Researchers have succeeded in developing a coating material that can be written on with UV light and then removed with oxygen. Adjustments on rewritable paper can help reduce paper waste in a variety of settings.
According to the diary applied chemistrythe substance consists of three non-toxic components and is synthesized in a single step.
To create a light-sensitive and rewritable system, Yadong Yin and colleagues at the University of California, Riverside (USA) focused on Titania (TiO2) nanocrystals.
Nanocrystalline TiO when treated with ultraviolet (UV) radiation2, semiconductor, black due to charge separation and titanium atom reduction. However, the color shift is not permanent because the oxygen in the air reoxidizes the titanium and restores clarity.
The study team focused on making the color shift take longer. They adorned the crystals with a common non-toxic chemical called diethylene glycol and used the nitrogen they obtained from urea as a dopant.
According to the scientists, the material that was introduced into the synthesis as a solvent was also important in color shift because it captured additional electron holes, slowed down reoxidation and return to a transparent state.
The nanocrystals formed a uniform coating that could be written on with UV light when applied to glass or paper. All that was needed was irradiation for 30 seconds with a light source with a wavelength of less than 400 nm to create a record.
The researchers stressed that a strong light source was not needed; lamps in the LED power range were sufficient to ensure a high level of contrast on the material.
The team experimented with two different light writing techniques. They started by illuminating a paper or glass substrate with a photomask to create patterns or printed text. They also used a laser pen to create freehand writing.
Both techniques created a high contrast design that remained stable for several hours and could either be wiped off or slowly faded due to oxidation. The researchers say that coating the film surface with a protective layer of non-toxic polymer and reducing its exposure to oxygen can extend the life of the print.
The main advantage of Yin technology and its team is its reuse. Research has found that up to 50 write and delete cycles can be performed without noticeable loss of contrast.
This means that the technology could be used in various sectors that need reusable / rewritable surfaces, such as daily tickets, information boards, data storage and sensor technologies.
The authors emphasize the simplicity of production, which uses common non-toxic starting components, as well as the excellent compatibility of the material with other materials.
Dr. Aleisa. R, et al. (2022) Fast high contrast photoreversible coloration of surface functionalized N-doped TiO2 Nanocrystals for rewritable light printing. applied chemistry doi: 10.1002 / anie.202203700.
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