of MnO2was54%in the degradation of methyl orange under3.5hours of irradiation of UV lamp, which showed photocatalytic activities in some degree; and without UV lamp, the adsorption rate was almost0.3. Through the SEM images and EDS analysis we knew that Bi2O3had already deposited onto nanometer a-MnO2/Ti nanoelectrode. Through the XRD analysis we knew the crystal structure of Bi2O3was β-Bi2O3. Bi2O3/Ti had a certain adsorption (3%) of methyl orange without illumination, however, Bi2O3-MnO2/Ti had better adsorption (10%) of methyl orange. The photodegradation rate of Bi2O3/Ti and Bi2O3-MnO2/Ti were65.2%and80.7%respectively in the degradation of methyl orange under3.5hours of irradiation of UV lamp. Bi2O3-Mn02/Ti nanoelectrode exhibited much higher UV-light activity than pure Bi2O3/Ti and MnO2/Ti.4. The selectronic structure of Bi doped MnO2was calculated using the first-principles based on density functional theory, analyzed the formation energies (Ef), band gap, band structure and density of states of Mn0.75Bi0.25O2. Calculations based on density functional theory (DFT) indicated that the conductivity and stability of Bi2O3-MnO2/Ti were excellent. The formation energy value of the Mn1-xBixO2was at its minimum (0.5eV) where the system was most stable when x was equal to0.06, the formation energy value increased with the increase of x and system stability decreased when x was above0.06. The Mn0.75Bi0.25O2valence and conduction bands were observed to overlap considerably at EF. No band gap exists at EF as a result, thus suggesting that Mn0.75Bi0.25O2theoretically exhibited metallic features. The MnO2band gap decreased with the addition of Bi as per the DOS of MnO2. the stability of Mn0.75Bi0.25O2was increased.