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Polymer/TiO2 Hybrid Nanoparticles with Highly Effective UV-Screening but Eliminated Photocatalytic Activity

Jie Xiao,Wenqin Chen,Fangyingkai Wang,Jianzhong Du

TiO2 nanoparticle has been considered as a safe sunscreen agent to reduce the skin cancer risk when exposed to sunlight. However, recently it was found that TiO2 particles accelerate the photodamage of skin due to their photocatalytic degradation activity. To effectively eradicate this unwanted effect, we present a new strategy toward the preparation of organic/inorganic hybrid polymer/TiO2 nanoparticles with highly effective UV-screening property but eliminated photocatalytic activity. We prepared new polymer micelles with corona–shell–core structure based on self-assembly of poly(ethylene oxide)-block-poly(2-(dimethylamino)ethyl methacrylate)-block-poly(styrene) (PEO-b-PDMA-b-PS) triblock copolymer. Selective deposition of hydrophobic tetrabutyl titanate (TBT) in the PDMA shell in polar solvent leads to a thin PDMA/TiO2 hybrid layer (∼8 nm), which can not only effectively reflect UV rays but also eliminate its photocatalytic ability to protect skin. The sol–gel reactions of TBTs in the PS core domain lead to a PS/TiO2 hybrid core, which can also absorb/reflect UV lights by PS/TiO2. The biocompatible PEO coronas can prevent direct contact of TiO2 with skin. Moreover, sol–gel reactions in the PDMA and PS domains can stabilize the triblock copolymer micelles, which offer the promising potential for further formulations in aqueous solution. The ATRP kinetics confirmed that PEO-b-PDMA-b-PS triblock copolymer can be synthesized in one pot, which simplified the synthetic procedure of copolymers. TEM and DLS studies revealed the morphology and size of self-assembled polymer micelles and the subsequent polymer/TiO2 hybrid nanoparticles upon sol–gel reactions. UV experiments confirmed the highly efficient UV screening activity but eliminated photocatalytic property of polymer/TiO2 hybrid nanoparticles. For example, at extremely low TiO2 content in solution (10 ppm of polymer/TiO2 solid), ∼70% UV radiation can be blocked compared to pure organic polymer micelle, which is also much more efficient than commercially available TiO2 nanoparticles (P25). UV and DLS studies confirmed the ultrahigh stability of polymer/TiO2 hybrid nanoparticles upon strong UV radiation, which is suitable for long-term applications. Nitrogen adsorption/desorption experiment revealed that the ultralow surface area of TiO2 nanoparticles (1.6 m2 g–1) is consistent with their extremely poor photocatalytic performance.