Preparation Of Metal Oxide Films Based On Liquid Phase Deposition Technique And Their Photoelectrocatalytic Performance Under Visible Light

Photoelectrocatalytic technique is one of the important advanced oxidation technologies for treatment of organic pollutants in the environment. And the performance of anode materials is a key factor that influences the efficiency of the photoelectrocatalytic system. Among the preparation methods of electrodes, liquid phase deposition (LPD) method exhibits significant advantages such as mild preparation process, low cost and no selectivity to substrate. In this thesis, ZnO film, Ag/ZnO composite film, α-Fe2O3 film and WO3/TiO2 film were successfully prepared by LPD and applied for photoelectrocatalytic degradation of organic pollutants under visible light illumination. The material and optical properties of the films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and UV-Visible diffuse reflectance spectra (DRS). The main contents of the thesis were described as follows:(1) A novel LPD method based on ZnO-HF and H3BO3 as precursors was developed to prepare ZnO films and the photoelectrocatalytic performance of the films were investigated through the degradation of Rhodamin B (RhB) and p-nitrophenol (PNP) under visible light illumination. The results demonstrated that the structure of ZnO film consisted of a layer of nanorods with irregular surface and the film exhibited certain absorption in the visible light region. The photoelectrocatalytic (PEC) performance of the ZnO film electrode could be tuned by controlling the mole ratio of ZnO and H3BO3. And the film prepared at the ratio 1:2 showed the highest PEC activity. On such a LPD ZnO film, nearly 43.3% of RhB was degraded after 240-min treatment and 75.1% of PNP was removed within 120 min under visible light illumination.(2) The Ag-loaded ZnO film electrode was prepared by LPD method combined with UV photocatalytic reduction technique. SEM and XPS analysis indicated that Ag nanoparticles formed on the ZnO nanorod and the loaded amount was increased with the prolonged duration of UV light. Compared with pure ZnO film, all the Ag/ZnO films exhibited higher PEC efficiency. The composite film prepared with 3 min of UV irradiation showed the highest PEC activity. The PEC degradation of RhB under visible light and 0.8 V biasing voltage over this electrode was 61.3%,18% higher than that on the pure ZnO film. The increase of the PEC activity could be ascribed to a higher utilization rate of visible light owing to the surface plasma resonance of Ag and the separation of photogenerated electron-hole pairs under the effect of the schottky barriers between Ag and ZnO.(3) a-Fe2O3 films were prepared from the solution system of FeOOH-NEUF·HF with H3BO3 by LPD process and the photoelectrocatalytic performance was investigated under visible light illumination. After calcined at 600 ℃, the film with a porous structure exhibited higher PEC activity than other samples calcined at different temperatures and its band gap was about 2.0 eV. On the α-Fe2O3 film,79.1% of methyl orange (MO) was degraded within 120 min and 46.8% of PNP was removed after 120-min treatment. Such a LPD a-Fe2O3 film possesses good PEC performance and stability.(4) The WO3/TiO2 film electrodes were prepared by LPD method via two-step processes. SEM and loaded amounts analysis indicated that the bottom layer TiO2 was composed of nanoparticles and the top layer WO3 showed a flower-like structure formed by the aggregation of nanoflaks. Moreover, the TiO2 film provided an excellent substrate for WO3 deposition while WO3 obviously expanded the absorption of TiO2 film to visible light. As a result, the PEC activity of TiO2 was increased under visible light irradiation. When the concentration of H3BO3 in WO3 precursor solution was 0.2 mol-L"1, the WCh/TiO2 film exhibited the best PEC performance and the degradation efficiency of Rhodamin B (RhB) was 50.9% within 240 min with 1.0V anodic bias potential and visible light simultaneously applied. Under the same condition, nearly 80% of 4-chlorophenol (4-CP) was removed after 90-min treatment. The results showed that the LPD WO3/TiO2 film possessed high PEC activity for efficient removal of various refractory organic pollutants.