Photocatalytic Reversible Color Switching Based on Titania Nanoparticles

The photoreversible color switching system holds great promise for applications in display and signage technologies, sensing devices, and security features, because light, in comparison to other stimuli such as heat and electricity, has the advantages of noninvasiveness and easy control of parameters including wavelength, intensity, coverage area, and illumination duration. Here, the recent advances in the design and synthesis of titania nanoparticles for catalytic photoreversible color switching of redox dyes and pigments, along with their applications in ink-free, light-printable rewritable paper and colorimetric oxygen indicators, are reviewed. Specifically, the importance of surface engineering and defect manipulation of titania nanoparticles for the color-switching purpose, by introducing a number of methods including surface binding of sacrificial capping ligands and creating oxygen vacancies through doping of metal ions, is highlighted. Finally, a summary and perspectives on current challenges and future research directions in this field are given.