| Coupling TiO2 with WO3 could not only promote the separation of photo-generated carriers, but also extend the photoresponse range of TiO2, resulting in the improvement of photocatalytic activity, due to that the energy levels of TiO2 and WO3 are a great match for each other. Thus, WO3/TiO2 composite semiconductors have a great potential in environmental treatment. However, most of current studies on WO3/TiO2 composite photocatalyst focus on the use of crystalline powder, which is easy to agglomerate and yet difficult to recycle. To promote practical application of WO3/TiO2 photocatalysis, it must be immobilized in film. Present preparation techniques of WO3/TiO2 composite film, such as magnetron sputtering and sol-gel, still face some difficulties, for instance, complicated equipment, hard process or poor adhesion between the film and the substrate, and so forth. Therefore, preparation of WO3/TiO2 composite film with good adhesion and high catalytic activity becomes one of the most important focuses in photocatalysis field.In this paper, Micro-arc Oxidation (MAO) technique was firstly chosen to prepare WO3/TiO2 composite film in alkaline sodium tungstate electrolyte in order to develop new immobilization and modification technique of TiO2 photocatalyst. The effects of electrolyte composition and power parameters on the microstructure and photocatalytic property of WO3/TiO2 composite film were investigated systematically. The effects of external factors, including pH of pollutant solution, inorganic anions, initial pollutant concentration and anodic bias, on the photocatalytic property of WO3/TiO2 composite film were studied. Visible-light-responsive WO3/TiO2 composite film was gained by changing electrolyte composition. The microstructure and visible-light catalytic property were studied and the visible-light-responsive mechanism is discussed. The overall results were as follows.MAO films were prepared on titanium in phosphate and tungstate electrolytes, respectively. The microstructure of two films was characterized by XRD, SEM and EDX. The film formed in phosphate electrolyte (TiO2 film) consisted of a mixture phase of anatase and rutile; while the film formed in tungstate electrolyte (WO3/TiO2 film) consisted of anatase, rutile and WO3. Both of these two films had a kind of rough and porous surface. But, more pores with larger specific surface area distributed uniformly on the surface of WO3/TiO2 film. According to spectrofluorimetry, the photo luminescene intensity of WO3/TiO2 film was lower than that of TiO2 film, implying that its separation between photo-generated electrons and holes was more effective. Compared with TiO2 film, WO3/TiO2 film had higher surface acidity, demonstrating stronger capacity of absorbing organic substance and hydroxyl group. More than 85% of rhodanmine was degraded by the WO3/TiO2 film while only 23% of rhodamine by the TiO2 film in UV light for 120 min.The degradation kinetics of rhodamine by TiO2 film and WO3/TiO2 film were studied, which were coherent with pseudo first order reaction. The kinetic equations caused by TiO2 film and WO3/TiO2 film were In (C0/Ct)=0.0023 t+0.029 and In (C0/Ct)=0.0161+ 0.1 and the corresponding apparent rate constant were 0.0023 and 0.016, respectively.The effects of electrolyte composition and power parameters on the microstructure and photocatalytic property of WO3/TiO2 film were investigated systematically. The content of tungsten, the crystallinity of WO3 and the surface acidity increased with the increase of tungstate concentration, but violent microarc discharge caused by excess Na2WO4 could destroy the surface structure of the film. The optimized electrolyte consisted of 14.7 g/L Na2WO4,2 g/L NaOH,2 g/L NaF. When the positive voltage, negative voltage, frequency, duty cycle and processing time were 400 V,-30 V,700 Hz,0.3 and 5 min, respectively, the prepared WO3/TiO2 film had best photocatalytic activity.Methyl orange was chosen as model pollutant, the effect of solution pH, inorganic anions, initial concentration and anodic bias on the photocatalytic property of WO3/TiO2 film was systematically studied. The degradation efficiency of methyl orange was the lowest in neutral solution, while that would be increased either in acidic or alkaline solution. Methyl orange was degraded faster with addition of NO3-, PO43- and HCO3-, and the best facilitation was caused by NO3- for OH·could be produced when NO3-was irradiated in the UV (λ＞290 nm). Thus, methyl orange was mainly degraded in solution rather than at the surface of WO3/TiO2 film. SO42- and Cl- inhibited the degradation of methyl orange through competitive adsorbing and capturing OH-. The degradation efficiency of methyl orange decreased as its concentration decreased.The influence of anodic bias on the photocatalytic activity of WO3/TiO2 film was investigated. The degradation efficiency of methyl orange increased with the increase of anodic bias. When the applied anodic bias is 4 V, the degradation efficiency of methyl orange exceeded that without bias by 78.5% approximately.Amorphous oxide film was prepared in the acidic sodium tungstate electrolyte by MAO technique, and sequentially subjected to high temperature calcination to get crystal WO3/TiO2 film. The microstructure and photocatalytic property of WO3/TiO2 film were investigated. The results showed that both cracks and white small particles of WO3 appeared at the surface of film after calcination. The total number and average size of pores in the inner of film increased. All of these increased the specific surface area of the film. The absorption edge of MAO-calcined WO3/TiO2 film was about 471 nm. Compared with anntase, a significant red-shift was obtained.55% Rhodamine can be effectively degraded by WO3/TiO2 film under visible light irradiation for 720 min. The visible-light-responsive mechanism of MAO-calcined WO3/TiO2 film was tentatively put forward on the basis of experiment and theoretical analysis.
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