Scientists have unveiled a computational design for a terahertz metasurface biosensor that combines five distinct materials—graphene, MXene, tungsten disulfide, gold, and copper—into a single multilayer architecture capable of detecting refractive-index changes associated with chikungunya virus infection. The study, published in Results in Optics by G. Arunachalam, A.R. Kalaiarasi, Giri.G. Hallur, and V. Parthasarathy, reports a numerically predicted sensitivity of 907 GHz per refractive-index unit, among the highest values reported for hybrid-material terahertz biosensors, and couples the electromagnetic design to an XGBoost machine-learning surrogate model that predicts sensor behavior with accuracies exceeding 99.8 percent.

Chikungunya virus is an enveloped, positive-sense single-stranded RNA alphavirus transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes. While mortality remains low, generally below 0.1 percent, the broader public health burden arises from severe polyarthralgia that can persist for months or even years in a substantial fraction of patients across tropical and subtropical regions. With no approved antiviral therapy or licensed vaccine currently available, diagnostic accuracy sits at the center of clinical management and transmission control. Yet existing diagnostic tools face significant practical constraints, particularly in point-of-care and field settings.

Serological methods such as enzyme-linked immunosorbent assay suffer from cross-reactivity with related alphaviruses, including Ross River and O’nyong-nyong viruses, reducing diagnostic specificity. Real-time reverse transcription polymerase chain reaction offers high sensitivity during the acute phase but depends on laboratory infrastructure, trained personnel, and controlled sample handling. Virus isolation in cell culture provides confirmatory results but requires biosafety level-3 facilities and extended processing time. These limitations have motivated the search for rapid, label-free sensing approaches capable of operating at clinically relevant concentrations in decentralized environments.

The new work turns to the terahertz band, spanning roughly 0.1 to 10 THz, which lies between microwave and infrared regions of the electromagnetic spectrum. Terahertz radiation is non-ionising, with photon energies in the millielectronvolt range, allowing interaction with biological samples without causing ionising damage. Crucially, terahertz waves couple to low-frequency vibrational and rotational modes of biomolecules such as proteins, nucleic acids, and polysaccharides, producing measurable spectral features that support label-free detection. Because biological media including blood plasma and viral suspensions exhibit refractive-index variations in this domain, differences on the order of 0.01 to 0.02 refractive-index units can shift resonance frequency and field distribution when coupled to resonant sensing structures.

The proposed sensor is built around a periodically repeated square unit cell containing two identical square resonators, 2000 nanometers on a side, coated with tungsten disulfide—a two-dimensional transition metal dichalcogenide with strong light–matter interaction, high carrier mobility, and excellent dielectric confinement. This layer localizes the electric field in the sensing region and increases the interaction volume between the resonant field and the surrounding analyte. A pair of concentric circular rings, 3200 and 3800 nanometers in diameter and functionalized with MXene, surrounds the resonators, enhancing electromagnetic coupling, promoting efficient charge transport, and strengthening plasmonic interactions between resonator elements. An outer gold ring, 6000 nanometers in diameter, serves as the main plasmonic resonator supporting strong localized surface plasmon resonances with low optical loss. The entire multi-resonant assembly is embedded within a monolayer graphene sheet measuring 14,000 by 14,000 nanometers, which acts as a broadband absorber and a high-mobility charge transport medium whose electrically tunable chemical potential allows dynamic, active control of the resonance characteristics. Copper elements woven into the architecture provide supplementary conductive pathways that reinforce current distribution and coupling among the hybrid resonators. The structure rests on a silicon dioxide substrate, chosen for its low dielectric loss and mechanical robustness, which preserves the resonance quality factor.

The authors stress that the multilayer design is compatible with established microfabrication techniques. Fabrication would begin with a cleaned silicon dioxide substrate, followed by polymer-assisted transfer of monolayer graphene and thermal annealing. Gold and copper resonators can be deposited through electron-beam evaporation or magnetron sputtering with lift-off patterning, MXene rings through solution-based deposition, and the tungsten disulfide layer through chemical vapor deposition or thin-film transfer. With a unit-cell dimension of approximately 14 micrometers, the required feature sizes fall comfortably within conventional photolithography capabilities, and because fabrication imperfections remain far smaller than the operating terahertz wavelength, moderate tolerances are expected to have only limited influence on the electromagnetic response. For biosensing, the graphene surface could subsequently be functionalized with chikungunya-specific antibodies or aptamers using EDC/NHS or pyrene-based linker chemistries.

The electromagnetic modeling, performed in COMSOL Multiphysics, reveals a pronounced resonance at 0.355 THz, where electric-field simulations show the strongest and most spatially extensive enhancement. Varying the graphene chemical potential from 0.1 to 0.9 electronvolts produced dramatic modulation of the transmission contrast, which increased roughly 36-fold at the highest bias, from less than one percentage point to more than 27 percentage points, while peak transmission remained essentially unchanged above 98.6 percent. This asymmetric response—stable maxima paired with strongly modulated minima—arises because increasing chemical potential enhances graphene’s intraband conductivity, deepening resonant absorption through stronger light–matter interaction. The sensor also demonstrated remarkable angular robustness, maintaining peak transmittance above 97.8 percent across incident angles from 0 to 80 degrees, an important tolerance for realistic deployment where normal incidence cannot always be guaranteed.

Geometric optimization identified an outer circular resonator radius of 2500 nanometers and a square resonator side length of 2500 nanometers as the dimensions that maximize resonance strength, driving minimum transmittance down to approximately 65 to 67 percent and signifying optimal electromagnetic confinement within the active sensing region. When evaluated across refractive indices from 1.33 to 1.39, a range encompassing reported values for healthy plasma (approximately 1.35 RIU), healthy platelets (1.39 RIU), chikungunya-infected plasma (1.33 RIU), and infected platelets (1.38 RIU), the optimized configuration achieved a maximum sensitivity of 907 GHz/RIU, a figure of merit of 18.519 RIU⁻¹, a minimum detection limit of 0.061 RIU, a sensor resolution of 55.178, and a refractive-index resolution of 0.001 RIU. In comparative benchmarks against recently reported graphene- and hybrid-material-based terahertz biosensors—including graphene/copper/aluminum, graphene/silicon dioxide, MXene–graphene–black phosphorus, and graphene-integrated copper–silver designs—the proposed architecture’s sensitivity exceeded most published values, reflecting the synergistic field confinement produced by the five-material stack.

The machine-learning component addresses one of the central bottlenecks in metasurface development: the computational cost of repeated full-wave finite-element simulations during structural optimization. The team trained an XGBoost regressor, an ensemble method based on gradient-boosted decision trees, on simulation data covering incidence-angle variation and circular-ring dimension variation, using stratified sampling with 80 percent of data for training and 20 percent held out for independent testing, alongside five-fold cross-validation and grid-search hyperparameter optimization. The model captured more than 99.7 percent of response variance on unseen data, with mean absolute percentage errors below 0.162 percent and prediction accuracies from 99.838 to 99.959 percent. Acting as a computational surrogate, the trained model enables rapid interpolation across the design space without sacrificing the fidelity of the underlying electromagnetic model.

The authors are careful to frame the work as a computational proof-of-concept rather than an experimentally validated diagnostic. The sensor detects changes in the local dielectric environment surrounding the resonators, not viral particles or nucleic acids directly, and refractive-index sensing alone cannot intrinsically distinguish chikungunya from other viruses with similar dielectric properties. Analytical specificity in practice will depend on surface biofunctionalization with chikungunya-specific recognition molecules immobilized on the graphene or gold sensing surface. Future work will focus on device fabrication, biofunctionalization, calibration with reference refractive-index standards, experimental validation with clinically relevant plasma and platelet samples, and systematic evaluation of selectivity against related arboviruses—steps that would transform this numerically validated platform into a practical tool for rapid, label-free infectious disease diagnostics in the field.

A single gram of crushed oyster shell pulled in up to around 1.5 grams of rare earth metal, more than the shell’s own weight, out of water spiked with the kind of contamination you would expect from severe industrial pollution. A throwaway material, the sort of thing you might crunch underfoot on a beach, holding more than its mass in metals that the electronics and clean-energy industries fight over.

That’s the finding a Trinity College Dublin team reported in early 2026. Below, we walk through what they actually did, why oysters won and mussels and cockles fell short, and how much of this holds up once you leave the lab bench.

What the researchers actually did

The setup was low-tech at the front end. As reported in The University Times, the team collected oyster, mussel and cockle shells from beaches around Dublin, cleaned them, dried them, and crushed them into small grains. Then they dropped those grains into solutions carrying three rare earth elements and watched what happened over time. The three metals were lanthanum, neodymium and dysprosium, at concentrations chosen to mimic badly polluted water.

The chemistry underneath is where it gets interesting. Shells are mostly calcium carbonate, and in the rare-earth-rich water that calcium carbonate dissolves and is replaced, more or less on the spot, by new solid minerals built around the rare earth metals. In the peer-reviewed paper, published in Science of the Total Environment, the crushed shells were reacted with the metal-rich solutions across a wide range of temperatures, 25 to 205 degrees Celsius for up to three months. What you end up with is not the original shell soaking up metal like a sponge, but the shell being rebuilt, mineral by mineral, into something new.

As principal investigator Juan Diego Rodriguez-Blanco put it, “the process is entirely mineral-driven – the shells naturally transform dissolved rare earth elements into new solid minerals, so this isn’t a process that is difficult to drive, or one that requires much financial outlay or technical equipment.” That last part is a lab-based expectation rather than a proven cost sheet, but the appeal is easy to see: no exotic reagents, no elaborate rig, just waste shell and time.

Why oysters won and the others didn’t

All three shells are made of the same basic stuff, so why did oysters run away with it? The answer is structure. Oyster shell has a porous, layered microstructure, and that lets the dissolve-and-replace reaction work its way right through the grain rather than stalling at the surface. That’s how oyster grains reached uptake of up to roughly 1.5 grams per gram.

Mussels and cockles behaved differently, and the reason is more physical than chemical. A crust of new mineral formed quickly on the outside and then sealed the grain off, so the reaction couldn’t reach the inside. In those shells, the study reports that more than half of the original shell was left unchanged once that crust became impermeable. Same starting material, very different outcome, decided by how the shell is put together.

Why pull rare earths out of water at all

Rare earth elements are the unglamorous ingredients in a lot of modern hardware, from the magnets in wind turbines and electric motors to phone components. Mining them is expensive and messy, and industrial processing can leave behind runoff carrying dissolved metals. Two problems are tangled together here: recovering a valuable resource, and cleaning up water that carries it.

The shell angle is attractive partly because the raw material is a nuisance to begin with. As first author Rémi Rateau described it, “every year, the global aquaculture industry generates millions of tonnes of shell waste, much of which is discarded or sent to landfill.”  Rateau also noted that “relatively small amounts of shell waste could remove substantial quantities of rare earth metals from contaminated water.” 

What this is, and what it isn’t

This is one study, and it is a lab result. The concentrations were high by design, the conditions were controlled, and real industrial wastewater is a far messier soup of competing ions, organics and pH swings than a prepared solution in a flask. The team is upfront that the work still needs pilot-scale testing under genuine conditions before anyone talks about a deployable cleanup system. A promising lead is not a finished product, and this sits firmly in the former category.

Our read lands roughly where the team’s does. The measured uptake is striking, the input material is cheap and otherwise wasted, and the driving chemistry looks simple. Rodriguez-Blanco frames the ambition plainly: “we can start designing” low-cost strategies to remove critical metals from contaminated waters while giving new value to a major waste product. Start designing is the honest verb. On the strength of these numbers, it’s a lead worth taking out of the beaker and testing against the real, dirty water it was built to handle.

The post Researchers picked oyster, mussel and cockle shells off Irish beaches, crushed the 3 kinds of shell into grains, and dropped them into water carrying rare earth metals at concentrations similar to badly polluted industrial runoff. The oyster grains took up as much as roughly 1.5 grams of metal for every gram of shell. appeared first on Space Daily.

Attractive interactions between particles do not necessarily lead to these particles aggregating. This is the new finding from researchers at the Tokyo University of Science in Japan who say this behaviour comes from non-reciprocal interactions amongst particles of different sizes that exert unequal forces on each other. These interactions could serve as a general design principle for creating active matter with a structure that continuously reorganizes rather than simply relaxing towards a static state.

Nature abounds with examples of active matter, with some well-known examples being flocks of birds, fish and insects, sheets of biological cells and swarms of bacteria. Researchers have been trying to copy this collective behaviour and make synthetic active materials – such as self-propelled colloids and dense phases of mechanically driven biopolymers – in the laboratory. Before such applications see the light of day, however, they need to first understand the fundamental physics of these systems.

In their new study, a team led by Yutaka Sumino and Kiwamu Yoshii of Tokyo University of Science’s department of applied physics, came across a system in which colloidal particles interact through electrohydrodynamic flow. “We found that mixing particles of two different sizes in such a system completely changed the collective behaviour of these particles,” explains Sumino. “Instead of forming increasingly large crystal-like aggregates, as is the case for particles with the same size, the system remained highly dynamic.”

The physicists’ experiment involved suspending polystyrene colloidal particles with radii of 1 and 1.5 µm in water and confining them between transparent indium tin oxide-coated electrodes. This set up allowed them track more than 10,000 particles and quantitatively analyse their dynamics for more than an hour, as opposed to just a few minutes in previous such studies.

Newton’s third law holds

When the researchers applied an alternating electric field to the system, they observed electrohydrodynamic flows around the particles, the strength of which increased strongly as the size of the particles became bigger. The electrohydrodynamic-mediated attractive interactions therefore became asymmetric, they explain, something that causes larger particles to attract smaller ones more strongly. This imbalance leads to non-reciprocal interactions, meaning that a larger particle pushes a smaller one, but a smaller one doesn’t push back.

While the effective interaction between the particles appears to break Newton’s third law, it doesn’t because there is no violation of momentum conservation, explains Sumino: momentum is transferred to the surrounding fluid through the induced flows and is ultimately dissipated through friction with the substrate.

The researchers also observed that particles of different sizes spontaneously pair together to form asymmetric structures with a distinct front and tail. These pairs behave as self-propelled units and move through the suspension – even though individual particles cannot propel themselves. As more self-propelled pairs form, they assemble into larger clusters, but these clusters do not continue growing into large aggregates and instead repeatedly fragment, rearrange themselves and reform. Importantly, they note: “the larger particle tends to be at the front of these moving pairs. This head-heavy size asymmetry, together with excluded-volume interactions, promotes the fragmentation of larger clusters and thereby prevents continuous coarsening”.

Sumino and Yoshii combined their experiments with numerical simulations, thereby identifying non-reciprocal pair motion as the microscopic origin of this behaviour.

The results, they say, suggest that non-reciprocal interactions can serve as a general design principle for creating active materials with structures that continuously reorganize rather than simply relaxing toward a static state. “An interesting aspect,” explains Sumino, “is that self-propulsion does not need to be built into each individual particle: it can emerge collectively from non-reciprocal interactions between particles that do not self-propel on their own.”

If such interactions can be controlled externally, they could provide a way to design microscopic systems that collectively gather, transport, fragment or mix materials, he tells Physics World. “Possible directions include programmable active materials and microrobotic systems, although these applications are still some way off.”

Reporting their findings in Physical Review Letters, the researchers say they would now like to understand how general this non-reciprocal mechanism is and whether the same principle – collective activity emerging from non-reciprocal interactions – can be transferred to other experimental systems. In the system studied in this work, the strength of the non-reciprocity depends on parameters such as particle size, composition and the applied electric field. By systematically tuning these parameters, they aim to explore what other types of collective states can be generated and whether transitions between them can be controlled.

“A more detailed hydrodynamic analysis of the system is also needed to develop a quantitative understanding of the interactions and ultimately predict the collective motion of the colloids,” says Sumino.

The post Non-reciprocal interactions keep particles in collective motion appeared first on Physics World.

Concrete is the second most-used substance on Earth after water, and the cement that holds it together is one of the biggest headaches in climate policy.

Making cement means heating limestone until it breaks down, a process that accounts for around 8 percent of global CO2 emissions. And we are not slowing down. Concrete production is projected to climb from roughly 14 billion cubic metres a year toward 20 billion by mid-century. So anything that lets you use less cement per wall, without the wall getting weaker, is worth a close look.

That is the claim in a new paper out of India, and it comes with an unusual ingredient: human waste. A team turned treated sewage sludge into a fine black powder, swapped it in for a tenth of the cement, and got concrete that ended up harder to crush, not softer.

It’s one study, and an early-access version still subject to edits, so treat what follows as a promising result, not a settled fact.

Why cement is the part worth fixing

The problem with concrete is not the gravel or the sand or the water. It is the cement paste that binds them together. Estimates of cement’s climate footprint vary a bit depending on how you count, landing somewhere between 5 and 8 percent of global human-caused CO2 emissions each year. Most of that comes from the chemistry of making cement, not the fuel in the furnace. That is why switching to cleaner energy alone will not fix it.

One line of research has spent years asking whether you can replace some of that cement with biochar. Biochar is a carbon-rich char made by heating organic matter with very little oxygen. The appeal is twofold: you use less cement, and the carbon in the char, which the original plant or waste pulled out of the air, gets locked inside the building instead of released. The open question has always been whether the concrete survives the swap.

What the Warangal team actually did

The material here started at a sewage-sludge treatment plant in Warangal, in the Indian state of Telangana, a facility set up as a public-private partnership to tackle the city’s sewage problem. Human solid waste that would otherwise be dumped or burned gets processed there.

V Srinivas Chary, whose institution is a partner on the project, praised the operation, saying that “From the toilet to the final conversion of the biochar, the process is scientific and comprehensive.” 

The research team, led by civil engineer Raghuvesh Tiwari of Manipal University Jaipur with colleagues at Louisiana Tech University, took that sludge, dried it, and heated it to between 350 and 450 degrees Celsius with very little oxygen. That heating step drives off gases and leaves char behind. They ground the char into a powder, then replaced 5, 10, and 15 percent of the cement in test concrete with it and ran the usual checks: how well it resisted crushing and bending, how much it shrank, how much water it soaked up, how many gaps it had inside.

Dumped waste versus a carbon sink in the wall

The study sets up a pointed contrast. Normally a city’s sewage sludge is a liability to be disposed of, and a builder’s cement is a material whose production loads the atmosphere. Both are problems flowing toward waste and emissions. The first is bigger than you might think: a single person produces up to around 400 grams of faeces a day, which across a city becomes a constant stream that has to go somewhere.

The idea here is to route that stream into the wall. The waste replaces some of the cement, and the carbon in the char stays put instead of being burned off. It is a tidy story on paper: two problems that might cancel out a slice of each other. The caveat is that this study did not actually measure the carbon side of that ledger, so the climate benefit is still an argument rather than a number the paper delivered.

Why it got stronger, not weaker

The surprise is that adding a char to concrete made it tougher. The study reports this clearly for the middle dose. As the authors put it, “After a 91-day curing period, concrete with a 10% biochar substitution demonstrated a 21% increase in compressive strength and a 42% increase in flexural strength.” The 5 percent mix was close behind, gaining about 20 percent in crushing strength and 36 percent in bending strength over the same period. Those gains are measured against this study’s own plain concrete, not a universal benchmark.

There is a limit, though, and the study found it. The 15 percent mix did worse. Past a certain point, the char stops helping and simply dilutes the cement, a useful reminder that the good result here depends on getting the dose right. The authors’ own summary is careful: the results indicate that biochar at the 5 and 10 percent levels “yields significant improvements in concrete properties.”

The catch, and what still has to be proven

A strong lab result is not a paving slab. Several things stand between this and a real building site, and the paper is upfront about the biggest one. Sewage sludge can carry heavy metals, and whether those slowly leak out of the finished concrete over time is an open question. That is not something you can wave away when the material might end up in a school foundation or a water channel.

How long it lasts is the other unknown. The tests ran to 91 days in controlled conditions. Real structures face decades of freezing and thawing, wetting and drying, weight and vibration, and nobody has shown yet how this concrete holds up over that span. The researchers say themselves that more work is needed to assess how it performs under real-world conditions such as freeze-thaw cycles and extreme temperatures. 

What the study earns, we think, is attention rather than adoption. The explanation is plausible, the numbers are real for the mix that was tested, and the idea that a waste stream and a carbon-heavy material might each solve part of the other’s problem is worth chasing. 

The post Researchers took biochar made from human waste at a treatment plant in Warangal, India, ground it into a fine black powder and mixed it into concrete in place of a tenth of the cement. After 91 days the concrete was 21 percent harder to crush. appeared first on Space Daily.

Scientists led by the Universitat Politècnica de Barcelona and the ESRF, the European Synchrotron, have revealed the chemical reactions in nanoparticles that created a unique, shimmering effect in the painting on ninth-century Islamic ceramics. The results are published in Science Advances.

Scientists led by the Universitat Politècnica de Barcelona and the ESRF, the European Synchrotron, have revealed the chemical reactions in nanoparticles that created a unique, shimmering effect in the painting on ninth-century Islamic ceramics. The results are published in Science Advances.

A yeast-based material turns Mars’s hostile environment into part of the construction process.

My guest in this episode of the Physics World Weekly podcast is Marco Caffio, who is co-founder of iGii. The UK-based company has developed a porous 3D carbon nanomaterial called Gii, which it manufactures for a range of customers and applications.

Caffio describes Gii as a 3D version of graphene that delivers many of the useful electronic, structural and chemical properties of that 2D wonder material. Unlike graphene, which can be difficult to manufacture and integrate into devices, Caffio explains that Gii can be customized for use in practical technologies such as chemical sensors, batteries and heaters.

We also chat about the genesis of the company and Caffio offers career advice to physicists who are keen on working in the materials-technology sector.

The post Porous material offers the benefits of graphene in 3D appeared first on Physics World.

Nickel disulfide, NiS₂, is an unusual material. Its interior behaves as an electrical insulator, blocking the flow of current, while certain parts of its surface conduct electricity freely. This contradiction has puzzled physicists for decades, and a recent study offers a detailed explanation. The conduction, it turns out, is confined to tiny one-dimensional steps on the surface, and these narrow conducting channels are a direct consequence of how electrons are arranged inside the crystal.

Mott insulator

NiS₂ shares its crystal structure with pyrite, the mineral sometimes called fool’s gold. At ordinary conditions, its electrons do not move freely through the lattice: the strong electrical repulsion between them opens an energy gap that keeps the bulk of the material insulating. This behaviour defines what physicists call a Mott, or charge-transfer, insulator, a category of materials that simple band theory cannot explain. Band theory predicts that any material with a partially filled outer electron shell should conduct electricity, yet compounds like nickel oxide obstinately insulate instead. In 1949, the physicist Nevill Mott showed why: if two electrons crowding the same atomic site cost more energy than is available, the electrons stay locked in place and no current flows, regardless of what band theory predicts. NiS₂ behaves in much the same way.

Yet electrical-transport measurements had repeatedly found that crystals of NiS₂ conduct through their surfaces. Earlier scanning-tunnelling experiments helped explain part of the puzzle: the broad, flat surface remains insulating, but the electronic gap narrows sharply near atomic-scale steps, tiny cliffs just one or two atoms high where the surface abruptly changes level. A new study ¹ confirms this picture and examines the steps with much higher spatial resolution than before.

A not that smooth surface

A scanning tunnelling microscope (STM) works by bringing an extremely sharp needle close enough to a surface that electrons can leak across the gap between tip and sample. Measuring that leakage at different energies reveals both the surface’s shape and how easily electrons can enter or leave it. In NiS₂, these measurements uncovered electronic states concentrated tightly along the step edges: the states extend for a long distance parallel to a step but stay confined to roughly one to two nanometres across it. In other words, the electrons are effectively free to move in one direction while remaining trapped in the other two, forming genuine one-dimensional conduction channels.

Two distinct kinds of surface step were observed, depending on whether the outermost atomic layer exposes nickel or sulfur atoms. Both carry electronic states associated with their steps, but they are not equally important. The nickel-terminated steps host states that sit right at the energy where electrical conduction happens, making them the most likely explanation for the surface conductivity that transport experiments had measured for years. The sulfur-terminated steps also host states inside the insulating gap, but their energy is positioned further away, making them less directly responsible for carrying current.

The study also tested what happens when a magnetic field is applied perpendicular to the surface. The step-edge states survived fields as strong as 10 tesla, a field far stronger than any produced by a laboratory magnet used for everyday purposes. Their intensity weakened somewhat, particularly on the sulfur-terminated steps, but the states were never destroyed. This robustness matters because NiS₂ already displays complicated magnetic behaviour of its own, which might easily have disrupted a more fragile conducting state.

The deeper explanation lies in how electrons are distributed inside the crystal. In an ordinary insulator, the occupied electronic states can usually be pictured as clouds centred on the atoms themselves. NiS₂ is different: calculations show that part of its electron density is naturally centred at special positions between atoms, specifically near the midpoints of pairs of sulfur atoms, where no atom actually sits. Physicists call these obstructed charge centres, and materials built around them belong to a class known as obstructed atomic insulators, a concept that grew out of a broader effort over the past decade to classify materials by the geometry, and not just the energy, of their electron states.

Not ordinary metallic defects

This arrangement is not a chemical accident; it is protected by the symmetry of the crystal. When the crystal is cut to form a surface, though, the special positions that hosted this electron density can no longer fit together the way they did in the bulk. At a step edge, this mismatch creates what is known as a filling anomaly: an imbalance in how the available electronic states can be occupied, which leaves behind a state inside the insulating gap, localized right at the edge. Calculations of artificial step structures reproduce the main features seen under the microscope, including this localization, supporting the idea that the conducting channels are not ordinary metallic defects caused by broken chemical bonds, but a direct consequence of the crystal’s underlying electronic geometry.

The study also settles a long-standing question about NiS₂’s magnetism at low temperature. Below about 39 kelvin, the nickel magnetic moments arrange themselves into a non-collinear antiferromagnetic pattern, with neighbouring moments pointing in different directions that largely cancel out. Below about 30 kelvin, they rearrange again into a state that produces a small but measurable net magnetization. New neutron-diffraction measurements support a revised model of this low-temperature arrangement, resolving a debate about the material’s magnetic ground state that had lasted for roughly fifty years.

Taken together, the results give NiS₂ a significance well beyond its peculiar conducting surface. The material shows that strong repulsion between electrons, magnetism, and the geometry of electronic states can coexist within a single crystal. Such geometric protection is normally associated with topological materials, in which certain electronic states are shielded from disorder or defects by the crystal’s symmetry. The new results suggest that this protection can survive even when strong interactions push a material into being an insulator, making NiS₂ a rare setting for studying how the quantum-mechanical arrangement of electrons decides where electricity is allowed to flow within an otherwise insulating crystal.

Author: César Tomé López is a science writer and the editor of Mapping Ignorance

Disclaimer: Parts of this article may have been copied verbatim or almost verbatim from the referenced research paper/s.

The post Why an insulator can conduct electricity along its edges appeared first on Mapping Ignorance.

In a development that could reshape how chemists recycle one of the most persistent classes of synthetic molecules ever made, researchers have reported a new catalytic strategy that strips fluorine atoms from perfluoroalkyl chains in a controlled, sequential fashion while installing a single boron group at the chain’s terminus. The work, published in Nature Communications, introduces what the authors call zipper polydefluorination-monoborylation, a transformation that walks down a perfluoroalkyl skeleton and removes multiple fluorine atoms in a stepwise cascade before capping the partially defluorinated product with a boron substituent. The achievement addresses a longstanding challenge in fluorine chemistry: while carbon-fluorine bonds are prized in materials and pharmaceuticals for their extraordinary stability, that same stability makes them notoriously difficult to break selectively, leaving chemists with few tools for converting perfluorinated waste streams into useful building blocks.

Perfluoroalkyl substances, often grouped under the umbrella of PFAS chemistry, owe their remarkable properties to the strength of the carbon-fluorine bond, which at roughly 485 kilojoules per mole in fully fluorinated chains ranks among the strongest single bonds that carbon forms. This bond strength, combined with the sheer electronegativity of fluorine, means that perfluoroalkyl groups resist oxidation, hydrolysis, and thermal degradation under nearly all conventional conditions. As a consequence, perfluorinated chains accumulate in the environment and resist standard degradation pathways, prompting intensive research into defluorination methods ranging from photocatalytic single-electron transfer to reductive hydrodefluorination with metal hydrides. Yet most existing approaches suffer from a common limitation: they either remove fluorine indiscriminately, collapsing the entire chain to a mixture of products, or they remove only a single fluorine atom, offering little control over the degree of defluorination. The new study demonstrates a way to achieve the best of both worlds, delivering multi-fluorine removal in a predictable pattern while simultaneously introducing a versatile functional handle.

The conceptual heart of the method lies in what the authors describe as a zipper mechanism. Rather than removing fluorine atoms at random positions along the chain, the reaction initiates at a defined site and then propagates along the perfluoroalkyl backbone one carbon at a time, much as a zipper opens tooth by tooth. At each step along the chain, a fluorine atom is expelled and replaced in sequence, with the reaction front advancing until a thermodynamic or kinetic stopping point is reached. The monoborylation component of the process ensures that once the zipper has run its course, the resulting olefinic or anionic intermediate is intercepted by a boron reagent, furnishing a product in which the boron group occupies a predictable position derived from the original perfluoroalkyl terminus. Organoboron compounds are among the most valuable intermediates in modern synthetic chemistry, serving as partners in Suzuki-Miyaura cross-coupling and as precursors to alcohols, amines, and halides, so their installation at a defluorination site effectively converts a chemical dead end into a synthetic launching pad.

Mechanistically, the transformation draws on the characteristic reactivity of organoboron reagents toward geminal difluoroalkenes, the partially defluorinated intermediates that arise when consecutive fluorine atoms are eliminated from a perfluoroalkyl chain. Perfluoroalkyl chains, when subjected to strong bases or reductive conditions, can undergo sequential beta-fluoride elimination events, each generating a more highly unsaturated species. The boron reagent in the reported system engages these unsaturated intermediates through addition pathways that install boron at the terminal carbon while generating a carbanionic center adjacent to the remaining difluoromethylene unit. That newly formed carbanion is perfectly positioned to expel another fluoride ion, regenerating an unsaturated handle one carbon further down the chain and setting up the next iteration of the cycle. This intimate coupling of borylation and defluorination is what gives the reaction its chain-walking character: each borylation event creates the conditions for the next defluorination event, and the process ripples along the chain until the fluorine reservoir is exhausted or the reagents are consumed.

The practical significance of the work becomes apparent when one considers the fate of the fluorine atoms themselves. In the zipper process, fluorine is released as fluoride ion, which under the reaction conditions is sequestered by silicon-containing trapping agents to form robust silicon-fluorine bonds. Fluorosilicates of this kind are stable, isolable, and, importantly, compatible with industrial processes for recycling fluorine back into hydrofluoric acid, the feedstock from which essentially all synthetic organofluorine compounds are made. In this sense, the method does more than transform perfluoroalkyl chains into borylated products; it also lays the groundwork for closing the fluorine cycle, recovering the fluorine content of persistent molecules in a form that can be fed back into the chemical economy. With global concern over PFAS contamination intensifying and regulatory pressure on fluorinated chemicals mounting, technologies that enable fluorine recovery rather than dilution into the environment carry considerable weight.

From a synthetic chemistry standpoint, the products of the reaction open multiple downstream avenues. Because the boron substituent is installed at a defined position on a partially fluorinated alkyl or alkenyl framework, the resulting molecules retain a programmable mixture of carbon-fluorine bonds and carbon-boron functionality. The remaining fluorine atoms can tune the lipophilicity, metabolic stability, and dipole moment of the scaffold, properties that are actively exploited in medicinal chemistry when designing fluorinated drug candidates. Meanwhile, the boron group serves as a convertible handle, allowing the defluorinated carbon center to be joined to aromatic rings through cross-coupling, oxidized to alcohols, or aminated in homologation reactions. In effect, the method converts a chemically inert perfluoroalkyl group, useful mainly as a passive coating or tail, into a functionalized partial-fluoro skeleton that can participate in the full toolkit of carbon-carbon and carbon-heteroatom bond formation.

The reported study also sheds light on the factors governing how far the zipper travels along a given chain. Chain length, the nature of the substituent anchoring the perfluoroalkyl group, and the stoichiometry of the base and boron reagent all influence the number of fluorine atoms removed and the distribution of products obtained. Through systematic variation of these parameters and careful analysis of the reaction mixtures by nuclear magnetic resonance spectroscopy and mass spectrometry, the authors map out the scope of the transformation across a range of perfluoroalkyl substrates, from short perfluoroethyl groups to longer chains approaching those found in commercial fluorosurfactants. Control experiments interrogating individual elementary steps support the proposed sequential elimination-addition mechanism and rule out alternative pathways involving radical fragmentation or random beta-scission, underscoring the unusually high degree of positional control the method achieves.

Beyond its immediate synthetic utility, the work contributes to a growing body of research aimed at taming the carbon-fluorine bond through the strategy of defluorinative functionalization. Over the past decade, chemists have developed an impressive repertoire of reactions that replace fluorine in perfluoroalkyl and fluoroarene substrates with groups ranging from hydrogen to sulfur, nitrogen, and carbon substituents. What distinguishes the zipper approach is its multiplicity and its directionality: instead of a single substitution event at a single site, the reaction performs many substitutions in a choreographed sequence along a chain, effectively treating the perfluoroalkyl group as a one-dimensional lattice to be patterned at will. This conceptual reframing, from defluorination as bond-breaking to defluorination as programmable editing, may inspire analogous strategies for other polyfluorinated motifs, including perfluoroarenes and perfluoropolyethers, two additional classes of highly persistent fluorinated materials.

Challenges remain before such chemistry can move from the laboratory bench to environmental remediation at scale. The reaction conditions reported rely on strong bases and moisture-sensitive boron reagents handled under inert atmosphere, and the substrates studied are discrete, soluble perfluoroalkyl compounds rather than the polymeric or adsorbed PFAS species that dominate environmental contamination. Scaling the chemistry will require sourcing boron reagents economically, managing the large quantities of fluoride generated, and integrating the transformation with upstream methods for extracting perfluoroalkyl pollutants from water and soil. Nevertheless, the demonstration that a perfluoroalkyl chain can be unzipped in a controlled manner, with fluorine captured in recyclable form and a valuable boron handle installed, establishes a credible chemical pathway toward defluorination that is both productive and selective, a combination that has eluded the field for decades.

As policymakers and scientists grapple with the legacy of fluorine chemistry, work of this kind illustrates a middle path between the wholesale abandonment of fluorinated molecules and their indefinite persistence in the biosphere. The fluorine atom confers properties that industry and medicine continue to depend upon, and the ability to disassemble fluorinated architectures on demand, recovering both the carbon skeleton as a functionalized building block and the fluorine content as a recyclable salt, points toward a more circular future for organofluorine chemistry. The zipper polydefluorination-monoborylation strategy reported in Nature Communications is an early but striking example of that vision made concrete at the molecular level, and it is likely to prompt rapid efforts to extend the concept across the breadth of persistent fluorinated chemicals.

The Metropolitan Transportation Authority, which runs the New York City subway system, had a problem in the late 1990s. It was in the middle of a major fleet modernisation programme that was going to retire roughly two and a half thousand ageing subway cars over the following decade. These were mostly the red-painted R-33 and R-36 cars that generations of New Yorkers had ridden through the 1970s, 80s and 90s, followed by the older stainless steel Brightliners that would come off the tracks later. Each retired car was worth essentially nothing as scrap. Each also cost the MTA roughly twelve thousand dollars to dispose of through conventional demolition. Which meant the total disposal bill for the fleet retirement, at prevailing rates, was going to run to something north of thirty million dollars. And the MTA, being a public transit authority in a permanent state of budget crisis, was not enthusiastic about that particular expense.

The solution the agency arrived at, in partnership with a handful of coastal state governments and the U.S. Fish and Wildlife Service, was one of the more counterintuitive recycling programmes of the early twenty-first century. Instead of paying to demolish the cars, the MTA would clean them, ship them south by rail and barge, and drop them into the ocean off the eastern seaboard. There they would form artificial reefs. The states would get new marine habitat for essentially free. The MTA would save the disposal costs. And the fish would, in theory, work out what to do with the rest.

How you turn a subway car into a reef

According to the New York Transit Museum’s own summary of the MTA Artificial Reefing Program, produced in collaboration with the programme’s former director Michael Zacchea and Robert Martore of the South Carolina Department of Natural Resources, the operation ran from August 2001 through to April 2010 and deployed more than 2,500 deaccessioned train cars to underwater sites off the coasts of New Jersey, Delaware, Virginia, South Carolina, and Georgia. The first phase concentrated on the Redbird fleet, which was already being pulled off the tracks in 2001, and which had a particularly recognisable red livery that made the sunken cars a photographable subject long after they had gone down. The Delaware Bay took approximately six hundred and nineteen Redbird cars alone, at a site now known as the Redbird Reef, located sixteen and a half nautical miles off Indian River Inlet at a depth of around eighty feet. Subsequent phases involved the stainless steel Brightliner fleet, which was deployed at reef sites further down the coast through the second half of the decade.

The engineering of the actual reef deployment was not trivial. Each car had to be stripped down first. According to the New Jersey Division of Fish and Wildlife’s own news bulletin on the deployment of 44 stainless steel subway cars at the Atlantic City Reef site in April 2008, every car went through a full preparation process before it went into the water. Windows were removed. Wiring was pulled out. Plastic components, degradable materials, hydraulic fluids, oils, and grease were all stripped or drained. The remaining shell was inspected to make sure that when the car eventually corroded, nothing toxic would leach into the surrounding marine environment. Only after that inspection was the cleaned steel body loaded onto a barge and towed offshore.

The actual sinking process was almost comically straightforward. The cars, weighing around eighteen tonnes each in their prepared state, were rolled off the deck of the barge by a hydraulic tipping mechanism and simply dropped through the water column to the seabed below. The MTA covered all of the cleaning, transport, and deployment costs. Individual cars in the New Jersey deployment measured roughly sixty feet long, ten feet wide, and eleven feet tall. Deployed in tight clusters at pre-selected coordinates, they formed roughly the same kind of hard-structure habitat that a natural rocky reef would offer, but at a scale and geometry that had never previously existed on the sandy Atlantic continental shelf.

What the fish did with them

What happened next surprised the marine biologists monitoring the sites, though it probably shouldn’t have. The subway car reefs, unlike almost any natural feature of the mid-Atlantic seabed, offered vertical structure. They offered cavities and shelter. They offered hard surfaces for sessile organisms to colonise. And they were essentially unlimited in supply. Marine invertebrates began settling on the exposed steel within weeks. Barnacles arrived. Blue mussels followed. Sponges and soft corals began to establish themselves on the vertical surfaces. Within a year or two, the once-bare metal shells of the retired subway cars had become the physical scaffolding of thriving benthic communities that had not existed anywhere on that stretch of ocean floor beforehand.

The fish arrived in response. Delaware’s Department of Natural Resources and Environmental Control has since documented that the invertebrate communities colonising the artificial reef structures provide up to four hundred times more food per square foot than the bare sandy ocean floor they replaced. Species that had been effectively absent from the region because of the lack of suitable habitat began to appear regularly at the sites. Sea bass, tautog, tuna, mackerel, flounder, scup, and triggerfish were all documented in significant numbers within a few years of the deployments. Recreational fishing operators in the coastal towns of Delaware, New Jersey, and Virginia found their nearshore catches rising. Dive operators found themselves with a genuinely unusual attraction to offer. The sunken subway cars, which had cost the MTA nothing to dispose of and had cost the states essentially nothing to acquire, became one of the more productive artificial reef complexes anywhere on the North American Atlantic coast.

The programme was not without complications. Inspection reports from New Jersey in 2009 found that some of the newer stainless steel subway cars were showing significant structural damage after only a few years underwater, which prompted the state to pause further stainless steel deployments while investigations continued. Not every car remained intact. Not every deployment site delivered the ecological returns the biologists had hoped for. And the specific question of whether artificial reefs simply concentrate existing fish populations rather than creating new ones is still debated within the marine biology community. But the general pattern held across the majority of the deployment sites through the 2010s and 2020s. The bare sand became structured habitat. The structured habitat became invertebrate communities. The invertebrate communities became feeding grounds. And the feeding grounds became fisheries.

By the time the programme officially ended on Earth Day 2010, 2,580 New York subway cars had been placed on ocean reef sites along the eastern seaboard of the United States. The MTA had saved something close to thirty million dollars in disposal costs. Delaware alone had received nearly a thousand of them. The Redbird Reef off Slaughter Beach now covers roughly 1.3 square miles of what used to be featureless sand and is one of the most biologically productive stretches of continental shelf in the entire mid-Atlantic region. Which is a strange kind of legacy for a fleet of subway trains that once carried millions of people through the tunnels underneath Manhattan and Queens. The trains never made it to the recycling yard. They made it to the ocean floor instead. And the fish have been living in them ever since.

The post More than 2,500 retired New York subway cars were dropped into the Atlantic between 2001 and 2010, not as illegal dumping but as a planned reef programme, and marine biologists who kept watch found the sunken trains quickly turned into some of the richest artificial habitats along the eastern seaboard. appeared first on Space Daily.

Since the discovery of graphene over two decades ago now, two-dimensional (2D) materials have revolutionized almost all areas of science and technology thanks to their unique properties compared with bulk materials. These include high electronic conductivity, high mechanical strength, transparency and flexibility, to name just a few. The problem since the beginning, however, has been to produce sheets of these materials large enough for real-world applications and, importantly, to be able to transfer them onto other substrates without cracking the sheets. A team of researchers in Amsterdam, the Netherlands, has now succeeded in doing just this, with the help of an unexpected material – kitchen cling film. Their work could help in the continuing development of next-generation electronic and optoelectronic devices.

“The method we developed allows us to, for the first time, pick up, transfer and place large (roughly 1-mm-sized) 2D layers on almost arbitrarily patterned surfaces,” explains Jorik van de Groep of the 2D Nanophotonics group at the UvA-Institute of Physics, who led this research study. “Being able to do this is crucial since it enables the integration of 2D materials with structures like larger electronic devices and photonic coatings. Most importantly, the transfer is no longer probabilistic (as were most other methods) but has a near-unity yield.”

In the early days of 2D materials, researchers obtained micron-sized mono- or multi-layers of these structures by mechanically shaving off, or exfoliating, flakes from the bulk material using sticky tape. This was first famously done for graphene, a sheet of carbon just one atom thick. More recently, a technique known as gold-assisted exfoliation has allowed them to produce high-quality centimetre-sized layers of technologically important materials like transition-metal dichalcogenides (TMDCs) and transfer these onto flat glass surfaces.

For the field of nanophotonics in particular, explains van de Groep, we need to be able to transfer large-area 2D materials onto both flat and patterned substrates – such as those with electrical contacts and optical coatings on them, for example – if we are to fabricate functional devices. The problem is that existing transfer techniques are limited in this respect.

Kitchen cling film to the rescue

The Amsterdam team – which also includes researchers from UvA’s Van ‘t Hoff Institute for Molecular Sciences, ARCNL and AMOLF – has now developed a simple method that allows them to reliably transfer both large-area monolayers of TMDCs and hexagonal boron nitride/monolayer heterostructures onto patterned or non-patterned substrates, ranging from flat surfaces to high-aspect ratio and low adhesion patterned interfaces. In their process, which is detailed in ACS Nano, they used low-density polyethylene (LDPE), or kitchen cling film, an inexpensive and widely available polymer that has a low melting temperature.

In their work, the researchers transferred a gold-assisted-exfoliated large-area monolayer of the TMDC tungsten disulphide (WS₂) from a silica (SiO₂) substrate to another target SiO₂ substrate. They began by fabricating a stamp made of a heat-resistant half-sphere covered by LDPE cling film. They then mounted the stamp on an xyz-micron precision stage and moved it slowly towards the WS₂ monolayer, which was heated to 70 °C, at a speed of 0.5 µm/s until it contacted with the LPDE.

“We used force sensors in the stage to measure the forces involved during the stamping procedure, both in the plane of the 2D material (Fx and Fy) and perpendicular to it (Fz),” explains van de Groep. “This not only offers better control and repeatability of the transfer, it also provides crucial information on the contact and friction dynamics throughout the process.”

During initial contact with the substrate, the normal force (Fz) increases to 120 mN, at which point the researchers stop moving the stamp. Once it has contacted the monolayer, they heat the system to 140 °C. This induces a phase transition at which the LDPE melts, so allowing it to strongly adhere to the monolayer. They then cool the ensemble back down to 70 °C to solidify the LDPE. Finally, they pull off the monolayer from the LPDE with the stage moving at 0.5 µm/s and clean it to remove any polymer residue.

Material retains its good photoluminescence properties

To assess how the transfer process affects the monolayer, the researchers imaged it before and after the procedure. Before transfer, cracks covered 8% of the material. This figure increased to 14% after, with the cracks mainly generated at the edge of the stamp contact area. “As such, the procedure only modestly increases the cracked area fraction and largely preserves the monolayer topography,” says van de Groep. “More importantly, the material retains its good photoluminescence properties.”

The new work could help 2D materials scientists working in a variety of different fields to build larger and more complex devices. “Already, we are using it to develop atomically thin optical elements, optical modulators, single-photon emitters and other optoelectronic devices,” van de Groep tells Physics World. “Also, and more fundamentally, the method we have developed could allow for the fabrication of complex heterostructures of interest for quantum materials.”

The Amsterdam team is now busy optimizing its method further by, for example, building a humidity-controlled environmental enclosure around the stamping setup. “2D materials and the (van-der-Waals) adhesion between them strongly depends on the surface chemistry and, as such, on the relative humidity during the stamping procedure,” explains van de Groep. “We’re also working on additional methods to characterize the thickness of the materials in situ, that is, during the stamping process.”

The post Cling film helps stamp two-dimensional materials onto patterned surfaces appeared first on Physics World.

A recycling law coming into force now could change fashion.

© Jonathan Nackstrand/Agence France-Presse — Getty Images

A recycling law coming into force now could change fashion.

The reagents of the feedstock are never produced by processes as on the early Earth. Production requires substantial energy and controlled industrial procedures

Source

Researchers at Nagoya University have built a graphene nanoribbon that can switch which way it twists using a natural solvent. Graphene nanoribbons are thin ribbon-shaped structures made of fused carbon rings. Twisted or helical versions of these ribbons show promise for advanced light and electronic devices. However, no graphene nanoribbon could switch that twist on demand, until now.

Scientists have worked out how to switch between a right-handed and left-handed twist (chirality) by changing the solvent around it. The discovery ¹ opens opportunities for new optical switches, chemical sensors, and spintronic components that adapt to changing environments.

Tomoyuki Ikai, lead author and professor at Nagoya University’s Graduate School of Engineering, is a polymer chemist inspired by natural helical structures such as DNA and proteins. Polymers are large molecules built from many small, repeating units linked together in a chain. Ikai had been working on ladder polymers, where each repeating unit is locked into place and cannot freely rotate around the bond connecting to its neighbor (unlike a typical flexible linear polymer).

In 2019, Ikai and his collaborators built the first rigid, helix-shaped polymer. In 2021, they perfected a chemical method to fuse these building blocks together without flaws. This method is what let them build the new graphene nanoribbon.

“We used the same fusion approach already used to make predictable helical ladder polymers. But instead of a stable building block, such as [6]helicene, we used [4]helicene, a 4-ring unit written off as too unstable to be useful,” Ikai said.

Soak, twist, repeat

These units are difficult to control on their own because they switch their chirality too fast to hold one handedness. The team’s method fuses these small, restless units into one long chain. Once joined, they found that a neighbor effect took hold: each unit’s twist began to match its neighbors, and long stretches of the ribbon settled into a single, shared spiral.

To lock it in one overall direction, the researchers dissolved the ribbon in a natural chiral liquid, a liquid made of molecules that come in two mirror-image versions. They tested six candidates before they found the right one: beta-pinene, a compound found in pine trees and citrus peel.

Because beta-pinene molecules can be arranged in left- and right-hand mirror-images, these two versions each push the ribbon toward the opposite spiral. This also changed the twist direction of light the ribbon gave off, a property called circularly polarized luminescence, and is the first graphene nanoribbon shown to switch its light this way.

The switching induced a remarkably high degree of helical bias, with almost all of the helicene units aligning in the same direction. The switching effect is strongest at –90°C and grows weaker as the temperature rises toward room temperature.

“For a long time, people saw [4]helicene as unsuitable for chiral materials, because it could not be controlled,” Ikai said. “In this paper, we show that once you link enough of these units together, the instability itself becomes the useful part.”

A chiral solvent’s nudge toward one handedness is usually very weak on its own. Here, the ribbon’s own structure, with each unit mechanically linked to its neighbors, amplifies that weak nudge into a strong, nearly one-handed result.

An adaptive material

The researchers point to several possible future uses: The switchable light could serve optical devices. The ribbon’s chemical sensitivity to beta-pinene suggests it may work as a chiral sensor, and a similar design could one day help detect hazardous or unstable chemicals. Because graphene conducts electricity well, the ribbon may also suit electronic sensors.

The molecule’s twisted shape connects to spintronics, a field that uses the spin of electrons rather than just their charge. Ikai noted that a right-handed or left-handed structure can, in principle, let electrons of one spin pass through more easily than the other, a property helical structures are known for in physics literature.

The current design only holds its twist while it stays in the chiral liquid. If the solvent is removed, the ribbon drifts back to a mixed, unstable state. Ikai’s next goal is a form of “chiral memory,” a way for the ribbon to lock in its twist even after the solvent is gone. This next step builds on memory techniques the researchers have explored in other helical systems and is now applied to graphene for the first time.

The post First switchable graphene nanoribbon that twists on demand appeared first on Mapping Ignorance.

Around the world, the demand for cleaner alternatives to petroleum-based jet fuel is rising.

By 2030, the European Union will require a minimum sustainable aviation fuel (SAF) blend of 6 percent, which will rise to 70 percent by 2050. Countries like the United Kingdom, Singapore, Japan, and Brazil are instituting similar policies, putting pressure on players in the global energy trade to ease reliance on crude oil.

SAF can come from all kinds of recycled waste byproducts like plant material, animal fat, and used cooking oil — the latter of which has already become a major source for existing SAF supplies. Unfortunately, the flow of extra spent fry oil is already slowing to a trickle as refiners swoop in to secure the gloop.

That’s where Chinese company Niutech comes in. In a new press release, first spotted by Interesting Engineering, Niutech announced a massive contract with an anonymous “global energy major” to build out an “industrial continuous waste plastic pyrolysis production line” capable of churning out 10,000 to 50,000 tons of plastic-derived SAF each year.

That might seem like a lot to unpack, but it’s really pretty simple. Basically, the Chinese firm is announcing the development of a massive supply line that turns plastic garbage into usable jet fuel. It plans to do so using a thermal decomposition process called pyrolysis, in which plastic waste is heated to extraordinary temperatures in an oxygen-free environment.

Though it isn’t new, pyrolysis remains something of a niche for the industrial-grade plastics-recycling space. For this approach to meet the growing need for SAF, it first has to graduate beyond the realm of small eco-startups into a widely-accepted industry standard — which appears to be Niutech’s goal.

Unlike previous SAF initiatives involving plastics, this particular production line will all be under one roof, cutting down on the need for costly shipping and handling. The Niutech refinery is also said to make use of a smorgasbord of plastics like polyethylene, nylon, polypropylene, and ABS, all “without complex pre-treatment such as washing, sorting or drying” — streamlining the complex process of sorting plastic and converting it to refinable oil at this kind of scale.

Should Niutech and its anonymous industry partner succeed in bringing the system online, it would undoubtedly serve as a constant source of plastics-based SAF for the global aviation industry, and as a role model for other refineries to follow.

“Large-scale pyrolysis projects impose stringent requirements on continuous operational capability,” a Niutech spokesperson said in the company’s press release. “Niutech has focused on pyrolysis technology for nearly 40 years and brings mature equipment and extensive project experience. This partnership is another validation of the strength of our industrial continuous technology.”

More on China: American Tech Companies Are Suddenly Sweating Bullets as China Catches Up on AI

The post China Installing Huge Facility That Turns Plastic Waste Into Jet Fuel appeared first on Futurism.

 

Arsenic contamination in drinking water poses a critical global public health hazard. Prolonged exposure to inorganic arsenic—predominantly present in groundwater as arsenate, where arsenic exists in its +5 oxidation state—can lead to severe dermatological lesions, cardiovascular diseases, and cancers. To mitigate these health risks, the World Health Organization has established a strict provisional safety guideline of 10 micrograms of total arsenic per liter of drinking water. Because arsenic occurs naturally through the weathering of rocks and minerals in aquifers worldwide, engineering low-cost, scalable, and highly efficient materials for water purification remains a central goal in modern materials chemistry.

Iron-based compounds, particularly iron oxyhydroxides, are among the most effective materials for trapping arsenate. At a fundamental chemical level, arsenate ions readily substitute for surface hydroxyl groups on iron oxyhydroxides, forming strong chemical bonds that permanently anchor the contaminant to the solid surface. However, translating this surface chemistry into practical filters presents a persistent engineering hurdle: maximizing the amount of active iron exposed to water. Simply increasing the iron concentration during material synthesis causes iron nanoparticles to aggregate into large, dense clusters. As these clusters grow, much of the iron becomes buried within the interior bulk, leaving only a tiny fraction accessible at the surface to bind arsenate.

A promising design strategy ¹ overcomes this limitation by decoupling the nucleation of iron particles from their subsequent growth on a flexible, high-surface-area polymer matrix. The foundation of this system is a composite fibrous membrane fabricated from poly(vinyl alcohol) and pectin via electrospinning. In electrospinning, a high-voltage electric field draws a liquid polymer mixture into ultra-fine threads, which solidify into an interconnected, highly porous mesh of nanofibers. Poly(vinyl alcohol) provides structural integrity and water stability upon heat treatment, while pectin—a natural polysaccharide rich in carboxyl and hydroxyl functional groups—serves as a molecular anchor capable of capturing iron ions from solution.

To grow high-density nanostructures without triggering particle agglomeration, a sequential, two-step chemical treatment is applied. First, the electrospun membrane is immersed in a solution containing iron(II) ions (Fe²⁺). The carboxylate groups on the pectin molecules coordinate with these cations, forming uniformly dispersed, nanometer-scale iron seed clusters (~2 nanometers in size) across the nanofiber surfaces as the material dries and oxidizes. In the second step, the seeded membrane is placed in a solution containing iron(III) ions (Fe³⁺). Instead of forming isolated new particles in solution, the newly added iron deposits onto the pre-existing seeds, driving controlled anisotropic growth along preferred crystallographic axes.

This seed-mediated approach yields an extraordinarily high density of surface-exposed iron nanostructures, achieving a 12-fold increase in surface atomic iron content compared to single-step doping methods. High-resolution electron microscopy reveals that these nanostructures adopt an elongated, rice-grain morphology measuring approximately 29 nanometers in width and 110 nanometers in length. Structural characterization using X-ray scattering, X-ray diffraction, and Mössbauer spectroscopy identifies the predominant active iron phase as akaganeite (β-FeOOH), a tunnel-structured, poorly crystalline iron oxyhydroxide known for its exceptional binding affinity toward arsenate.

When evaluated in water purification tests, the nanostructured membrane demonstrates exceptional superadsorbent performance. Using a minimal material dosage of 1 gram per liter, the membrane reduces initial arsenate concentrations from 1000 micrograms per liter down to below 10 micrograms per liter within 24 hours at pH 6, achieving roughly 99% arsenic removal and satisfying WHO safety limits. The material retains high efficiency across a broad operational pH range of 5 to 8, and ICP analysis confirms that iron leaching into the treated water remains safely below 5 micrograms per liter.

Kinetic and isotherm analyses reveal that arsenate removal occurs via surface chemisorption governed by cooperative binding behavior. As initial arsenate molecules bind to active sites on the akaganeite surface, local chemical and electrostatic interactions make adjacent sites even more receptive to further adsorption, resulting in accelerated uptake kinetics. Furthermore, the material performs reliably in complex water environments. Naturally occurring co-contaminants such as fluoride do not interfere with arsenate capture, and the presence of heavy metal cations—such as copper and cadmium—actually enhances arsenate removal by forming secondary surface complexes that create additional binding sites. Although chemical regeneration using sodium hydroxide solution results in a slight decrease in capacity over repeated cycles due to incomplete desorption, the membrane maintains an 81% to 87% removal efficiency, demonstrating strong potential for practical, reusable water remediation systems.

Author: César Tomé López is a science writer and the editor of Mapping Ignorance

Disclaimer: Parts of this article may have been copied verbatim or almost verbatim from the referenced research paper/s.

The post A polymer membrane that grows its own arsenic-catching surface appeared first on Mapping Ignorance.

Two-dimensional (2D) materials have attracted a lot of attention in recent years for their excellent electronic, thermal and mechanical properties, as well as their interesting quantum effects. While graphene has gathered the most commercial attention, there are hundreds of 2D materials, all of which have different combinations of properties for different applications. A research team headed up at the University of Chicago has discovered some unusual behaviour in the 2D material Fe₅GeTe₂.

Some 2D materials exhibit superconductivity properties and charge orders (in which the electrons are confined in a specific arrangement rather than being able to move freely). Charge orders arise from the reshaping of ground states in the electronic bands of a 2D materials to create flat electronic bands. And these flat bands cause the electrons to move very slowly in the lattice, at speeds much slower than expected.

Extremely flat electronic bands can often become incoherent, due to an ultrastrong electronic interaction strength between charge carriers. In research published in Science Advances, Shuolong Yang and colleagues found that Fe₅GeTe₂ exhibits a charge-ordered state where electrons move both collectively and very slowly, while remaining quantumly coherent.

“I was originally motivated by the fact that Fe₅GeTe₂ was discovered to host multiple structural phases with nearly the same stoichiometry. Each structural phase is associated with its unique electronic and magnetic phase,” says Yang. “These different structural phases have almost degenerate energies, which means that they can all be stabilized at room temperature.”

According to Yang, this discovery prompted two key research questions: What is the nature of each phase? Can we utilize these nearly energy-degenerate phases to encode information?

Fe₅GeTe₂ is part of specific class of 2D materials called van der Waals magnets, which could be used to develop new memory technology. The researchers probed the electronic structure and magnetic states of Fe₅GeTe₂ using angle-resolved photoemission spectroscopy (ARPES). “We were able to surgically probe the electronic band structure of each individual phase region (tens of microns in size) and figure out the physics,” Yang tells Physics World. “This immediately allows us to answer the question of ‘What is the nature of each phase?’”

After discovering that the electronic band was flat in Fe₅GeTe₂, further studies into the material showed that the charge order in Fe₅GeTe₂ was caused by the folding of electronic bands in the Brillouin zone within 30 meV of the Fermi level.

“We revealed a so-called Kondo-like phase, so the localized electronic states strongly interact with itinerant states, resulting in very peculiar, quantum coherent flat bands right at the Fermi level which dictates low-temperature transport,” says Yang. “The discovery of an effective Kondo lattice in a ferromagnetic phase [instead of magnetically non-ordered phase] is quite a surprise from a theoretical point of view, which forced us to go back to the drawing board to understand its physics. We think that that our surprising finding originates from a many-body localized state interacting with the conduction electrons.”

Because of the flat bands, the electronic system wants to spontaneously break the space-translation symmetry. It then forms a new superlattice order commensurate with the original lattice. “Our results provide the first experimental evidence that an interaction-driven flat band can itself drive electronic ordering through flat-band nesting, without relying on Moiré or geometrically frustrated flat-band engineering,” Yang explains. He notes that this “peculiar physics” used to be something obtained in delicately designed, twisted 2D materials. This finding, however, provides a new avenue to study complex many-body physics enabled by flat bands in stoichiometric and strongly correlated materials.

There’s the potential that the material’s different magnetic states could encode information for memory systems. This idea is being trialled by the team by using a micro-focused laser to switch between this observed quantum many-body phase and other phases.

“We’re using carefully designed laser pulses of different frequencies to switch between the multiple phases of Fe₅GeTe₂, including our discovered Kondo-like phase. If successful, we will utilize the many-body physics for some real memory operations,” Yang explains. This follow-on aims to tackle the second stated research question. However, to be practical, it will have to work at room temperature, and these quantum effects have so far only been realised at ultralow temperatures.

“Fundamental work is underway to understand the exact nature of this Kondo-like phase, whether it has any topological properties, and whether it connects to structural defects,” says Yang. “Eventually we want to understand how to microscopically describe such an exotic system.”

The post Two-dimensional material shows promise for long-term memory, thanks to slow electrons appeared first on Physics World.

The kind of technology that can deliver sound to a single listener—like something out of a spy film—may soon become a reality. Researchers at Pohang University of Science and Technology (POSTECH) have developed a speaker system that can direct speech to a specific person. ¹

Light and sound behave differently. Light from a flashlight or laser travels in a straight line, whereas sound readily spreads in all directions—that is why voices can be heard over a wall. The question, “Could sound, like light, be sent only where we want it?” led to the team’s highly directional speaker, MiPAL. By modulating ultrasound with audible content, the system can deliver sound only within a targeted area. A representative technology is the parametric array loudspeaker (PAL), which uses the nonlinear interaction of two ultrasonic waves in air to generate and concentrate audible sound in a specific direction.

 

Compared with conventional speakers, PALs can confine sound to a much narrower region. Traditional systems, however, require tens to hundreds of ultrasonic emitters to be precisely arranged and individually controlled, making them expensive and structurally complex. More recent PAL designs have simplified the hardware, but the vibrating diaphragm can also excite unwanted vibration modes, allowing sound to leak sideways and undermining directivity.

 

The team addressed this problem by integrating two types of metamaterials into a single ultrasonic transducer. An acoustic metasurface was mounted at the front. Acting like a lens for sound, it reshapes the irregular ultrasonic wavefronts radiated by the diaphragm into a straight, narrow beam, much like a laser. Elastic meta-units were placed at the rear. Acting more like a sound barrier, they suppress unwanted vibrations at selected frequencies and keep sound from leaking to the sides. In effect, the design uses a double safeguard: it focuses the sound at the front and blocks parasitic noise at the back.

As a result, the single-element device directed sound over a frequency range of 500 Hz to 10 kHz—more than four octaves, covering a large portion of the audible spectrum. The researchers also conducted an experiment simulating aircraft seating, where different announcements or music might need to reach individual passengers without disturbing their neighbors. After playing real broadcast and music signals and measuring sound intensity at different angles, they observed a clear improvement after the elastic meta-units were added.

 

Another key advantage is ease of fabrication and adaptation. The metamaterial structures are modular and can be produced using 3D printing, allowing the device to be readily redesigned for different seat spacing, angles and other operating conditions.

 

Once commercialized, the technology could let passengers on planes or trains listen to personalized announcements or content without disturbing the person next to them. In museums and exhibition halls, explanations could be heard only by visitors standing in front of a particular display. The “sound only I can hear” once seen only in films may soon become part of everyday life.

 

“By co-designing the metamaterials and the ultrasonic device as a single system, we overcame the limitations of cost, complexity and design flexibility at the same time,” said Professor Junsuk Rho. “Research on acoustic and elastic metamaterials has largely remained at the stage of validating principles and demonstrating concepts. This study is the first to integrate metamaterials into functional device and demonstrate their potential for practical use.”

 

The post Delivering sound to a specific listener appeared first on Mapping Ignorance.