The review, authored by Asma Nouira of the University of Évora and University of Tunis El Manar and Imene Bekri-Abbes of the CNRSM Technopole of Borj Cédria, systematically analyzes how different carbon structures transform the properties of polyaniline, known to materials scientists as PANI. The numbers are striking. A composite of polyaniline anchored covalently inside a three-dimensional porous skeleton of reduced graphene oxide and helical carbon nanotubes achieved a specific capacitance of 696.75 farads per gram, compared with 274.75 farads per gram for pure PANI. More dramatically, the composite retained 93.57 percent of its capacitance over 3,500 charge-discharge cycles, while the pristine polymer managed only 72.3 percent retention after just 2,500 cycles.

The roots of the problem lie in polyaniline’s own chemistry. The rigid conjugated backbone that makes the polymer electrically conductive also renders it mechanically brittle, prone to cracking and delamination when strained. Its highly conductive emeraldine salt form is stable only below pH 4, which severely limits biomedical and environmental uses that operate near neutral conditions. During electrochemical cycling, the polymer swells and contracts with each doping and dedoping event, generating mechanical stress that destroys films over time. And because PANI chains aggregate into densely packed granules, many potentially useful electroactive sites are simply locked away from the electrolyte.

Carbon nanomaterials attack each of these weaknesses in a different way. One-dimensional carbon nanotubes act as electron highways, allowing charge to travel through the nanotube network rather than relying solely on the polymer backbone, while simultaneously reinforcing the composite like nanoscale rebar. Two-dimensional graphene offers exceptional conductivity and mechanical strength, though its pristine hydrophobic surface must usually be functionalized, most commonly through oxidation to graphene oxide and subsequent reduction, to disperse in water and bind with aniline monomers. Zero-dimensional carbon dots and graphene quantum dots introduce quantum confinement effects and, when covalently linked to aniline molecules before polymerization, serve as multifunctional crosslinking nodes that prevent chain aggregation.

The choice of synthesis route turns out to matter as much as the choice of carbon. In situ polymerization, in which aniline is polymerized directly in the presence of dispersed carbon nanomaterials, remains the most scalable and industrially viable method, though achieving uniform dispersion at large volumes is challenging. Electrochemical polymerization offers exquisite control over film thickness and doping level by driving aniline oxidation on a conductive substrate with cyclic voltammetry, but it is fundamentally limited to thin films on conducting electrodes. Microwave-assisted synthesis, which heats polar molecules directly through dielectric heating, can be extraordinarily fast: one recent study prepared CNT/Ag/PANI composite electrodes in just 50 seconds.

More exotic techniques push performance further. Cryo-polymerization carries out oxidative polymerization at temperatures between minus 20 and minus 78 degrees Celsius, using growing ice crystals as a sacrificial template to create lightweight, three-dimensional macroporous aerogels. Composites of polyaniline with carbon nanofibers made this way reached gravimetric capacitances of 201 farads per gram, three to six times higher than carbon-fiber-free counterparts. Gamma radiation-assisted fabrication, meanwhile, generates free radicals that initiate polymerization and crosslinking without any chemical oxidant, a clean route recently used to produce flexible energy-storage electrodes from sugarcane bagasse waste.

Perhaps the strongest message of the review is that covalent bonding between the polymer and its carbon scaffold yields qualitatively better materials than simple physical mixtures. Where the two phases are chemically linked, phase separation and delamination under mechanical load largely disappear. The synergy is visible across applications: a ternary composite of polyaniline, reduced graphene oxide and single-walled carbon nanotubes raised electrochromic optical contrast from 0.38 to 0.52 and cut switching times to as fast as 0.78 seconds, enabling smart windows and low-power displays that change color on demand.

The applications extend well beyond electronics. Nitrogen-rich polyaniline binds carbon dioxide through acid-base and dipole-quadrupole interactions, and when combined with hierarchically porous carbon aerogels containing ultramicropores of 0.54 to 0.64 nanometers, it achieved a CO2 capture capacity of 6.04 millimoles per gram. In microbial fuel cells, a polyaniline coating on a covalent organic framework-carbon nanotube cathode delivered power densities 8.65 times higher than a blank cathode, using bacteria to convert wastewater organic matter into electricity. Magnetic activated carbon composites functionalized with polyaniline removed lead ions from water at 348.39 milligrams per gram, while biomass-derived activated carbons from coconut husk and date seeds are turning agricultural waste into supercapacitor electrodes with retention above 98 percent after 50,000 cycles.

The review’s authors are candid about what still stands between the laboratory and the factory. Long-term operational stability under realistic conditions, with high current densities, neutral pH and repeated mechanical deformation, remains poorly characterized, and few studies subject materials to simultaneous electrochemical and mechanical fatigue. Only in situ polymerization is currently suitable for tonne-scale production; covalent conjugation, despite its superior interfacial quality, has been demonstrated only at milligram-to-gram scale and relies on hazardous solvents and coupling reagents. The authors also point to machine learning as an underexploited accelerator: with a design space spanning carbon type, dimensionality, loading, dopant acid and processing parameters, data-driven models trained on hundreds of composite systems could predict conductivity and sensing performance far faster than trial-and-error experimentation.

What emerges from the analysis is a portrait of a mature field at an inflection point. The fundamental science, linking the dimensionality and surface chemistry of carbon nanomaterials to the electrochemical, mechanical and optical behavior of the resulting composites, is now well established. Biomass-derived porous carbons, green oxidants and continuous-flow reactors are beginning to address the sustainability deficits of conventional synthesis. If scalable manufacturing and rigorous durability testing catch up with the materials themselves, polyaniline’s century-and-a-half-long journey from an obscure blue-black precipitate to the backbone of flexible supercapacitors, electrochromic windows and carbon-capturing aerogels may finally reach its commercial destination.

Subject of Research: Polyaniline-carbon nanocomposite synthesis, properties and emerging applications

Article Title: Design and functional performance of polyaniline-carbon nanocomposites: synthesis, properties, and emerging applications

Article References: Nouira, A., & Bekri-Abbes, I. (2026). Design and functional performance of polyaniline-carbon nanocomposites: synthesis, properties, and emerging applications. Frontiers in Carbon, 5, Article 1925654. https://doi.org/10.3389/frcrb.2026.1925654

Image Credits: AI Generated

DOI: 10.3389/frcrb.2026.1925654

Keywords: polyaniline, carbon nanomaterials, supercapacitors, graphene, carbon nanotubes, electrochromic devices, CO2 capture, energy storage, nanocomposites, conducting polymers, biomass-derived carbon, electrochemical stability

The context for the study is stark. Ammonia, carbon monoxide, and sulfur dioxide are among the most consequential toxic gases in both industrial and domestic settings. Ammonia is ubiquitous in fertilizer production, refrigeration, and the chemical industry, and excessive exposure irritates the eyes, skin, and respiratory tract. Carbon monoxide is a colorless, odorless byproduct of incomplete fuel combustion, and even low concentrations can cause serious poisoning or death. Sulfur dioxide, released from industrial emissions and fossil fuel combustion, drives respiratory illness, acid rain, and broader atmospheric pollution. Sensors capable of monitoring these gases in real time at room temperature, without heating elements, are therefore a major goal in environmental sensing research.

Yet the environmental cost of sensors themselves has rarely been front and center. Most modern gas sensors are fabricated on petroleum-based polymer substrates such as polydimethylsiloxane, polyurethane, polystyrene, polyethylene terephthalate, polycarbonate, nylon, and polyimide. These materials are not biodegradable, which makes recovering valuable metals from the electrode materials of used devices a genuinely difficult process. As electronic waste has become one of the fastest-growing global waste streams, the research team argues that biodegradable substrates offer a promising alternative: at the end of a sensor’s lifetime, the substrate can disintegrate naturally, easing the recovery of harmful and valuable materials.

The active material at the heart of the new sensors is a modified polyaniline the authors call PAMD, standing for polyaniline doped with maleic acid and integrated with the anionic surfactant dioctyl sodium sulfosuccinate. Polyaniline is one of the most celebrated conducting polymers for gas sensing, but it has an Achilles heel: it is notoriously difficult to dissolve in either aqueous or organic media, which limits how it can be processed and applied. Solubility can be introduced by attaching alkyl or alkoxy groups to the aromatic ring through copolymerization, or, as in this study, by integrating surfactant molecules directly with the polymer chain.

To make PAMD, the team used chemical oxidative polymerization of aniline in water, adding ammonium peroxydisulfate as the oxidizing initiator, maleic acid as the dopant, and dioctyl sodium sulfosuccinate as the surfactant. After screening different molar ratios, they settled on an aniline to oxidant to dopant to surfactant ratio of 1:1:1:0.2, which yielded a dark green material with an electrical conductivity of about 10 to the power of minus 4 siemens per centimeter and, crucially, good solubility in organic solvents such as dimethylformamide and dimethyl sulfoxide. The surfactant’s role is to graft hydrophilic and hydrophobic functionality onto the polyaniline chains, rendering the polymer processable in both aqueous and non-aqueous conditions. At low surfactant concentrations the material was extremely difficult to prepare, while higher concentrations gave a well-dispersed product.

Characterization confirmed the design worked as intended. Ultraviolet-visible spectroscopy showed absorption bands at 300, 430, 590, and 880 nanometers, a pattern indicating the protonated, doped state of the polymer, with the band at 590 nanometers revealing incomplete doping that accounts for the modest conductivity. Fourier-transform infrared spectroscopy revealed the telltale signatures of the surfactant’s aliphatic carbon-hydrogen stretches alongside the quinoid and benzenoid ring vibrations characteristic of polyaniline, plus a strong carbonyl band confirming that the maleic acid dopant was incorporated into the chain. X-ray diffraction displayed peaks near 20 and 25 degrees in two-theta, corresponding to periodicity parallel and perpendicular to the polymer chains, indicating that the dopant and surfactant left the essential structural features of conventional polyaniline intact.

The coating process is strikingly simple. The researchers stirred 0.1 grams of PAMD into a milliliter of dimethylformamide to form a thick green paste, which was brushed onto cleaned, dried substrates cut into one-centimeter squares. Fish scales were recovered from fish waste, banana bracts were collected from a local vegetable market, and ordinary A4 printing paper was used as received. Two coats were applied and dried, and silver paint was added at two diametrically opposed edge points to provide electrical contact. The weight gain from coating was only about 26 milligrams, underscoring how little active material is needed.

When the coated substrates were exposed to ammonia at 5 parts per million, carbon monoxide at 7.1 parts per million, and sulfur dioxide at 3 parts per million, all at room temperature, the results revealed a clear hierarchy among the substrates. Fish scales coated with PAMD gave the strongest responses by far: exposure to ammonia drove resistance from 6.024 megaohms up to 7.001 megaohms in just two minutes, carbon monoxide dropped resistance from 7.416 to 6.808 megaohms, and sulfur dioxide lowered it from 5.202 to 4.955 megaohms. By contrast, the pressed PAMD pellets, with resistances in the kiloohm range, showed almost negligible changes, and paper and banana bract substrates fell in between. The explanation lies in morphology: a compact pellet packs polymer particles too tightly for gases to penetrate effectively, while the loosely packed coating on fish scales leaves ample polymer surface accessible to analytes. On paper and banana bracts, PAMD tends to occupy the pores of the substrate, limiting gas access.

The direction of the resistance change is itself diagnostic. Polyaniline is a p-type conducting polymer, so ammonia, a reducing gas, donates electrons that fill holes in the polymer, raising resistance. Carbon monoxide, through the positive charge of its resonance structure, withdraws electrons from unprotonated amine nitrogens and introduces additional holes, lowering resistance. Sulfur dioxide acts as an electron acceptor, drawing electrons from the polymer and likewise decreasing resistance. Recovery behavior was excellent: for both carbon monoxide and sulfur dioxide, resistance returned to within a fraction of its baseline in under two minutes, faster than the response time, and the sensors maintained repeatable performance over ten exposure cycles, retaining a high percentage of their initial response. Ammonia showed a larger residual drift, particularly on the fish scale substrate, because adsorbed ammonia molecules adhere more firmly and desorb more slowly.

Placed in context, the performance is genuinely competitive. Comparable polyaniline-based sensors typically detect ammonia at tens to hundreds of parts per million or sulfur dioxide at 10 to 50 parts per million, sometimes requiring elevated temperatures or ultraviolet light assistance, whereas the PAMD-coated biodegradable sensors responded to ammonia at 5 ppm, carbon monoxide at 7.1 ppm, and sulfur dioxide at 3 ppm with no additives and no heating. The authors suggest future work on optimizing coating thickness, selectivity, humidity effects, and flexible, wearable formats. If the field follows through, the humble fish scale, usually destined for the bin, may become a template for a new generation of disposable, compostable environmental monitors that protect human health without costing the planet.

Subject of Research: Processable polyaniline coated on biodegradable substrates for room-temperature chemiresistive detection of toxic gases

Article Title: Processable polyaniline modified biodegradable substrates as the electrode material for gas sensor application

Article References: Himadri Reddy, P. C., Sunitha, M. S., & Chandrasekaran, S. (2026). Processable polyaniline modified biodegradable substrates as the electrode material for gas sensor application. Frontiers in Sensors, 7, Article 1889042. https://doi.org/10.3389/fsens.2026.1889042

Image Credits: AI Generated

DOI: 10.3389/fsens.2026.1889042

Keywords: gas sensors, polyaniline, biodegradable substrates, fish scales, banana bracts, ammonia detection, carbon monoxide, sulfur dioxide, conducting polymers, room-temperature sensing, electronic waste, surfactant doping

Thermoelectric materials sit at the intersection of heat and electricity: when one side of such a material is hotter than the other, charge carriers diffuse from the hot region to the cold one, generating a voltage. The efficiency of this conversion is governed by a dimensionless figure of merit, ZT, which depends on the Seebeck coefficient, the electrical conductivity, and the thermal conductivity of the material. The problem, famously, is that these three quantities are entangled in awkward ways. Improving one often degrades another, which is why the best inorganic thermoelectrics — bismuth telluride and its relatives — are expensive, brittle, and often built from scarce or toxic elements such as tellurium, antimony, and lead.

Conducting polymers offer an appealing escape route. Polyaniline in particular is inexpensive, mechanically flexible, lightweight, and far less toxic than its inorganic rivals, and it can be synthesized by simple oxidative polymerization of aniline in water. Its weakness has always been modest thermoelectric performance: its electrical conductivity and Seebeck coefficient are individually unremarkable, and the power factor — the product of the Seebeck coefficient squared and the conductivity — has remained low. The new study attacks that limitation not by adding metal nanoparticles or carbon fillers, but by redesigning the polymerization chemistry itself with tailor-made ionic liquids.

Ionic liquids are salts that are liquid at or near room temperature, composed of bulky organic cations paired with organic or inorganic anions. Their defining virtues are negligible vapor pressure, high thermal stability, and an extraordinary capacity for structural tuning. In polymer synthesis they can play several roles at once: as solvents, as soft templates that steer the growing polymer into particular morphologies, and as dopants that insert counter-ions into the polymer backbone. Earlier work has shown that ionic liquids can drive polyaniline to form nanofibers and other nanostructures, and that adding ionic liquids to conducting polymer films can raise conductivity while preserving or even enhancing the Seebeck coefficient.

The research team, led by Mohamed Ali Mokrani of the Ecole Militaire Polytechnique in Algiers, together with colleagues at INSA Lyon and Université Paris-Est, took this idea further by employing peroxydisulfate-based ionic liquids as oxidants. Two variants were tested: EMImS₂O₈, built on the 1-ethyl-3-methylimidazolium cation, and BMImS₂O₈, based on the 1-butyl-3-methylimidazolium cation. Because the peroxydisulfate anion is itself a strong oxidizing agent, these ionic liquids could initiate the polymerization of aniline while simultaneously acting as structural modifiers, their bulky imidazolium cations interfering with the way polymer chains aggregate. A third ionic liquid, the Brønsted acidic HMImHSO₄, served as the dopant, protonating the emeraldine form of polyaniline to create mobile charge carriers.

The resulting composites were subjected to a battery of characterization techniques. Fourier-transform infrared spectroscopy and Raman spectroscopy confirmed the formation of the emeraldine salt phase and revealed interactions between the polymer and the imidazolium species, including hydrogen bonding of the kind previously documented between polyaniline and imidazolium salts. UV-Vis spectroscopy tracked the doping state of the polymer, X-ray diffraction probed its crystallinity and chain ordering, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy mapped the morphology and elemental composition of the composites. Together these measurements showed that the ionic liquids had substantially reorganized the polymer’s microstructure relative to polyaniline synthesized without them.

The thermoelectric measurements told the most compelling story. The composite prepared with the ethyl-substituted oxidant, PANI–EMImS₂O₈–HMImHSO₄, delivered an electrical conductivity of 106.97 S per meter at room temperature together with a Seebeck coefficient of 33.21 microvolts per kelvin. While the Seebeck coefficient remained moderate — as is typical for heavily doped conducting polymers — the combination produced a markedly improved power factor, the quantity that determines how much electrical power a thermoelectric leg of given geometry can deliver. The dimensionless figure of merit reached 5.76 × 10⁻⁴ at room temperature, approximately four hundred times the value measured for neat polyaniline synthesized under otherwise similar conditions.

The comparison with the butyl-substituted variant proved equally instructive. Changing only the alkyl chain length on the imidazolium cation altered the final thermoelectric performance, underscoring that the cation is not a passive spectator but an active participant in shaping chain packing, doping efficiency, and charge transport. This sensitivity to molecular architecture gives chemists a genuine design lever: by selecting cation size, anion chemistry, and dopant identity, they can tune the microstructure of the polymer at the nanoscale without ever changing its fundamental composition. The finding echoes the group’s earlier work on imidazolium ionic liquids in polypyrrole, in which the anionic moiety of the ionic liquid was shown to influence thermoelectric properties, and it aligns with broader evidence that ionic-liquid processing can simultaneously raise conductivity and Seebeck coefficient in polymers such as PEDOT:PSS.

It is important to keep the absolute numbers in perspective. A ZT of 5.76 × 10⁻⁴ is still far below the values of one to two that define state-of-the-art inorganic thermoelectrics, so nobody should expect polyaniline films to compete with bismuth telluride modules in high-power applications any time soon. But the relevant comparison for many emerging applications is not with power stations; it is with the alternatives for low-grade, distributed energy harvesting, where flexibility, processability, low cost, and mechanical compliance matter as much as raw efficiency. Flexible thermoelectric generators for wearable electronics, self-powered sensors, and coating of curved surfaces are exactly the niches where organic materials hold structural advantages that inorganic crystals cannot match.

The study also carries a broader message about how materials chemistry advances. Rather than searching for an entirely new polymer, the researchers showed that a rational, molecularly precise modification of a well-known synthesis route — swapping a conventional oxidant for an ionic liquid that doubles as a structural template — can multiply performance by orders of magnitude. The work was supported by the Ecole Militaire Polytechnique and the Ecole Nationale Préparatoire aux Etudes d’Ingéniorat, and its authors suggest that rationally designed ionic liquid systems offer a general route to tailoring the microstructure and optimizing the thermoelectric properties of conductive polymers. If subsequent studies can push the power factor further, perhaps by combining ionic-liquid templating with nanostructuring or hybrid fillers, the dream of wrapping waste-heat harvesters around engines, pipes, and even skin may come one flexible step closer to reality.

Subject of Research: Ionic liquid-assisted synthesis of polyaniline composites for enhanced thermoelectric performance

Article Title: Evaluation of thermoelectric performance of polyaniline-based peroxydisulfate ionic liquid composites

Article References: Mokrani, M. A., Bekkar Djelloul Sayah, Z., Chabane, H., Mekki, A., Bourenane Cherif, Y., Nedjar, L., Kaufa, M., Slimani, Z. Y., Livi, S., & Durastanti, J. F. (2026). Evaluation of thermoelectric performance of polyaniline-based peroxydisulfate ionic liquid composites. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13899-y

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13899-y

Keywords: thermoelectrics, polyaniline, ionic liquids, peroxydisulfate, conducting polymers, waste heat recovery, power factor, Seebeck coefficient, doping, energy materials, imidazolium, figure of merit

The significance of the target analytes is difficult to overstate. Hexavalent chromium, released into surface and groundwater by leather tanning, electroplating, pigment manufacturing and other industries, is a recognised carcinogen whose oxyanion species readily cross cell membranes and wreak oxidative damage on DNA and proteins. Ferric iron, while an essential nutrient, becomes a contaminant of its own when excessive concentrations stain water, promote the growth of iron bacteria in distribution systems, and, in biological contexts, catalyse the formation of hydroxyl radicals through Fenton chemistry, a process implicated in neurodegenerative disease pathology. Conventional detection of these ions relies on instrumental techniques such as atomic absorption spectroscopy or inductively coupled plasma mass spectrometry, which are accurate but expensive, laboratory-bound and poorly suited to real-time field screening. Fluorescent chemosensors offer an attractive alternative because the signal can be read with a simple spectrometer or even the naked eye under ultraviolet light.

The Indian team’s material is a marriage of two well-understood components. Polyaniline is the archetypal conducting polymer, prized for its reversible acid-base doping chemistry, environmental stability and intrinsic fluorescence, while sulfonated phenol formaldehyde is a water-soluble anionic resin whose sulfonate groups act as dopant and steric stabiliser at once. By polymerising aniline in the presence of varying amounts of the sulfonated resin, the researchers tuned the composition of the resulting composites, and the interplay between the conducting polymer backbone and the sulfonated matrix proved decisive for every property they measured. The composites were characterised exhaustively by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis and thermogravimetric analysis, confirming successful composite formation and revealing how the resin content reshapes the polymer’s morphology and thermal behaviour.

Electrical conductivity measurements singled out one member of the family. The PANI–SPF 3 composite, with an intermediate resin loading, achieved a conductivity of 6.31 multiplied by 10 to the power of minus 3 siemens per centimetre, the highest in the series. This optimum reflects a classic doping balance: enough sulfonated resin to protonate and order the polyaniline chains into the electrically favourable emeraldine salt form, but not so much that the insulating resin dilutes the conductive pathways. The same intermediate composition also turned out to be the star performer optically and biologically, a coincidence the authors attribute to the density of accessible binding sites and the quality of the photophysical pathway within the material.

The sensing experiments were carried out in a dimethyl sulfoxide and water mixture, nine parts to one by volume, using ultraviolet-visible absorption and fluorescence spectroscopy. In the pristine state, the PANI–SPF 3 composite emits a measurable fluorescence signal. When aliquots of Cr6+ or Fe3+ are added, that emission is progressively extinguished, and the degree of quenching follows a linear Stern-Volmer relationship across the concentration range studied. Linearity in Stern-Volmer plots is the fingerprint of a well-behaved quenching mechanism, and it is what allows the intensity ratio to be converted directly into an ion concentration. The nanomolar detection limits derived from these plots represent an extraordinary amplification factor: a few hundred millionths of a gram of toxic metal per litre is enough to visibly darken the sensor’s output.

Several physical mechanisms can drive fluorescence turn-off in conducting polymer composites, and the authors discuss the likely contributors in terms of complex formation between the metal ions and the electron-rich nitrogen and sulfonate sites on the composite. Divalent and trivalent metal cations can coordinate to these sites, opening non-radiative decay channels or promoting photoinduced electron transfer that drains the excited-state energy before a photon can be emitted. Inner filter effects, in which the metal ion absorbs the excitation or emission light, may also contribute. The density functional theory calculations reported in the paper lend computational weight to this picture, modelling the complexes formed between the composite’s constituent units and the metal ions and clarifying why Cr6+ and Fe3+ quench so efficiently. The same computational framework was extended to rationalise the observed antimicrobial effects, connecting the electronic structure of the material to its biological activity.

The antimicrobial results are arguably the study’s most surprising dimension. All six composites were screened against Escherichia coli, a Gram-negative bacterium, and Staphylococcus aureus, a Gram-positive one, and PANI–SPF 3 again led the pack, producing zones of inhibition that the authors describe as notable in comparison with Gentamicin, a clinical antibiotic used as the reference standard. Conducting polymers have a growing reputation as antimicrobial agents, with proposed mechanisms including disruption of bacterial membrane potentials, electrostatic adhesion of the positively charged polymer backbone to negatively charged cell surfaces, and interference with electron transport across the membrane. The sulfonated resin component may add further activity by chelating essential metal ions from the microbial environment. A dual-function material that both reports contamination and suppresses microbial growth is an unusual and appealing combination for water treatment and packaging applications.

Safety is the perennial question for any material proposed for contact with drinking water, and the team addressed it directly. An MTT cytotoxicity assay, which measures the metabolic activity of cultured cells as a proxy for viability, showed that the PANI–SPF 3 composite is non-cytotoxic at concentrations up to 500 micrograms per millilitre. That margin provides a measure of reassurance for applications in which the sensor might contact potable water or come into contact with biological surfaces, although the authors are careful to frame this as an early-stage result rather than a regulatory clearance. The work also builds on the group’s own recent lineage of sulfonated-resin composites, including polyaniline and polypyrrole paired with sulfonated naphthalene formaldehyde and sulfonated melamine formaldehyde systems, which targeted chromium speciation, lead and mercury sensing, antifungal action and corrosion protection, suggesting a versatile materials platform rather than a one-off discovery.

What distinguishes this study within the crowded field of fluorescent heavy-metal sensors is the combination of sensitivity, simplicity and multifunctionality achieved with inexpensive, water-processable ingredients. Many high-performance chemosensors rely on elaborate organic syntheses, rare-earth dopants or quantum dots that complicate scale-up and raise their own toxicity questions. Here, the synthesis is a one-pot oxidative polymerisation in water, the characterisation is standard, and the resulting material conducts electricity, senses two priority contaminants at nanomolar levels, and kills bacteria on contact. The linear Stern-Volmer response means quantification requires nothing more exotic than a fluorescence spectrometer and a calibration curve, and the turn-off format, while inherently susceptible to false positives from other quenchers, benefits from the strong selectivity implied by the complexation chemistry and the DFT analysis.

The road from laboratory cuvette to field deployment remains long, as it always does for fluorescent sensors, with real water matrices, competing ions, pH variation and sensor regeneration all demanding attention. But the PANI–SPF work offers a compelling proof of concept that the humblest of industrial polymers, phenol formaldehyde chemistry dating back more than a century, can be re-engineered through sulfonation and combination with a conducting polymer into a twenty-first-century analytical tool. If subsequent studies confirm the selectivity in genuine environmental samples and establish long-term stability, composites of this kind could find their way into portable water-quality kits, smart packaging indicators and antimicrobial filtration membranes, turning the glow of a polymer film into an early-warning system for the contaminants that most threaten the world’s drinking water.

Subject of Research: Fluorescent PANI–SPF polymer composite chemosensor for detecting Cr6+ and Fe3+ ions in water with antimicrobial and DFT analysis

Article Title: Development of a polyaniline – sulfonated phenol formaldehyde (PANI–SPF) composite as a fluorescence ‘Turn-off’ chemosensor for Cr6+ and Fe3+ ions, antimicrobial application and DFT investigation

Article References: Rajeswari, M., & Kumar, K. K. S. (2026). Development of a polyaniline – sulfonated phenol formaldehyde (PANI–SPF) composite as a fluorescence ‘Turn-off’ chemosensor for Cr6+ and Fe3+ ions, antimicrobial application and DFT investigation. Polymer Bulletin, 83(12), Article 679. https://doi.org/10.1007/s00289-026-06738-2

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06738-2

Keywords: polyaniline, sulfonated phenol formaldehyde, fluorescence chemosensor, hexavalent chromium, ferric iron, heavy metal detection, Stern-Volmer quenching, antimicrobial activity, DFT, water quality, conducting polymer, limit of detection

The star of the study is the MXene, a family of two-dimensional carbides and nitrides first discovered by etching layered ceramics into atomically thin flakes. Unlike graphene, which is pure carbon, MXenes carry a menagerie of surface terminations, including oxygen, fluorine, and hydroxyl groups, that make them hydrophilic and electrically conductive. That combination has made them one of the most closely watched electrode materials of the past decade. Yet MXenes carry a stubborn flaw: their flat, sticky sheets love to restack, collapsing into dense layers that block the electrolyte from reaching much of the stored charge. A supercapacitor electrode, after all, works only where ions can go, and a restacked film is an ion-proof fortress.

The Indian team’s answer was to wedge polyaniline between the MXene sheets. Polyaniline, or PANI, is one of the oldest and cheapest conducting polymers, prized for its ease of synthesis and its ability to store charge through fast, reversible redox reactions. When the two materials share an electrode, each covers the other’s weaknesses. The MXene supplies a robust, metallically conductive scaffold and mechanical resilience; the polymer chains pry the sheets apart, preventing restacking, and add pseudocapacitance of their own. Field-emission scanning electron microscopy in the new work confirmed the outcome: the polymer effectively suppressed MXene restacking and generated a porous, interconnected architecture that lets ions move freely through the film.

The fabrication route is the study’s quiet revolution. Rather than growing polymers directly on the MXene surface through in-situ polymerization, grafting, or supercritical fluid processing, techniques that many earlier MXene-PANI papers have relied on, the researchers prepared a composite slurry and coated it onto a graphite substrate. Slurry coating is the same workhorse method used to mass-produce lithium-ion battery electrodes, which means the approach inherits an industrial pedigree that laboratory-only synthesis routes lack. The authors describe the method as simple, cost-effective, and scalable, and they deliberately set out to establish a correlation between the structural, morphological, and electrochemical properties of the resulting films, connecting what the material looks like to how it performs.

The electrochemical numbers are where the synergy becomes measurable. The composite electrode delivered a specific capacitance of 406 farads per gram at a current density of 0.5 amperes per gram, a figure that comfortably exceeded what the researchers measured for pristine MXene and pristine polyaniline electrodes prepared the same way. Specific capacitance measures how much charge an electrode can store per unit mass, and values above 400 farads per gram at modest current densities place the material among the competitive performers in the aqueous supercapacitor literature. Just as important, the electrode showed improved rate capability, meaning it held onto a substantial fraction of that capacitance even when charged and discharged faster, a property that matters enormously for real devices that must deliver power in bursts rather than at leisure.

Impedance measurements added a third pillar of evidence. The composite exhibited low internal resistance, which the authors attribute to the synergistic interaction between the conductive MXene layers and the PANI chains. In an electrode, internal resistance is the enemy of both power and efficiency: every ohm lost inside the material turns charging energy into waste heat and slows the delivery of current. By facilitating rapid electron transport along the metallic MXene sheets and efficient electrolyte penetration through the polymer-opened pores, the hybrid architecture attacks resistance from both directions at once, the electronic and the ionic.

Durability, the graveyard of many promising pseudocapacitive materials, is where the study delivers its most striking result. After 10,000 full charge-discharge cycles, the electrode retained 85.4 percent of its initial capacitance and maintained a coulombic efficiency of 95.1 percent. Coulombic efficiency measures how much of the charge pumped into the electrode comes back out on each cycle, and values in the mid-nineties indicate that parasitic side reactions, the slow chemical leaks that degrade electrodes and electrolytes, are being kept firmly in check. For a polymer-containing electrode, which might otherwise swell, crack, or shed material over thousands of cycles, that level of stability suggests the MXene scaffold is doing real mechanical work, anchoring the polymer chains as they repeatedly accept and release ions.

The physical chemistry behind that synergy is worth unpacking. Supercapacitors store charge in two complementary ways. Electric double-layer capacitance accumulates ions at the electrode surface, a process that is fast but limited by available area. Pseudocapacitance, by contrast, involves fast surface redox reactions in which the electrode material itself changes oxidation state, storing far more charge per unit of surface. MXenes contribute both mechanisms, thanks to their conductive sheets and their redox-active surface terminations, while polyaniline is a pseudocapacitive workhorse that shuttles between distinct protonated and deprotonated states. In the hybrid, the polymer’s redox capacity is wired directly into the MXene’s conductive network, so electrons generated in the polymer have an immediate highway out of the film, and ions arriving from the electrolyte find a porous, wetted landscape rather than a sealed stack of sheets.

Context matters for judging the advance. MXene-PANI composites have been reported before, including organ-like Ti3C2 architectures made by chemical grafting, hierarchical hybrids on carbon fibers, and self-assembled films in which polymer nanoparticles open ion-transport channels between sheets. Many of those routes, however, involve multi-step synthesis, specialized reagents, or processing conditions that complicate scale-up. The new work does not claim a record capacitance; instead, its contribution is methodological and diagnostic, demonstrating that a straightforward slurry-coating route can produce an electrode whose performance rivals composites made by far more convoluted chemistry, while explicitly mapping the link between microstructure and electrochemistry. In a field where reproducibility and manufacturability often lag behind headline numbers, that emphasis is significant.

The broader stakes are considerable. Flexible and wearable electronics, regenerative braking systems, grid buffering for renewable power, and fast-charging transport all need storage devices that tolerate high power and hundreds of thousands of shallow cycles, a niche where supercapacitors outperform batteries. Electrode materials that combine high capacitance, low resistance, and long cycle life, made by processes compatible with existing coating lines, are the raw material of that future. The VIT-AP team, supported by the university’s RGEMS grant and a Collaborative Research Scheme project from UGC-DAE CSR, has shown that one of the most celebrated material pairings in electrochemistry can be brought to life with a method simple enough to be handed to a factory. If the slurry-coated MXene-polyaniline architecture can be translated from graphite substrates in the laboratory to full devices on production lines, the humble coating step may prove to be the most consequential part of the whole supercapacitor.

Subject of Research: MXene/polyaniline composite electrodes for supercapacitor energy storage

Article Title: Facile fabrication of a MXene/PANI hybrid electrode for enhanced electrochemical performance in supercapacitors

Article References: M, T., & Karuppanan, S. (2026). Facile fabrication of a MXene/PANI hybrid electrode for enhanced electrochemical performance in supercapacitors. Ionics. https://doi.org/10.1007/s11581-026-07545-5

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07545-5

Keywords: MXene, polyaniline, supercapacitor, energy storage, electrode materials, pseudocapacitance, slurry coating, electrochemistry, two-dimensional materials, cycle stability, specific capacitance, conducting polymers

The target molecule in the study, Murexide, is an anionic dye with a complex aromatic structure, and it serves as a representative challenge for a much broader class of water pollutants. Synthetic dyes are notoriously difficult to remove with conventional biological treatment because their chemical stability and intense coloration persist through standard processing. Adsorption, the process by which dissolved molecules bind to the surface of a solid material, remains one of the most attractive alternatives because it is simple, scalable, and can be tuned by engineering the adsorbent itself. The question the Tunisian team set out to answer was which surface chemistry works best, and whether combining two very different materials produces something better than either alone.

The first adsorbent they tested was pure polyaniline, or PANI, a nitrogen-rich conducting polymer that has long fascinated materials scientists for its tunable electronic states and dense array of amine and imine functional groups. In its doped emeraldine state, the form confirmed in this study by physicochemical characterization, PANI carries protonated sites that can attract negatively charged dye molecules through electrostatic forces. The second adsorbent, labeled ACPO, was produced by converting raw Posidonia oceanica biomass into a hierarchically porous activated carbon. This seagrass, which forms vast underwater meadows across the Mediterranean and washes ashore in enormous quantities, has previously attracted attention as a low-cost precursor for carbon materials, including in studies targeting hexavalent chromium removal. The third material was a hybrid composite in which PANI was incorporated homogeneously throughout the porous carbon framework.

Characterization of the composite revealed something crucial about why the hybrid works. Strong interfacial interactions, mainly π–π stacking between the aromatic backbones of the polymer and the graphitic planes of the carbon, along with hydrogen bonding, ensured that the polymer phase dispersed evenly across the carbon surface rather than clumping into inaccessible aggregates. This good dispersion preserved the accessible adsorption sites of both components, meaning the composite retained the structural porosity of the activated carbon while gaining the surface functionality of the polymer. In practical terms, the hybrid material offers two complementary capture mechanisms in a single particle: the internal pore network of the carbon and the chemically active polymer coating on its surfaces.

The performance numbers tell a striking story. Pure PANI achieved a maximum adsorption capacity of 333.33 milligrams of Murexide per gram of material, while the PANI/ACPO composite reached 322.58 milligrams per gram, a nearly identical figure. The activated carbon alone, by contrast, managed only 149.25 milligrams per gram. The conclusion is unambiguous: the polymer phase dominates the uptake chemistry, and the carbon’s primary contribution is architectural rather than chemical. Yet this is precisely what makes the composite so interesting from a sustainability standpoint. By using the seagrass-derived carbon as a scaffold, the researchers can deliver PANI-level performance while consuming far less of the synthetic polymer, cutting both cost and the environmental footprint of adsorbent production.

Equilibrium modeling added another layer of insight. For both PANI and the composite, the experimental data fit the Langmuir isotherm model, which describes adsorption as a process approaching a finite monolayer of dye molecules on energetically uniform sites, with correlation coefficients above 0.96. The bare activated carbon behaved differently, following the Freundlich model with a correlation coefficient of approximately 0.966, a signature of surface heterogeneity and multilayer adsorption. This divergence makes physical sense. The raw carbon presents a patchwork of different pore sizes and surface chemistries, each binding dye with different strengths, whereas the polymer-coated materials present a more uniform population of binding sites dominated by the polymer’s functional groups.

Kinetic analysis showed that uptake over time followed the pseudo-second-order model for all three materials, indicating that the rate-limiting step involves chemisorption-like interactions between the dye and the surface rather than simple mass transfer alone. However, the researchers also found that intraparticle diffusion and boundary layer effects contributed to the overall adsorption rate, particularly for the activated carbon. This observation highlights the role of pore diffusion in mass transfer: dye molecules must physically travel through the tortuous internal network of the carbon before reaching binding sites deep within its structure. For the composite, the polymer’s presence on external and near-surface sites shortens this journey, which helps explain why the hybrid matches pure PANI despite containing less of the high-capacity polymer phase.

Thermodynamic measurements completed the mechanistic portrait. The Gibbs free energy change was negative, confirming that adsorption is spontaneous; the enthalpy change was positive, meaning the process is endothermic and actually improves at elevated temperatures; and the entropy change was positive, indicating increasing randomness at the solid–liquid interface as dye molecules are released from solution and immobilized on the surface. Taken together, these parameters point to adsorption dominated by physical interactions rather than strong chemical bond formation. The mechanistic picture that emerges is one of coexisting uptake pathways: electrostatic attraction between protonated polymer sites and the anionic dye, π–π donor–acceptor associations between aromatic moieties on the adsorbent and the dye’s ring system, hydrogen bonding, and diffusion through the porous network.

What makes this work resonate beyond the laboratory is the circular economy logic at its core. Posidonia oceanica is not a cultivated crop; it is a naturally shed biomass that accumulates on beaches in quantities large enough to create disposal problems for coastal municipalities. Converting this waste stream into a hierarchically porous activated carbon transforms a nuisance into a functional material, and pairing it with a modest loading of polyaniline yields performance comparable to the pure polymer at a fraction of the polymer cost. The authors report that the research received no specific grant funding, and they declare no competing interests, framing the work as a straightforward contribution to the growing field of biomass-derived adsorbents for wastewater remediation.

The study also arrives amid intensifying global concern about water pollution and its health consequences, with recent literature documenting human health risks from contaminated water and the challenges that conventional biological and physicochemical treatments face against persistent organic pollutants. Adsorption with sustainable, low-cost materials is increasingly viewed as a practical complement to advanced treatment trains, particularly in regions where expensive imported adsorbents are out of reach. By systematically comparing a conducting polymer, a marine-biomass carbon, and their hybrid across isotherms, kinetics, and thermodynamics, Hassen and Ben Slimane have provided a template for how such materials should be evaluated before deployment. The PANI/ACPO composite, combining structural porosity with rich surface functionality, stands out as a sustainable candidate for efficient Murexide removal, and the mechanistic framework established here should transfer readily to other anionic dyes and ionic pollutants. As Mediterranean coastlines continue to receive their annual deliveries of dead seagrass, the idea that this humble biomass could anchor next-generation water treatment technology is no longer speculative; it is now supported by quantitative, mechanistically grounded evidence.

Subject of Research: Development and comparative evaluation of polyaniline, Posidonia oceanica-derived activated carbon, and their composite as sustainable adsorbents for Murexide dye removal from water

Article Title: From marine biomass to sustainable adsorbents: comparative evaluation of polyaniline, Posidonia oceanica-derived activated carbon, and their composite for Murexide removal

Article References: Hassen, A., & Ben Slimane, A. (2026). From marine biomass to sustainable adsorbents: comparative evaluation of polyaniline, Posidonia oceanica-derived activated carbon, and their composite for Murexide removal. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38260-3

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38260-3

Keywords: adsorption, polyaniline, activated carbon, Posidonia oceanica, Murexide, dye removal, wastewater treatment, marine biomass, composite materials, isotherm modeling, adsorption kinetics, water pollution

The rationale behind the design rests on the complementary strengths of its two nanomaterials. Polyaniline is prized among conducting polymers for its mechanical robustness, low cost, electrical conductivity and chemically active conjugated backbone of alternating diamine and diimine units. However, its conductivity drops markedly at neutral pH, precisely the condition under which environmental water samples are typically analysed. Quantum dots, by contrast, offer quantum confinement effects, abundant edge sites and favourable electronic properties. By marrying the two, the researchers aimed to create a synergistic nanocomposite in which the quantum dots act as electron mediators, reducing charge transfer resistance and compensating for polyaniline’s weakness at neutral pH.

Fabrication began with the aqueous synthesis of the quantum dots themselves. Gadolinium chloride was combined with 3-mercaptopropionic acid in an alkaline solution, where the deprotonated thiol groups coordinated to the rare-earth metal, a transition signalled by the solution turning from clear to white. Separate sodium borohydride reductions of tellurium and selenium powders generated the chalcogenide precursors, which were injected sequentially into the gadolinium solution, the more reactive tellurium first. After refluxing at 100 degrees Celsius for an hour under anaerobic conditions, the reaction was quenched in an ice bath and the product washed and centrifuged. The result was a water-soluble, thiol-capped quantum dot suitable for biological interfacing.

The polyaniline layer was grown directly on a glassy carbon electrode by electropolymerising aniline in hydrochloric acid over thirty cyclic voltammetry cycles, producing the thin green deposit characteristic of the emeraldine salt form. This form matters: of polyaniline’s three redox states, only the emeraldine salt is both electrically conductive and stable in air and moisture, unlike the fully oxidised pernigraniline or the fully reduced leucoemeraldine. The nanocomposite was then co-deposited from a solution containing aniline, the quantum dots and acid, with the carboxylic acid termini of the capping ligand activated by EDC and NHS chemistry to form stable amide bonds with the amine groups of the polymer.

Spectroscopic characterisation confirmed the chemistry. Fourier transform infrared spectra of the nanocomposite showed a new band at 881 wavenumbers assigned to the gadolinium-sulfur stretching vibration, alongside shifts at 2977 and 1639 wavenumbers consistent with conversion of the carboxylic acid group into an amide linkage. Raman spectroscopy of the modified electrode revealed the characteristic D and G bands of graphitic carbon, with a decreasing defect-to-graphitic ratio indicating that the polymer coating dominated over disordered carbon sites. X-ray diffraction confirmed a cubic crystal structure for the quantum dots with crystallite sizes between 10 and 32 nanometres, averaging 17 nanometres.

Imaging and scattering analyses added further detail. Scanning electron microscopy showed quantum dot nanocrystals bound along the polymer nanofibres in a well-defined distribution, and energy-dispersive X-ray spectroscopy detected carbon, oxygen, sulfur, nitrogen, tellurium and selenium, with gadolinium present only in trace amounts, a limitation the authors attribute to the detection threshold of the EDS system. Small-angle X-ray scattering revealed that the quantum dots adopt core-shell shapes while the composite takes on a dumbbell geometry, and that introducing the dots onto polyaniline actually reduced particle size, improving dispersion and preventing the agglomeration that could otherwise impair conductivity and sensing performance.

The sensing element itself is a thiolated aptamer, a short single-stranded DNA sequence that folds into a defined three-dimensional structure upon binding its target. The team compared thiolated and non-thiolated versions of the CoV-RBD-4C aptamer and found the thiolated variant superior, reaching optimal electrocatalytic performance after just seven minutes of incubation in the presence of 10 nanomolar spike glycoprotein, compared with eleven minutes for the non-thiolated version. The rapid response reflects the strong covalent attachment achieved through thiol-ene chemistry between the aptamer’s thiol group and alkene functionalities on the nanocomposite surface, which produces a well-oriented monolayer with improved accessibility and stability. Bovine serum albumin was then applied to block any remaining non-specific binding sites.

When the finished sensor was exposed to increasing concentrations of spike glycoprotein, the anodic current decreased in proportion to concentration, an inverse relationship the authors explain through the aptamer’s conformational switch. Upon binding the spike protein, the aptamer folds into its three-dimensional recognition structure, and the resulting electrostatic repulsion hinders electron transfer through the film. Using square wave voltammetry across a concentration range of 0 to 0.95 femtomolar in phosphate-buffered saline, the team obtained a linear response between 0.45 and 0.80 femtomolar, with a limit of detection of 0.04 femtomolar and a limit of quantification of 0.4 femtomolar, alongside a sensitivity of 7.55 times ten to the minus four microamperes per femtomolar.

The critical test came with real environmental samples. Effluents from two South African wastewater treatment plants, Darville and Goudkoppies, were spiked with spike glycoprotein at three concentrations spanning 0.40 to 0.80 femtomolar. The sensor achieved recoveries of 98.6 to 101.4 percent with relative standard deviations below 1.4 percent in the Darville samples, and 91.5 to 103.1 percent with deviations up to 2.5 percent at Goudkoppies, performance figures that demonstrate the device can function in the chemically complex matrix of treated wastewater rather than only in idealised buffer solutions.

The implications extend beyond the current pandemic. Wastewater-based epidemiology has relied largely on reverse transcription polymerase chain reaction, the gold standard, but that approach requires laboratory infrastructure that many low-income and rural regions lack. Because the aptasensor is portable, inexpensive and amenable to miniaturisation, the authors suggest it could serve as an alternative environmental or clinical diagnostic tool during future disease outbreaks, and potentially be adapted to other biomarkers. They note that further work should optimise the number of electropolymerisation cycles to probe stability, and test the sensor against structurally similar proteins to fully establish its selectivity and durability in the field.

Subject of Research: An electrochemical aptasensor combining polyaniline and gadolinium telluride selenide quantum dots for ultrasensitive detection of SARS-CoV-2 spike glycoprotein in wastewater

Article Title: Polyaniline metal dichalcogenide-based amplified aptasensor for SARS-CoV-2 spike glycoprotein detection in wastewater

Article References: Gazu, N. T., Fuku, X., Cabunda, Z. N., Mamba, B. B., & Feleni, U. (2026). Polyaniline metal dichalcogenide-based amplified aptasensor for SARS-CoV-2 spike glycoprotein detection in wastewater. Discover Electrochemistry, 3(1), Article 59. https://doi.org/10.1007/s44373-026-00146-x

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00146-x

Keywords: aptasensor, SARS-CoV-2, spike glycoprotein, wastewater surveillance, polyaniline, quantum dots, electrochemical biosensor, nanocomposite, thiolated aptamer, gadolinium telluride selenide, femtomolar detection, waterborne epidemiology

The synthetic route is deliberately straightforward. Either m-aminophenol or m-chloroaniline, or both together at ratios ranging from 9:1 down to 1:9, is dissolved in 1 M hydrochloric acid and polymerised at 0–5 °C by the dropwise addition of ammonium persulfate, a strong oxidising agent. After five hours of stirring and an overnight rest, a dark green precipitate of the conducting salt form is recovered, washed, dried, and ground into powder. Yields for the homopolymers and copolymers all exceeded 70 percent, indicating that the oxidative polymerisation procedure is efficient and reproducible. The colour changes that accompany the reaction tell their own story: the initially colourless monomer solution turns blue as oligomeric species form and then deepens to dark green as the emeraldine salt of the conductive polymer accumulates. This autocatalytic behaviour, the study notes, is shaped by the choice of oxidant and the concentrations of both dopant and reactants.

Structural confirmation came primarily from Fourier transform infrared spectroscopy. In the homopolymers, characteristic O–H and N–H stretching peaks appear near 3230 and 3348–3315 cm⁻¹ respectively, while in the copolymers these vibrations merge into a broad band between 3196 and 3244 cm⁻¹, a signature the author attributes to weak hydrogen bonding between the hydroxyl group and nitrogen atoms along the chain. The asymmetric stretching modes of the quinoid and benzenoid rings, found at 1598 and 1495 cm⁻¹ in the homopolymers, shift to 1564 and 1477 cm⁻¹ in the copolymers, confirming the formation of a genuinely conjugated backbone in which both monomer units are incorporated. The C–Cl stretching band, located at 775 cm⁻¹ in homopolychloroaniline, shifts to 779 cm⁻¹ in the copolymers and, crucially, grows in intensity as the chloroaniline fraction of the feed increases, providing direct visual evidence that monomer composition is faithfully transferred into copolymer composition.

Ultraviolet–visible spectroscopy reinforced this picture of a tunable conjugated system. The first absorption band, arising from the π–π* transition of the benzenoid ring, appears at 283 nm for poly(m-aminophenol) and 281 nm for poly(m-chloroaniline), while the copolymers show values that shift with composition, reaching 305 nm at the highest chloroaniline loading. A second broadband near 377 nm corresponds to an n–π* transition, essentially a charge transfer from the benzenoid ring to the quinoid ring, and broad polaron bands in this region indicate significant doping, protonation, and hydrogen bonding within the polymer chain. As the chloroaniline content rises, the absorption maximum red-shifts and the vibronic fine structure sharpens, both hallmarks of an extended π-conjugated system whose electronic structure is being systematically reshaped by the electron-withdrawing chlorine substituent at the meta position.

Perhaps the most striking quantitative result concerns electrical conductivity, measured in solution at 250 ppm in dimethyl sulfoxide. Homopoly(m-aminophenol) conducts at 441.4 μS cm⁻¹, while homopoly(m-chloroaniline) manages only 341 μS cm⁻¹, the latter hampered by the meta-positioned chlorine atom, which produces a non-planar conformation, increases disorder in the backbone, and restricts electron mobility. The copolymers, however, chart a clear upward trajectory as chloroaniline content increases: from 436 μS cm⁻¹ at the 10 percent loading to 989 μS cm⁻¹ at 70 percent, and a maximum of 1277 μS cm⁻¹ at 90 percent. The explanation lies in a productive electronic partnership: electron-rich aminophenol rings sit adjacent to electron-deficient chloroaniline units, generating enhanced electron resonance and charge carriers, while the hydroxyl group promotes conjugation, hydrogen bonding, and electron delocalisation that collectively outweigh the inductive damping effect of chlorine.

Beyond qualitative band assignment, the study exploits FTIR as a genuine quantitative analytical tool. Using the C–N–C absorption near 1280 cm⁻¹ as an internal standard because it appears regardless of composition, and the 779 cm⁻¹ C–Cl band as the composition-sensitive peak, the author applied the Beer–Lambert law with a tangent baseline to calculate absorbance ratios. The ratio of the C–Cl to C–N–C intensities scales linearly with the chloroaniline fraction in the feed, passing through the origin, and the data show high accuracy and reproducibility. This quantitative approach, the paper notes, has broad practical relevance, from monitoring copolymer composition and detecting additives to tracking plastic waste recycling and microplastic pollution, and it demonstrates that infrared spectroscopy can serve as a rapid, solvent-free quality-control method for these conductive materials.

Thermal stability was assessed by thermogravimetric analysis under nitrogen at a heating rate of 10 °C per minute up to 900 °C. All samples showed a characteristic four-stage degradation profile. Initial weight loss between 22 and 100 °C, about 9.3 percent for homopolymers and 6.1 percent for copolymers, reflects the removal of trapped water and physically adsorbed molecules. A second stage between 100 and 200 °C, roughly 16.5 percent, corresponds to the loss of dopant species such as water and hydrochloric acid. The third stage, spanning 200 to 350 °C with a 20–31.5 percent loss, involves the elimination of oligomers and low-molecular-weight fractions, and the final stage from 350 to 550 °C, with a dramatic 76–80 percent decline, represents the chemical breakdown of the backbone itself, leaving a carbon-rich residue of about 20–22 percent. Encouragingly, all homopolymers and copolymers remain thermally stable up to approximately 500 °C, placing them comfortably within the operating window of most electronic and sensing applications.

Scanning electron microscopy revealed how composition sculpts surface morphology. Poly(m-aminophenol) alone displays a rough surface studded with randomly distributed spherical structures on microscopic particles. As the chloroaniline fraction increases, the morphology progressively evolves toward that of poly(m-chloroaniline), and porosity rises in step with composition. This is far from a cosmetic detail: greater porosity means more surface area and more active binding sites, which makes the copolymers attractive candidates for dye adsorption and gas sensing. Related polyaniline derivatives are already proven performers in water purification, with poly-m-chloroaniline removing anionic dyes such as indigo carmine and eosin Y at rates of 98 and 99 percent within 25 minutes, driven by hydrogen bonding, π interactions, and electrostatic attraction between the dye molecules and the amine, imine, and chlorine functional groups on the polymer surface.

The biological findings add an unexpected dimension. Tested by agar diffusion against Gram-negative E. coli and Gram-positive Staphylococcus sp., the polymers showed clear antibacterial activity that tracked with composition. Poly(m-aminophenol) proved most effective against E. coli, while poly(m-chloroaniline) was the weakest, and increasing the chloroaniline content in the copolymers reduced their activity against that organism. The mechanism, as the study and prior literature describe it, rests on the polymers’ ability to form hydrogen bonds with phosphorus- and sulfur-rich components of bacterial cells, including proteins and DNA, and on the positively charged, protonated state of polyaniline-type backbones, which bind to the negatively charged lipopolysaccharide membranes of Gram-negative bacteria. Hydrophobic phenyl segments then disrupt the membrane core, causing leakage of cellular contents, loss of membrane potential, and ultimately cell lysis, while the polymers can also promote the release of hydrogen peroxide and hydroxyl radicals that oxidise bacterial biomolecules.

Taken together, the study shows that chemical oxidative copolymerisation offers a simple yet remarkably effective lever for tailoring conductive polyaniline derivatives. By varying only the monomer feed ratio, the author produced a family of materials whose solubility, conjugation length, conductivity, porosity, and antibacterial potency all shift in predictable, composition-dependent ways. The 1:9 aminophenol-to-chloroaniline copolymer emerged as the best conductor of the series, a result that points toward applications in antistatic materials, chemical sensors, and other electrically active polymer systems where processing ease and tunable conductivity matter. The author cautions that this work focused primarily on synthesis, spectroscopic characterisation, and conductivity, and that future studies should probe how oxidant concentration, acid strength, temperature, and polymerisation time influence molecular weight, morphology, and performance. Even so, the central message is clear: mixing a hydrophilic, electron-donating monomer with a hydrophobic, electron-withdrawing one yields conductive polymers that are more soluble, more processable, and in some cases more biologically active than either parent homopolymer alone.

Subject of Research: Chemical synthesis, spectral characterisation, stability, conductivity, and antibacterial activity of poly(m-aminophenol-co-m-chloroaniline) copolymers

Article Title: Chemical synthesis, quantitative and qualitative spectral characterisation, stability, and biological activity study of some electrically conductive co -polyaniline derivatives

Article References: Ibrahim, K. (2026). Chemical synthesis, quantitative and qualitative spectral characterisation, stability, and biological activity study of some electrically conductive co-polyaniline derivatives. Results in Chemistry, 30, Article 103872. https://doi.org/10.1016/j.rechem.2026.103872

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103872

Keywords: polyaniline, conducting polymers, m-aminophenol, m-chloroaniline, oxidative polymerisation, FTIR spectroscopy, UV-Vis spectroscopy, electrical conductivity, thermal stability, antibacterial activity, copolymerisation, materials science

The first stage of the modification targets the fundamental chemistry of the membrane itself. The researchers synthesized poly(sodium p-styrene sulfonate), or PSS, a polymer densely decorated with negatively charged sulfonate groups, and wove it into the PVDF matrix during membrane fabrication. Rather than simply blending the two polymers, which risks the hydrophilic component washing away over time, the team used a one-pot approach combining free-radical polymerization with non-solvent induced phase separation, the standard industrial casting technique. The result is a semi-interpenetrating polymer network, in which linear PVDF chains are physically entangled with a crosslinked PSS network at the molecular level. This interlocking creates what polymer scientists call a forced compatibility effect: the two dissimilar phases cannot easily separate, component leaching is suppressed, and the sulfonate groups remain permanently anchored where they can attract water molecules.

The consequences of this structural change ripple through the entire architecture of the membrane. During phase inversion, the sulfonate groups draw water into the casting film, accelerating the exchange between solvent and non-solvent and promoting the formation of finger-like pores in the supporting layer, which replaced the sponge-like structure of the unmodified PVDF membrane. Scanning electron microscopy revealed fewer large surface defects and a far more efficient pore network for water transport. The water contact angle, a measure of surface wettability, dropped from 81.3 degrees for the pristine membrane to 63.3 degrees after the first modification. Pure water flux surged more than fivefold, from 141.54 to 737.20 liters per square meter per hour, though the protein rejection rate of 86.83 percent still fell short of the 90 percent benchmark demanded of practical ultrafiltration membranes. That shortfall set the stage for the second modification.

The team explored two distinct routes to grow a polyaniline layer on the membrane surface. In the first, the membrane was soaked in an aniline solution so that protonated monomers adsorbed electrostatically onto the negatively charged sulfonate sites, then transferred to an oxidizing solution to trigger polymerization. In the second, a custom reactor delivered monomer and oxidant simultaneously across a liquid-liquid interface at the membrane surface, enabling polymerization to proceed directly where it was wanted. Both routes exploit the same anchoring chemistry: the protonated imine nitrogen atoms of the growing polyaniline chains form ionic bonds with the sulfonate groups of PSS, reinforced by hydrogen bonding, effectively locking the functional layer in place. The films announced their presence visually, turning one membrane dark brown and the other green depending on the oxidation state of the polyaniline.

The choice between the two polymerization methods proved decisive. With adsorption followed by polymerization, aniline monomers penetrated into the membrane pores before reacting, and the polyaniline formed inside partially blocked the channels, throttling flux to 265.39 liters per square meter per hour. Synchronous polymerization, by contrast, confined the reaction largely to the surface, producing a thin, uniform and dense sieving layer that left the transport channels open. The resulting membrane, designated M3, achieved a pure water flux of 401.03 liters per square meter per hour while rejecting 99.02 percent of bovine serum albumin, a standard protein foulant. Its water contact angle fell to 42.9 degrees, and its surface carried a stronger negative charge at neutral pH than either precursor membrane, sharpening the electrostatic repulsion that keeps negatively charged proteins at bay.

Antifouling performance, the metric that ultimately determines whether a membrane survives real-world service, improved dramatically. After a cycle of protein filtration and a simple water rinse, the pristine PVDF membrane recovered only 54.30 percent of its original flux, while the dual-modified M3 membrane recovered 95.59 percent. Its irreversible fouling ratio, the portion of fouling that physical cleaning cannot remove, dropped to just 4.41 percent, compared with 45.69 percent for the unmodified control. Static adsorption experiments told the same story: the M3 membrane bound the least protein of all four samples tested. The researchers attribute this resilience to a stable hydration layer, in which hydrophilic PSS and PANI chains hold water molecules at the surface as a sacrificial barrier, combined with steric hindrance from the anchored polymer layer that physically blocks proteins from entering the pores.

The membrane also showed unexpected muscle against biological fouling, one of the most expensive problems in water treatment. In plate-counting assays, the M3 membrane inhibited 88.00 percent of Escherichia coli and 87.38 percent of Staphylococcus aureus colonies, far outperforming the modest effects of the PSS-only membrane. The mechanism, according to the study, hinges on the positively charged imino sites of polyaniline, which bind to the negatively charged bacterial cell membranes and disrupt the potential gradient across bacterial ion channels, destroying the cells. Because the polyaniline is anchored ionically rather than merely coated onto the surface, this antibacterial activity should persist through cleaning cycles rather than being lost, addressing a common failure mode of antimicrobial membrane coatings.

Chemical robustness tests reinforced the picture of a membrane built for harsh duty. After 28 days of immersion in acidic solution at pH 2, the dual-modified membrane still rejected 86.83 percent of albumin, and after 28 days in alkaline solution at pH 10, it retained 84.67 percent rejection, with flux increases far smaller than those of the unmodified control. The semi-interpenetrating network raises the thermal degradation temperature of the matrix as well, limiting the motion of PVDF chains under heat. Stability against component loss is equally important: unlike conventional blended membranes, in which hydrophilic additives gradually leach into the treated water, the interlocked PSS network and ionically bonded polyaniline layer resist dissolution, a property the authors link directly to the high and repeatable flux recovery observed across filtration cycles.

Perhaps most striking is the membrane’s performance against dye pollution. Treating simulated wastewater containing Methylene Blue and Congo Red at 10 milligrams per liter, the M3 membrane rejected 99.99 percent of both dyes, relying on a combination of surface adsorption, size exclusion, electrostatic repulsion or attraction, and steric hindrance from the PANI layer. Cationic Methylene Blue was initially captured by the negatively charged surface, forming a concentration-polarization layer that then repelled further deposition, while anionic Congo Red was largely deflected electrostatically and blocked by the aggregation of its molecules in solution. After extended filtration and cleaning, dye fluxes remained stable above 200 liters per square meter per hour, with recovery rates near 97 percent. An economic analysis estimated production costs at roughly 3 to 3.5 dollars per square meter, far below typical commercial PVDF membrane costs, suggesting that this laboratory-scale dual-modification strategy could, if it survives scale-up, offer an affordable route to treating protein-rich and dye-laden industrial wastewater.

Subject of Research: Dual hydrophilic and antibacterial modification of PVDF ultrafiltration membranes for wastewater treatment

Article Title: Dual-modified PVDF ultrafiltration membranes via semi-interpenetrating polymer network construction and PANI surface polymerization

Article References: Zhang, J., Han, Y., Wu, M., Zhang, D., Zhao, W., Shi, C., Xu, J., & Cui, H. (2026). Dual-modified PVDF ultrafiltration membranes via semi-interpenetrating polymer network construction and PANI surface polymerization. Journal of Saudi Chemical Society, 30(4), Article 48. https://doi.org/10.1007/s44442-026-00099-1

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00099-1

Keywords: PVDF, ultrafiltration membrane, semi-interpenetrating polymer network, polyaniline, poly(sodium p-styrene sulfonate), antifouling, antibacterial, dye removal, wastewater treatment, NIPS, membrane fouling, BSA rejection

Polyaniline belongs to a family of materials called conducting polymers, which behave in many respects like reactive macromolecular gels when wet. When an electric current is passed through them, their polymer chains undergo oxidation or reduction, gaining or losing electrons. This triggers the exchange of counterions and solvent molecules with the surrounding electrolyte, causing the chains to swell, shrink, relax or compact. The researchers draw a striking parallel with living cells: in both cases, electrical stimuli drive chemical reactions in macromolecular chains that produce conformational movement, ionic exchange and solvent exchange, in other words, a reversible change in the chemical composition of the entire polymer-ion-solvent system. It is precisely this biomimetic quality that makes polyaniline attractive for applications ranging from sensors and artificial muscles to supercapacitors, smart windows and drug delivery systems.

The chemical mechanism underlying the switching is formally described as an anion-driven process. In the reduced state, polyaniline chains carry sigma bonds between consecutive monomeric units, allowing free rotation and numerous conformations. Upon oxidation, radical cations form along the chain, introducing new pi bonds that restrict rotation and effectively turn the chain into a molecular motor. To maintain charge neutrality, chloride anions from the 1 M hydrochloric acid electrolyte diffuse into the polymer, and water molecules follow for osmotic balance. During reduction, the reverse occurs: protons are incorporated, and chloride ions and water are expelled. The multistep redox chemistry connects three canonical forms of the polymer, leucoemeraldine, emeraldine and pernigraniline, with anodic peaks observed at 0.30 V and 0.53 V and corresponding reduction peaks at 0.44 V and 0.078 V in the team’s cyclic voltammograms.

The central innovation of the study lies in coulovoltammetry, a technique in which the cyclic voltammogram is integrated to plot the consumed charge directly against the applied potential. The resulting closed or open loops encode an enormous amount of information. A perfectly closed loop indicates that the anodic and cathodic charges are equal, meaning only reversible redox processes are occurring. Between 0 and -0.3 V on the cathodic side, and up to 0.7 V on the anodic side, the team found just such a window of pure reversibility for polyaniline in hydrochloric acid. Beyond these limits, new irreversible processes appear, identified as hydrogen evolution on the cathodic side and overoxidation or oxygen evolution on the anodic side, whose associated charges grow exponentially with increasingly extreme potential limits.

More remarkably still, the coulovoltammogram allows the authors to separate four distinct structural faradaic processes, in line with the Electrochemically Stimulated Conformational Relaxation model developed by Toribio Otero and colleagues. Starting from the fully oxidized state, the fast reduction-shrinking stage proceeds under diffusion control of counterions leaving the swelling film. Once the shrinking chains close the gel structure at a characteristic closing potential, further reduction cannot stop but slows dramatically, because the departing anions must physically push polymer chains apart to open their exit pathways. This slow reduction-compaction stage even persists into the beginning of the subsequent anodic sweep, a phenomenon the team calls reduction electrochemical inertia, which they confirmed using chronocoulograms showing continuous faradaic charge decay. Conversely, oxidation begins with a slow relaxation process that opens the compact structure and generates free volume for incoming anions, followed by fast oxidation-swelling, and finally an oxidation inertia that continues past the anodic potential limit into the cathodic sweep.

The analysis also yielded an unexpected energetic finding. By integrating the coulovoltammetric areas, the researchers calculated the electrical energy consumed during oxidation and reduction across different potential windows. The reduction energies turned out to be almost twice the oxidation energies, revealing a pronounced charge symmetry but energy asymmetry in the reaction. The authors attribute this asymmetry to the inherently different structural processes on the two sides of the cycle, including conformational relaxation, swelling, shrinking, compaction, ion trapping and electrochemical inertia, compounded by osmotic solvent exchange. Intriguingly, they suggest this mirrors the asymmetry of reaction-driven biological functions, noting that muscles perform work during contraction but not relaxation, and that ionic channels in living systems pass ions preferentially in one direction.

Perhaps the most consequential demonstration is that polyaniline’s electrochemical reaction is self-sensing, meaning it can report on its own working conditions without any additional sensor hardware. The team derived theoretical sensing equations from the reaction kinetics and Faraday’s laws, then verified them experimentally. The charge consumed by the reversible reaction showed a clean double-logarithmic linear dependence on the scan rate, with an excellent correlation coefficient of 0.993, and the same held true when frequency was used as the electrical variable. At slower scan rates, the reaction has more time to drive deep conformational changes, exchange large numbers of ions and solvent molecules, and consume correspondingly more charge and energy; at faster rates, the polymer only partially switches. The consumed electrical energy likewise varied linearly in semi-logarithmic plots against scan rate, with distinct sensitivity slopes of -6.77 J g-1 per logarithmic unit for reduction and -2.15 for oxidation.

The same logic extended to chemical and thermal conditions. When the electrolyte concentration was varied from 1 M down to 0.075 M hydrochloric acid, the consumed charge increased in a double-logarithmic fashion with concentration, because higher concentrations provide more chemical energy for deeper oxidation and greater counterion uptake. The consumed energy per gram of polymer also rose linearly with concentration, with sensitivity slopes of 2.948 J g-1 per logarithmic unit for reduction and 0.608 for oxidation. Temperature produced analogous behaviour: as the working temperature increased, thermal energy pushed the reaction toward deeper redox states, and the charge obeyed the semilogarithmic Arrhenius-derived sensing equation, with a temperature sensitivity slope of -601.28, while consumed energy rose linearly by 0.152 J g-1 per degree Celsius for reduction and 0.061 for oxidation.

Because the sensing parameters here are simply the consumed charge and the consumed electrical energy during the reaction, any electrochemical device built on polyaniline, whether a supercapacitor electrode, an actuator, an electrochromic window or a drug delivery platform, could in principle monitor its own instantaneous operating state without separate instrumentation. The authors emphasize that this differs fundamentally from conventional chemical sensing, which aims to identify or quantify specific analytes; the goal instead is a material whose reaction is intrinsically aware of the energetic and chemical ambient in which it operates, much as biological macromolecular motors simultaneously generate actuation and sense their surroundings through the same underlying reaction.

The study represents the first systematic coulovoltammetric analysis of chemically synthesized polyaniline, extending to this polymer a methodology previously applied mainly to polypyrrole, and tackling the added complexity of polyaniline’s multistep proton-coupled redox transitions. The researchers synthesized the material by chemical oxidative polymerization of aniline with ammonium persulphate in hydrochloric acid, characterized it by FTIR spectroscopy, dielectric spectroscopy, thermogravimetric analysis and electron microscopy, and coated it onto glassy carbon electrodes for electrochemical testing with a Zennium Pro workstation. Supported by fellowships from the University Grants Commission and the Kerala State Council for Science, Technology and Environment, the work contributes both to the fundamental structural electrochemistry of conducting polymers and, the authors argue, to the development of soft, wet, reactive multifunctional biomimetic devices that could reshape soft robotics, bioelectronics and biomedicine in the years ahead.

Subject of Research: Coulovoltammetric analysis of structural electrochemistry, charge-energy asymmetry and reactive self-sensing capabilities of polyaniline

Article Title: Understanding the electrochemistry of polyaniline structural processes, charge, energy and reactive sensing capabilities through coulovoltammetry

Article References: Sidheekha, M. P., Rajan, L., Prakash, S., Shabeeba, A., & Ismail, Y. A. (2026). Understanding the electrochemistry of polyaniline structural processes, charge, energy and reactive sensing capabilities through coulovoltammetry. Discover Electrochemistry, 3(1), Article 84. https://doi.org/10.1007/s44373-026-00172-9

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00172-9

Keywords: polyaniline, coulovoltammetry, conducting polymers, structural electrochemistry, redox switching, ESCR model, energy asymmetry, self-sensing materials, biomimetic devices, electrochemical sensors, charge trapping, conformational relaxation