Photocatalytic activity and characterization of the sol-gel derived Pb-doped TiO2 thin films

Photocatalytically active Pb-doped TiO2 thin films were prepared on a soda-lime glass substrate by sol-gel dip-coating technique using TiO2 sols containing lead(II) nitrate. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-VIS spectroscopy and X-ray diffraction (XRD). A shift of the UV-VIS absorption towards longer wavelengths was observed, which indicated a decrease in the band-gap of TiO2 upon Pb doping. XRD results showed both pure and Pb-doped TiO2 thin films were polycrystalline, anatase type, and oriented predominantly to the (101) plane. A slight shift in the d-spacing for the Pb-doped film indicated the incorporation of Pb into the TiO2 lattice to form PbxTi1-xO2 solid solution. AFM results showed Pb-doped TiO2 thin films were composed of larger TiO2 particles and had rougher surface, compared with un-doped TiO2 thin films. XPS results showed that except for the enrichment of Pb near the surface, Pb exists in the forms of PbxTi1-xO2 and PbO. Dimethyl-2,2-dichlorovinyl phosphate (DDVP) was efficiently degraded in the presence of the Pb-doped TiO2 thin films by exposing the insecticide solution to sunlight. The mechanism of photocatalytic activity enhancement of the Pb-doped TiO2 thin films was discussed.