Metal oxides with a wide band gap absorb and reflect UV energy from the sun. Such metal oxides include the broadly-utilized TiO2 and zinc oxide (ZnO). These metal oxides are often used as UV filters in the cosmetics industry, and as pigments and fillers in applications such as polymer processing, coatings and adhesives. Their photocatalytic capabilities also are used in photovoltaic, antibacterial, water treatment, air purification and self-cleaning applications.
Photocatalytic reactions derived from these metal oxides normally lead to the decomposition of the organic materials with which they come into contact. This photoactive reactivity results in the generation of singlet oxygen1 and other reactive oxygen species (ROS).2-4 Such consequences are not desired in personal care or industrial applications, so to alleviate these unwanted reactions, surface modifications are made to the metal oxides. However, currently available treatments do not completely eliminate the photoreactivity of these metal oxides; some of these surface treatments are provided in the product literature of major metal oxide suppliers for the personal care industry.5, 6
TiO2 and ZnO therefore need improved protection to eliminate their adverse effects in personal care and industrial applications, in turn making them safer and more effective UV filters. In relation, propenoic acid derivatives are known to form interacting complexes with Lewis acid species such as TiO2.7-10 In this study, the authors evaluate a member of the propenoic acid ester family—a 2-ethylhexyl ester of 2-cyano-3-(4-methoxyphenyl)-3-phenyl-2-propenoic acid (EHCMPPPa)—for its potential to safeguard TiO2 in cosmetic applications.