Localised Al(OH)₃ quantum dot passivation for safe-by-design rutile TiO₂ nanomaterials for UV protection

Titanium dioxide (TiO₂) is a cornerstone UV-filtering material, yet its intrinsic photocatalytic activity continues to raise concerns regarding safety and photostability in cosmetic applications. Here, we introduce a quantum-dot (QD) surface passivation approach that transforms photoactive rutile TiO₂ into a safe-by-design (SbD) nanomaterial without compromising its UV-protection efficiency. Ultrathin Al(OH)₃ QDs (<5 nm) are selectively nucleated on TiO₂ surfaces via a scalable aqueous synthesis, forming discontinuous passivation domains that suppress surface photoactivity through localised charge trapping and recombination control. Comprehensive spectroscopy and microscopy analyses reveal preserved crystal integrity and a >90% reduction in photocatalytic activity. The resulting nanocomposites demonstrate preserved biocompatibility, reduced phototoxicity, and superior transparency when integrated into prototype sunscreen formulations. This study establishes a generalizable framework for nanoscale photocatalytic suppression via selective quantum-dot passivation, advancing ceramic-based nanomaterials for safe, sustainable UV protection and beyond.