Research On Preparation, Modification And Photocatalytic Performance Of TiO₂Films Based On Micro-arc Oxidation

TiO2has been investigated extensively in the photocatalysis field because of its good stability, high catalytic activity, low price and non-toxic. However, it is difficult for TiO2powder to be recycled and reused, which restricts the application range of TiO2. The porous TiO2photocatalytic film can be prepared at the surface of Ti or Ti alloys through micro-arc oxidation (MAO) technique, the immobilization of photocatalyst can be achieved through MAO because the combination between MAO TiO2film and substrate is compact. Therefore, MAO is a very promising technique in the photocatalytic field. However, The visible light response ability and photo-quantum efficiency of TiO2photocatalytic film prepared by common MAO are low, which affects its photocatalytic avtivity. Therefore, MAO TiO2photocatalytic film should be modified so that its visible light response ability and photo-quantum efficiency can be improved, by which the photocatalytic acitivity of TiO2film can be improved. These modification measures are very important for application of MAO in the photocatalysis field.Firstly, the ZrO2/TiO2film and V2O5/TiO2film was prepared in the electrolyte containing Zr(OH)4colloidal particles and NaV03electrolyte through MAO, respectively. Secondly, the MAO-TiO2film transformed to MAO-H-V2O5/TiO2film by hydrothermal and calcination treatment. Thirdly, the TiO2nanotube film was prepared through the method which combined MAO and hydrothermal technique. Furthermore, the morphology, phase composition, crystal structure and photophysical properties of the films were investigated by ESEM、FSEM、TEM、XRD、XPS、UV-Vis spectrophotometry and Fluorescence spectrophotometry. The photocatalytic activity of films were investigated through the degradation of Rhodamine B and Methylene blue (MB). The results are as follows.The phase composition of ZrO2/HTiO2film were anatase, rutile and ZrO2. Compared with TiO2film, the surface of ZrO2/TiO2film was rougher and had more pores. Furthermore, there were lots of white particles at the surface of ZrO2/TiO2film. The optical absorption edges of the ZrO2/TiO2film and the T1O2film were about421and412nm, respectively. Compared with TiO2film, the optical absorption edge of ZrO2/TiO2film shifted towards longer wavelength, but the optical absorption ability in the range of visible light decreased. Furthermore,35%and16%of Rhodamine B were degraded with the film and the TiO2film under the UV irradiation of600min, respectively.films had the sheet-like morphologies; The holes was produced at the surface of film when the concentration of NaVO3was8.54g/L; the sheet-like morphology was destroyed when the concentration of NaVO3was12.2g/L. The phase composition of V2O5/TiO2film was anatase when the concentration of NaVO3was lower than6.10g/L; The V2O5phase appeared in the films when the concentration of NaVO3was higher than6.10g/L. Furthermore, not only V2O5was coupled in the films, but also V4+was doped into the lattice of anatase.Compared with the TiO2film, the absorption edges of V2O5/TiO2films shifted towards longer wavelength and the band gap energy of V2O5/TiO2films decreased greatly. Furthermore, the photocatalytic acivity of V2O5/TiO2films under visible light irradiation were high. With the increase of NaVO3concentration, the absorption edges of V2O5/TiO2films increased and then decreased, band gap energy decreased and then increased, photocatalytic activity increased and then decreased. When the NaVO3concentration was8.54g/L, the V2O5/TiO2film had the longest absorption edge (603nm), the narrowest band gap energy (1.89eV) and best photocatalytic activity,93%of Rhodamine B was degraded under the visible light irradiation of840min.V2O5at the surface of MAO-H-V2O5/TiO2film was granular and clusters. Compared with V2O5/TiO2film, MAO-H-V2O5/TiO2film has longer absorption edge (612nm) and narrower band gap energy (1.35eV).91%of MB was degraded with MAO-H-V2O5/TiO2film under the UV irradiation of120min, and92%of MB was degraded with MAO-H-V2O5/TiO2film under the visible light irradiation of120min.When TiO2nanotube films were prepared through hydrothermal technique, the layered nanosheets at the surface of film became bigger gradually and the curving and wrapping of nanosheets to nanotubes happened finally with the increase of NaOH concentration. Furthermore, higher NaOH concentration would result in thinner and denser nanotubes. The layered nanosheets at the surface of film tranformed into nanotubes with the increase of reaction temperature. However, further increase of reaction temperature would result that many microspheres appeared at the surface of film.After hydrothermal treatment, sodium titanate nanotubes transformed into titanate nanotubes through acid treatment, but the morphology of nanotube film was not changed. The surface morphology of films were not changed under the calcination temperature of400℃and500℃.However, the nanotubes began to collapse at600℃and completely collapsed to form short nanorods when the calcination temperature increased to700℃. Calcination resulted in crystallization of the nanotubes from amorphous state to single-crystalline anatase phase. Furthermore, the increase of calcination temperature was beneficial to the improvement of crystallization degree and resulted in the increase of gram size.With the increase of calcination temperature, the absorption edges of TiO2nanotube films increased and then decreased, light absorption ability increased and then decreased, band gap energy decreased and then increased. The TiO2nanotube film calcined at600℃exhibited longer absorption edge, narrower band gap energy, stronger UV light absorption ability and the weaker band-band PL intensity compared with the other TiO2nanotube films. The absorption edge and the band gap energy of TiO2nanotube film calcined at600℃were375nm and3.18eV, respectively. Furthermore, the photocatalytic acivity of TiO2nanotube films increased and then decreased with the increase of calcination temperature. The TiO2nanotube film calcined at600℃showed the best photocatalytic activity,74%of MB was degraded under the UV irradition of300min.