Environmental aging alters Al(OH)3 coating of TiO2 nanoparticles enhancing their photocatalytic and phototoxic activities

Abstract

As a component of sunscreen formulations, TiO₂ engineered nanomaterials (ENM) are coated to prevent reactive oxygen species from causing damage to skin. We investigated the stability of an Al(OH)₃ coating by exposing 25 nm Al(OH)₃·TiO₂ ENM to simulated swimming pool water (SPW) for 45 minutes, 1, 3, 10, or 14 days. Electron microscopy and spectroscopy indicated that exposure to SPW caused a redistribution of the Al(OH)₃ coating allowing photocatalytic formation of hydroxyl radicals. Aged ENM showed significantly greater phototoxicity under UVA irradiation than un-aged ENM in a human-derived retinal pigment epithelium cell line (ARPE-19). Photocatalytic activity and phototoxicity of aged Al(OH)₃·TiO₂ was significantly less than that of the positive control—uncoated P25 TiO₂. In summary, the aging of Al(OH)₃·TiO₂ ENM in SPW redistributed the coating and reduced its protective properties, thereby increasing reactivity and potential phototoxicity.