Rewritable paper can be printed with text or images — and then erased and reused more than six months later.
Wei Huang at the Nanjing University of Posts and Telecommunications in China and his colleagues coated paper with layers of polymers and highly reactive chemical groups, or ligands. The team also created a range of inks by dissolving salts of iron, copper or other metals in water. Each metallic salt, when daubed on the paper, reacted with the ligand to create a different colour.
The group produced luminescent prints by changing the ligand. And ligands that included zinc ions allowed plain water to be used as environmentally friendly ink.
To wipe the paper clean, the researchers treated the paper with either solvents or heat, which break the connection between the ligand and the metal ions.