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Interaction of TiO2 nano-particles with organic UV absorbers

Lookup NU author(s): Dr Terry Egerton, John Mattinson, Ian Tooley

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Abstract

The yellowing caused by the addition of butyl methoxy dibenzoylmethane (BMDBM), or benzophenone, to dispersions of titania has been measured quantitatively for a range of uncoated and surface-treated nano-particulate TiO2 materials. FTIR spectra of BMDBM adsorbed on the uncoated titania were interpreted with the aid of corresponding spectra of adsorbed acetyl acetonate and supporting DFT calculations. The IR spectra suggest that chemisorption of BMDBM by bidentate chelation of the diketone anion to surface titaniums is responsible for the observed yellowing. Silica coatings, deposited on the TiO2 surface led to a large reduction in yellowing with both BMDBM and benzophenone-3. This was consistent with the coating uniformity and coherence inferred from reduction in the rates of propan-2-ol photo-oxidation. It is proposed that silica coating reduces interactions of butyl methoxy dibenzoylmethane (BMDBM) and benzophenone-3 with the highly polarizing Ti surface cations. A beneficial practical consequence is that aesthetically undesirable discolouration of cosmetic formulations containing combinations of these active ingredients is reduced. Propan-2-ol oxidation suggested that, on the same TiO2, alumina coatings were less uniform. Patchier coverage led to more yellowing of the titania because it allowed greater access of the organic to the underlying TiO2. In addition, at low levels of alumina the coating induced more yellowing than on the uncoated metal oxide surface. This was attributed to coordination to coordinatively unsaturated aluminiums. The presence of an organic coating, such as surface bound stearate, further reduced yellowing interactions with organic UV absorbers probably because the stearate competes effectively for (i.e. blocks) surface sites. © 2007 Elsevier B.V. All rights reserved.

Publication metadata

Author(s): Egerton TA, Everall NJ, Mattinson JA, Kessell LM, Tooley IR

Publication type: Article

Publication status: Published

Journal: Journal of Photochemistry and Photobiology A: Chemistry

Year: 2008

Volume: 193

Issue: 1

Pages: 10-17

ISSN (print): 1010-6030

ISSN (electronic): 1873-2666

Publisher: Elsevier SA

URL: http://dx.doi.org/10.1016/j.jphotochem.2007.06.001

DOI: 10.1016/j.jphotochem.2007.06.001

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