Structural evidence of sunscreen enhanced stability in UV filter-Zeolite hybrids

Organic UV filters are used in many applications (personal-care products, components in packaging, dyes, etc). However, many issues remain related to their safety; their release into the environment is toxic for many organisms and their photodegradation products are possibly dangerous. Encapsulation of these molecules in a zeolitic matrix can avoid their dispersion and promote the enhancement of their properties. In this study, we report the structural characterization of the new LTL/OMC ZEOfilter, produced by encapsulating the organic UV filter octinoxate (OMC, C18H26O3) into synthetic zeolite L. In fact, for the further exploitation and the realization of tailor-made materials, it is fundamental to understand the interactions between the filter and the matrix. X ray powder diffraction, Rietveld structural analysis and Monte Carlo simulations result in a detailed description of the molecules' setting and configuration. To fit the pores of the zeolite, the conformation of OMC molecules assumes a bent tail, allowing suitable intermolecular distances and host-guest interactions. These results were also corroborated by FT-IR experiments. The host-guest interaction is the key point for the stability and efficacy of LTL/OMC ZEOfilter and may explain why, among different ZEOfilters, the cationic zeolites, and especially zeolite L, display the most promising features.