The numbers tell a striking story. A Scopus search for publications on Pickering emulsions shows year-on-year growth since 2000, peaking at 1,366 papers in 2025. The appeal is easy to understand: Pickering emulsions are simple to prepare, remarkably stable, and versatile across applications ranging from catalysis and filtration membranes to drug delivery, antibacterial coatings, cosmetics, nutraceuticals, and food technology. What the Mexican team, Miguel Rosales-Guzmán, María Esther Treviño Martínez, and Enrique Saldívar-Guerra, add to this crowded literature is a dual focus that has been largely missing until now. Their review concentrates specifically on stabilizers drawn from carbon allotropes and carbon-rich materials, and it devotes unusual attention to emulsion polymerization, the industrial workhorse process in which monomers are polymerized inside emulsion droplets to produce the latexes behind countless commercial and high-tech polymers.

The physics underlying Pickering stabilization is elegant. Solid particles that are partially wetted by both oil and water lodge themselves at the oil-water interface, where they form a mechanical barrier. The decisive parameter is the three-phase contact angle at the point where particle meets interface. If that angle is below 90 degrees, the particle is more hydrophilic and favors oil-in-water emulsions; above 90 degrees, it is more hydrophobic and favors water-in-oil systems. If a particle is completely wetted by either phase, stabilization fails entirely. Crucially, the energy required to rip a particle off the interface is typically far higher than thermal energy, which is why Pickering emulsions can be dramatically more stable than their surfactant-stabilized cousins. For spherical particles, this detachment energy scales with the square of the particle radius and the interfacial tension, and analogous expressions exist for disk-like and rod-shaped particles, geometries that matter greatly when the stabilizers are flat graphene sheets.

That is where graphene oxide enters the picture. Pristine graphene and carbon nanotubes are stubbornly hydrophobic, but oxidizing graphite to graphene oxide grafts hydroxyl and epoxy groups across the planar surface and carboxyl groups mainly at the flake edges. The result is a material that is broadly hydrophilic with localized hydrophobic zones, an inherently amphiphilic character that makes it naturally suited to stabilizing oil-in-water emulsions. Even better, those oxygen-bearing functional groups are chemical handles: researchers can attach hydrophobic alkyl amines, polymers, surfactants, or inorganic nanoparticles to tune the wettability for whatever emulsion type a given application demands. The review highlights how the degree of oxidation itself shifts the contact angle, with reported values of 63.6, 55.8, and 90.6 degrees corresponding to different oxygen-to-carbon ratios, giving formulators a dial they can turn.

The functionalization toolbox is impressively broad. A redox reaction between graphene oxide and ferrous ions decorates the sheets with magnetic iron oxide nanoparticles, while treatment with chloroauric acid yields gold-decorated hybrids. One-pot hydrothermal routes can simultaneously reduce graphene oxide to graphene and graft amine groups from polyacryloyl hydrazide, producing stabilizers for olive oil and n-decane emulsions. Ball milling offers a scalable alternative, and pyrolyzing citric acid at 200 degrees Celsius in air generates hydrophilic graphene quantum dots just nanometers across, which can then be functionalized with amines to stabilize dodecane-in-water emulsions or with histidine for styrene-in-water systems. Carbon nanotubes, meanwhile, can be tamed with oxygen plasma or nitric acid oxidation. Selective modification can even produce Janus particles with two chemically distinct faces, an asymmetry prized for interfacial work.

The most conceptually intriguing section of the review concerns polymerization inside graphene oxide-stabilized emulsions. In conventional emulsion polymerization, water-soluble initiators generate radicals that enter monomer-swollen particles, and the compartmentalization of radicals, at most one per particle at any time, governs the kinetics and molecular weights. But in the reported graphene oxide systems, the initiator of choice has been AIBN, which dissolves in the organic phase, hinting that the mechanism may resemble miniemulsion polymerization instead. The large graphene oxide platelets cloaking each droplet may also impede radical exchange between phases. The authors are candid that the mechanism remains an open question, noting that most published studies vary only one or two parameters and use inconsistent emulsion preparation methods, making firm conclusions impossible. What is clear is that the approach works: polystyrene microspheres sheathed in graphene oxide platelets have been produced since the end of the first decade of this century, and polymerizations have focused mainly on styrene and methyl methacrylate.

The applications catalogued in the review read like a tour of modern materials science. Phase-change materials such as paraffins can be encapsulated with extraordinary efficiency; one system using 7.4 weight percent graphene oxide achieved 100 percent encapsulation and a thermal conductivity of 1.3 watts per meter-kelvin for personal thermal management textiles. Self-healing coatings exploit graphene oxide microcapsules that rupture to release healing agents, with one epoxy system reducing concrete’s capillary water absorption by 98.3 percent. Freeze-drying emulsions yields porous aerogels for pressure sensors, electromagnetic interference shielding composites reach 41.4 decibels of shielding effectiveness, catalytic desulfurization systems remove 97 percent of sulfur from fuel oil, and graphene oxide quantum dots have even served as adjuvants boosting immune responses to a Chlamydia trachomatis vaccine. Each droplet can act as a nanoreactor, as demonstrated by the synthesis of 2-aminothiazole with isolated yields of 85 to 90 percent.

Among carbon-based stabilizers, the hierarchy is unambiguous. Graphene oxide dominates, accounting for more than 75 percent of recent literature entries, followed by other graphene derivatives, carbon nanotubes, and carbon quantum dots. The reasons are practical: graphene oxide is comparatively easy to prepare, inherently amphiphilic, and endlessly modifiable. Carbon nanotubes, despite their industrial maturity driven largely by lithium-ion battery electrodes, are harder to synthesize reproducibly and require more elaborate chemistry to become amphiphilic. Production costs for graphene derivatives and nanotubes remain relatively high but are expected to fall over the next five to ten years as volumes increase, and because these stabilizers are used in small proportions, cost may not be prohibitive for many emulsion applications.

Challenges remain, and the review does not shy away from them. The single greatest obstacle to real-world deployment is scaling up graphene oxide production so that the material performs reproducibly as a stabilizer, since current processes suffer significant batch-to-batch variability. Toxicity is another open question: carbon nanomaterials show varying toxicity depending on dimensions, surface modification, and purity, with nanotubes appearing potentially more harmful than graphene derivatives, though surface modification seems to attenuate the risk. The environmental fate of these materials at end of life has been largely overlooked. The authors argue that future research must pivot from proof-of-concept toward practical implementation, with attention to scalability, efficiency, and recyclability, and that unraveling the polymerization mechanism and the self-assembly processes that govern final material properties will require systematic studies across monomer types, oxidation degrees, sheet sizes, and temperatures. For a field that grew from a century-old curiosity into a 1,366-papers-a-year enterprise, the next chapter will be written not in the laboratory alone but in the pilot plant.

Subject of Research: Pickering emulsions stabilized by graphene oxide and other carbon-rich particles, including their use in emulsion polymerization and applications

Article Title: Pickering emulsions: emulsion polymerization and systems stabilized with carbon allotropes or carbon-rich materials

Article References: Rosales-Guzmán, M., Treviño Martínez, M. E., & Saldívar-Guerra, E. (2026). Pickering emulsions: emulsion polymerization and systems stabilized with carbon allotropes or carbon-rich materials. Frontiers in Soft Matter, 6, Article 1908524. https://doi.org/10.3389/frsfm.2026.1908524

Image Credits: AI Generated

DOI: 10.3389/frsfm.2026.1908524

Keywords: Pickering emulsions, graphene oxide, emulsion polymerization, carbon nanotubes, graphene quantum dots, colloids, interfacial science, phase change materials, self-healing coatings, aerogels, drug delivery, nanomaterials

The central insight of the new work is that the three most desirable properties of an air filter need not live in the same solid material. Conventional fibrous filters, including the melt-blown polypropylene media used in respirators and the dense glass-fibre mats inside HEPA units, capture particles mechanically or electrostatically on solid surfaces. Every captured particle stays put, gradually blocking the pores, raising the pressure drop across the filter and eventually forcing a costly replacement. The CILF instead delegates capture to a dynamic liquid lining that is continuously replenished, so that trapped contaminants are swept away rather than accumulated.

The researchers organise the capture process into three stages that operate in sequence. In the first stage, long-range electrostatic attraction draws airborne particles toward the filter from a distance, exploiting electric charges to overcome the fundamental weakness of purely mechanical filtration, in which only particles that happen to collide with a fibre are removed. In the second stage, particles arriving at the liquid interface are captured rapidly at the surface, where capillary and electrostatic forces combine to pull them across the boundary between air and liquid. In the third stage, the liquid bulk itself acts as a high-capacity sink, absorbing and storing the collected particles deep within its volume.

This division of labour is what gives the filter its durability. Because the liquid lining is refillable and continuously renewed, particles that would otherwise clog a solid filter are instead dissolved or suspended in the liquid phase and carried off. The team reports that the filter maintained high performance throughout 3,500 hours of continuous operation, a figure that dwarfs the service intervals typical of high-efficiency solid filters, which often degrade noticeably within weeks of intensive use. The self-cleaning behaviour of the moving liquid lining means the filter does not progressively blind itself, and the pressure drop across it remains stable rather than climbing over time.

The design builds on a growing body of work on liquid-based filtration. In 2022, a team reported in Nature a continuous air purification approach based on aqueous interface filtration and absorption, demonstrating that liquids could serve as active capture media rather than passive wetting agents. Related efforts have explored liquid-gating mechanisms with tunable multiphase selectivity and antifouling behaviour, first described in Nature in 2015, as well as biomimetic systems inspired by the human circulatory and respiratory systems. The new contribution of the CILF is to combine the liquid approach with charge-induced capture, adding the long-range electrostatic attraction that pure liquid-interface systems lack while retaining their resistance to clogging.

The physics of the interfacial capture stage draws on well-studied phenomena. Particles sitting at liquid interfaces experience capillary forces that can bind them strongly to the boundary, and electric fields can induce attractive interactions between like-charged particles at such interfaces, an effect documented experimentally more than two decades ago. By engineering the charge state of the liquid lining, the researchers harness these forces deliberately: particles approaching the interface are pulled in and then drawn into the bulk liquid, where the vast absorption capacity of the liquid phase stores them far from the airstream. Supplementary videos accompanying the paper show charge-induced adsorption on solid surfaces, bulk-phase absorption in the liquid, and the dynamic liquid lining performing its self-cleaning function.

To demonstrate that the laboratory performance translates into practical air cleaning, the team built a full-scale air cleaner prototype incorporating the CILF. In a thirty-cubic-metre test chamber, the prototype achieved a clean-air delivery rate of 377 cubic metres per hour, a measure of how much purified air a device can supply and one of the key metrics used to compare commercial air purifiers. The tests were conducted under industry standard conditions, providing a benchmark that allows direct comparison with existing filtration technologies rather than relying solely on laboratory-scale measurements.

Perhaps the most striking aspect of the work is the breadth of applications the researchers demonstrate. The team implemented the filters across a range of real-world settings, from personal protective masks to air purification systems compatible with microgravity environments. The microgravity application is particularly notable: conventional filters rely on gravity-assisted settling and replaceable cartridges that generate waste, both of which are problematic on spacecraft, where every kilogram of consumables must be launched at great expense. A filter whose capture medium is a refillable liquid, and whose performance does not depend on gravity, offers an intriguing option for long-duration missions. At the other end of the scale, a liquid-lined filter in a face mask could in principle maintain high efficiency without the breathing resistance that builds up as solid mask filters load with particles.

The energy and sustainability implications are significant. Because the filter maintains a low and stable pressure drop, the fans driving air through it consume less power than they would against a progressively clogging medium, and the refillable liquid lining replaces the steady stream of discarded filter cartridges that conventional high-efficiency systems generate. Prior analyses of air filtration have highlighted both the monetary cost of replacing high-efficiency filters and the environmental burden of disposing of them, and low-cost do-it-yourself air cleaners popularised during the COVID-19 pandemic underscored the demand for affordable, durable alternatives. A filter that combines HEPA-level efficiency with long service life and simple maintenance addresses precisely the gap that has kept such alternatives from matching professional equipment.

Challenges remain before charge-induced liquid-lined filters appear in homes, hospitals and spacecraft. The nature and management of the working liquid, its consumption rate, the electrical power needed to sustain the charge-induced capture, and the behaviour of the system across extremes of temperature and humidity are all questions that the broader deployment of the technology will need to answer, and the paper’s supplementary materials, including extensive notes and tables, suggest the authors have begun mapping this terrain in detail. Still, the headline numbers are difficult to ignore: 99.6 percent single-pass efficiency at a face velocity of one metre per second, 3,500 hours of continuous high performance, and a clean-air delivery rate of 377 cubic metres per hour in a full-scale prototype. If the approach scales as the authors suggest, the familiar ritual of replacing clogged filters may one day give way to simply topping up a liquid reservoir, and the trade-off that has defined air purification for decades may finally be resolved in favour of clean air that is simultaneously efficient, durable and affordable.

Subject of Research: A charge-induced liquid-lined filter for high-efficiency, durable and low-maintenance air purification

Article Title: Highly efficient air purification by a charge-induced liquid-lined filter

Article References: Zhang, J., Li, M., Chen, S., Guo, Z., Yang, B., Li, L., Zhou, X., Zhang, J., Ye, C., Liu, J., Yao, W., Zhang, Y., & Hou, X. (2026). Highly efficient air purification by a charge-induced liquid-lined filter. Nature Sustainability. https://doi.org/10.1038/s41893-026-01920-w

Image Credits: AI Generated

DOI: 10.1038/s41893-026-01920-w

Keywords: air purification, liquid-lined filter, electrostatic capture, particulate matter, Nature Sustainability, filter durability, clean-air delivery rate, interfacial science, self-cleaning, microgravity, sustainable technology, fluidics