The study was led by Ziheng Wang of The University of Manchester, working with Majid Sedighi, and examined what happens when extremely fine particles shed from carbon-based adsorbents remain suspended in treated water. The team’s central discovery is what researchers call co-transport: dissolved contaminants bind to microscopic carbon fragments, and those fragments then travel through sand filters and even membranes with pores far smaller than the particles themselves appear to be. In their experiments, the overwhelming majority of lead remaining after fine-sand filtration was not dissolved in the water at all but riding on residual carbonaceous particles.

The numbers are striking. After fine-sand filtration, particle-bound lead accounted for 84.5 percent of the total lead detected in filtrates from activated carbon, and reached as much as 90.2 percent for biochar produced from corn straw. In other words, when the researchers measured what was actually left in the water after treatment, nearly nine parts in ten of the model contaminant were attached to particles rather than floating freely as dissolved ions. Any assessment that looked only at the dissolved fraction would have dramatically underestimated how much lead remained in the system.

Activated carbon is a staple of drinking water and wastewater treatment worldwide, prized for its enormous internal surface area and its affinity for a broad range of pollutants. Biochar, a close cousin produced by heating biomass such as wood and crop residues in low-oxygen conditions, is attracting growing interest as a potentially lower-cost alternative, with the added appeal of turning agricultural waste into a useful remediation material. Both work by adsorption: pollutant molecules and ions adhere to surfaces and pores, effectively pulled out of the water column and immobilized on the solid.

But solids are not immortal. Physical breakdown, erosion, and the simple presence of very fine material in the original product mean that some carbonaceous fragments inevitably escape the adsorbent bed and move downstream. The Manchester team set out to quantify this under controlled conditions, testing activated carbon alongside three biochars made from hardwood, wheat straw, and corn straw, with lead serving as a representative heavy-metal contaminant. Their experimental toolkit combined adsorption experiments with fixed-bed filtration, stirred suspensions, sand filtration, and membrane filtration at pore sizes of 0.45 and 0.02 micrometers.

What they found in the filtrates was a population of residual particles with size features clustered around 100 to 200 nanometers, around 0.5 to 1 micrometer, and an apparent fraction near 5 micrometers. The researchers are careful about that largest figure. It is unlikely, they caution, that intact 5-micrometer particles passed directly through the pores of a 0.45-micrometer membrane. A more plausible explanation is that smaller particles aggregated during filtration, sample handling, concentration, or measurement, creating larger apparent structures. Further experiments, they note, are needed to verify exactly how this aggregation occurs.

The most consequential result emerged when the team separated dissolved lead from particle-carried lead. Even after 0.45-micrometer membrane filtration, a standard step in many analytical and treatment workflows, lead remained associated with particles in the 0.02 to 0.45 micrometer size range. That means conventional filtration and dissolved-phase measurements can overlook part of the contaminant load entirely. A water sample that appears clean by dissolved-metal standards may still carry a substantial hidden burden of pollutant, provided it is attached to particles small enough to pass through the filter.

This distinction has implications that reach well beyond the laboratory bench. Common analytical procedures often filter water samples before measuring dissolved metals, precisely to remove particles and obtain what is considered the truly dissolved concentration. But if a significant share of the contaminant is particle-bound, that pre-filtration step removes the contaminants along with the particles, potentially giving an incomplete, even misleading, picture of contaminant transport. In practical terms, a treatment plant could report low dissolved lead while substantial lead continues moving through the system on carbon fragments too fine to see. The authors argue that water-treatment performance should therefore be evaluated using both dissolved contaminants and contaminants carried by residual particles, treating the two fractions as distinct components of the total load.

The researchers are careful to frame their findings within the limits of the study. All experiments were conducted under controlled laboratory conditions, and real treatment systems are messier places. Water chemistry, including pH, ionic strength, natural organic matter, and dissolved ions, could change how stable the residual particles are and how readily they and their attached contaminants move through actual treatment trains. Natural organic matter, for instance, is known in colloid science to alter particle surfaces and aggregation behavior, so the fractions measured in the laboratory may shift in different water matrices. The authors call for future work to test representative drinking water and wastewater matrices rather than idealized solutions.

They also point toward practical countermeasures that could be evaluated in follow-up research. These include pre-washing adsorbents before deployment to remove loose fines, mechanical stabilization of the carbon materials, granulation to reduce the generation of mobile fragments, improved coagulation and flocculation downstream to capture escaping particles, and combined sand and membrane filtration schemes designed to intercept the finest fractions. None of these measures is proposed as a proven fix; each is a candidate for testing against the co-transport pathway the study has now documented. The broader message is a recalibration of expectations for two of the most widely studied materials in water treatment. Activated carbon and biochar remain excellent adsorbents, and the study does not challenge their capacity to bind pollutants. What it challenges is the assumption that binding equals removal. As Wang put it, if very small carbon particles remain mobile, the contaminants attached to them may also continue moving through the treatment system. For engineers, regulators, and researchers, that means the particles leaving an adsorbent bed deserve the same scrutiny as the water flowing past them, and the dissolved fraction alone can no longer stand in for the whole story of what a filter has, and has not, removed.

Subject of Research: Co-transport of particle-bound contaminants by residual superfine activated carbon and biochar particles in water filtration

Article Title: Tiny carbon particles may carry contaminants through water treatment filters

Article References: Tiny carbon particles may carry contaminants through water treatment filters. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: activated carbon, biochar, water treatment, co-transport, lead contamination, sand filtration, membrane filtration, adsorption, particle-bound pollutants, dissolved metals, colloids, water quality

The central achievement of the work is reconfigurability. Non-Abelian braiding, in which the outcome of swapping two objects depends on the order in which the swaps are performed, has previously been demonstrated in superconducting processors, trapped-ion systems, photonic chips and acoustic metamaterials. Those platforms are powerful but require cryogenic temperatures, intricate nanofabrication, or fixed on-chip geometries. The new experiment brings the same mathematical structure into an ordinary liquid crystal cell sitting at ambient conditions, where the relevant objects are micron-scale defect lines entangled around colloidal particles, and where the control knob is simply light.

Disclination lines are the skeletons of disorder within an ordered medium. In a nematic liquid crystal, rod-like molecules align with a local direction called the director; a disclination line marks a seam where that alignment field cannot be smoothly defined, much like the seam on a tennis ball marks a place where the covering cannot lie flat. When colloidal particles are dispersed in the nematic, their surfaces impose orientation constraints on the surrounding director, and defect lines become entangled among the particles, forming stable, topologically protected structures. The team exploited this entanglement by photonically manipulating the colloids, using patterned light to reorient the director field at the cell surface and drive the particles through cooperative molecular reorientations.

By sweeping this optical control, the researchers wove disclination lines into chiral double-helix entanglements, structures in which pairs of defect lines wind around one another in either a left-handed or right-handed twist. The handedness of the helix is not merely decorative; it serves as a binary degree of freedom that the team calls a nematic bit, or nbit. Depending on whether the surface director is rotated counterclockwise or clockwise by the incident light, the entanglement settles into one or the other chiral state, effectively writing a bit into the topology of the defect network. Supplementary videos accompanying the paper show the process unfolding in real time, with double-helix entanglements forming around assemblies of up to nine colloids and even coexisting regions of opposite chirality within a single four-particle structure.

With this encoding in hand, the team implemented a complete set of braid operations, the elementary moves in which defect lines pass over and under one another, and demonstrated their non-commutativity in networks of three lines. In an Abelian world, performing operation A and then operation B yields the same final configuration as performing B and then A. In the nematic platform, the order matters: two braid sequences that differ only in their ordering leave the network in topologically distinct states. This order-dependence is the defining signature of non-Abelian behaviour and the property that makes braided anyons attractive as a basis for fault-tolerant information processing, because the encoded state depends on the global history of exchanges rather than on any local measurement.

A crucial advantage of the soft-matter setting is that the braid gates themselves can be moved. The colloidal particles act as physical gates that pin and route the disclination lines, and by repositioning these particles with optical tweezers and light-driven transport, the researchers reprogrammed the braiding sequence in situ without rebuilding the sample. Small variations in colloid position or local line curvature leave the topological state unchanged, a robustness the team verified directly by perturbing the networks and observing that the encoded configuration survived. The method also extends beyond three-line demonstrations to multiline architectures, suggesting a path toward larger braiding networks assembled from the same elementary components.

Perhaps the most forward-looking contribution is the establishment of an inverse-design framework. Rather than working forward from operations to outcomes, the team developed an algebraic procedure that runs in reverse: given a desired topological transformation, the framework compiles it into prescribed spatial routing of the defect lines together with layer-by-layer phase corrections. This compiler-like capability mirrors how electronic design automation tools translate logic descriptions into circuit layouts, and it transforms the platform from a demonstration apparatus into a programmable one. The researchers note that the scalability of light-driven manipulation makes this design loop practical, since the same optical interface that writes a single bit can in principle address many.

The significance of the result lies in its bridging role. Topological information processing has been dominated by quantum proposals, where non-Abelian anyons would protect quantum states against local noise. Realizing the same braiding algebra in a classical, room-temperature material does not produce a quantum computer, but it provides a tangible, inexpensive laboratory in which non-Abelian logic can be studied, visualized and engineered. The authors position the system as a programmable classical platform for robust topological transformations, one that connects the soft-matter physics of liquid crystals with the emerging field of topological information processing. Because liquid crystals are already the workhorse of display technology, there is also a plausible engineering pathway: the optical and electro-optical toolkits for addressing nematic cells at high resolution are mature and commercially available.

The work also builds on a rich lineage. Knot-theoretic descriptions of nematic defects date back more than a decade, when theorists showed that disclination networks carry invariants analogous to braids and that rewiring operations among them can be classified. Experimentalists later demonstrated reconfigurable knots and links in chiral nematic colloids, and recent theoretical work proposed nematic bits and universal logic gates based on defect topology. What the new study adds is dynamics and control: the ability to actively drive the system through braid operations on demand, to verify non-commutativity experimentally, and to reprogram the network at will. Earlier light-driven studies from the same group had shown collective transport and reconfigurable assembly of nematic colloids and active transformations of disclination networks, providing the technical foundation for the present braiding results.

Looking ahead, the researchers suggest that the platform could serve as a testing ground for algorithms and error models relevant to topological computing, while also raising its own questions about how complex braid networks relax, hold information and fail. The combination of a mathematical structure once confined to abstract group theory with something as tangible as soap-like molecules and glass beads, manipulated by nothing more exotic than patterned light, is a reminder that some of the deepest ideas in physics can be made to run, quite literally, at room temperature. For now, the nematic bits weave their helices quietly under a microscope, but they weave them on command, in any order the operator chooses, and undo nothing by accident.

Subject of Research: Light-driven reconfigurable non-Abelian braiding of disclination lines in nematic liquid crystals

Article Title: Reconfigurable non-Abelian braiding of nematic bits

Article References: Lei, Z., Zheng, X., Zhang, J., Tang, W., Tian, K., Song, G., Asilehan, Z., Chen, Z., Vergara, F., Guan, Y., Zhang, R., Jiang, J., & Peng, C. (2026). Reconfigurable non-Abelian braiding of nematic bits. Nature Materials. https://doi.org/10.1038/s41563-026-02728-x

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02728-x

Keywords: non-Abelian braiding, nematic liquid crystals, topological defects, disclination lines, nematic bits, colloids, topological information processing, soft matter, inverse design, liquid crystal colloids, chiral double helix, optical control