Microwave photocatalysis III. Transition metal ion-doped TiO2 thin films on mercury electrodeless discharge lamps: preparation, characterization and their effect on the photocatalytic degradation of mono-chloroacetic acid and Rhodamine B

BACKGROUND: Mercury electrodeless discharge lamps (Hg-EDLs) were used to generate UV radiation when exposed to a microwave field. EDLs were coated with doped TiO2 in the form of thin films containing transition metal ions Mn+ (M = Fe, Co, Ni, V, Cr, Mn, Zr, Ag). Photocatalytic degradation of mono-chloroacetic acid (MCAA) to HCl, CO2, and H2O, and decomposition of Rhodamine B on the thin films were investigated in detail. RESULTS: Polycrystalline thin doped TiO2 films were prepared by clip-coating of EDL via a sol-gel method using titanium n-butoxide, acetylacetone, and a transition metal acetylacetonate. The films were characterized by Raman spectroscopy, UV/Vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), electron microprobe analysis and by atomic force microscopy (AFM). The photocatalytic activity of doped TiO2 films was monitored in the decomposition of Rhodamine B in water. Compared with the pure TiO2 film, the UV/Vis spectra of V, Zr and Ag-doped TiO2 showed significant absorption in the visible region, and hence the photocatalytic degradation of MCAA had increased. The best apparent degradation rate constant (0.0125 min(-1)), which was higher than that on the pure TiO2 film by a factor of 1.7, was obtained with the Ag(3%)/TiO2 photocatalyst. The effect of doping level of vanadium acetylacetonate on the photocatalytic efficiency of the V-doped TiO2 was determined. CONCLUSIONS: Transition metal ion-doped TiO2 thin films showed significant absorption in the visible region. The metal doped TiO2 photocatalyst (with an appropriate amount of V, Zr and Ag) on the Hg-EDLs increased the degradation efficiency of MCAA in a microwave field. (C) 2009 Society of Chemical Industry