Not only do the ligand-metal images last much longer than previous attempts at rewritable paper — some of which faded in less than 24 hours — but they are fully erasable. That’s because the ligand-metal bonds that produce the colors can be broken by exposure to a compound called tetrabutylammonium fluoride — TBAF for short — leaving the page as white as new.
Future printers could be armed with a cartridge of TBAF to erase a page before reprinting.
Interestingly, the researchers calculated that the cost of printing on rewritable paper is one-fifth the cost of traditional inkjet printing, assuming that a single sheet is used eight times.
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But even though rewritable paper technology would ultimately save a lot of paper, and potentially money, what about toxicity and sustainability issues associated with all of the chemicals used to make the paper and ink? The researchers tested the ligands and metal salts against an array of lab-grown human cells and found the chemicals to be low in toxicity, but that doesn’t mean that they’re not exploring greener options.
In the second part of the Nature Communications paper, the scientists discussed a second experimental technique for rewritable paper that uses pure water as the “ink.” For that to work, the researchers made a new type of multilayered paper with a special zinc-ligand complex that naturally reflected orange light. When exposed to water, the paper emitted a blue hue under UV light.
The initial water-jet printed images were fainter than the first experiment and could only be printed in one color, but the researchers hope that this initial proof-of-concept technology will lead to even greener and cleaner methods of extending the life of paper.
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