The material belongs to a family of substances known as geopolymers — amorphous, metastable aluminosilicates first developed by Joseph Davidovits in 1970. They are synthesized by reacting an aluminosilicate precursor, such as calcined clay, fly ash, or natural pozzolans, with an alkaline activator like sodium hydroxide at temperatures below 100 degrees Celsius. At the molecular level, the result is an anionic framework of corner-sharing SiO4 and AlO4 tetrahedra, into which charge-balancing cations such as sodium or potassium are incorporated from solution. This architecture gives geopolymers a set of properties that make them unusually attractive for water treatment: low-cost and abundant precursors, tunable porosity, chemical stability, and a synthesis route that is gentle on the environment. Their adjustable surface chemistry and robust structural framework also support adsorption efficiency and recyclability, addressing two of the biggest weaknesses of conventional adsorbents.

What distinguishes the new work is its dual pore-generation strategy and its systematic exploration of precursor composition. The team calcined kaolin from Zettlitz in the Czech Republic at 700 degrees Celsius for three hours to produce metakaolin, then blended it with silica fume — an ultrafine byproduct of ferrosilicon and silicon metal production, containing more than 96 percent amorphous silica and a surface area of roughly 20,000 square meters per kilogram. Silica fume replaced metakaolin at proportions ranging from 0 to 25 weight percent, serving as a reactive silica source within the alkaline activator system. To open up the internal architecture, the researchers added hydrogen peroxide at 5 weight percent as a foaming agent, which decomposes to generate gas-induced pores, and corn oil at 1 weight percent as a templating phase that promotes interconnected voids. The paste was cured at 60 degrees Celsius for 12 hours, followed by hydrothermal curing for another 24 hours, before being crushed, sieved to particles below 100 micrometers, washed with hot water, and dried.

The screening experiments revealed a striking optimum. When six adsorbent formulations were tested against a 10 milligram per liter methylene blue solution at natural pH with a dosage of 1 gram per liter, both adsorption capacity and removal efficiency climbed as silica fume content rose to 10 percent, where the S(10) formulation achieved roughly 90 percent removal. Beyond that threshold, performance declined. The explanation lies in the structural evolution of the geopolymer: at 10 weight percent, the additional reactive silica facilitates more complete polycondensation, producing a robust and well-distributed sodium aluminosilicate hydrate gel with a balanced silicon-to-aluminum ratio that maximizes negatively charged surface sites for cationic attraction. Above that level, particle agglomeration reduces available surface area, partially blocks mesoporous channels, and increases paste viscosity — which hinders uniform distribution of the hydrogen peroxide foam and yields a less interconnected pore structure riddled with physical defects.

With the optimal composition identified, the researchers mapped how operating conditions shape performance. Increasing the adsorbent dosage from 0.5 to 2.5 grams per liter raised removal efficiency from 60 to 93 percent, though the amount adsorbed per gram of material fell from 11.52 to 3.84 milligrams as sites began to overlap and aggregate. pH proved decisive: removal efficiency rose from 58.5 percent at pH 1 to 93 percent at pH 7, then slipped slightly to 90.5 percent at pH 9. The chemistry is intuitive — under acidic conditions, the geopolymer surface is surrounded by hydrogen ions and acquires a positive charge, electrostatically repelling the cationic dye, while neutral conditions maximize the attraction between dye cations and the negatively charged surface. Notably, the optimum coincides with the material’s point of zero charge, and because real textile effluents often require expensive pH adjustment before treatment, the ability to perform best at near-neutral conditions could meaningfully cut operational costs. Contact time experiments showed 73.05 percent removal within the first 30 minutes, reaching equilibrium at 60 minutes with 93.6 percent removal.

Kinetic modeling pointed to a chemical rather than purely physical binding process. The pseudo-second-order model fit the data with a correlation coefficient of 0.99, far outperforming the pseudo-first-order model at 0.84 and the Elovich model at 0.7 — a signature of chemisorption, in which electron sharing or exchange between adsorbent and adsorbate governs the rate. The intraparticle diffusion model fit poorly, and its non-zero intercept confirmed that pore diffusion is not the sole rate-limiting step; boundary layer resistance and film diffusion also contribute to mass transfer. On the equilibrium side, the Langmuir isotherm described the data best with a correlation coefficient of 0.98, ahead of the Freundlich model at 0.94 and the Temkin model at 0.92. Together, the kinetic and isotherm analyses indicate monolayer chemisorption on energetically equivalent sites, with a maximum adsorption capacity of 12.30 milligrams per gram and a separation factor of 0.064 confirming favorable adsorption.

Spectroscopic and microscopic analyses supplied direct evidence of how the dye molecules attach. Fourier transform infrared spectroscopy showed a reduction and shift of the primary silicon-oxygen-aluminum vibration band between 850 and 1200 wavenumbers after dye uptake, alongside the appearance of methylene blue-specific signals near 1243, 1100, and 1400 wavenumbers, attributed to C–N and N–N stretching and aromatic ring deformations. Changes in the broad hydroxyl stretching region near 3400 wavenumbers suggested hydrogen bonding between surface hydroxyl groups and the dye. X-ray diffraction revealed the characteristic broad amorphous hump of the N-A-S-H gel, which broadened slightly after adsorption but returned to its original profile after regeneration, confirming structural stability. Nitrogen sorption measurements classified the material as mesoporous, with a Type IV isotherm and H3-type hysteresis loop indicating slit-like or ink-bottle-shaped pores, a specific surface area of 12.515 square meters per gram, and an average pore diameter of 31.7 nanometers — dimensions that facilitate rapid transport of dye molecules to internal active sites. Scanning electron microscopy showed pores partially coated and filled after adsorption, with elemental mapping revealing increased carbon and nitrogen content that vanished after regeneration.

The adsorption mechanism that emerges is a layered one. Negatively charged siloxo and alumoxo sites on the geopolymer surface attract the cationic dye electrostatically, while charge-balancing sodium ions within the pores undergo direct ion exchange with methylene blue cations. The dye molecule adopts a more planar configuration, lying flat on the surface, which facilitates π–π interactions between its aromatic rings and silanol groups, and the presence of aluminum and sodium ions combined with the dye’s conjugated structure may induce additional n–π interactions. Hydrogen bonding with surface functional groups further enhances uptake. Initial capture is assisted by van der Waals forces, dipole–dipole interactions, and physical pore filling within the mesoporous network, but the rate is ultimately governed by the abundance of accessible surface sites rather than diffusion alone.

Perhaps most importantly for real-world deployment, the adsorbent proved reusable. Over five adsorption–desorption cycles, removal efficiency declined from 93.6 percent to approximately 73 percent when regenerated with hydrochloric acid and to about 80 percent when regenerated with ethanol. Ethanol proved the superior regenerant: its lower dielectric constant weakens the electrostatic grip between dye cations and the negatively charged surface, while it competes for silanol and aluminol binding sites through hydrogen bonding and solvates the dye’s aromatic rings. The residual capacity loss stems from irreversible chemisorption at high-energy sites and partial pore masking in narrow mesopores, where dye molecules bound through strong chemical interactions resist displacement. Even so, retaining 80 percent efficiency after five cycles is a commendable result that addresses the common criticism that adsorption merely transfers pollutants from water to a solid that must then be discarded.

The researchers are candid about the material’s limits. Its maximum capacity of 12.30 milligrams per gram trails some highly porous commercial adsorbents and engineered materials, a consequence of the relatively modest surface area and the absence of additional surface functionalization. Yet the comparison that matters may be economic rather than absolute: the removal efficiency of 93.6 percent rivals that of far more elaborate systems, and the synthesis route relies on low-cost, widely available industrial wastes — silica fume from ferroalloy furnaces and calcined clay — while operating at mild temperatures without energy-intensive processing. The team suggests that surface tailoring, chemical modification, or the incorporation of carbon-based materials, metal oxides, or nanoscale additives could push performance further, and that testing under real wastewater conditions, long-term reuse, and continuous-flow systems will be needed to establish broader applicability. For now, the study demonstrates that two industrial waste streams, a splash of hydrogen peroxide, and a spoonful of cooking oil can be transformed into a working water-cleaning material — a small but compelling example of circular chemistry aimed at one of the world’s most persistent pollution problems.

Subject of Research: Porous metakaolin–silica fume geopolymer adsorbents for removing methylene blue dye from contaminated water

Article Title: Eco-friendly production of porous metakaolin–silica fume geopolymer for adsorptive removal of methylene blue from water

Article References: Oshani, F., Mahinroosta, M., & Ghasemi, E. (2026). Eco-friendly production of porous metakaolin–silica fume geopolymer for adsorptive removal of methylene blue from water. Results in Engineering, 32, Article 113419. https://doi.org/10.1016/j.rineng.2026.113419

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113419

Keywords: geopolymer, methylene blue, adsorption, silica fume, metakaolin, wastewater treatment, dye removal, porous materials, chemisorption, water purification, industrial byproducts, sustainability

The target of the study, methylene blue, is far more than a laboratory curiosity. This cationic thiazine dye is produced on an enormous scale for textile dyeing, paper coloring, and medical applications, and its release into waterways poses genuine ecological risks. Studies cited by the authors document toxic effects of methylene blue on the growth, reproduction, and physiology of aquatic organisms such as Daphnia magna, the tiny freshwater crustacean that serves as a sentinel species in ecotoxicology. Conventional remediation approaches, including activated carbon derived from apricot stones, olive pits, and walnut shells, can adsorb the dye, but they bind indiscriminately. In real effluents, where dozens of dissolved organic species compete for binding sites, that lack of selectivity quickly exhausts the adsorbent’s capacity for the one contaminant that actually matters.

The Hacettepe team’s answer draws on molecular imprinting, a technique often described as building a molecular mold. In classical imprinting, the target molecule is mixed with functional monomers and a cross-linker before polymerization; as the polymer network forms around the template, it locks in binding sites complementary to the template’s size, shape, and chemical functionality. Removing the template afterward leaves behind synthetic recognition cavities that can rebind the target with an affinity and selectivity that mimic, in a crude but useful way, the behavior of antibodies. The approach has matured over two decades into a versatile platform, with imprinted polymers now used for sensors detecting proteins, viruses, and biomarkers, as well as for selective extraction of pharmaceuticals, herbicides, and heavy metal ions from environmental waters.

What distinguishes the new study is the method used to attach the imprinted layer to the magnetic core: admicellar polymerization. Surfactant molecules adsorbed onto the nanoparticle surface assemble into bilayers known as admicelles, which solubilize the monomers and the template dye in their hydrophobic interior. Polymerization is then initiated within these surfactant assemblies, growing a thin polymeric film directly on the particle surface. Because the template is present during film formation, the resulting polymer carries imprinted cavities oriented outward, where they are accessible to the surrounding water. The technique, previously applied to coat cellulose, cotton fabric, nanocellulose, titanium dioxide particles, and carbon nanotubes, has the advantage of producing well-defined, surface-localized films without burying recognition sites deep inside a bulky polymer matrix, a common failing of bulk imprinting that leaves many sites unreachable.

The magnetic core beneath the silica shell and polymer film is what makes the system practical. Magnetite nanoparticles respond to an external magnetic field, so once the adsorbent has done its work in a batch of contaminated water, it can be collected in seconds with a simple magnet rather than filtered or centrifuged. The silica coating, a widely used architecture in nanomaterials science, stabilizes the iron oxide core against dissolution and aggregation while providing a chemically versatile surface for further modification. The authors verified each layer of this onion-like structure using a battery of characterization techniques: Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance confirmed the chemical bonds introduced at each modification step, X-ray Photoelectron Spectroscopy probed the surface elemental composition, and Transmission Electron Microscopy imaged the morphology of the coated particles.

Performance testing revealed a system governed by chemistry rather than chance. Adsorption kinetics followed a pseudo-second-order model with a coefficient of determination above 0.99, indicating that the rate-limiting step involves chemical interactions between the dye and the binding sites rather than simple diffusion or weak physical adhesion. The maximum binding capacity of the imprinted polymer-modified nanoparticles was determined to be 5.64 milligrams per gram, with a 95 percent confidence interval spanning 4.52 to 6.76 milligrams per gram. Equilibrium data fit the Freundlich isotherm model better than alternative models, with R squared again exceeding 0.99, a signature of heterogeneous adsorption behavior across binding sites of varying energy. That heterogeneity is exactly what theory predicts for molecularly imprinted systems, where the population of cavities inevitably includes a distribution of imperfectly formed sites alongside a subset of well-ordered, high-affinity ones.

The selectivity results are the study’s most striking numbers. The imprinting factor for methylene blue, which compares binding by the imprinted polymer to binding by a non-imprinted control, reached 7.18. When structurally related competitors were tested, the factor dropped to 3.11 for methylene violet and 1.97 for indigo carmine, showing that the cavities discriminate sharply in favor of the molecule that shaped them. Selectivity coefficients of 2.41 for methylene violet and 3.18 for indigo carmine confirmed the preferential recognition quantitatively. In practical terms, this means the adsorbent can distinguish between dyes that are close chemical cousins, a feat impossible for generic activated carbons whose binding depends only on nonspecific surface interactions. The optimum operating conditions proved refreshingly mild: a neutral pH of 7 and an incubation time of just 35 minutes, conditions compatible with straightforward deployment in real treatment settings.

Reusability, often the Achilles heel of engineered adsorbents, held up impressively. The material maintained its adsorption performance over seven consecutive adsorption-desorption cycles without significant loss of efficiency, a result that matters enormously for any realistic cost assessment of nanomaterial-based water treatment. The authors also moved beyond synthetic laboratory solutions, validating the system on real water samples collected from different natural sources. Demonstrating performance in genuine environmental matrices, with their dissolved salts, natural organic matter, and competing contaminants, is a critical step that many adsorbent studies omit, and it strengthens the case that the imprinted magnetic nanoparticles could function outside the controlled conditions of a chemistry bench.

The broader context makes the work timely. Dye-laden wastewater remains one of the most visible forms of industrial pollution, and the field has seen a surge of interest in magnetically modified adsorbents, from biomass-derived activated carbons to magnetic kaolinite clays and metal-organic framework composites. Molecularly imprinted magnetic adsorbents have been developed for targets as varied as tetracycline, diclofenac, bisphenol-A, phenoxy acid herbicides, and penicillin G, and the Hacettepe group itself previously used admicellar polymerization to build a tetracycline-selective magnetic adsorbent. The new study extends that methodology to a dye pollutant and provides a full analytical treatment of kinetics, isotherms, selectivity, and reusability, the standard metrics by which adsorption science judges a candidate material.

Challenges remain before such materials could see large-scale use, including the economics of nanoparticle synthesis at industrial volumes and the regulatory questions surrounding engineered nanomaterials in environmental applications. Yet the design principles demonstrated here, combining magnetic recoverability, a protective silica interface, and a selectively imprinted polymer skin applied by a scalable surface polymerization technique, point toward a future in which water treatment is not a blunt instrument but a targeted one. If adsorbents can be programmed to recognize specific pollutants the way this one recognizes methylene blue, the prospect of cleaning contaminated water without collateral losses of capacity becomes considerably more tangible.

Subject of Research: Molecularly imprinted polymer-modified magnetic nanoparticles for selective removal of methylene blue dye from water

Article Title: Surface modification of silica-coated magnetic nanoparticles for effective removal of methylene blue from water samples

Article References: Söylemez, M. A., Ozer, D., & Icten, O. (2026). Surface modification of silica-coated magnetic nanoparticles for effective removal of methylene blue from water samples. Journal of Nanoparticle Research, 28(10), Article 266. https://doi.org/10.1007/s11051-026-06789-6

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06789-6

Keywords: magnetic nanoparticles, molecularly imprinted polymers, methylene blue, dye removal, wastewater treatment, admicellar polymerization, silica coating, adsorption kinetics, Freundlich isotherm, selectivity, water purification, nanomaterials

Rhodamine B is not a harmless colorant. The xanthene dye is widely used in textiles, inks, and even as a tracer in water studies, but exposure has been linked to harmful effects in aquatic organisms. Recent research cited by the team documents damage to the antioxidant system and photosynthesis of the aquatic plant Hydrilla verticillata, as well as ALS-like behavioral symptoms in zebrafish. Because conventional treatment plants are not designed to remove such synthetic organic molecules, adsorption has emerged as an attractive remediation strategy: it is simple, does not produce toxic byproducts when the right adsorbent is chosen, and can be scaled using packed columns or batch dosing. The challenge lies in finding adsorbents that are fast, efficient, and reusable, which is precisely where the graphene family enters the story.

The researchers prepared their two adsorbents from the same starting point. Graphene oxide was synthesized using the well-established Hummers method, in which graphite is oxidized and exfoliated into single sheets decorated with oxygen-containing functional groups such as hydroxyl, epoxy, and carboxyl moieties. Reduced graphene oxide was then produced by treating the graphene oxide with hydrazine hydrate under ultrasonication, a process that strips away many of those oxygen groups and restores a more graphitic, carbon-rich surface. The difference between the two materials is subtle but chemically profound: graphene oxide is hydrophilic and negatively charged across a wide pH range, while reduced graphene oxide is more hydrophobic and carries fewer charged sites. To confirm what they had made, the team deployed a battery of characterization tools, including Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, and zeta potential measurements, each of which tracks the structural and surface changes that accompany reduction.

The adsorption experiments were systematic, varying solution pH, contact time, adsorbent dosage, and initial dye concentration. The results revealed a striking dependence on acidity. Graphene oxide performed best at pH 4, where it removed 99.94 percent of the dye, while reduced graphene oxide reached its optimum under alkaline conditions at pH 8, achieving 99.83 percent removal. This divergence makes chemical sense. Rhodamine B is a cationic dye, meaning it carries a positive charge in solution, and it is therefore drawn electrostatically to negatively charged surfaces. Graphene oxide, dense with ionizable oxygen groups, presents a strongly negative surface at acidic to neutral pH, maximizing the attraction. Reduced graphene oxide, having lost many of those groups, relies more on pi-pi interactions between the aromatic rings of the dye and the restored graphitic domains, and its optimum shifts accordingly. Equilibrium was reached remarkably quickly: ten minutes for graphene oxide and fifteen minutes for reduced graphene oxide.

Speed alone does not reveal mechanism, so the team fitted their kinetic data to established models. The pseudo-second-order model described the process best for both adsorbents, a result with real mechanistic weight. Unlike the pseudo-first-order model, which assumes the uptake rate depends only on the amount of vacant surface sites, the pseudo-second-order model implies that the rate-limiting step involves chemical interactions between the adsorbate and the surface, a hallmark of chemisorption. In practical terms, the dye molecules are not merely weakly clinging to the carbon sheets through van der Waals forces; they are engaging in specific electronic interactions, whether electrostatic attraction to charged sites, hydrogen bonding with oxygen groups, or pi-pi stacking with aromatic regions. This conclusion was reinforced by the isotherm analysis, which examined how much dye the materials could hold as a function of equilibrium concentration.

Among the isotherm models tested, the Redlich-Peterson equation provided the best fit, with the exponent beta taking values of 0.811 for graphene oxide and 0.880 for reduced graphene oxide. Because beta lies between zero and one, the result signals that neither a purely homogeneous Langmuir surface nor a purely heterogeneous Freundlich surface applies; instead, adsorption proceeds across a heterogeneous landscape of binding sites with varying energies. The maximum experimental adsorption capacities came out at 9.99 milligrams per gram for graphene oxide and 4.80 milligrams per gram for reduced graphene oxide. The lower capacity of the reduced material reflects its diminished inventory of oxygen functional groups, even though it compensates with superior stability. For a water-treatment engineer, these numbers matter less for their absolute magnitude than for what they reveal: the chemistry of the surface, not just its area, dictates performance.

To probe the interaction at the level of individual electrons, the researchers turned to density functional theory, a quantum-chemical method that computes the electronic structure of molecules and surfaces. The calculations confirmed favorable adsorption energies and electronic interactions between the Rhodamine B molecule and both graphene oxide and reduced graphene oxide surfaces, lending theoretical support to the experimental picture of chemisorption on heterogeneous sites. Computational studies of this kind are increasingly common in adsorption research because they can distinguish between competing binding geometries and identify which functional groups contribute most to the interaction, information that is difficult to extract from bulk experiments alone. Here, the agreement between simulation and measurement strengthens confidence that the proposed mechanism is not an artifact of curve fitting.

Reusability is where many promising adsorbents stumble, since spent materials that cannot be regenerated quickly become waste themselves. Both adsorbents in this study maintained significant dye-removal activity over four consecutive adsorption-desorption cycles, with reduced graphene oxide showing enhanced stability across the repeated use. That durability, combined with the rapid equilibration times, suggests a practical pathway toward real deployment, although the authors’ data cover laboratory-scale batch experiments rather than continuous-flow systems. The modest adsorption capacities also indicate that these materials would likely be most valuable as polishing agents for low-concentration dye streams, or as components of composites, rather than as bulk sorbents for heavily contaminated industrial effluent.

Perhaps the most socially resonant finding concerns what happens after the dye is gone. The team evaluated the treated water using seed germination experiments, a standard phytotoxicity assay in which seeds are grown in the treated solution and their germination and early growth are compared against controls. Water that had been treated with the graphene-based adsorbents showed minimal harmful effects on germination, indicating that the cleanup did not merely relocate the toxicity into the water column and that the effluent could potentially be repurposed for irrigation or discharge with reduced environmental risk. Given that Rhodamine B contamination is a documented problem in regions with dense textile manufacturing, a treatment train that ends with water safe enough for plants represents a meaningful step toward circular water use.

The study, funded by the Centre of Excellence in Emerging Materials at TIET and India’s DST-PURSE program, adds to a growing body of evidence that two-dimensional carbon materials are versatile platforms for water remediation. Its particular contribution lies in the head-to-head comparison of graphene oxide and reduced graphene oxide under identical conditions, which isolates the role of surface oxygen chemistry in dye capture, and in the multi-pronged verification that spans experiment, modeling, and computation. As dye pollution continues to threaten aquatic ecosystems, the message from Patiala is that sometimes the fastest cleanup comes from the thinnest materials, and that understanding why they work is the key to making them work better.

Subject of Research: Adsorption of Rhodamine B dye from water using graphene oxide and reduced graphene oxide

Article Title: Adsorption and kinetics study on Rhodamine B removal over graphene oxide and reduced graphene oxide

Article References: Tyagi, A., Chudasama, B., & Ali, A. (2026). Adsorption and kinetics study on Rhodamine B removal over graphene oxide and reduced graphene oxide. Environmental Science and Pollution Research, 33(28), 14178-14200. https://doi.org/10.1007/s11356-026-38167-z

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38167-z

Keywords: graphene oxide, reduced graphene oxide, Rhodamine B, adsorption, water treatment, dye removal, adsorption kinetics, pseudo-second-order model, Redlich-Peterson isotherm, density functional theory, phytotoxicity, environmental remediation

The choice of ingredients is deliberate and each component plays a distinct structural role. Diatomite, a silica-rich sedimentary rock formed from the fossilized frustules of microscopic algae and sourced from Lampang in northern Thailand, supplies an intrinsically porous mineral framework that facilitates mass transfer of dye molecules into the pellet interior. Metakaolin, produced by calcining kaolin clay from Ranong, serves as the reactive aluminosilicate precursor that forms the chemically stable geopolymer network when activated with a mixture of sodium silicate solution and 10 M sodium hydroxide. Water hyacinth residue collected in Chiang Mai brings oxygen-rich functional groups and a fibrous morphology that modify the pore architecture and surface reactivity of the final composite. The researchers cast pastes containing 20 weight percent calcined diatomite, 15 weight percent metakaolin, and the alkaline activator, adding water hyacinth at 0, 1, 2, and 3 weight percent to produce a series labeled DG-WH0 through DG-WH3, which were then cured at room temperature for up to 28 days.

Structural analysis revealed how the biomass reshapes the material from the inside out. X-ray diffraction showed that quartz remained the dominant crystalline phase in all compositions, inherited largely from unreacted portions of the diatomite and metakaolin precursors, while a broad diffuse feature between roughly 20 and 35 degrees two-theta confirmed the presence of a poorly ordered aluminosilicate geopolymer matrix. Fourier-transform infrared spectroscopy identified the characteristic Si-O-T asymmetric stretching band near 1016 to 1021 per centimeter, along with hydroxyl and carbonate features, and small shifts in these bands after dye exposure hinted at interactions between methylene blue and the composite surface. Scanning electron microscopy told a more visually striking story: the biomass-free pellet was relatively dense, but increasing water hyacinth content progressively introduced interfacial gaps, larger voids, and interconnected pore channels, particularly in the 2 and 3 percent formulations.

Quantitative measurements reinforced what the micrographs suggested. Apparent porosity rose from 58.57 to 62.03 percent across the series, while water absorption climbed sharply from 58.30 to 79.55 percent, and bulk density fell from 1.22 to about 1.08 grams per cubic centimeter. Nitrogen physisorption on the two endpoint compositions showed that the BET specific surface area of the 3 percent pellet reached 14.843 square meters per gram, roughly 86 percent higher than the 7.986 square meters per gram of the biomass-free control, while total pore volume increased by about 75 percent. In other words, the invasive weed was effectively blowing open the internal architecture of the pellet, creating more pathways and more exposed surface for dye molecules to reach.

Surface charge added a second, electrostatic dimension to the story. Zeta potential measurements at pH 7 showed that all pellets carried negative surface charges, becoming progressively more negative as water hyacinth content increased, from minus 67.3 millivolts for the control to minus 74.9 millivolts for the highest-biomass pellet. The point of zero charge of the best-performing composition was approximately 2.22, meaning that at the pH used in the adsorption experiments the surface was decisively negative and therefore electrostatically attractive to positively charged methylene blue cations. Deprotonated surface hydroxyl groups on the aluminosilicate framework, generating negatively charged siloxide and aluminate sites, are thought to contribute to this favorable electrostatic environment.

The adsorption experiments bore out the design logic. At pH 2, performance was poor, with removal efficiencies between roughly 49 and 54 percent, because the flood of hydrogen ions competed with dye cations for adsorption sites. Performance peaked at pH 4, where the 3 percent pellet removed 77.25 percent of methylene blue with an equilibrium capacity of 19.31 milligrams per gram, and remained high but essentially flat from pH 6 through 10, indicating that electrostatics alone do not govern the process. Kinetic measurements showed rapid initial uptake followed by a gradual plateau between about 800 and 1080 minutes, with 24-hour removal reaching 77.03 percent and a capacity of 19.26 milligrams per gram for the best pellet. Increasing the initial dye concentration from 50 to 250 milligrams per liter lowered the removal percentage from 95.26 to 77.40 percent while raising the per-gram capacity from about 4.76 to 19.35 milligrams per gram, the classic signature of a fixed number of sites being progressively saturated.

Equilibrium data fit the Langmuir isotherm model better than the Freundlich model, with a linearized correlation coefficient of 0.9998 and a maximum monolayer capacity of 22.32 milligrams per gram, while both linearized and nonlinear kinetic analyses consistently favored the pseudo-second-order model. Against the backdrop of published geopolymer adsorbents, the 22.32 milligrams per gram figure is competitive, outperforming lightweight geopolymer-expanded glass composites, metakaolin/slag geopolymers, red mud and rice husk ash systems, and coal gangue-based materials, and landing close to reduced graphene oxide/geopolymer composites, though some fly ash and metakaolin systems report higher capacities. The authors caution that direct comparisons across studies are complicated by differences in material form and experimental conditions, and their pellets carry an inherent mass-transfer penalty because dye molecules must diffuse through the pellet interior rather than contacting a loose powder directly.

That penalty is the price of practicality, and the study is unusually candid about the trade-offs involved. Compressive strength after 28 days of curing fell from 21.5 megapascals for the biomass-free pellet to 9.1, 6.5, and 5.5 megapascals at 1, 2, and 3 percent water hyacinth, because the fibrous additive and its interfacial discontinuities disrupt the continuity of the load-bearing geopolymer matrix. The modest gain in equilibrium capacity at the highest biomass loading does not fully compensate for the substantial loss of mechanical robustness, so the researchers suggest that an intermediate water hyacinth content may offer the best balance for applications where pellets must survive handling. Reusability testing over five adsorption-desorption cycles showed another honest limitation: removal efficiency declined to about 33 percent of its initial value by the fifth cycle, even though the pellets retained roughly 99 percent of their mass, pointing to a need for improved regeneration protocols.

What makes this work resonate beyond its numbers is the circular economy story it tells. Water hyacinth is a global nuisance, clogging waterways, blocking navigation, and starving aquatic ecosystems of light and oxygen, yet here its residue becomes a functional ingredient in a low-cost ceramic adsorbent built from abundant local minerals. The study also models a kind of scientific honesty that is increasingly valued in materials research: rather than claiming a single dominant mechanism, the authors attribute dye uptake to coupled effects, including electrostatic attraction to the negatively charged surface, possible hydrogen bonding through hydroxyl-containing groups, and improved pore accessibility, while explicitly declining to claim mechanisms, such as pi-pi interactions, that their characterization could not verify. They note that methylene blue served only as a model cationic dye, and that real textile wastewater, with its mixtures of dyes, salts, and organic matter, will pose stiffer competitive challenges. Future work on mixed-pollutant systems, thermodynamic analysis, and regeneration chemistry will determine whether these weed-powered pellets can graduate from elegant laboratory concept to working technology for the dye-polluted rivers that need them most.

Subject of Research: Pelletized diatomite-based geopolymer composites incorporating water hyacinth biomass for the adsorptive removal of methylene blue dye from wastewater

Article Title: Pelletized diatomite-based geopolymer-water hyacinth composites for methylene blue adsorption: insights into structure-property-performance relationships

Article References: Thammarong, S., Zhang, W., Pimpha, N., Saenkam, K., Boontakam, W., Tandorn, S., Randorn, C., Srichumpong, T., Pengpat, K., & Rujijanagul, G. (2026). Pelletized diatomite-based geopolymer-water hyacinth composites for methylene blue adsorption: insights into structure-property-performance relationships. Results in Chemistry, 31, Article 103923. https://doi.org/10.1016/j.rechem.2026.103923

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103923

Keywords: geopolymer, water hyacinth, diatomite, methylene blue, adsorption, wastewater treatment, dye removal, metakaolin, porous materials, biomass composites, isotherm modeling, mechanical strength

Crystal violet is not merely a cosmetic nuisance. The triarylmethane dye, widely used in textile printing, paper production, and even as a biological stain, is toxic to aquatic life and suspected of harmful effects in humans, which is why researchers worldwide are racing to find cheap, sustainable ways to capture it before it reaches rivers and groundwater. Adsorption, the process by which dye molecules cling to the surface of a solid material, remains one of the most practical removal strategies, but the performance of any adsorbent depends heavily on how much accessible surface it offers.

That is where electrospinning comes in. The technique applies a high voltage to a droplet of polymer solution, stretching it into a whip-like jet that whips through the air, solvent evaporating along the way, until it lands as fibers with diameters measured in nanometers. Because these fibers pack enormous surface area and high porosity into a small mass of material, they expose a vast number of adsorption sites to the surrounding water. The Iranian team exploited this by blending polyvinyl alcohol, a water-friendly synthetic polymer, with gum arabic, a natural exudate from acacia trees prized for its biocompatibility and abundance of functional groups.

The twist in this study is the addition of carbon dots, nanoscale carbon-based particles that have attracted enormous interest for their fluorescence, low toxicity, and ease of green synthesis. Embedded within the electrospun nanofiber matrix, the carbon dots contribute additional interaction sites and functional chemistry that boost the composite’s ability to bind positively charged crystal violet molecules. The researchers prepared the composite solution and spun it directly into the final adsorbent, avoiding harsh chemicals and keeping the entire fabrication route aligned with green chemistry principles.

To confirm that the material was what they intended, the authors subjected it to a battery of characterization techniques. Fourier transform infrared spectroscopy mapped the chemical bonds and functional groups present in the fibers, verifying that the polymer, gum, and carbon dot components were integrated. X-ray diffraction probed the internal structure, while scanning electron microscopy revealed the fibrous morphology, showing the continuous, porous network that gives the material its high surface area. Energy dispersive X-ray analysis confirmed the elemental composition, and transmission electron microscopy allowed the team to visualize the nanoscale architecture, including the distribution of carbon dots within the fibers.

With the adsorbent in hand, the group systematically tested how well it captured crystal violet from water and, just as importantly, how the process worked. Adsorption kinetics were evaluated using three classical models: pseudo-first-order, pseudo-second-order, and intraparticle diffusion. The data aligned best with the pseudo-second-order model, a result with real mechanistic meaning, since it indicates that the rate-limiting step involves chemical interactions, such as electron sharing or electrostatic attraction, between the dye molecules and the binding sites on the fiber surface, rather than simple physical deposition.

The equilibrium behavior told a complementary story. When the team fitted their adsorption data to the Langmuir, Freundlich, and Temkin isotherm models, the Langmuir model provided the best description. That outcome implies that crystal violet molecules occupy a finite set of energetically equivalent sites on the nanofiber surface, forming at most a single molecular layer, and that once a site is filled it can no longer accept another dye molecule. Such monolayer adsorption on a uniform surface is exactly what one hopes for in a well-behaved, predictable adsorbent, making it easier to design treatment systems around the material.

Thermodynamic analysis added further insight into the driving forces at play. The results showed that the adsorption process is spontaneous and exothermic, meaning it proceeds willingly at the tested conditions and releases heat as the dye binds. An exothermic signature typically points to physical and electrostatic interactions dominating the uptake and suggests that lower temperatures favor adsorption, information that matters when engineers consider real-world wastewater streams whose temperatures vary with season and location.

Perhaps the most encouraging finding for practical deployment came from the reusability tests. Many promising adsorbents falter in regeneration, losing capacity after a handful of cycles as their binding sites clog or their structure degrades. The carbon dot-embedded PVA/gum arabic nanofibers, by contrast, demonstrated high recoverability with no considerable loss in adsorption performance over six consecutive adsorption-desorption cycles. That durability addresses one of the biggest economic hurdles for nanomaterial-based water treatment, since a sorbent that must be replaced after every use quickly becomes prohibitively expensive.

The study sits within a broader surge of interest in biopolymer-based electrospun adsorbents, from gum-based fibers explored for food packaging to hydrogels and aerogels built from chitosan, alginate, and cellulose for capturing dyes, heavy metals, and pharmaceuticals. What distinguishes this work is the combination of three benign ingredients, a scalable fiber fabrication method, and rigorous kinetic, isotherm, and thermodynamic modeling that together demonstrate a coherent, sustainable package. As textile industries in water-stressed regions face tightening discharge rules, materials like these green nanofibers could offer a route to cleaner effluent that does not trade one environmental problem for another, turning tree sap, a common polymer, and carbon nanodots into an effective filter for one of the dye industry’s most persistent pollutants.

Subject of Research: Green carbon dot-embedded electrospun PVA/gum arabic nanofibers for adsorptive removal of crystal violet dye from water

Article Title: Green carbon dot–embedded Electrospun PVA/gum arabic nanofibers for efficient crystal violet removal from aqueous media

Article References: Safaei, A., Giyahban, F., & Ebrahimzadeh, H. (2026). Green carbon dot–embedded Electrospun PVA/gum arabic nanofibers for efficient crystal violet removal from aqueous media. Environmental Science and Pollution Research, 33(30), 15784-15798. https://doi.org/10.1007/s11356-026-38234-5

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38234-5

Keywords: carbon dots, electrospun nanofibers, gum arabic, polyvinyl alcohol, crystal violet, dye removal, adsorption, wastewater treatment, Langmuir isotherm, pseudo-second-order kinetics, green adsorbent, water purification

The environmental stakes are considerable. Synthetic dyes such as Methylene Blue and Safranin-O are discharged in large volumes by textile, paper, leather, and printing industries, and even trace concentrations can color water bodies, block sunlight penetration, and disrupt photosynthesis in aquatic ecosystems. Methylene Blue in particular has documented toxic effects on freshwater microalgae, interfering with growth and metabolism at environmentally relevant concentrations. Conventional treatment approaches, including biological degradation, membrane filtration, and advanced oxidation, often struggle with the chemical stability of these dyes, which is precisely why adsorption has remained one of the most attractive remediation strategies. Adsorbents are comparatively inexpensive, simple to deploy, and can be regenerated, but the search for materials that are simultaneously effective, stable, and sustainable has proven elusive.

The Indian team’s answer was to engineer a hydrogel network from the ground up. Pullulan, a polysaccharide produced by the fungus Aureobasidium pullulans, and carboxymethyl cellulose, a widely used cellulose derivative, were crosslinked with epichlorohydrin, a small molecule that forms covalent bridges between polymer chains. Crucially, the synthesis was carried out under microwave irradiation, a technique that heats the reaction mixture uniformly and from within, dramatically accelerating gelation compared with conventional thermal methods. Microwave-assisted synthesis has become increasingly popular in hydrogel research because it shortens reaction times, promotes homogeneous crosslinking, and often yields more porous structures, all qualities that translate directly into better adsorption performance.

Montmorillonite was the third and perhaps most decisive ingredient. This smectite clay consists of stacked silicate sheets with a high cation-exchange capacity and an enormous internal surface area. When dispersed into the polymer matrix, the clay platelets reinforce the hydrogel mechanically, preventing the collapse and dissolution that plague purely polysaccharide gels, while simultaneously contributing their own adsorption sites. The researchers systematically optimized every major synthesis parameter, including microwave power, irradiation time, crosslinker concentration, solvent volume, the ratio of the two polymers, the amount of montmorillonite, and the pH of the medium, using the maximum swelling percentage as the optimization target. Swelling behavior matters because a hydrogel must expand enough to let dye molecules diffuse into its interior, but not so much that the network disintegrates.

To confirm that the composite had actually formed as designed, the team deployed a full battery of characterization techniques. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy verified the chemical bonds linking the polymers and the crosslinker. X-ray diffraction revealed how the clay layers were dispersed within the matrix, a key indicator of whether the composite is truly intercalated or merely a physical blend. Scanning electron microscopy mapped the internal pore architecture, energy-dispersive X-ray analysis confirmed elemental composition, and thermogravimetric analysis demonstrated that both the clay incorporation and the chemical crosslinking improved the thermal stability of the network. Zeta potential measurements rounded out the picture by characterizing the surface charge of the material across conditions, an essential quantity for understanding how the hydrogel interacts with charged dye molecules.

The adsorption results were striking. The hydrogel achieved a maximum removal efficiency of 96.17 plus or minus 0.57 percent for Safranin-O at a contact time of 280 minutes, and 92.24 plus or minus 0.33 percent for Methylene Blue at 210 minutes. Both dyes are cationic, meaning they carry positive charges that can interact with the negatively charged sites distributed across the hydrogel, from the carboxylate groups of the cellulose derivative to the clay surfaces. The pH-responsive character of the material stems from these ionizable groups: as the acidity of the solution changes, the degree of protonation shifts, altering both the swelling of the gel and the electrostatic attraction it exerts on dissolved pollutants. This tunability means the adsorbent’s performance can be modulated simply by adjusting the water’s pH, an advantage for real-world treatment trains.

Modeling the adsorption data revealed the underlying mechanism. The equilibrium data fit the Langmuir isotherm best, which describes monolayer adsorption onto a surface with a finite, homogeneous set of identical binding sites. In practical terms, each binding location on the hydrogel captures at most one dye molecule, and once those sites are occupied, no further adsorption occurs. The kinetic data, meanwhile, followed the pseudo-second-order model, a signature of chemisorption, in which actual chemical interactions, such as electrostatic attraction, hydrogen bonding, or ion exchange, govern the rate of uptake rather than simple mass transfer. Together, these two models paint a coherent picture: dye molecules migrate into the swollen network and lock onto specific, chemically active sites distributed uniformly throughout the composite.

Perhaps the most important result for practical deployment is reusability. Many promising adsorbents perform brilliantly on their first cycle and then degrade rapidly, forcing operators to dispose of them as contaminated waste. The PA-CMC@MMT hydrogel, by contrast, retained its performance over five successive adsorption-desorption cycles, a durability the authors attribute to the structural reinforcement provided by the montmorillonite and the covalent crosslinking. This combination of high capacity, chemical robustness, and regenerability is what separates a laboratory curiosity from a material with genuine potential for wastewater treatment plants, textile effluent polishing, or emergency response to dye spills.

The broader context makes the advance timely. Recent literature documents an intense global effort to develop biopolymer and clay-based adsorbents, from bentonite-pectin nanocomposites for Safranin-O removal to biochar derived from kitchen waste for Methylene Blue capture, and from lignin-alginate hydrogels to magnetic nanocomposites optimized with machine learning tools. What distinguishes the new work is the deliberate marriage of microwave-assisted green synthesis, dual biopolymer chemistry, and clay reinforcement, all tuned through systematic parameter optimization. Because pullulan and carboxymethyl cellulose are abundant, biodegradable, and derived from renewable feedstocks, the material’s lifecycle footprint is far lighter than that of purely synthetic sorbents, and its biocompatibility opens the door to applications beyond wastewater, including sensing and biomedical hydrogels that share the same pH-responsive design principles.

Challenges remain before the hydrogel can leave the laboratory. The study evaluated performance in controlled aqueous solutions of two model cationic dyes, whereas real textile effluents contain mixtures of dyes, salts, surfactants, and suspended solids that can compete for binding sites or foul the gel. Scaling microwave-assisted synthesis from grams to kilograms, and engineering the material into beads, membranes, or packed columns compatible with continuous-flow treatment, will require further development. Nevertheless, the demonstration that a humble combination of fungal polysaccharide, modified cellulose, and common clay can be transformed into a stable, reusable, pH-tunable pollutant sponge offers a compelling template. As industries worldwide face tightening limits on dye discharge, materials like PA-CMC@MMT suggest that the future of water purification may lie not in exotic nanomaterials, but in cleverly engineered versions of the most abundant polymers nature provides.

Subject of Research: A pH-responsive biopolymer-clay composite hydrogel for adsorptive removal of cationic dyes from contaminated water

Article Title: pH-Responsive carboxymethyl cellulose-pullulan/montmorillonite composite adsorbent for the removal of methylene blue and safranin-O from aqueous solution

Article References: Rahul, & Jindal, R. (2026). pH-Responsive carboxymethyl cellulose-pullulan/montmorillonite composite adsorbent for the removal of methylene blue and safranin-O from aqueous solution. Polymer Bulletin, 83(11), Article 620. https://doi.org/10.1007/s00289-026-06669-y

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06669-y

Keywords: hydrogel, adsorption, pullulan, carboxymethyl cellulose, montmorillonite, methylene blue, safranin-O, wastewater treatment, dye removal, pH-responsive, microwave synthesis, biopolymers

The urgency behind the work is easy to grasp. Textile manufacturing is among the largest industrial consumers of water and one of the biggest dischargers of colored effluent. Methylene blue, a cationic dye used in cotton, silk, paper, and ink production, and Congo red, an anionic diazo dye common in textiles and diagnostic tests, are both prized for their color stability and water solubility, which is precisely what makes them so persistent once they enter rivers and groundwater. Exposure to these compounds has been linked to respiratory irritation, damage to mucous membranes, dizziness, vomiting, diarrhea, genetic abnormalities, and harm to the nervous system. Because the dyes resist biodegradation, conventional biological treatment plants struggle to break them down, leaving adsorption as one of the most practical remediation routes.

Adsorption, in which pollutant molecules stick to the surface of a solid material, has long been favored for its simplicity, low cost, and versatility. The catch is finding an adsorbent with enough surface area, the right surface chemistry, and sufficient structural stability to perform well cycle after cycle. Previous studies have explored fly ash, activated carbons, crushed brick, cedar sawdust, and carbon nanotubes, and graphene-family materials have attracted particular attention because of their enormous surface-to-volume ratios and rich arrays of oxygen-containing functional groups. Zinc oxide, meanwhile, is cheap, widely available, and environmentally benign, but on its own it tends to form clusters that bury its active sites. The new research set out to combine the two materials so that each compensates for the other’s weaknesses.

The synthesis followed well-established chemistry. The team produced graphene oxide using the modified Hummer’s method, oxidizing graphite powder with sulfuric acid, sodium nitrate, and potassium permanganate under carefully controlled temperature steps, then purifying and drying the resulting sheets. Zinc oxide nanoparticles were prepared separately by chemical co-precipitation, dissolving zinc acetate dihydrate in water and raising the pH to 12 with sodium hydroxide, followed by washing, drying, and calcination at 400 degrees Celsius for four hours. Finally, the two components were merged by ultrasonication: graphene oxide was dispersed in deionized water, zinc oxide was gradually added at a three-to-one mass ratio, and the mixture was stirred at 60 degrees Celsius for three hours before being collected and dried.

Characterization confirmed that the composite had formed as intended. UV-visible spectroscopy showed the characteristic ZnO band-gap absorption near 376 nanometers alongside the graphene oxide peaks at roughly 244 and 363 nanometers. Fourier transform infrared spectroscopy revealed the oxygenated functional groups of graphene oxide, including C-O, C-OH, C=C, C=O, and O-H bands, together with a strong ZnO vibration near 650 wavenumbers, evidence that the nanoparticles were anchored to the sheets. X-ray diffraction displayed the full set of wurtzite ZnO crystal planes plus the graphene oxide (001) reflection, while electron microscopy showed crumpled, interconnected graphene sheets decorated with ZnO particles, forming a porous, wrinkled network. Energy-dispersive X-ray analysis put the composition at about 37.2 percent carbon, 38.1 percent oxygen, and 20.4 percent zinc by weight. A zeta potential of minus 21.5 millivolts indicated a negatively charged, moderately stable colloid.

The adsorption experiments revealed how sensitively performance depends on solution chemistry. For methylene blue, removal improved steadily as pH increased, because deprotonation of the composite’s surface groups accumulated negative charge that electrostatically attracted the cationic dye. Congo red behaved in the opposite fashion: removal rose as pH climbed from 2 to 6 and then fell at higher pH, where strong negative surface charge repels the anionic dye. The point of zero charge was measured at pH 7.1, meaning the surface is positive under acidic conditions and negative under alkaline ones. Adsorbent dose mattered too, with removal climbing as dosage increased from 10 to 40 milligrams and then plateauing once all available dye molecules had been captured. Raising the initial dye concentration from 30 to 150 milligrams per liter reduced the percentage removed, since a fixed number of active sites becomes saturated, and equilibrium was reached after about 80 minutes of contact.

Modeling of the equilibrium data showed that the Langmuir isotherm, which assumes monolayer adsorption on a homogeneous surface, described the process better than the Freundlich, Temkin, or Dubinin-Radushkevich models. According to the Langmuir fit, the composite achieved a maximum adsorption capacity of 320.12 milligrams of methylene blue per gram, more than double the 175.24 milligrams per gram recorded for Congo red. Kinetic analysis told a complementary story: the pseudo-second-order model fit best, with the Elovich model also performing well, indicating that chemisorption, the formation of actual chemical bonds between dye and surface, dominated the uptake. An intra-particle diffusion constant that did not pass through the origin showed that diffusion inside the pores was only one of several rate-controlling steps.

Thermodynamic measurements added further depth. Gibbs free energy values ranged from minus 2.98 to minus 10.95 kilojoules per mole across temperatures from 5 to 30 degrees Celsius, confirming that adsorption was spontaneous at every temperature tested. Positive enthalpy changes of 87.34 kilojoules per mole for methylene blue and 89.94 kilojoules per mole for Congo red marked the process as endothermic and pointed to strong adsorbent-dye interactions, possibly involving dehydration of both surfaces before binding. Positive entropy changes exceeding 10 joules per mole per kelvin suggested a dissociative mechanism at the solid-liquid interface. Optimal removal occurred at 20 degrees Celsius, after which the surface saturated.

The proposed mechanism is genuinely multi-pronged. Electrostatic attraction between the negatively charged composite and cationic methylene blue drives much of that dye’s uptake, while hydrogen bonding, pi-pi stacking between dye aromatic rings and graphene domains, surface complexation at ZnO sites, and penetration of dye molecules into the pores all contribute. Infrared spectra taken after adsorption showed new bands corresponding to methylene blue’s C-N and trimethylammonium groups and Congo red’s sulfonate groups, along with shifts in the O-H and C=O features, direct spectroscopic fingerprints of the binding interactions. The synergy between the two components appears central: graphene oxide’s vast surface area and functional groups disperse the zinc oxide nanoparticles, preventing the aggregation that cripples standalone ZnO, while the nanoparticles add extra active sites and structural stability.

Perhaps most importantly for real-world deployment, the material can be regenerated. Washing with ethanol followed by 0.1 molar hydrochloric acid released the bound dyes, and the recovered composite retained useful performance over five consecutive adsorption-desorption cycles, with methylene blue efficiency declining from 97.25 to 68.06 percent and Congo red from 93.89 to 63.35 percent. Compared against previously reported adsorbents, including pine tree bark, sunflower-husk-derived silica materials, and various graphene and zinc oxide systems, the ZnO-GO composite stands out for combining high capacity for both a cationic and an anionic dye with straightforward synthesis and reusability. The authors argue that this balance of performance, cost, and sustainability makes the nanocomposite a credible candidate for scaling up to industrial wastewater treatment, where a single material that can capture dyes of opposite charge could simplify remediation trains considerably.

Subject of Research: Adsorptive removal of cationic and anionic textile dyes from water using a zinc oxide-graphene oxide nanocomposite

Article Title: Enhanced adsorptive removal of methylene blue and Congo red from aqueous solution using zinc oxide-graphene nanocomposite

Article References: Kadian, J., Yadav, S., Dhawan, M., Kumar, A., & Chahar, M. (2026). Enhanced adsorptive removal of methylene blue and Congo red from aqueous solution using zinc oxide-graphene nanocomposite. Discover Chemistry, 3(1), Article 527. https://doi.org/10.1007/s44371-026-00984-z

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00984-z

Keywords: zinc oxide, graphene oxide, nanocomposite, adsorption, methylene blue, Congo red, wastewater treatment, dye removal, chemisorption, Langmuir isotherm, water pollution, nanomaterials

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 technique, known as electrocoagulation, sounds almost deceptively simple. Two metal rods are immersed in the contaminated water and connected to a direct current power supply. As current flows, the anode dissolves, releasing metal ions—in this case ferrous and ferric ions from iron, or trivalent aluminum ions—directly into the solution. Meanwhile, at the cathode, water molecules are reduced, generating hydrogen gas bubbles and hydroxide ions. The metal ions and hydroxide ions then combine to form a cascade of hydroxide and polyhydroxide species, ultimately precipitating as freshly formed, amorphous flocs of iron or aluminum hydroxide. These gelatinous particles act as molecular sponges, adsorbing dissolved and colloidal pollutants and sweeping them out of the water either by settling to the bottom or by floating to the surface on the rising gas bubbles—a process called electroflotation. Crucially, the coagulant is generated in situ, eliminating the need for added chemical reagents and slashing the volume of secondary sludge that plagues conventional coagulation-flocculation treatments.

In the new study, published in Discover Chemistry, the researchers treated 400-milliliter batches of simulated dye wastewater in a 500-milliliter glass reactor fitted with two rod electrodes spaced 1.5 centimeters apart—a configuration chosen to limit ohmic losses while preventing clogging. Sodium chloride was added as a supporting electrolyte to boost conductivity, and the team applied a voltage of 30 volts at currents ranging from 100 to 400 milliamperes. Dye concentrations were tracked by UV-visible spectrophotometry at 528 nanometers, the wavelength of maximum absorbance for neutral red, with removal efficiency calculated from the change in concentration using the Beer-Lambert law. All experiments were conducted at a controlled 25 degrees Celsius, and samples were withdrawn every ten minutes, filtered, and analyzed after a 30-minute settling period.

The first variable probed was current intensity, and the results revealed a striking optimum. With iron electrodes, dye removal climbed from 58.27 percent at 100 milliamperes to a peak of 92.12 percent at 200 milliamperes, then fell back to 90.94 percent at 300 milliamperes and 79.23 percent at 400 milliamperes after 60 minutes of electrolysis. Aluminum electrodes followed the same pattern but with higher values: 59.31, 98.58, 90.27, and 80.45 percent at the same four currents. The researchers attribute the initial improvement to the greater flux of dissolving metal ions and hydroxide flocs as current rises, while the decline at higher currents reflects energy wasted in parasitic side reactions—including the oxidation of chloride to chlorine species at the anode and excessive water oxidation—which consume electricity without contributing to dye capture. Aluminum’s superior electrical conductivity helps explain its edge at equivalent currents.

Initial dye concentration told a complementary story. At low loadings of 25 milligrams per liter, both systems excelled, with iron achieving 96.76 percent removal and aluminum 98.27 percent after an hour. As concentrations rose to 75 and 100 milligrams per liter, performance dropped markedly—iron managed only 80.32 and 61.65 percent respectively at 60 minutes. The explanation lies in stoichiometry: at high pollutant loads, the electrochemically generated coagulant becomes insufficient, and the dense accumulation of hydroxide ions and gas at the cathode can even create a physical barrier between the multiplying particles and the electrodes, choking off the process. pH, meanwhile, acted as a chemical switch that favored one metal over the other. Iron performed best under acidic conditions, removing 94.13 percent of the dye at pH 3, where ferric hydroxide complexes form most abundantly, while removal sagged to 56.46 percent at pH 11. Aluminum showed the mirror-image behavior, peaking at 96.24 percent under strongly alkaline conditions at pH 11, where polymeric hydroxy complexes polymerize most effectively, and dipping to 67.76 percent at pH 3.

The two metals also produced visibly different treatment dynamics. With aluminum electrodes, the effluent remained clear and stable, and the hydrogen bubbles rising from the cathode efficiently floated the flocs to the surface for removal. With iron, the water first turned yellow, then greenish and turbid, as iron(II) and iron(III) hydroxides formed, and floc removal proceeded mainly by settling rather than flotation. The team notes that for the same quantity of electricity, roughly three times more iron dissolves than aluminum, generating a correspondingly larger mass of flocs—a factor that shapes both the kinetics and the sludge-handling profile of each system.

To move beyond one-variable-at-a-time testing, the researchers employed response surface methodology coupled with a centered composite design, an statistical framework that maps how multiple factors interact simultaneously while minimizing the number of experiments required. Eighteen trials explored three variables—initial dye concentration from 25 to 100 milligrams per liter, pH from 5 to 9, and electrolysis time from 20 to 60 minutes—and the resulting data were fitted to second-degree polynomial models. Analysis of variance confirmed the models’ significance, with Fisher statistics of 8.86 for iron and 9.19 for aluminum and p-values of 0.008 and 0.0024 respectively. The coefficients of determination reached 90.88 percent for the iron system and 91.18 percent for aluminum, with adjusted values above 80 percent, indicating the models retain genuine predictive power without overfitting. A paired t-test found no significant difference between experimental and predicted efficiencies, and validation metrics—bias factors of 0.99 and 1.001 and accuracy factors of 1.007 and 1.003—fell comfortably within accepted thresholds.

The three-dimensional response surfaces uncovered subtle interactions that single-factor experiments would have missed. For iron electrodes, a strong synergy emerged between pH and electrolysis time: neither parameter could compensate for an unfavorable value of the other, and yields above 90 percent required combining alkaline pH with sufficiently long treatment. For aluminum, the surfaces displayed a dome-like morphology with a narrow optimal window centered near neutral pH and intermediate concentrations, reflecting the amphoteric nature of aluminum hydroxide, which dissolves as soluble species at both very acidic and very alkaline extremes. Optimization converged on remarkably similar conditions for both metals—around 62 milligrams per liter of dye—but diverged in the details. Iron reached its maximum predicted efficiency of 98.05 percent at pH 8.42 after just 25.68 minutes, while aluminum required pH 7.50 and 34.50 minutes to achieve 95.39 percent.

Experimental runs under those optimal conditions validated the predictions, delivering 97.54 percent removal with iron and 96.89 percent with aluminum. The iron system’s roughly ten-minute kinetic advantage translates directly into lower energy consumption per batch, an economically meaningful margin at industrial scale, and the authors recommend iron as the preferred electrode for treating textile wastewater. Both systems comfortably exceeded 95 percent efficiency, underscoring electrocoagulation’s credentials as a compact, easily automated, low-sludge alternative to biological treatment, chemical coagulation, and costly advanced oxidation processes. The team points toward future work on energy optimization, electrode reuse, and the recovery of the metal-rich sludge, but the central message is already clear: with the right electrode and a statistically tuned recipe, electricity alone can strip a stubborn synthetic dye from water in under half an hour.

Subject of Research: Comparative electrocoagulation removal of neutral red dye using iron and aluminum electrodes optimized by response surface methodology

Article Title: Comparative study of the use of iron and aluminum electrodes for the removal of neutral red by electrocoagulation

Article References: Richard, D., Blaise, K., Bong, A. M., Carelle, M. W. L., Danièle, B. K., Amos, K., & Samomssa, I. (2026). Comparative study of the use of iron and aluminum electrodes for the removal of neutral red by electrocoagulation. Discover Chemistry, 3(1), Article 553. https://doi.org/10.1007/s44371-026-00990-1

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00990-1

Keywords: electrocoagulation, neutral red, iron electrodes, aluminum electrodes, textile wastewater, dye removal, response surface methodology, central composite design, water treatment, electrochemistry, decolorization, optimization

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