Aqueous aging of a silica coated TiO 2 UV filter used in sunscreens: investigations at the molecular scale with dynamic nuclear polarization NMR
2020
Slomberg, Danielle | Catalano, Riccardo | Ziarelli, Fabio | Viel, Stéphane | Bartolomei, Vincent | Labille, Jérôme | Masion, Armand | International Consortium for the Environmental Implications of Nanotechnology iCEINT ; Europôle de l'Arbois, 13545 Aix en Provence | Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement (CEREGE) ; Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE) | Spectropôle - Aix Marseille Université (AMU SPEC) ; Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS) | Institut de Chimie Radicalaire (ICR) ; Aix Marseille Université (AMU)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS) | ANR-11-LABX-0064,SERENADE,Vers une conception de nanomatériaux innovants, durables et sûrs(2011)
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Show more [+] Less [-]English. Short-term, aqueous aging of a commercial nanocomposite TiO2 UV filter with a protective SiO2 shell was examined in abiotic simulated fresh- and seawater. Under these conditions, the SiO2 layer was quantitatively removed (similar to 88-98%) within 96 hours, as determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). While these bulk ICP-AES analyses suggested almost identical SiO2 shell degradation after aging in fresh- and seawater, surface sensitive Si-29 dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (SSNMR), with signal enhancements of 5-10x compared to standard SSNMR, was able to distinguish differences in the aged nanocomposites at the molecular level. DNP-SSNMR revealed that the attachment of the silica layer to the underlying TiO2 core rested on substantial Si-O-Ti bond formation, bonds which were preserved after freshwater aging, yet barely present after aging in seawater. The removal of the protective SiO2 layer is due to ionic strength accelerated dissolution, which could present significant consequences to aqueous environments when the photoactive TiO2 core becomes exposed. This work demonstrates the importance of characterizing aged nanocomposites not only on the bulk scale, but also on the molecular level by employing surface sensitive techniques, such as DNP-NMR. Molecular level details on surface transformation and elemental speciation will be crucial for improving the environmental safety of nanocomposites.
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