Despite the common appearing of tablet computers and e-readers, we simply cannot break our addiction to paper. An estimated four billion trees are cut down every year to make paper or cardboard, an energy-consuming process with a vast environmental footprint. Now chemist Yadong Yin of the University of California, Riverside, and his colleagues have developed "rewritable" paper that could help controlthat impact.
Printed rewritable paper is made using Prussian blue nanoparticles (纳米粒子). The researchers coated conventional paper with nanoparticles of two chemicals: Prussian blue that gives blueprints their characteristic color, and titanium dioxide (二氧化钛), a substance used in sunscreens.
UV light makes the titanium dioxide nanoparticles donate electrons (电子) to their Prussian blue neighbors, shifting its color from midnight blue to milky white.
By shining that UV light through a transparent (透明的) screen marked with black text, the researchers "printed" blue text on a white background. The text lasts about five days and then naturally fades away: "Every morning I could just push a button, and a printer would give me a fresh newspaper to read over breakfast," Yin says.
The paper can also be reset by heating and reused more than 80 times, a significant improvement over previous types of rewritable paper. "The key advantages are high reusability and stability, easy handling and low cost," says Sean X. Zhang, a materials scientist at Jilin University in China, who was not involved in the study but has also worked on developing rewritable paper. By comparison, technologies such as electronic ink—used for Amazon's Kindle Paperwhite—involve moving charged black-and-white particles around, which requires electronics.
Since reporting their invention in Nano Letters early this year, the scientists have used a digital projector to replace their transparent screen. They are now working on increasing the number of times the paper can be reused. Zhang says a key difficulty will be persuading companies to develop the unconventional UV control needed for widespread use. Even though commercialization could be a few years away, Yin says, "We've had a lot of discussions with industry investors."
