Confined‐Synthesis of Ceria in Tubular Nanoclays for UV Protection and Anti‐Biofilm Application

Abstract UV radiation is the main cause of skin aging and cancers. Commercial sunscreens suffer from low efficacy and poor safety, while ceria nanocrystals are promising inorganic UV filters. Herein, the lumen of natural halloysite clay nanotubes (HNTs) is employed for the confined growth of ceria nanocrystals, which can effectively tailor the particle size, morphology, distribution, and oxygen vacancies of the ceria. The ceria in HNTs lumen exhibits increased UV protection and catalytic activity, while the outer surfaces of HNTs can be retained for additional modification. Ceria‐loaded HNTs (named CeO x @HNTs) can act as oil–water interfacial stabilizers to develop skin‐friendly Pickering emulsion sunscreens. Attributed to the Pickering emulsion interfacial catalytic effect of CeO x @HNTs, the UV absorption performance of the sunscreens is enhanced by 3.1 times after emulsification, achieving a sun protection factor of 58.5. In vitro and in vivo studies confirm the effectiveness of the prepared sunscreen in mitigating DNA damage, apoptosis, and malignant transformation. In addition, the sunscreen inhibits biofilm formation by disturbing membrane homeostasis through oxidative stress. This work develops a confined‐growth method of rare earth oxides within tubular nanoclays, which shows promising applications in many fields, such as aging resistance, photoluminescence, and chemical catalysis.