Development of surface coating technology of TiO2 powder and improvement of photocatalytic activity by surface modification

We have synthesized the titanium dioxide (TiO2) powders with the similar structure as a commercially available Degussa P-25 TiO2 powder for TiO2-based photocatalysts. To improve the photocatalytic activity, electronic modification on the TiO2-based photocatalysts by chemical solution deposition (CSD) coating was also carried out with metal oxides such as Fe2O3 and Al2O3. The structural and compositional changes as well as optical characteristics are mainly investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy, and ellipsometry measurements. In addition, electron spin resonance (ESR) studies have also been carried out to verify the existence of paramagnetic species such as OH and H2O radicals on UV-irradiated TiO2-based photocatalysts. ESR data showed that the hydroxy radicals could decompose organic pollutants into harmless products because they have high oxidizing power. From the reduction test of nitrobenzene, it is found that the photocatalytic effect of TiO2-based photocatalysts coated with Fe2O3 is twice better than that of commercially available noncoated TiO2 photocatalysts. In the case of photocatalytic oxidation reaction of phenol under UV irradiation, moreover, the experimental results showed a consistency with ESR data indicating that TiO2 coated with metal oxides would be one of the most effective photocatalysts. (C) 2004 Elsevier B.V. All rights reserved.