The use of particulate titanium dioxide (TiO2) as an active sunscreen ingredient has raised concerns about potential risks from TiO2-mediated free radical formation. To date, remediation attempts have concentrated on reducing the yield of free radical generation by TiO2 upon sunlight exposure. The problem with this approach is that given the band gap in TiO2, production of radical and the ensuing reactive oxygen species (ROS) is completely normal. Our strategy is based on a nontoxic, biocompatible shell that neutralizes the free radicals by scavenging them with natural antioxidants before they exit the particle. The new lignin@TiO2 composites preserve the scattering and absorption properties of TiO2 because the particles retain their nanoscale dimensions as preferred by the cosmetic industry. Although the target properties for photocatalysis and sun-protection applications are opposite, we argue that exactly the same knowledge is required to optimize either one.

Ultraviolet light can cause photodamage to the skin, such as sunburn and melanomas. TiO2 is introduced in sunscreen formulations to reflect and scatter UV radiation. However, it can also photocatalyze the production of reactive species like O 2 .and OH .. Here, we aimed to remove the photocatalytic activity of TiO2 (anatase and rutile), while preserving the UV filter property. Anatase and rutile were modified through two preparative protocols. The first used HCl lignin precipitation of ethylene glycol lignin solution in the presence of the cross-linker glutaraldehyde and anatase or rutile nanoparticles. The second protocol used HNO3 lignin precipitation of lignin aqueous solution in the presence of anatase or rutile nanoparticles. Both methodologies were performed at room temperature and ambient pressure in green media, with vigorous mixing followed by 20-kHz sonication. The composite materials obtained were fully characterized by SEM, XRD analysis and FT-IR spectroscopy, and their photostability, and photo and shielding activities were evaluated through reference reactions: oxidation of 2-propanol, an ene-reaction conducted on an α,β-unsaturated carboxylic derivative and photochemical transformation of o-nitrobenzaldehyde to o-nitrosobenzoic acid. Therefore, in the near future, industrial use of these new clusters can help to minimize TiO2 phototoxicity in sunscreen formulations, while preserving the sunscreen photoprotection activity.