The Encapsulation of Natural Organic Dyes on TiO2 for Photochromism Control

Abstract

Titanium dioxide (TiO2) 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 TiO2 changes gradually to blue or yellow with UV irradiation, which affects its color realization. We encapsulated TiO2 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 TiO2 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 TiO2 and dye encapsulated TiO2. The unique structure utilized natural dyes to preserve photochromism based on the physical barrier and automatically controlled the electronic transition of core TiO2. 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 TiO2. Dye encapsulated TiO2 was manipulated into lipstick to verify its color realization and retention.