While paper remains the most important and popular information medium, its production has caused fast growing threats to the environment, such as deforestation and pollution. Rewritable paper may provide an efficient solution to lower the demand for paper.

Yadong Yin and colleagues, University of California, Riverside, USA, have fabricated rewritable paper using simple commercial redox-active dyes (e.g., methylene blue) and TiO₂ nanocrystals as a photocatalyst. For instance, the blue color of methylene blue disappears when it is photoreduced to the colorless leuco form, and reappears through the reverse reaction upon heating in the air, which enables photo-printing and heat-erasing, respectively.

The paper prototype can tolerate at least 20 printing-erasing cycles, and the prints remain legible for more than 3 days under ambient conditions. In addition, other common redox dyes, such as neutral red and acid green, can be used to achieve RGB colors along with methylene blue.

• Photocatalytic colour switching of redox dyes for ink-free light-printable rewritable paper,
  Wenshou Wang, Ning Xie, Le He, Yadong Yin,
  Nat. Commun. 2014, 5, 5459.
  DOI: 10.1038/ncomms6459