Hollow amorphous TiO2 particles for transparent UV shielding film

Abstract

Crystalline titanium dioxide (C-TiO₂) particles are widely used as inorganic filters in coatings due to their high refractive indexes (n) and functions in photocatalysis. However, these particles may pose environmental and health risks due to their crystalline nature. Additionally, the long-term use of C-TiO₂ has the potential to damage organic contents due to their photocatalytic properties. These drawbacks make amorphous TiO₂ (A-TiO₂) appealing for use in non-catalysis applications, e.g., coatings. This study aims to develop an alternative UV filter derived from A-TiO₂ with a hollow structure (HA-TiO₂) that can be used in coatings. The hollow interior of the designed HA-TiO₂ structure compensates for its lower n through multiple light scattering, enhancing the UV shielding performance. Furthermore, the amorphous structure also promotes the transparency of the composite film. To obtain HA-TiO₂, TiO₂-coated silica (SiO₂@TiO₂) particles were synthesized using the modified sol-gel method. Selective etching was employed to remove the dense (D) SiO₂ core (hard template). The resulting HA-TiO₂ particles possessed higher UV absorption properties than D-SiO₂, SiO₂@TiO₂, dense amorphous (DA) TiO₂ particles, and commercial C-TiO₂ (TiONA® 595, rutile). Poly(vinyl alcohol) films containing HA-TiO₂ particles displayed the highest UV shielding performance, effectively blocking the photodegradation of methylene blue while maintaining film transparency. The integration of high UV shielding performance of the hollow structure and transparency of the amorphous matter provided synergistic effects. Overall, HA-TiO₂ shows promise as a safer alternative to current inorganic UV filters in a variety of applications, including coatings, textiles, and packaging.