Application of Bimetallic Heterojunction Nanoparticle-Based Multishelled Porous Hollow Microspheres as a Two-in-One Inorganic UV Filter

Zinc oxide (ZnO) and titanium dioxide (TiO2), two inorganic UV filters, have taken the center stage in the talks of photoprotection. These days, sunscreens incorporate ZnO and TiO2 nanoparticles that are generally less than 100 nm in size. Concerned about the adverse effects of nanoparticles (NPs) on human health and the environment, we have synthesized TiO2@ZnO porous hollow multishelled microspheres (PHMMs) through a sequential template procedure (STP) and employed them as a two-in-one inorganic UV filter. For better understanding, we also compared their performances with TiO2 and ZnO NPs. Morphological characterization showed that TiO2 NPs are well equipped with ZnO NPs and formed a type II heterojunction structure. After 5 h of UV irradiation, we assessed the toxicity and photostability of these compounds. The TiO2@ZnO PHMMs show significant photostability with no significant cytotoxicity, whereas the ZnO and TiO2 NPs show significantly less photostability with cytotoxicity. The band gap widening in TiO2@ZnO PHMMs resulted in excellent UV absorption, and the recombination center of the photogenerated e–/h+ pair leads to reduced production of H2O2 and OH (ROS). Besides, the microspheres’ highly porous nature decreases visible light reflection, which results in less skin whitening. The formulated sunscreen with TiO2@ZnO PHMMs revealed higher SPF values with low photodegradation.