Highly photoactive anatase foams prepared from lyophilized aqueous colloids of peroxo-polytitanic acid

• Anatase foam was prepared from lyophilized aqueous colloids of peroxo-polytitanic acid.
• Foam consists of perfectly crystalline intergrown nanoparticles forming thin foils.
• Photoactivity exceeds significantly the Degussa P25 photocatalyst.

Peroxo-polytitanic acid foams annealed at temperature above 500 °C lose volatile components and excess of oxygen providing anatase in the form of thin leaves consisting of intergrown nanocrystalline anatase particles which transform at temperatures above 850 °C to rutile. The size and shape of the initial leaflets forming the foam is preserved up to ∼900 °C. We observed that the annealed material is highly photoactive, owing to highly anisotropic shape of anatase aggregates and their perfect crystallinity. Outstanding photocatalytic activity determined by measuring the kinetics of degradation of Methylene Blue (MB) and 4-chlorphenol (4-CP) as well as measuring the formation of hydroxyl radical spin adducts by EPR spectroscopy was observed. All three methods demonstrated significantly higher activity in comparison with the Degussa P25 photocatalyst. Both methods used for photoactivity tests provided similar results, the activity increased with increasing annealing temperature in order 500 °C < Degussa P25 < 600 °C < 850–950 °C. Results of measurement of formation of OH radicals by EPR also confirmed the unusually high activity of our materials. In comparison with the Degussa P25, the sample annealed at 950 °C showed significantly higher production of OH radicals.

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