Mitigating Photoinduced Reactive Oxygen Species From TiO ₂ and ZnO UV Filters: Materials Design and Evaluation

ABSTRACT

Titanium dioxide (TiO ₂ ) and zinc oxide (ZnO) are widely used ultraviolet (UV) attenuating materials, but photoexcitation of these semiconductors can generate reactive oxygen species (ROS) through interfacial redox reactions. Their oxidative activity is not an intrinsic constant, but depends on crystal structure, particle size and morphology, surface defects, coatings, aggregation, surrounding matrix, and irradiation conditions. This Review critically examines particle engineering, doping, surface passivation, antioxidant functionalization, composite architectures, and formulation strategies for controlling photoinduced ROS. Representative studies report reductions in ROS‐related or photocatalytic signals ranging from approximately 30%–40% with selected dopants and 60%–70% with inorganic surface coatings to approximately 80%–90% with immobilization or multilayer passivation, while optimized metal–phenolic network coatings have achieved >99% suppression of measured photoinduced ROS. Analytical approaches, including electron paramagnetic resonance, chemical probes, photocatalytic oxidation assays, chromatographic analysis, and biological oxidative‐stress endpoints, are critically compared according to the processes they actually measure. A three‐tier framework is proposed in which comparative screening is followed by mechanistic confirmation and application‐relevant validation. Because no universal ROS threshold currently defines UV‐filter safety, the framework emphasizes complementary endpoints, complete reporting of irradiation and material characteristics, and confirmation that ROS mitigation persists in the finished formulation without compromising photoprotection.