Visible light absorption of surface modified TiO2 powders with bidentate benzene derivatives

• Adjustment of optical properties of commercial and mesoporous TiO2 powders.
• Charge transfer complex formation between surface Ti atoms and benzene derivatives.
• Extent of absorption in visible proportional to the specific surface area of TiO2.
• Tunable optical properties are not exclusive for “small” TiO2 particles.

TiO2 powders with different specific surface area were prepared using reproducible, sol–gel synthetic route and their ability to form hybrids with catechol and 5-amino salicylic acid was compared with the commercially available Degussa P25 TiO2 powder. Microstructural characterization involving transmission electron microscopy, X-ray diffraction analysis and nitrogen adsorption–desorption isotherms indicated that TiO2 samples cover reasonably wide size and/or specific surface area range (50–115 m2/g). The surface modification of TiO2 powders with catechol and 5-amino salicylic acid induced significant shift of absorption to the visible spectral region due to charge transfer complex formation. It should be emphasized that tunable optical properties of TiO2 in powder form have never been reported in the literature. The largest red shift of the absorption onset was observed for sample with the largest specific surface area upon surface modification with both ligands. The binding of the modifier molecules to the surface Ti atoms was studied using Fourier transform infrared spectroscopy.

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