Hollow amorphous TiO<inf>2</inf> 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.