chemistry

Researchers engineer bacteria to produce plastics

biochemistry, bioengineering, Biology, chemistry, plastics, Science / Shannon Garcia / March 18, 2025

Image of a series of chemical reactions, with enzymes driving each step forward. — One of the enzymes used in this system takes an amino acid (left) and links it to Coenzyme A. The second takes these items and links them into a polymer. Credit: Chae et. al.

Normally, PHA synthase forms links between molecules that run through an oxygen atom. But it’s also possible to form a related chemical link that instead runs through a nitrogen atom, like those found on amino acids. There were no known enzymes, however, that catalyze these reactions. So, the researchers decided to test whether any existing enzymes could be induced to do something they don’t normally do.

The researchers started with an enzyme from Clostridium that links chemicals to Coenzyme A that has a reputation for not being picky about the chemicals it interacts with. This worked reasonably well at linking amino acids to Coenzyme A. For linking the amino acids together, they used an enzyme from Pseudomonas that had four different mutations that expanded the range of molecules it would use as reaction materials. Used in a test tube, the system worked: Amino acids were linked together in a polymer.

The question was whether it would work in cells. Unfortunately, one of the two enzymes turns out to be mildly toxic to E. coli, slowing its growth. So, the researchers evolved a strain of E. coli that could tolerate the protein. With both of these two proteins, the cells produced small amounts of an amino acid polymer. If they added an excess of an amino acid to the media the cells were growing in, the polymer would be biased toward incorporating that amino acid.

Boosting polymer production

However, the yield of the polymer by weight of bacteria was fairly low. “It was reasoned that these [amino acids] might be more efficiently incorporated into the polymer if generated within the cells from a suitable carbon source,” the researchers write. So, the researchers put in extra copies of the genes needed to produce one specific amino acid (lysine). That worked, producing more polymer, with a higher percentage of the polymer being lysine.

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Small charges in water spray can trigger the formation of key biochemicals

biochemistry, Biology, chemistry, origin of life, Physics, Science / Beth Washington / March 16, 2025

Once his team nailed how droplets become electrically charged and how the micro-lightning phenomenon works, they recreated the Miller-Urey experiment. Only without the spark plugs.

Ingredients of life

After micro-lightnings started jumping between droplets in a mixture of gases similar to that used by Miller and Urey, the team examined their chemical composition with a mass spectrometer. They confirmed glycine, uracil, urea, cyanoethylene, and lots of other chemical compounds were made. “Micro-lightnings made all organic molecules observed previously in the Miller-Urey experiment without any external voltage applied,” Zare claims.

But does it really bring us any closer to explaining the beginnings of life? After all, Miller and Urey already demonstrated those molecules could be produced by electrical discharges in a primordial Earth’s atmosphere—does it matter all that much where those discharges came from? Zare argues that it does.

“Lightning is intermittent, so it would be hard for these molecules to concentrate. But if you look at waves crashing into rocks, you can think the spray would easily go into the crevices in these rocks,” Zare suggests. He suggests that the water in these crevices would evaporate, new spray would enter and evaporate again and again. The cyclic drying would allow the chemical precursors to build into more complex molecules. “When you go through such a dry cycle, it causes polymerization, which is how you make DNA,” Zare argues. Since sources of spray were likely common on the early Earth, Zare thinks this process could produce far more organic chemicals than potential alternatives like lightning strikes, hydrothermal vents, or impacting comets.

But even if micro-lightning really produced the basic building blocks of life on Earth, we’re still not sure how those combined into living organisms. “We did not make life. We just demonstrated a possible mechanism that gives us some chemical compounds you find in life,” Zare says. “It’s very important to have a lot of humility with this stuff.”

Science Advances, 2025. DOI: 10.1126/sciadv.adt8979

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Brewing tea removes lead from water

chemistry, food chemistry, lead contamination, Science, tea / Kelly Newman / February 26, 2025

Testing the teas

Scanning electron microscope image of black tea leaves, magnified by 500 times. Black tea, which is wilted and fully oxidized, exhibits a wrinkled surface, potentially increasing the available surface area for adsorption. Credit: Vinayak P. Dravid Group/Northwestern University

To test their hypothesis, the authors purchased Lipton and Infusions commercial tea bags, as well as a variety of loose-leaf teas and herbal alternatives: black tea, green tea, white peony tea, oolong tea, rooibos tea, and chamomile tea. The tea bags were of different types (cotton, cellulose, and nylon). They brewed the tea the same way daily tea drinkers do, steeping the tea for various time intervals (mere seconds to 24 hours) in water spiked with elevated known levels of lead, chromium, copper zinc, and cadmium. Tea leaves were removed after steeping by pouring the tea through a cellulose filter into a separate tube. The team then measured how much of the toxic metals remained in the water and how much the leaves had adsorbed.

It turns out that the type of tea bag matters. The team found that cellulose tea bags work the best at adsorbing toxic metals from the water while cotton and nylon tea bags barely adsorbed any contaminants at all—and nylon bags also release contaminating microplastics to boot. Tea type and the grind level also played a part in adsorbing toxic metals, with finely ground black tea leaves performing the best on that score. This is because when those leaves are processed, they get wrinkled, which opens the pores, thereby adding more surface area. Grinding the tea further increases that surface area, with even more capacity for binding toxic metals.

But the most significant factor was steeping time: the longer the steeping time, the more toxic metals were adsorbed. Based on their experiments, the authors estimate that brewing tea—using a tea bag that steeps for three to five minutes in a mug—can remove about 15 percent of lead from drinking water, even water with concentrations as high as 10 parts per million.

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Researchers figure out how to get fresh lithium into batteries

batteries, chemistry, materials science, Science / Shannon Garcia / February 22, 2025

In their testing, they use a couple of unusual electrode materials, such as a chromium oxide (Cr₈O₂₁) and an organic polymer (a sulfurized polyacrylonitrile). Both of these have significant weight advantages over the typical materials used in today’s batteries, although the resulting batteries typically lasted less than 500 cycles before dropping to 80 percent of their original capacity.

But the striking experiment came when they used LiSO₂CF₃ to rejuvenate a battery that had been manufactured as normal but had lost capacity due to heavy use. Treating a lithium-iron phosphate battery that had lost 15 percent of its original capacity restored almost all of what was lost, allowing it to hold over 99 percent of its original charge. They also ran a battery for repeated cycles with rejuvenation every few thousand cycles. At just short of 12,000 cycles, it still could be restored to 96 percent of its original capacity.

Before you get too excited, there are a couple of things worth noting about lithium-iron phosphate cells. The first is that, relative to their charge capacity, they’re a bit heavy, so they tend to be used in large, stationary batteries like the ones in grid-scale storage. They’re also long-lived on their own; with careful management, they can take over 8,000 cycles before they drop to 80 percent of their initial capacity. It’s not clear whether similar rejuvenation is possible in the battery chemistries typically used for the sorts of devices that most of us own.

The final caution is that the battery needs to be modified so that fresh electrolytes can be pumped in and the gases released by the breakdown of the LiSO₂CF₃ removed. It’s safest if this sort of access is built into the battery from the start, rather than provided by modifying it much later, as was done here. And the piping needed would put a small dent in the battery’s capacity per volume if so.

All that said, the treatment demonstrated here would replenish even a well-managed battery closer to its original capacity. And it would largely restore the capacity of something that hadn’t been carefully managed. And that would allow us to get far more out of the initial expense of battery manufacturing. Meaning it might make sense for batteries destined for a large storage facility, where lots of them could potentially be treated at the same time.

Nature, 2025. DOI: 10.1038/s41586-024-08465-y (About DOIs).

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Turning the Moon into a fuel depot will take a lot of power

chemistry, oxygen, oxygen production, Science, Space, Space exploration / Shannon Garcia / February 18, 2025

Getting oxygen from regolith takes 24 kWh per kilogram, and we’d need tonnes.

Without adjustments for relativity, clocks here and on the Moon would rapidly diverge. Credit: NASA

If humanity is ever to spread out into the Solar System, we’re going to need to find a way to put fuel into rockets somewhere other than the cozy confines of a launchpad on Earth. One option for that is in low-Earth orbit, which has the advantage of being located very close to said launch pads. But it has the considerable disadvantage of requiring a lot of energy to escape Earth’s gravity—it takes a lot of fuel to put substantially less fuel into orbit.

One alternative is to produce fuel on the Moon. We know there is hydrogen and oxygen present, and the Moon’s gravity is far easier to overcome, meaning more of what we produce there can be used to send things deeper into the Solar System. But there is a tradeoff: any fuel production infrastructure will likely need to be built on Earth and sent to the Moon.

How much infrastructure is that going to involve? A study released today by PNAS evaluates the energy costs of producing oxygen on the Moon, and finds that they’re substantial: about 24 kWh per kilogram. This doesn’t sound bad until you start considering how many kilograms we’re going to eventually need.

Free the oxygen!

The math that makes refueling from the Moon appealing is pretty simple. “As a rule of thumb,” write the authors of the new study on the topic, “rockets launched from Earth destined for [Earth-Moon Lagrange Point 1] must burn ~25 kg of propellant to transport one kg of payload, whereas rockets launched from the Moon to [Earth-Moon Lagrange Point 1] would burn only ~four kg of propellant to transport one kg of payload.” Departing from the Earth-Moon Lagrange Point for locations deeper into the Solar System also requires less energy than leaving low-Earth orbit, meaning the fuel we get there is ultimately more useful, at least from an exploration perspective.

But, of course, you need to make the fuel there in the first place. The obvious choice for that is water, which can be split to produce hydrogen and oxygen. We know there is water on the Moon, but we don’t yet know how much, and whether it’s concentrated into large deposits. Given that uncertainty, people have also looked at other materials that we know are present in abundance on the Moon’s surface.

And there’s probably nothing more abundant on that surface than regolith, the dust left over from constant tiny impacts that have, over time, eroded lunar rocks. The regolith is composed of a variety of minerals, many of which contain oxygen, typically the heavier component of rocket fuel. And a variety of people have figured out the chemistry involved in separating oxygen from these minerals on the scale needed for rocket fuel production.

But knowing the chemistry is different from knowing what sort of infrastructure is needed to get that chemistry done at a meaningful scale. To get a sense of this, the researchers decided to focus on isolating oxygen from a mineral called ilmenite, or FeTiO₃. It’s not the easiest way to get oxygen—iron oxides win out there—but it’s well understood. Someone actually patented oxygen production from ilmenite back in the 1970s, and two hardware prototypes have been developed, one of which may be sent to the Moon on a future NASA mission.

The researchers propose a system that would harvest regolith, partly purify the ilmenite, then combine it with hydrogen at high temperatures, which would strip the oxygen out as water, leaving behind purified iron and titanium (both of which may be useful to have). The resulting water would then be split to feed the hydrogen back into the system, while the oxygen can be sent off for use in rockets.

(This wouldn’t solve the issue of what that oxygen will ultimately oxidize to power a rocket. But oxygen is typically the heavier component of rocket fuel combinations—typically about 80 percent of the mass—and so the bigger challenge to get to a fuel depot.)

Obviously, this process will require a lot of infrastructure, like harvesters, separators, high-temperature reaction chambers, and more. But the researchers focus on a single element: how much power will it suck down?

More power!

To get their numbers, the researchers made a few simplifying assumptions. These include assuming that it’s possible to purify ilmenite from raw regolith and that it will be present in particles small enough that about half the material present will participate in chemical reactions. They ignored both the potential to get even more oxygen from the iron and titanium oxides present, as well as the potential for contamination from problematic materials like hydrogen sulfide or hydrochloric acid.

The team found that almost all of the energy is consumed at three steps in the process: the high-temperature hydrogen reaction that produces water (55 percent), splitting the water afterwards (38 percent), and converting the resulting oxygen to its liquid form (five percent). The typical total usage, depending on factors like the concentration of ilmenite in the regolith, worked out to be about 24 kW-hr for each kilogram of liquid oxygen.

Obviously, the numbers are sensitive to how efficiently you can do things like heat the reaction mix. (It might be possible to do this heating with concentrated solar, avoiding the use of electricity for this entirely, but the authors didn’t analyze that.) But it was also sensitive to less obvious efficiencies. For example, a better separation of the ilmenite from the rest of the regolith means you’re using less energy to heat contaminants. So, while the energetic cost of that separation is small, it pays off to do it effectively.

Based on orbital observations, the researchers map out the areas where ilmenite is present at high enough concentrations for this approach to make sense. These include some of the mares on the near side of the Moon, so they’re easy to get to.

A map of the lunar surface with locations highlighted in color. — A map of the lunar surface, with areas with high ilmenite concentrations shown in blue. Credit: Leger, et. al.

On its own, 24 kWh doesn’t seem like a lot of power. The problem is that we will need a lot of kilograms. The researchers estimate that getting an empty SpaceX Starship from the lunar surface to the Earth-Moon Lagrange Point takes 80 tonnes of liquid oxygen. And a fully fueled starship can hold over 500 tonnes of liquid oxygen.

We can compare that to something like the solar array on the International Space Station, which has a capacity of about 100 kW. That means it could power the production of about four kilograms of oxygen an hour. At that rate, it’ll take a bit over 10 days to produce a tonne, and a bit more than two years to get enough oxygen to get an empty Starship to the Lagrange Point—assuming 24-7 production. Being on the near side, they will only produce for half the time, given the lunar day.

Obviously, we can build larger arrays than that, but it boosts the amount of material that needs to be sent to the Moon from Earth. It may potentially make more sense to use nuclear power. While that would likely involve more infrastructure than solar arrays, it would allow the facilities to run around the clock, thus getting more production from everything else we’ve shipped from Earth.

This paper isn’t meant to be the final word on the possibilities for lunar-based refueling; it’s simply an early attempt to put hard numbers on what ultimately might be the best way to explore our Solar System. Still, it provides some perspective on just how much effort we’ll need to make before that sort of exploration becomes possible.

PNAS, 2025. DOI: 10.1073/pnas.2306146122 (About DOIs).

John is Ars Technica’s science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.

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AI used to design a multi-step enzyme that can digest some plastics

AI, biochemistry, Biology, catalysts, chemistry, Computer science, enzymes, Science / Mike M. / February 16, 2025

And it worked. Repeating the same process with an added PLACER screening step boosted the number of enzymes with catalytic activity by over three-fold.

Unfortunately, all of these enzymes stalled after a single reaction. It turns out they were much better at cleaving the ester, but they left one part of it chemically bonded to the enzyme. In other words, the enzymes acted like part of the reaction, not a catalyst. So the researchers started using PLACER to screen for structures that could adopt a key intermediate state of the reaction. This produced a much higher rate of reactive enzymes (18 percent of them cleaved the ester bond), and two—named “super” and “win”—could actually cycle through multiple rounds of reactions. The team had finally made an enzyme.

By adding additional rounds alternating between structure suggestions using RFDiffusion and screening using PLACER, the team saw the frequency of functional enzymes increase and eventually designed one that had an activity similar to some produced by actual living things. They also showed they could use the same process to design an esterase capable of digesting the bonds in PET, a common plastic.

If that sounds like a lot of work, it clearly was—designing enzymes, especially ones where we know of similar enzymes in living things, will remain a serious challenge. But at least much of it can be done on computers rather than requiring someone to order up the DNA that encodes the enzyme, getting bacteria to make it, and screening for activity. And despite the process involving references to known enzymes, the designed ones didn’t share a lot of sequences in common with them. That suggests there should be added flexibility if we want to design one that will react with esters that living things have never come across.

I’m curious about what might happen if we design an enzyme that is essential for survival, put it in bacteria, and then allow it to evolve for a while. I suspect life could find ways of improving on even our best designs.

Science, 2024. DOI: 10.1126/science.adu2454 (About DOIs).

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Gecko feet inspire anti-slip shoe soles

biomimicry, chemistry, friction, geckos, polymers, Science / DJ Henderson / February 5, 2025

Just add zirconia nanoparticles…

diagram of wet ice's quasi slippery layer and design of anti-slip shoe soles inspired by gecko and toad foot pads — Credit: V. Richhariya et al., 2025

It’s the “hydrophilic capillary-enhanced adhesion”of gecko feet that most interested the authors of this latest paper. Per the World Health Organization, 684,000 people die and another 38 million are injured every year in slips and falls, with correspondingly higher health care costs. Most antislip products (crampons, chains, studs, cleats), tread designs, or materials (fiberglass, carbon fiber, rubber) are generally only effective for specific purposes or short periods of time. And they often don’t perform as well on wet ice, which has a nanoscale quasi-liquid layer (QLL) that makes it even more slippery.

So Vipin Richhariya of the University of Minho in Portugal and co-authors turned to gecko toe pads (as well as those of toads) for a better solution. To get similar properties in their silicone rubber polymers, they added zirconia nanoparticles, which attract water molecules. The polymers were rolled into a thin film and hardened, and then a laser etched groove patterns onto the surface—essentially creating micro cavities that exposed the zirconia nanoparticles, thus enhancing the material’s hydrophilic effects.

Infrared spectroscopy and simulated friction tests revealed that the composites containing 3 percent and 5 percent zirconia nanoparticles were the most slip-resistant. “This optimized composite has the potential to change the dynamics of slip-and-fall accidents, providing a nature-inspired solution to prevent one of the most common causes of accidents worldwide,” the authors concluded. The material could also be used for electronic skin, artificial skin, or wound healing.

DOI: ACS Applied Materials & Interfaces, 2025. 10.1021/acsami.4c14496 (About DOIs).

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A solid electrolyte gives lithium-sulfur batteries ludicrous endurance

batteries, chemistry, electrolyte, lithium battery, lithium-sulfur battery, Science, solid electrolyte / 9u50fv / January 17, 2025

Sulfur can store a lot more lithium but is problematically reactive in batteries.

If you weren’t aware, sulfur is pretty abundant. Credit: P_Wei

Lithium may be the key component in most modern batteries, but it doesn’t make up the bulk of the material used in them. Instead, much of the material is in the electrodes, where the lithium gets stored when the battery isn’t charging or discharging. So one way to make lighter and more compact lithium-ion batteries is to find electrode materials that can store more lithium. That’s one of the reasons that recent generations of batteries are starting to incorporate silicon into the electrode materials.

There are materials that can store even more lithium than silicon; a notable example is sulfur. But sulfur has a tendency to react with itself, producing ions that can float off into the electrolyte. Plus, like any electrode material, it tends to expand in proportion to the amount of lithium that gets stored, which can create physical strains on the battery’s structure. So while it has been easy to make lithium-sulfur batteries, their performance has tended to degrade rapidly.

But this week, researchers described a lithium-sulfur battery that still has over 80 percent of its original capacity after 25,000 charge/discharge cycles. All it took was a solid electrolyte that was more reactive than the sulfur itself.

When lithium meets sulfur…

Sulfur is an attractive battery material. It’s abundant and cheap, and sulfur atoms are relatively lightweight compared to many of the other materials used in battery electrodes. Sodium-sulfur batteries, which rely on two very cheap raw materials, have already been developed, although they only work at temperatures high enough to melt both of these components. Lithium-sulfur batteries, by contrast, could operate more or less the same way that current lithium-ion batteries do.

With a few major exceptions, that is. One is that the elemental sulfur used as an electrode is a very poor conductor of electricity, so it has to be dispersed within a mesh of conductive material. (You can contrast that with graphite, which both stores lithium and conducts electricity relatively well, thanks to being composed of countless sheets of graphene.) Lithium is stored there as Li₂S, which occupies substantially more space than the elemental sulfur it’s replacing.

Both of these issues, however, can be solved with careful engineering of the battery’s structure. A more severe problem comes from the properties of the lithium-sulfur reactions that occur at the electrode. Elemental sulfur exists as an eight-atom ring, and the reactions with lithium are slow enough that semi-stable intermediates with smaller chains of sulfur end up forming. Unfortunately, these tend to be soluble in most electrolytes, allowing them to travel to the opposite electrode and participate in chemical reactions there.

This process essentially discharges the battery without allowing the electrons to be put to use. And it gradually leaves the electrode’s sulfur unavailable for participating in future charge/discharge cycles. The net result is that early generations of the technology would discharge themselves while sitting unused and would only survive a few hundred cycles before performance decayed dramatically.

But there has been progress on all these fronts, and some lithium-sulfur batteries with performance similar to lithium-ion have been demonstrated. Late last year, a company announced that it had lined up the money needed to build the first large-scale lithium-sulfur battery factory. Still, work on improvements has continued, and the new work seems to suggest ways to boost performance well beyond lithium-ion.

The need for speed

The paper describing the new developments, done by a collaboration between Chinese and German researchers, focuses on one aspect of the challenges posed by lithium-sulfur batteries: the relatively slow chemical reaction between lithium ions and elemental sulfur. It presents that aspect as a roadblock to fast charging, something that will be an issue for automotive applications. But at the same time, finding a way to limit the formation of inactive intermediate products during this reaction goes to the root of the relatively short usable life span of lithium-sulfur batteries.

As it turns out, the researchers found two.

One of the problems with the lithium-sulfur reaction intermediates is that they dissolve in most electrolytes. But that’s not a problem if the electrolyte isn’t a liquid. Solid electrolytes are materials that have a porous structure at the atomic level, with the environment inside the pores being favorable for ions. This allows ions to diffuse through the solid. If there’s a way to trap ions on one side of the electrolyte, such as a chemical reaction that traps or de-ionizes them, then it can enable one-way travel.

Critically, pores that favor the transit of lithium ions, which are quite compact, aren’t likely to allow the transit of the large ionized chains of sulfur. So a solid electrolyte should help cut down on the problems faced by lithium-sulfur batteries. But it won’t necessarily help with fast charging.

The researchers began by testing a glass formed from a mixture of boron, sulfur, and lithium (B₂S₃ and Li₂S). But this glass had terrible conductivity, so they started experimenting with related glasses and settled on a combination that substituted in some phosphorus and iodine.

The iodine turned out to be a critical component. While the exchange of electrons with sulfur is relatively slow, iodine undergoes electron exchange (technically termed a redox reaction) extremely quickly. So it can act as an intermediate in the transfer of electrons to sulfur, speeding up the reactions that occur at the electrode. In addition, iodine has relatively low melting and boiling points, and the researchers suggest there’s some evidence that it moves around within the electrolyte, allowing it to act as an electron shuttle.

Successes and caveats

The result is a far superior electrolyte—and one that enables fast charging. It’s typical that fast charging cuts into the total capacity that can be stored in a battery. But when charged at an extraordinarily fast rate (50C, meaning a full charge in just over a minute), a battery based on this system still had half the capacity of a battery charged 25 times more slowly (2C, or a half-hour to full charge).

But the striking thing was how durable the resulting battery was. Even at an intermediate charging rate (5C), it still had over 80 percent of its initial capacity after over 25,000 charge/discharge cycles. By contrast, lithium-ion batteries tend to hit that level of decay after about 1,000 cycles. If that sort of performance is possible in a mass-produced battery, it’s only a slight exaggeration to say it can radically alter our relationships with many battery-powered devices.

What’s not at all clear, however, is whether this takes full advantage of one of the original promises of lithium-sulfur batteries: more charge in a given weight and volume. The researchers specify the battery being used for testing; one electrode is an indium/lithium metal foil, and the other is a mix of carbon, sulfur, and the glass electrolyte. A layer of the electrolyte sits between them. But when giving numbers for the storage capacity per weight, only the weight of the sulfur is mentioned.

Still, even if weight issues would preclude this from being stuffed into a car or cell phone, there are plenty of storage applications that would benefit from something that doesn’t wear out even with 65 years of daily cycling.

Nature, 2025. DOI: 10.1038/s41586-024-08298-9 (About DOIs).

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Graphene-enhanced ceramic tiles make striking art

chemistry, graphene, materials science, Science, science and art / Shannon Garcia / October 28, 2024

In recent years, materials scientists experimenting with ceramics have started adding an oxidized form of graphene to the mix to produce ceramics that are tougher, more durable, and more resistant to fracture, among other desirable properties. Researchers at the National University of Singapore (NUS) have developed a new method that uses ultrasound to more evenly distribute graphene oxide (GO) in ceramics, according to a new paper published in the journal ACS Omega. And as a bonus, they collaborated with an artist who used the resulting ceramic tiles to create a unique art exhibit at the NUS Museum—a striking merger of science and art.

As reported previously, graphene is the thinnest material yet known, composed of a single layer of carbon atoms arranged in a hexagonal lattice. That structure gives it many unusual properties that hold great promise for real-world applications: batteries, super capacitors, antennas, water filters, transistors, solar cells, and touchscreens, just to name a few.

In 2021, scientists found that this wonder material might also provide a solution to the fading of colors of many artistic masterpieces. For instance, several of Georgia O’Keeffe’s oil paintings housed in the Georgia O’Keeffe Museum in Santa Fe, New Mexico, have developed tiny pin-sized blisters, almost like acne, for decades. Conservators have found similar deterioration in oil-based masterpieces across all time periods, including works by Rembrandt.

Van Gogh’s Sunflower series has been fading over the last century due to constant exposure to light. A 2011 study found that chromium in the chrome yellow Van Gogh favored reacted strongly with other compounds like barium and sulfur when exposed to sunlight. A 2016 study pointed the finger at the sulfates, which absorb in the UV spectrum, leading to degradation.

Even contemporary art materials are prone to irreversible color changes from exposure to light and oxidizing agents, among other hazards. That’s why there has been recent work on the use of nanomaterials for conservation of artworks. Graphene has a number of properties that make it attractive for art-conservation purposes. The one-atom-thick material is transparent, adheres easily to various substrates, and serves as an excellent barrier against oxygen, gases (corrosive or otherwise), and moisture. It’s also hydrophobic and is an excellent absorber of UV light.

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Simple voltage pulse can restore capacity to Li-Si batteries

batteries, chemistry, electrochemistry, lithium, Science, silicon / Mike M. / October 19, 2024

The new work, then, is based on a hypothetical: What if we just threw silicon particles in, let them fragment, and then fixed them afterward?

As mentioned, the reason fragmentation is a problem is that it leads to small chunks of silicon that have essentially dropped off the grid—they’re no longer in contact with the system that shuttles charges into and out of the electrode. In many cases, these particles are also partly filled with lithium, which takes it out of circulation, cutting the battery’s capacity even if there’s sufficient electrode material around.

The researchers involved here, all based at Stanford University, decided there was a way to nudge these fragments back into contact with the electrical system and demonstrated it could restore a lot of capacity to a badly degraded battery.

Bringing things together

The idea behind the new work was that it could be possible to attract the fragments of silicon to an electrode, or at least some other material connected to the charge-handling network. On their own, the fragments in the anode shouldn’t have a net charge; when the lithium gives up an electron there, it should go back into solution. But the lithium is unlikely to be evenly distributed across the fragment, making them a polar material—net neutral, but with regions of higher and lower electron densities. And polar materials will move in an uneven electric field.

And, because of the uneven, chaotic structure of an electrode down at the nano scale, any voltage applied to it will create an uneven electric field. Depending on its local structure, that may attract or repel some of the particles. But because these are mostly within the electrode’s structure, most of the fragments of silicon are likely to bump into some other part of electrode in short order. And that could potentially re-establish a connection to the electrode’s current handling system.

To demonstrate that what should happen in theory actually does happen in an electrode, the researchers started by taking a used electrode and brushing some of its surface off into a solution. They then passed a voltage through the solution and confirmed the small bits of material from the battery started moving toward one of the electrodes that they used to apply a voltage to the solution. So, things worked as expected.

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Desalination system adjusts itself to work with renewable power

chemistry, electrochemistry, materials science desalination, renewable energy, Science, Sustainability / Mike M. / October 18, 2024

Instead of needing constant power, new system adjusts to use whatever is available.

Image of a small tanker truck parked next to a few shipping container shaped structures, which are connected by pipes to storage tanks.

Mobile desalination plants might be easier to operate with renewable power. Credit: Ismail BELLAOUALI

Fresh water we can use for drinking or agriculture is only about 3 percent of the global water supply, and nearly 70 percent of that is trapped in glaciers and ice caps. So far, that was enough to keep us going, but severe draughts have left places like Jordan, Egypt, sub-Saharan Africa, Spain, and California with limited access to potable water.

One possible solution is to tap into the remaining 97 percent of the water we have on Earth. The problem is that this water is saline, and we need to get the salt out of it to make it drinkable. Desalination is also an energy-expensive process. But MIT researchers led by Jonathan Bessette might have found an answer to that. They built an efficient, self-regulating water desalination system that runs on solar power alone with no need for batteries or a connection to the grid.

Probing the groundwaters

Oceans are the most obvious source of water for desalination. But they are a good option only for a small portion of people who live in coastal areas. Most of the global population—more or less 60 percent—lives farther than 100 kilometers from the coast, which makes using desalinated ocean water infeasible. So, Bessette and his team focused on groundwater instead.

“In terms of global demand, about 50 percent of low- to middle-income countries rely on groundwater,” Bessette says. This groundwater is trapped in underground reservoirs, abundant, and, in most places, present at depths below 300 meters. It comes mostly from the rain that penetrates the ground and fills empty spaces left by fractured rock formations. Sadly, as the rainwater seeps down it also picks up salts from the soil on its way. As a result, in New Mexico, for example, around 75 percent of groundwater is brackish, meaning less salty than seawater, but still too salty to drink.

Getting rid of the salt

We already have the ability to get the salt back out. “There are two broad categories within desalination technologies. The first is thermal and the other is based on using membranes,” Bessette explains.

Thermal desalination is something we figured out ages ago. You just boil the water and condense the steam, which leaves the salt behind. Boiling, however, needs lots of energy. Bringing 1 liter of room temperature water to 100° Celsius costs around 330 kilojoules of energy, assuming there’s no heat lost in the process. If you want a sense of how much energy that is, stop using your electric kettle for a month and see how your bill shrinks.

“So, around 100 years ago we developed reverse osmosis and electrodialysis, which are two membrane-based desalination technologies. This way, we reduced the power consumption by a factor of 10,” Bessette claims.

Reverse osmosis is a pressure-driven process; you push the water through a membrane that works like a very fine sieve that lets the molecules of water pass but stops other things like salts. Technologically advanced implementations of this idea are widely used at industrial facilities such as the Sydney Desalination Plant in Australia. Reverse osmosis today is the go-to technology when you want to desalinate water at scale. But it has its downsides.

“The issue is reverse osmosis requires a lot of pretreatment. We have to treat the water down to a pretty good quality, making sure the physical, chemical, or biological foul doesn’t end up on the membrane before we do the desalination process,” says Bessette. Another thing is that reverse osmosis relies on pressure, so it requires a steady supply of power to maintain this pressure, which is difficult to achieve in places where the grid is not reliable. Sensitivity to power fluctuations also makes it challenging to use with renewable energy sources like wind or solar. This is why to make their system work on solar energy alone, Bessette’s team went for electrodialysis.

Synching with the Sun

“Unlike reverse osmosis, electrodialysis is an electrically driven process,” Bessette says. The membranes are arranged in such a way that the water is not pushed through them but flows along them. On both sides of those membranes are positive and negative electrodes that create an electric field, which draws salt ions through the membranes and out of the water.

Off-grid desalination systems based on electrodialysis operate at constant power levels like toasters or other appliances, which means they require batteries to even out renewable energy’s fluctuations. Using batteries, in most cases, made them too expensive for the low-income communities that need them the most. Bessette and his colleagues solved that by designing a clever control system.

The two most important parameters in electrodialysis desalination are the flow rate of the water and the power you apply to the electrodes. To make the process efficient, you need to match those two. The advantage of electrodialysis is that it can operate at different power levels. When you have more available power, you can just pump more water through the system. When you have less power, you can slow the system down by reducing the water flow rate. You’ll produce less freshwater, but you won’t break anything this way.

Bessette’s team simplified the control down to two feedback loops. The first outer loop was tracking the power coming from the solar panels. On a sunny day, when the panels generated plenty of power, it fed more water into the system; when there was less power, it fed less water. The second inner loop tracked flow rate. When the flow rate was high, it applied more power to the electrodes; when it was low, it applied less power. The trick was to apply maximum available power while avoiding splitting the water into hydrogen and oxygen.

Once Bessette and his colleagues figured out the control system, they built a prototype desalination device. And it worked, with very little supervision, for half a year.

Water production at scale

Bessette’s prototype system, complete with solar panels, pumps, electronics, and an electrodialysis stack with all the electrodes and membranes, was compact enough to fit in a trailer. They took this trailer to the Brackish Groundwater National Research Facility in Alamogordo, New Mexico, and ran it for six months. On average, it desalinated around 5,000 liters of water per day—enough for a community of roughly 2,000 people.

“The nice thing with our technology is it is more of a control method. The concept can be scaled anywhere from this small community treatment system all the way to large-scale plants,” Bessette says. He said his team is now busy building an equivalent of a single water treatment train, a complete water desalination unit designed for big municipal water supplies. “Multiple such [systems] are implemented in such plants to increase the scale of water desalination process,” Bessette says. But he also thinks about small-scale solutions that can be fitted on a pickup truck and deployed rapidly in crisis scenarios like natural disasters.

“We’re also working on building a company. Me, two other staff engineers, and our professor. We’re really hoping to bring this technology to market and see that it reaches a lot of people. Our aim is to provide clean drinking water to folks in remote regions around the world,” Bessette says.

Nature Water, 2024. DOI: 10.1038/s44221-024-00314-6

Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.

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Despite stricter regulations, Europe has issues with tattoo ink ingredients

chemistry, Science, tattoo ink / Shannon Garcia / October 2, 2024

Swierk et al. use various methods, including Raman spectroscopy, nuclear magnetic resonance spectroscopy, and electron microscopy, to analyze a broad range of commonly used tattoo inks. This enables them to identify specific pigments and other ingredients in the various inks.

Earlier this year, Swierk’s team identified 45 out of 54 inks (90 percent) with major labeling discrepancies in the US. Allergic reactions to the pigments, especially red inks, have already been documented. For instance, a 2020 study found a connection between contact dermatitis and how tattoos degrade over time. But additives can also have adverse effects. More than half of the tested inks contained unlisted polyethylene glycol—repeated exposure could cause organ damage—and 15 of the inks contained a potential allergen called propylene glycol.

Meanwhile, across the pond…

That’s a major reason why the European Commission has recently begun to crack down on harmful chemicals in tattoo ink, including banning two widely used blue and green pigments (Pigment Blue 15 and Pigment Green 7), claiming they are often of low purity and can contain hazardous substances. (US regulations are less strict than those adopted by the EU.) Swierk’s team has now expanded its chemical analysis to include 10 different tattoo inks from five different manufacturers supplying the European market.

According to Swierk et al., nine of those 10 inks did not meet EU regulations; five simply failed to list all the components, but four contained prohibited ingredients. The other main finding was that Raman spectroscopy is not very reliable for figuring out which of three common structures of Pigment Blue 15 has been used. (Only one has been banned.) Different instruments failed to reliably distinguish between the three forms, so the authors concluded that the current ban on Pigment Blue 15 is simply unenforceable.

“There are regulations on the book that are not being complied with, at least in part because enforcement is lagging,” said Swierk. “Our work cannot determine whether the issues with inaccurate tattoo ink labeling is intentional or unintentional, but at a minimum, it highlights the need for manufacturers to adopt better manufacturing standards. At the same time, the regulations that are on the books need to be enforced and if they cannot be enforced, like we argue in the case of Pigment Blue 15, they need to be reevaluated.”

Analyst, 2024. DOI: 10.1039/D4AN00793J (About DOIs).

Despite stricter regulations, Europe has issues with tattoo ink ingredients Read More »