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  1. It might look like any old 18-carat nugget of gold, but it hides a secret. Produced in the lab, this shiny disc weighs just a fraction of what it should, and has other interesting properties to boot. Unlike a typical chunk of the bright metal, here the gold nanocrystals are held together with a framework of protein fibres and polymer latex, giving it a much lower density than regular gold. The research team who developed this material thinks weight can be reduced by up to 5-10 times compared to the standard mixture used for gold trinkets – three-quarters gold, one-quarter copper – which means watches and jewellery could soon get significantly lighter. Replacing the metal alloys usually mixed with gold to lighten the weight and reduce the density could have benefits beyond jewellery as well, in fields such as chemistry, electronics, and radiation shielding. "This gold has the material properties of a plastic," says material scientist Raffaele Mezzenga, from ETH Zurich in Switzerland. "As a general rule, our approach lets us create almost any kind of gold we choose, in line with the desired properties." To achieve these results, the scientists mixed gold nanocrystals, protein fibres, and a polymer latex with water and salt to create a gel, before replacing the water with alcohol. When put into a high pressure CO2 chamber, the alcohol reacts with carbon dioxide, producing a gossamer-like aerogel. With the application of heat, that aerogel can be moulded as needed. It can be shaped at just above 105 degrees Celsius (221 degrees Fahrenheit), which is much lower than the 1,064 degrees Celsius (1,947 degrees Fahrenheit) needed to melt pure 24-carat gold. As you can see from the video below, when dropped, the material acts and sounds like plastic, but the genuine 18-carat purity is preserved. "This new 18-carat gold can fill a niche which is currently unoccupied in the realm of industrially relevant gold blends and open the way to unexplored applications," write the researchers in their paper. What helps the gold chunk achieve its lightness are the many microscopic air pockets inside it. The overall density of the material is a mere 1.7 grams per cubic centimetre, compared to around 15 g/cm3 for 18-carat gold made with a metal alloy. People do tend to associate weight with quality when it comes to gold and jewellery in general, so it may not end up replacing the materials used to make bracelets, watches, necklaces and other items – but there are plenty of other options for putting this lightweight, low-density gold to good use. Mezzenga and his colleagues previously created super-light gold from milk protein – light enough to float on top of a cup of coffee – but its properties made it difficult to get it into places where gold is used. The new version should have a much wider range of potential applications. "The [previous] material was too unstable and couldn't be worked," says Mezzenga. "This time we set ourselves the clear goal of creating a lightweight gold, that can also actually be processed and used in most of the applications where gold is used today." The research has been published in Advanced Functional Materials. source
  2. Can science break its plastic addiction? Gloves, sample tubes, and vials—labs produce millions of tonnes of waste each year. Enlarge / There is no shortage of plastic in your average science lab. © Daniel Stier at Twenty Twenty and Miren Marañón at East Photographic for Mosaic Lucy Gilliam has an infectious passion for environmental action. Today, she works in Brussels on environmental transport policy. But in the early 2000s, she was a molecular microbiologist in Hertfordshire. Like many in her field, Gilliam got through a lot of disposable plastics. It had become a normal part of 21st-century science, as everyday as coffee and overtime. Gilliam was, in her words, a “super high user” of the sort of plastic, ultra-sterilized filter pipettes that could only be used once. Just as so many of us do in our domestic lives, she found she was working with what anti-pollution campaigners call a “produce, use, discard” model. The pipettes would pile up, and all that plastic waste just seemed wrong to her. Science’s environmental impact had begun to worry her. It wasn’t just a matter of plastics. She also wanted to know why there weren’t solar panels on the roof of the new lab building, for example, and why flying to conferences was seen more as a perk than a problem. “I used to bitch about it over coffee all the time,” Gilliam tells me. “How can it be that we’re researching climate science, and people are flying all over the place? We should be a beacon.” She tried to initiate recycling programmes, with some success. She invited the suppliers in to discuss the issue, and worked out ways the research teams could at least return the boxes pipettes came in for re-use, even if the pipettes themselves would still be used and discarded. It felt like a battle, though. Sensing that progress was likely to be slow, she started to ask herself where exactly she could make change happen, and moved to work in environmental policy. Scientific research is one of the more hidden users of disposable plastics, with the biomedical sciences a particularly high-volume offender. Plastic petri dishes, bottles of various shapes and sizes, several types of glove, a dizzying array of pipettes and pipette tips, a hoard of sample tubes and vials. They have all become an everyday part of scientific research. Most of us will never even see such equipment, but we all still rely on it. Without it, we wouldn’t have the knowledge, technologies, products and medicines we all use. It is vital to 21st-century lives, but it is also extremely polluting. In 2015, researchers at the University of Exeter weighed up their bioscience department’s annual plastic waste, and extrapolated that biomedical and agricultural labs worldwide could be responsible for 5.5 million tonnes of lab plastic waste a year. To put that in context, they pointed out it’s equal to 83 per cent of the plastic recycled worldwide in 2012. The problem with plastic is that it is so durable; it won’t decompose. We throw it in the rubbish, it stays there. It is thought that there may now be more Lego people on Earth than actual people, and these minifigs will outlive us all. When plastic products like these minifigs—or pipettes, bottles or drinking straws—do eventually break down, they stick around as small, almost invisible fragments called microplastics, which also come from cosmetics and clothing fibres. A 2017 study found microplastics in 81 per cent of tap water samples globally. In the past few years, in mountain ranges in the USA and France, researchers even found microplastics in rain. They have recently been found in the Arctic, too. Modern science has grown up with disposable plastics, but times are changing. This autumn, the first wave of young people to follow the Swedish climate activist Greta Thunberg and go on “school strike for the climate” started undergraduate degrees. Universities can expect these young people to bring fresh and sometimes challenging questions about how scientific research is conducted. At the same time, many of those from Generation Z (those born from the mid-1990s onwards) are now starting PhDs, and millennials (born from the early 1980s) are leading more and more labs. As more universities challenge themselves to eradicate disposable plastics, as well as to go zero-carbon, in the next few years or decades, scientific waste is increasingly being put under the microscope. Enlarge / Cleaning, still kinda plastic-reliant. Credit: © Daniel Stier at Twenty Twenty and Miren Marañón at East Photographic for Mosaic In a sign of how far things have moved on since Gilliam left her career in research, last November the University of Leeds pledged to go single-use-plastic-free by 2023. Recently, UCL has announced it will follow suit, with the only slightly less ambitious target of 2024. These new policies won’t just banish disposable coffee cups from campus, but a lot of everyday scientific equipment too. Lucy Stuart, sustainability project officer at Leeds, says that reaction among researchers has been mixed, but they are gradually making progress. “For us, as a university, we are here to inspire the next generation,” she says. “Also, we are a research-based institution that is creating groundbreaking innovation every day, so we didn’t want to say the solutions aren’t possible, because we are the people that help create those solutions.” The ambitious target has helped focus everyone’s attention, as has the clear sign that it has support all the way through the institution from the top of university management down. However, “We don’t want to implement top-down policies,” Stuart emphasizes. “We want individual researchers and employees to take ownership and look at the problem within their area, and then make a change.” Elsewhere, many scientists are already pushing ahead on their own initiative. When David Kuntin, a biomedical researcher at the University of York, was discussing plastic waste with his lab mates, he soon found he wasn’t the only one who had noticed how much they were getting through. “Using plastics on a daily basis—in science, it is kind of impossible to avoid nowadays. And someone just said, ‘Oh, we could fill a room after a week!’ and it got us discussing what we could do.” One reason lab plastics are such a sticky problem is that they can get contaminated with the biological or chemical matter being researched; you can’t simply put them in the campus recycling bins with your coffee cup. Usually, lab waste plastics are bagged and autoclaved—an energy- and water-hungry sterilisation process—before being sent to landfill. But, Kuntin says, not all plastic waste is too contaminated to recycle. Rather than simply classing everything as hazardous, straight off, he and his colleagues did an audit of the plastic they used, to see what they could decontaminate. “The contamination we deal with is probably less dangerous than a mouldy tin of beans you might have in your recycling after a few weeks,” Kuntin says. So, just as the team had learned that they had to wash their tins of beans before they put them in the council recycling bin, they learned ways to decontaminate their lab waste, too. They developed a “decontamination station” with a 24-hour soak in a high-level disinfectant, followed by a rinse for chemical decontamination. They also looked at the plastics they were buying, to pick ones that would be easier to recycle. As a result of these measures, they’ve reduced the plastic they were previously sending to landfill by about a tonne a year. “That’s 20 workers, 20 of us,” he says, sounding as if he still doesn’t quite believe that so few researchers could pile up so much waste. “We used a tonne of plastic that we can recycle.” They worked out it was enough to fill 110 bathtubs. And because they have also cut down how much equipment has to be autoclaved, they are saving energy and water, too. “I think as scientists, we need to be responsible about what we’re doing,” Kuntin tells me. Not least, he says, because it is public money they are spending. “You can’t, with a clean conscience, just be using a tonne of plastic.” More than a plastic puzzle At the University of Bristol, technicians Georgina Mortimer and Saranna Chipper-Keating have also set up schemes for sorting and recycling lab waste. “The waste in the lab was very easy for people to see. They were like, ‘I do this at home,’” says Mortimer. © Daniel Stier at Twenty Twenty and Miren Marañón at East Photographic for Mosaic They have been trialling glove and ice pack recycling through a company that specializes in hard-to-recycle waste, including contact lenses, crisp packets and cigarette butts as well as the sorts of plastics that come out of labs. They are keen to think more about re-use and reduction, too, knowing that recycling can only take them so far. They have worked out how they can bulk buy whenever possible, to cut down on packaging waste, for example. Plastics is only part of the sustainable lab puzzle for them. “We have a lot of ULT freezers, ultra-low temperature freezers,” Mortimer says. The freezers “have thousands, thousands of samples going back more than 20 years”. And they are all stored at minus 80ºC. Or at least they used to be. Anna Lewis, sustainable science manager at Bristol, showed them some research from the University of Colorado Boulder, demonstrating that most samples can be safely stored at minus 70, saving up to a third of the energy. They have now raised the temperature of their ULT freezers. The Bristol technicians have also been thinking about what they’re storing in these freezers, how, and whether it needs to be there. “There are samples that have just been left there for years,” says Mortimer. We’ve been discovering what these actually are, if they’re still usable, consolidating the space.” This hasn’t just saved energy and money, it’s also made working with the freezers more manageable. It’s simply easier to find things. Martin Farley held the first lab sustainability post in the UK, at the University of Edinburgh back in 2013. He now specializes in ways research labs can become more sustainable, working in a similar role to Lewis at a couple of London universities. He first got into the issue because of plastics, but quickly found a whole range of issues to work on. Farley points out that these ULT freezers can use as much energy as a house. So if you’re worried about energy use in the houses in your street, you should be worried about it in the fridges in your university too. Ultimately, as the climate emergency intensifies, Farley argues, “every facet of society needs to change”. Labs might not be a “behemoth” like the oil and gas industry, he says, but they have a significant and often ignored environmental impact. In a research-intensive university, Farley reckons the labs will account for about two-thirds of the energy bill. If a university is looking to reduce its energy use, research sciences are a good place to start. “We have people recycling at home, and doing nothing in their labs. I did a rough back-of-the-envelope calculation,” he tells me, and, depending on your research area, “your impact on the environment is 100–125 times more than at home.” Enlarge / Gloves remain necessary (and remain plastic). Credit: © Daniel Stier at Twenty Twenty and Miren Marañón at East Photographic for Mosaic Tracing back through the history of science, it’s hard to tell exactly when disposable plastics arrived in labs. “That’s a job of work to be done, to figure out when plastic starts to get used in scientific instruments, scientific material culture, and how, and how it changes,” says Simon Werrett, a historian at UCL who specializes in the materials of science. He says that there’s plastic in a lot of historical scientific objects, but because museums don’t catalogue items in those terms, it’s hard to date it exactly. Still, he suspects science’s plastic problem followed everyone else’s. Production of the thing we call plastic started in the late 19th century. Today, we’re increasingly used to seeing plastic as a threat to wildlife, but back then, if anything synthetic products saved nature from being chewed up by human consumption. As the game of billiards became popular, manufacturers looked for a way to produce the balls from something more reliable than the trade in ivory. One firm launched a $10,000 competition to find an alternative material, which led to the patenting of celluloid (a mix of camphor and gun cotton) by American inventor John Wesley Hyatt in 1870. Hyatt formed the Celluloid Manufacturing Company with his brother Isaiah, and developed a process of “blow molding”, which allowed them to produce hollow tubes of celluloid, paving the way for mass production of cheap toys and ornaments. One of the advantages of celluloid was that it could be mixed with dyes, including mottled shades, allowing the Hyatts to produce not just artificial ivory but coral and tortoiseshell too. At the turn of the century, the ever-expanding electrical industry was running low on shellac, a resin secreted by the female lac bug which could be used as an insulating material. Spotting a market, Leo Baekeland patented an artificial alternative in 1909, which he named Bakelite. This was marketed in the 1920s as “the material of a thousand uses”, soon joined by a host of new plastics throughout the 1930s and 1940s too. Nylon, invented in 1935, offered a sort of synthetic silk, useful for parachutes and also stockings. Plexiglass was helpful in the burgeoning aviation industry. Wartime R&D put rocket boosters on plastic innovation, and just as plastic products speedily started to fill up the postwar home, a plethora of plastic goods entered the postwar lab, too. Werrett emphasizes that today’s problems are a product not just of plastics but of the emergence of cultures of disposability. We didn’t used to throw stuff away. Disposability pre-dates plastics slightly. Machines of the late industrial revolution, around the middle of the 19th century, made cloth and paper much easier to produce. At the same time, people were becoming more and more aware, and worried, about the existence of germs—for example, after John Snow identified the Broad Street water pump as the source of a cholera outbreak in Soho, London, in 1854. Just as Joseph Lister pioneered the use of antiseptics in medicine from the 1860s onwards, disposable dressings gradually became the norm. “So you have things like cotton buds, and condoms and tampons, and sticking plasters,” Werrett explains, as well as paper napkins and paper cups. As mass production advanced, it soon became cheaper and easier to throw things away than to clean and re-use them—or pay someone else to. Cloth- and paper-based disposable products arrived over a relatively short period, but the new throwaway culture they instigated paved the ground for the plastic problem we have today. Paper cups and straws soon became plastic ones, and the idea of “produce, use, discard” became normal. Still, the introduction of disposable plastics in postwar science and medicine wasn’t necessarily simple. Looking at medical journals from the 1950s and 1960s, Werrett has found a few complaints. © Daniel Stier at Twenty Twenty and Miren Marañón at East Photographic for Mosaic “There’s a tradition that surgeons have a pair of gloves, and they use that for their whole career,” he explains. These gloves would have been rubber—first introduced by William Stewart Halsted at Johns Hopkins Hospital in Maryland in the 1890s—but designed to last, boiled for sterilisation and repaired rather than disposed of in favor of a new pair. “By the end of their career, they’ve got repairs and stains,” Werrett says, “and that’s a sign or mark of your experience as a surgeon.” Then disposable gloves came in, and not everyone was happy to leave these marks of experience behind. Nurses had to be taught to throw things away, rather than keep them, he notes. “It wasn’t self-evident that disposability was a valuable thing. If anything, the default is to re-use things. You have to train people to see disposability as a valuable practice.” Glassware is cool again For those looking for a plastic-free future for science, a technological fix could well be found in the history. Back in Bristol, Georgina Mortimer has been eyeing up the old glass cabinets. “We’re trying to get back into glassware, trying to make it cool again within our department,” she says, smiling. In Brussels, Lucy Gilliam tells me about her grandmother, who worked in a hospital lab, and all the dishwashing assistance she had to support their use of glassware. “And now we do it all by ourselves. We’re like little research islands. And you know, plastic—and single-use disposable things—is filling the gap of people. “There was a time when we were doing really advanced science without using plastics. And it’s not to say that all of the science that we do now can be done without plastics. But there is science that we were doing back then, and that we’re still doing now, that could be done without plastics.” Plastic has become apparently indispensable for modern science. It can keep materials protected, even when we transport them. It keeps us out of them (for materials we don’t want to contaminate) and them out of us (for hazardous materials that might hurt us). It can be moulded into a range of shapes. Some areas of science—not least DNA research—have grown up in an era of disposable plastics. Re-using glass has its own logistical additions, like repeat washing and sterilization. © Daniel Stier at Twenty Twenty and Miren Marañón at East Photographic for Mosaic In some cases, though, a return to glass might be the answer. “Use glassware—it’s there, it’s available, it’s sterilized,” Mortimer enthuses. “All the universities will have a glass room just full to the ceilings of stuff that we can be using rather than plastics.” Along with Saranna Chipper-Keating, she has been tasked with producing a whole-life costing exercise on glass versus plastics. In theory, it should be cheaper to re-use glass than to buy plastics again and again, especially as there are often costs associated with dumping these plastics. But re-using glass means it must be washed and sterilized, and that takes resources, too. This is a concern for Lucy Stuart in Leeds; they don’t want their plastic-free pledge to simply replace one environmental problem with another. In York, David Kuntin is also concerned about the knock-on effects of switching back to glass. “Every day, we use reagents like cell culture media, a nutrient broth that cells thrive in,” he tells me. These broths have been developed for decades, and since most cells are grown on plastic, that’s what the reagents have been optimized for. On top of this, researchers like Kuntin are interested in the finest details of cell behavior—and what they’re grown on could have an influence. “We know that cells are very responsive to their environment, and they can sense things like the roughness or stiffness of the surface they grow on,” he explains. Unexpected changes in behavior could be misinterpreted as a consequence of an experiment, when really it’s just that the cells are behaving differently on glass. Another problem is how much time re-using glass could take. Disposable pipette tips are just quicker. And time, along with water and heat, could cost the lab money. Ultimately, though, they don’t know until they do a full analysis. “We could do a whole-life costing exercise, and it may well be that plastics are so much cheaper,” Anna Lewis says. “In which case, we would need subsidies.” Lewis argues that any real change will require a change in how science is funded, with universities ideally needing to demonstrate some level of sustainability before they could apply for certain grant schemes. There is only so far they can go working with the goodwill and interest of a few enthusiasts. She sees scope to address this, if not in the next Research Excellence Framework (for assessing the quality of research in the UK) in 2021, then in the one after that. Whether the ecological crisis can wait for us to slowly negotiate yet another decade of science policy is another matter. "I want to do more" Martin Farley certainly sees a stronger appetite for change from the scientific community, compared to when he first started greening labs, back in 2013. “Five or six years ago, when I told my lab mates I was doing this, people laughed. There was a little bit of interest, like ‘Sure, I’ll recycle more’, and some jokes. Now, I get emails on almost a weekly basis. People out of the blue that are saying, ‘How can I do something? I want to do more.’” The University of Leeds is keen to link with other organisations, too. They’ve created a network around Leeds, including other universities, the Yorkshire Ambulance Service, the city council, and Yorkshire Water. They are also in discussions with one of the national research councils. Stuart says these sorts of collaborations are essential if they want to address disposable plastics on campus, because everything that comes in is part of the broader local economy. But it’s also part of the whole point of the project, seeing themselves as “a civic university”, ensuring that their research and innovation is used in a way that benefits the local area. For researchers wanting to dive into the problem of plastic waste on their own, though, Gilliam has some simple advice: “First of all, see if you can get some buddies. Send out a note and convene a little meeting. Say, ‘I've seen these things, I’m concerned about it, does anybody have any ideas?’” In the event that no one will engage with you, she suggests you just start segregating some of your plastic anyway, putting it in a box and sending it back, sharing a photo on social media as you go. You might well find comrades in other labs if not your own. “Start by doing something different, even if it feels like it’s really small and really pointless. Even small actions like that can have a ripple effect.” This article first appeared on Mosaic and is republished here under a Creative Commons license. Thanks to UCL and the Francis Crick Institute for their help with this story. All items photographed are laboratory waste, so no plastic was harmed in this shoot. Source: Can science break its plastic addiction? (Ars Technica)
  3. Newly engineered enzyme can break down plastic to raw materials The resulting chemicals can be used to make brand-new bottles. Enlarge Orange County NC 58 with 45 posters participating Plastics have a lot of properties that have made them fixtures of modern societies. They can be molded into any shape we'd like, they're tough yet flexible, and they come in enough variations that we can tune the chemistry to suit different needs. The problem is that they're tough enough that they don't break down on their own, and incinerating them is relatively inefficient. As a result, they've collected in our environment as both bulk plastics and the seemingly omnipresent microplastic waste. For natural materials, breaking down isn't an issue, as microbes have evolved ways of digesting them to obtain energy or useful chemicals. But many plastics have only been around for decades, and we're just now seeing organisms that have evolved enzymes to digest them. Figuring they could do one better, researchers in France have engineered an enzyme that can efficiently break down one of the most common forms of plastic. The end result of this reaction is a raw material that can be reused directly to make new plastic bottles. An unwanted PET The plastic in question is polyethylene terephthalate, or PET. PET has a variety of uses, including as thin films with very high tensile strength (marketed as mylar). But its most notable use is in plastic drink bottles, which are a major component of environmental plastic waste. PET was first developed in the 1940s, and the first living organism that can break down and use the carbon in PET was described in 2016—found in sediment near a plastic recycling facility, naturally. While microbes like this could solve the plastic waste issue, they don't make plastics any more sustainable since the carbon backbone of PET ends up being broken down completely. That means we have to constantly supply new material to replace PET containers as they're broken down—material that currently comes from petrochemicals. The French team was interested in creating a circular PET process, in which existing material gets broken down in a way that allows it to be immediately reused to make new PET products. PET is a long collection of carbon rings linked by oxygen and carbon atoms. To break it down in a way that allows recycling, these carbon-oxygen links haven't been broken, releasing a large collection of rings that can then be re-linked. The microbes that currently digest PET break down that ring as well, making them unsuitable for recycling. But a number of enzymes that can break the links in PET have already been identified. These all function to break down the waxy coating on the surfaces of leaves, called "cutin" (making these enzymes cutinases). These provided the starting materials for the new work. To begin with, the researchers took a panel of cutinases and tested their activities in breaking down PET. The one with the highest activity turned out to have a name that indicated where it was originally found: in a compost pile (it's called "leaf-branch compost cutinase"). I’m melting To understand the researchers' next steps, we have to understand a bit about PET itself. While all versions of PET have the same chemical formula, the material can solidify into two forms: a tightly packed crystalline form and a more loose, disordered form. Most materials made of PET have different amounts of these two forms, as their ratios can allow manufacturers to tune the material's properties. The tight packing of the crystalline form, however, makes it difficult to digest for even the most efficient enzyme. Fortunately, there's a partial solution: heating any form of PET causes some of the crystalline PET to melt into a disordered form, allowing more of it to be digested. That, unfortunately, creates a problem, as the enzymes themselves often melt and are inactivated at the temperatures involved (65°C, or 150°F). In addition, these enzymes evolved to break down a different polymer and wouldn't be expected to work as well on PET, which is chemically distinct from anything on plants' leaves. These were the two big hurdles faced by the researchers. To get the enzyme to work better on PET, the researchers looked up the cutinase structure and ran chemical simulations to figure out where PET would interact with the enzyme. They found it fit into a groove on the enzyme's surface that included the location where the PET would be cut. To improve PET's fit into this groove, the researchers created a large panel of mutant versions of the enzyme that, in different combinations, changed every single amino acid on the inside of the groove. While most of these nearly eliminated the enzyme's activity, a few actually improved it and were used for further studies. The second problem was the issue of the enzyme's ability to tolerate high temperatures. Here, studies with related enzymes provided a hint: many were stabilized by interacting with a metal ion that holds two parts of the enzyme together. Starting with the original version of the enzyme, the researchers engineered in two amino acids that could form a chemical bond between those two parts (for those who know biochemistry, that's a disulfide bridge). This version was more stable at high temperatures than the original one. By combining all these changes, the researchers created two versions that they then tested on PET obtained by shredding drink bottles. Cheap and effective Given this source of PET, the original enzyme could digest about half in 20 hours. The researchers' best modified version only needed 15 hours to hit 85 percent digestion. Optimizing the conditions, they were able to hit 90 percent breakdown of PET in under 10 hours. While there was still some crystalline PET left over, they found that they could take 1,000kg of PET waste and produce 863kg of raw materials from it. Put in different terms, their redesigned enzyme is more efficient at digesting PET than our digestive enzymes are at breaking down starches. They then used this raw material to make new PET products using standard industrial reactions. The new product's ability to withstand pressure was only 5 percent off from the value measured for PET made from standard chemical sources. Appearance wise, it was within 10 percent of the PET produced the regular way. How much would using recycled PET cost compared to starting with petrochemical feedstocks? The authors estimate that, if the protein can be made for about $25 a kilogram, then the cost of the process will end up being about 4 percent of what you can get with for the PET made from it. While that might not be as cheap as petrochemicals—especially now, after oil prices have collapsed—it's going to be relatively immune to future price shocks and is far more sustainable. Nature, 2020. DOI: 10.1038/s41586-020-2149-4 (About DOIs). Source: Newly engineered enzyme can break down plastic to raw materials (Ars Technica)
  4. If recycling plastics isn’t making sense, remake the plastics New catalytic approaches convert plastic into liquid fuels, nanotubes. Enlarge / Workers sort plastic waste as a forklift transports plastic waste at Yongin Recycling Center in Yongin, South Korea. Bloomberg/Getty Images 87 with 45 posters participating A few years back, it looked like plastic recycling was set to become a key part of a sustainable future. Then, the price of fossil fuels plunged, making it cheaper to manufacture new plastics. Then China essentially stopped importing recycled plastics for use in manufacturing. With that, the bottom dropped out of plastic recycling, and the best thing you could say for most plastics is that they sequestered the carbon they were made of. The absence of a market for recycled plastics, however, has also inspired researchers to look at other ways of using them. Two papers this week have looked into processes that enable "upcycling," or converting the plastics into materials that can be more valuable than the freshly made plastics themselves. Make me some nanotubes The first paper, done by an international collaboration, actually obtained the plastics it tested from a supermarket chain, so we know it works on relevant materials. The upcycling it describes also has the advantage of working with very cheap, iron-based catalysts. Normally, to break down plastics, catalysts and the plastics are heated together. But in this case, the researchers simply mixed the catalyst and ground up plastics and heated the iron using microwaves. Like water, iron absorbs microwave radiation and converts it into heat. This causes the heat to be focused on the site where catalytic activities take place, rather than being evenly spread throughout the reaction. The difference is striking. Compared to traditional heating, the microwave heating released over 10 times as much hydrogen from the plastic, leaving very little other than pure carbon and some iron carbide behind. Better yet, the carbon was almost entirely in the form of carbon nanotubes, a product with significant value. And it all happened extremely quickly, with hydrogen being released less than a minute after the microwaves were applied. The process was completed in less than two minutes. Although some of the iron ended up being linked to carbon, this didn't inactivate the catalyst. The researchers found that they could mix in more ground-up plastic and start the process over again, repeating it up to 10 times in their tests, although hydrogen production was clearly dropping by cycle 10. On the plus side, the later cycles produced almost pure hydrogen, as contaminants like oxygen and water had been removed by the earlier cycles. And, at the end of 10 cycles, the carbon-rich material was 92-percent nanotubes by weight. The only thing that's missing from the work is an indication of how easy it would be to reform the iron into iron oxide, the catalytic form of the material. We’ll take that hydrogen If you were at all worried about what to do with that hydrogen, a US-based group has a potential answer. The group was also concerned about the problems the other researchers saw when they simply heated a catalyst and plastic together: the results were a complicated mix of chemicals, rather than the two clean products seen when rapid heating was done using microwaves. But this team looked to biology for possible solutions. Enzymes digest polymers all the time. And, in many cases, they produce clearly defined products by chewing the polymer from one end, releasing one subunit of the polymer at a time. Typically, this works because the polymer fits into a slot on the surface of the enzyme that includes the catalytic site, and the enzyme moves along it, advancing as each reaction removes a piece of the polymer. It should be possible, the researchers reasoned, to make an artificial catalyst that works in similar ways. To do so, the researchers created a silicon oxide surface with lots of pores, then placed a platinum catalyst at the base of each pore. In the right solvent, long plastic polymers would have a higher affinity for the surface of the silicon oxide and thus attach themselves to the surface. From there, a number would inevitably enter the pore and end up running into the catalyst. Thus, the catalyst would get the chance to act on one end of the polymer only, rather than running into it at some random location in the middle of the chain. Feed me polyethylene And the method largely worked when fed polyethylene. The catalyst wasn't as specific as an enzyme—instead of lopping off a single part of the polyethylene chain, it tended to release a small chunk about 14 carbons long. But it also liberated molecules containing anywhere from eight to 30 carbons—14 just happened to be the most frequent length. But, by making the pores deeper, the researchers were able to shift this value to 16 and 18 carbons, allowing them to tune the population of molecules that come out of the reaction. The utility of this is that, by adjusting the average length of the population that comes out of the reaction, it's possible to produce mixtures of hydrocarbons that will work better as fuel, or as lubricants. In other words, you can turn polyethylene into whatever type of hydrocarbon mixture that's most valuable at the time. Overall, however, there are more significant drawbacks here. Platinum, used in the catalyst, is quite expensive, and it only works on a single type of plastic—although other catalysts might be amenable to being placed at the end of pores. The reactions have to be run at an elevated temperature, and it requires a supply of hydrogen to work. So, it's substantially less flexible than the one run by microwaved iron. But the ability to turn any plastics into liquid fuel certainly has potential utility. Nature Catalysis, 2020. DOI: 10.1038/s41929-020-00518-5, 10.1038/s41929-020-00519-4 (About DOIs). If recycling plastics isn’t making sense, remake the plastics
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