Synthesis and Characterization of TiO₂@Zn₂SnO₄ Composite as a Novel UV Filter with Reduced Photocatalytic Activity and Low Toxicity for Sunscreen Applications

This study builds upon our recent investigation, which utilized various morphologies and particle sizes of Zn₂SnO₄ and TiO₂. Zn₂SnO₄ can block UVB and part of UVA and shows much less photocatalytic activity than TiO₂. Herein, the current study aims to reduce the photocatalytic activity of TiO₂, a compound often utilized as an ultraviolet (UV) filter in sunscreen, by incorporating Zn₂SnO₄ as a composite. Since Zn₂SnO₄ produces much fewer free radicals, in terms of the reactive oxygen species (ROS), due to its low photocatalytic activity. To overcome or minimize the high photocatalytic activity of TiO₂, composite materials TiO₂@Zn₂SnO₄ were prepared by combining synthesized TiO₂ and Zn₂SnO₄ nanoparticles in different weight ratios (75/25, 50/50, and 25/75 wt%) for use as a novel UV filter in sunscreen. We investigated these composites to evaluate their ability to filter UV rays in sunscreen formulation. The sun protection factor (SPF) test indicated that Zn₂SnO₄ can protect the skin similarly to TiO₂, blocking the UVB and partially blocking UVA. TiO₂@Zn₂SnO₄ as a composite made TiO₂ much less effective as a photocatalyst while still maintaining efficient UV blocking. The TiO₂@Zn₂SnO₄ composite with Zn2SnO4-rich composition has the best balance of performance. In vitro genotoxicity experiments also showed that both synthesized TiO₂ and Zn₂SnO₄ were safe as physical UV filters, as they maintained cell viability. These findings indicate that the novel TiO₂@Zn₂SnO₄ composite system could serve as a safe and efficient alternative UV filter in next-generation sunscreen formulations.