Visible light photoactive titanium dioxide aqueous colloids and coatings

• Simple method of synthesis of colloids and coatings based on TiO2 is presented.
• Stable colloids are formed in aqueous medium at neutral pH.
• New nanomaterials are active upon visible light irradiation (up to 550–600 nm).
• Photosensitization does not comprise any heavy metals.
• New photoactive nanomaterials may be used for short-term applications in medicine.

A synthesis of highly dispersed nanocrystalline materials based on titanium dioxide in aqueous media at neutral pH has been developed. The surface modification of TiO2 with tiron, ascorbic acid and rutin afforded colored, transparent, colloidal solutions. Stability of yellow-orange colloids at pH = 7 has been achieved. Photoactivity of materials has been assessed by photocurrent measurements. For all modified materials visible light induced photocurrents have been recorded. The photocurrents were significantly amplified in the presence of dissolved oxygen due to O2 reduction to superoxide. The studied materials have been used to prepare thin films on glass substrates applying spin coating technique. Fabrication of visible light responsive thin films, well bound to the substrate, involves synthesis of films of unmodified TiO2, followed by their sintering and impregnation with the solutions of modifiers. SEM images showed the formation of compact layers of titanium dioxide with particles of diameter within 15–30 nm. The photocatalytic activity of synthesized films has been demonstrated in the reaction of terephthalic acid oxidation to 2-hydroxyterephthalic acid, proving photogeneration of hydroxyl radicals upon visible light irradiation (λ > 400 nm).

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