Using light to produce medication and plastics more efficiently
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RADICALS GENERATED BY LIGHT CAN ONLY UNFOLD THEIR REACTIVITY AS SOON AS THEY BREAK OUT OF A KIND OF "CAGE" THAT THE SOLVENT FORMS AROUND THEM. RESEARCHERS IN BASEL SHOW HOW TO MAKE THIS "CAGE ESCAPE" MORE SUCCESSFUL AND HOW IT LEADS TO MORE EFFICIENT PHOTOCHEMISTRY.
view moreCREDIT: UNIVERSITY OF BASEL, JO RICHERS
Anyone who wants to produce medication, plastics or fertilizer using conventional methods needs heat for chemical reactions – but not so with photochemistry, where light provides the energy. The process to achieve the desired product also often takes fewer intermediate steps. Researchers from the University of Basel are now going one step further and are demonstrating how the energy efficiency of photochemical reactions can be increased tenfold. More sustainable and cost-effective applications are now tantalizingly close.
Industrial chemical reactions usually occur in several stages across various interim products. Photochemistry enables shortcuts, meaning fewer intermediate steps are required. Photochemistry also allows you to work with less hazardous substances than in conventional chemistry, as light produces a reaction in substances which do not react well under heat. However, to this point there have not been many industrial applications for photochemistry, partly because supplying energy with light is often inefficient or creates unwanted by-products.
The research group led by Professor Oliver Wenger at the University of Basel now describes a fundamental principle which has an unexpectedly strong impact on the energy efficiency of photochemistry and can increase the speed of photochemical reactions. Their results are published in Nature Chemistry.
In the case of this kind of reaction, the starting molecules are in a liquid solution. If they receive energy in the form of light, they can exchange electrons with one another and form radicals. These extremely reactive molecules always occur in pairs and remain surrounded by solvent, which encloses the pairs of radicals like a kind of cage. In order for the radicals to be able to continue to react to the desired target products, they need to “break out” of this cage and find a reaction partner outside of it. The team surrounding Wenger and his postdoc Dr. Cui Wang identified this process of breaking out as a decisive step which limits the energy efficiency and the speed of photochemical reactions.
Radicals break free
As long as the radicals remain in pairs in the solvent cage, they can spontaneously react with one another back into the starting materials. This reverse reaction wastes energy because it only uses the light already absorbed to get back to the starting point. The Basel team was able to slow down this reverse reaction and therefore give the radicals more time to leave the cage. The longer the unwanted reverse reaction became, the more radicals were able to break out and the more energy efficient and faster the desired target products developed.
Wang, who now holds the position of assistant professor at Osnabrück University, used two particular dyes in her study, both of which absorb light and store its energy for a short period before using it to form pairs of radicals. However, one of the two dyes examined was able to store significantly more energy than the other and transfer it to the radicals. Due to the additional energy, the radicals were able to leave the solvent cage up to ten times more efficiently. Consequently, the target products are produced with up to ten times higher energy efficiency. “This direct link between the radicals breaking out of the solvent cage and the efficient formation of the target products is astonishingly clear,” stated Wang.
Dyes are key
The key finding is that certain dyes can release more radicals than others per the amount of light absorbed. “The choice of dye can be used to boost the energy efficiency of photochemical reactions,” emphasizes Wenger. In turn, he states that energy efficiency is also a decisive criterion for the industrial use of photochemistry.
JOURNAL
Nature Chemistry
ARTICLE TITLE
Cage escape governs photoredox reaction rates and quantum yields.
ARTICLE PUBLICATION DATE
18-Mar-2024
Holographic message encoded in simple plastic
Important data, such as a Bitcoin wallet address, can be stored and concealed quite easily in ordinary plastic using 3D printers and terahertz radiation, scientists at TU Wien show.
VIENNA UNIVERSITY OF TECHNOLOGY
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EVAN CONSTABLE
view moreCREDIT: TU WIEN, EVAN CONSTABLE
There are many ways to store data - digitally, on a hard disk, or using analogue storage technology, for example as a hologram. In most cases, it is technically quite complicated to create a hologram: High-precision laser technology is normally used for this.
However, if the aim is simply to store data in a physical object, then holography can be done quite easily, as has now been demonstrated at TU Wien: A 3D printer can be used to produce a panel from normal plastic in which a QR code can be stored, for example. The message is read using terahertz rays – electromagnetic radiation that is invisible to the human eye.
The hologram as a data storage device
A hologram is completely different from an ordinary image. In an ordinary image, each pixel has a clearly defined position. If you tear off a piece of the picture, a part of the content is lost.
In a hologram, however, the image is formed by contributions from all areas of the hologram simultaneously. If you take away a piece of the hologram, the rest can still create the complete image (albeit perhaps a blurrier version). With the hologram, the information is not stored pixel by pixel, but rather, all of the information is spread out over the whole hologram.
"We have applied this principle to terahertz beams," says Evan Constable from the Institute of Solid State Physics at TU Wien. "These are electromagnetic rays in the range of around one hundred to several thousand gigahertz, comparable to the radiation of a cell phone or a microwave oven - but with a significantly higher frequency."
This terahertz radiation is sent to a thin plastic plate. This plate is almost transparent to the terahertz rays, but it has a higher refractive index than the surrounding air, so at each point of the plate, it changes the incident wave a little. "A wave then emanates from each point of the plate, and all these waves interfere with each other," says Evan Constable. "If you have adjusted the thickness of the plate in just the right way, point by point, then the superposition of all these waves produces exactly the desired image."
It is similar to throwing lots of little stones into a pond in a precisely calculated way so that the water waves from all these stones add up to a very specific overall wave pattern.
A piece of cheap plastic as a high-tech storage unit for valuable items
In this way, it was possible to encode a Bitcoin wallet address (consisting of 256 bits) in a piece of plastic. By shining terahertz rays of the correct wavelength through this plastic plate, a terahertz ray image is created that produces exactly the desired code. "In this way, you can securely store a value of tens of thousands of euros in an object that only costs a few cents," says Evan Constable.
In order for the plate to generate the correct code, one first has to calculate how thick the plate has to be at each point, so that it changes the terahertz wave in exactly the right way. Evan Constable and his collaborators made the code for obtaining this thickness profile available for free on Github. "Once you have this thickness profile, all you need is an ordinary 3D printer to print the plate and you have the desired information stored holographically," explains Constable. The aim of the research work was not only to make holography with terahertz waves possible, but also to demonstrate how well the technology for working with these waves has progressed and how precisely this still rather unusual range of electromagnetic radiation can already be used today.
JOURNAL
Scientific Reports
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Encoding terahertz holographic bits with a computer-generated 3D-printed phase plate
ARTICLE PUBLICATION DATE
18-Mar-2024
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