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.