The Encapsulation of Natural Organic Dyes on TiO 2 for Photochromism Control.

Titanium dioxide (TiO 2 ) plays a pivotal role in photocatalytic reactions and holds great promise for the cosmetic and paint industries due to its white color and high refractive index. However, the original color of TiO 2 changes gradually to blue or yellow with UV irradiation, which affects its color realization. We encapsulated TiO 2 with several natural organic dye compounds, including purpurin, curcumin, and safflower, to control its photochromism and realize a range of different colors. The chemical reaction between TiO 2 and dyes based on their functional group was investigated, and the light absorption was tested via FTIR and UV-Vis spectroscopy. The changes in morphology and size distribution additionally supported their successful encapsulation. The discoloration after UV irradiation was evaluated by measuring the color difference (ΔE) of control TiO 2 and dye encapsulated TiO 2 . The unique structure utilized natural dyes to preserve photochromism based on the physical barrier and automatically controlled the electronic transition of core TiO 2 . In particular, the color difference values of purpurin and curcumin were 4.05 and 3.76, which is lower than the 5.36 of the control TiO 2 . Dye encapsulated TiO 2 was manipulated into lipstick to verify its color realization and retention.