The study, published in Results in Chemistry, describes a dual-functional geopolymer concrete composite synthesised from ground granulated blast-furnace slag, a byproduct of steel processing sourced from Ballari, and sugarcane bagasse ash collected from a sugar factory in the Belagavi district. The researchers combined the two precursors in equal mass and activated them with an alkaline solution of 8 molar sodium hydroxide and sodium silicate mixed at a 1:1.5 mass ratio. Binder, fine aggregate and coarse aggregate were blended at a 1:1.72:2.59 mass ratio, cast into moulds, compacted and cured at room temperature. The result was a workable concrete, with a slump of 112 millimetres, whose compressive strength climbed from 8.53 megapascals at three days to 20.44 megapascals at seven days and 28.97 megapascals at 28 days, comfortably meeting the M25 structural grade target.

What makes the material interesting chemically is the reactive aluminosilicate matrix that forms during geopolymerization. When the alkaline activator dissolves the silica and alumina in the slag and ash, the dissolved species polycondense into a gel network rich in silicon, aluminium and calcium. Scanning electron microscopy revealed a heterogeneous surface studded with irregular particles, agglomerated regions and interconnected voids, the kind of porous architecture that offers both mechanical integrity and abundant access points for pollutant molecules. Energy-dispersive X-ray spectroscopy confirmed a composition dominated by calcium oxide at 48.34 percent, silicon dioxide at 28.09 percent and aluminium oxide at 12.06 percent, with smaller amounts of iron, sodium, magnesium, potassium and sulfur oxides traceable to the precursor wastes and activators.

Spectroscopic analysis filled in the molecular picture. Fourier transform infrared spectroscopy identified broad hydroxyl stretching bands between 3200 and 3600 reciprocal centimetres, H-O-H bending near 1630 to 1650, and the strong asymmetric Si-O-Al and Si-O-Si vibrations between 950 and 1100 that fingerprint the geopolymeric network. X-ray diffraction showed crystalline quartz and a calcium-sodium aluminosilicate phase called bytownite embedded within a broad amorphous hump between 20 and 35 degrees two-theta, the signature of alkali-activated binders. X-ray photoelectron spectroscopy found the surface dominated by oxygen at 37.95 atomic percent, followed by carbon, silicon, sodium, calcium, aluminium and magnesium, indicating a calcium-aluminosilicate surface rich in oxygen-containing groups. Thermogravimetric analysis showed the composite retained roughly 79.2 percent of its mass at 800 degrees Celsius, a mark of good thermal stability.

Porosimetry added the final structural detail: a specific surface area of 49.51 square metres per gram, a total pore volume of 0.076 cubic centimetres per gram and an average pore diameter of 8.03 nanometres, placing the material firmly in the mesoporous regime under IUPAC classification. The nitrogen sorption isotherms displayed an H3-type hysteresis loop between relative pressures of roughly 0.4 and 0.9, associated with slit-shaped pores and irregular, interconnected networks formed by particle aggregation and gel development. Rather than a neatly ordered framework, the pore system is a heterogeneous mix of mesopores, interparticle voids and surface irregularities, which the authors argue is well suited to ferrying phenol molecules toward adsorption sites buried inside the matrix.

Batch adsorption experiments, run in duplicate in 250-millilitre flasks agitated at 150 revolutions per minute, mapped how the composite performs under varying conditions. Adsorption surged during the first hour, reaching 12.21 milligrams per gram, then slowed as internal pores filled and sites became occupied, with equilibrium effectively reached at 180 minutes. Dosage told a classic trade-off story: at 1 gram per litre the capacity peaked near 18.92 milligrams per gram but removal was only about 19 percent, while at 10 grams per litre removal rose to 51.56 percent even as capacity fell to 8.59 milligrams per gram, a consequence of particle aggregation and sites left idle by the fixed phenol concentration. The team settled on 3 grams per litre as the practical optimum, balancing removal efficiency of about 37 percent with efficient use of the material.

Concentration and pH shaped the equilibrium behaviour in revealing ways. As the initial phenol concentration rose from 1 to 100 milligrams per litre, capacity climbed from 0.28 to 18.15 milligrams per gram while removal efficiency dropped from 82.96 to 54.44 percent, reflecting saturation of available sites. Adsorption increased as pH rose from 3 to 9, reaching 16.32 milligrams per gram, but fell back at pH 11. The explanation lies in acid-base chemistry: phenol, with a pKa near 9.9, stays mostly in its neutral molecular form below that threshold, while the composite’s point of zero charge sits around pH 10, so electrostatics play little role. Instead, the gains up to pH 9 reflect reduced competition from hydrogen ions and favourable hydrogen bonding between surface hydroxyl groups and phenol’s oxygen. At pH 11, deprotonation to phenolate ions, a negatively charged surface and hydroxide competition all conspire to suppress uptake. Because performance at neutral pH was nearly as good, the team chose pH 7 for practical operation.

Modelling pinned down the mechanism. Kinetic data fitted the pseudo-second-order model best, with a correlation coefficient of 0.9915 and a calculated equilibrium capacity of 13.81 milligrams per gram closely matching the experimental 12.21, pointing to chemisorption at the surface as the dominant rate behaviour. Intra-particle diffusion plots showed two linear stages, with a non-zero intercept indicating that diffusion alone does not control the rate, and liquid-film diffusion analysis confirmed that external mass transfer contributes during the early phase. On the equilibrium side, the Langmuir model won decisively with a correlation coefficient of 0.9985 and a maximum monolayer capacity of 11.08 milligrams per gram, while the Freundlich model’s strong fit of 0.9951 acknowledged some surface heterogeneity. The Dubinin-Radushkevich model’s poor performance suggested pore-filling is secondary to surface interactions. Taken together with post-adsorption changes in the hydroxyl band of the infrared spectrum and the partially filled pores seen in electron micrographs, the evidence points to hydrogen bonding with hydroxylated aluminosilicate sites, aided by pore diffusion and pore filling, as the principal uptake pathway, with sodium- and calcium-bearing sites playing possible supporting roles.

Reusability results were encouraging if not spectacular. Across six consecutive adsorption-desorption cycles using distilled water as the eluent, desorption efficiency declined from 74.58 percent in the first cycle to 57.33 percent in the sixth, a pattern consistent with a mix of reversible surface interactions and stronger, harder-to-reverse binding, plus some pore blockage. The authors suggest that alternative desorbing agents such as dilute acids, alkaline solutions or organic solvents, along with thermal or oxidation-based regeneration, could push performance further. Benchmarked against previously reported adsorbents, whose capacities range from 1.47 milligrams per gram for sawdust to 14.76 for African potato waste carbon, the composite’s 11.08 milligrams per gram at neutral pH is competitive, and it achieved that figure at a modest 3 grams per litre within 180 minutes.

The broader significance of the work lies in the fusion of two functions usually kept apart. Adsorbents are typically powders or granules with no structural role, while concrete is structural material with no environmental function; this composite is both, valorising two troublesome waste streams in the process. The authors are candid about what remains to be done: fixed-bed column trials to test continuous-flow performance, multi-pollutant experiments to probe competitive and synergistic adsorption, standardised heavy-metal leaching tests to confirm environmental safety, and optimised regeneration strategies for long-term reuse. But the concept, a load-bearing concrete that scrubs phenol from water while diverting steel slag and sugar ash from landfills, offers a glimpse of infrastructure that does more than stand up. It could, in principle, quietly clean as it carries.

Subject of Research: Dual-functional geopolymer concrete from agro-industrial wastes for phenol adsorption from water

Article Title: Evaluation of agro-industrial waste-derived concrete composite for phenol adsorption: Process optimization, kinetics, isotherm modelling and mechanistic insights

Article References: S.V., M., B.V., C., M.S., S., K., S., Y.M., P., S., S., Girish, C. R., Mohan, B., & A., S. M. (2026). Evaluation of agro-industrial waste-derived concrete composite for phenol adsorption: Process optimization, kinetics, isotherm modelling and mechanistic insights. Results in Chemistry, 31, Article 103954. https://doi.org/10.1016/j.rechem.2026.103954

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103954

Keywords: geopolymer concrete, phenol adsorption, ground granulated blast-furnace slag, bagasse ash, waste valorization, water treatment, adsorption kinetics, Langmuir isotherm, mesoporous materials, alkali activation, hydrogen bonding, sustainable construction

The study, published in the journal Results in Engineering, was carried out by Irina Ceban, Crina Vicol and Maria Mihet, who prepared two activated carbons from walnut shells using citric acid as a mild, biodegradable modifying agent. The shells were washed, dried at 150 degrees Celsius for 24 hours, crushed and sieved, then impregnated with a 50 percent citric acid solution before thermal treatment. The researchers deliberately chose two very different processing routes: one sample, designated AC450-A, was heated to 450 degrees Celsius in air, while the second, AC600-N, was heated to 600 degrees Celsius under a flow of nitrogen. After treatment, both materials were washed to constant filtrate pH and dried, yielding two carbons with strikingly different personalities.

The central question was deceptively simple: does it pay more to preserve the oxygen-rich functional groups that citric acid installs on a carbon surface, or to build a more carbonized, thermally stable structure? Citric acid is prized in adsorbent design because it grafts carboxylic, hydroxyl and carbonyl functionalities onto carbon, creating sites that can bind metal ions through ion exchange, electrostatic attraction and surface complexation. But heat works against this chemistry. As treatment temperature rises, the carbon framework condenses and aromatizes, becoming more stable, while thermally labile oxygen groups are progressively burned off or transformed. The Moldovan team set out to quantify exactly where that balance falls.

Characterization told the story in fine detail. Elemental analysis showed carbon content climbing from 81.37 percent in AC450-A to 84.90 percent in AC600-N, while hydrogen fell from 3.92 to 2.93 percent, a signature of deeper carbonization and structural condensation. Sulphur was undetectable in both samples, confirming the purity of the walnut shell precursor. Fourier-transform infrared spectroscopy revealed the chemical consequences: the lower-temperature sample retained stronger O-H, C=O and C-O bands, indicating abundant oxygen-containing surface groups, whereas the 600-degree sample showed enhanced aromatic C=C features and diminished oxygen signals, consistent with a more condensed, carbon-rich framework.

Perhaps the most surprising finding came from nitrogen adsorption measurements. Both carbons exhibited extremely low BET surface areas, just 0.35 square metres per gram for AC450-A and 0.98 square metres per gram for AC600-N, three orders of magnitude below conventional activated carbons, which typically range from several hundred to more than 1000 square metres per gram. The isotherms were Type II-III, indicating essentially nonporous or macroporous materials with negligible microporosity. Yet both samples removed iron efficiently. This apparent paradox, a carbon with almost no measurable porosity that still captures metal ions, points squarely at surface chemistry rather than physical surface area as the dominant retention mechanism, echoing classic work by Boehm and others showing that oxygen functionalities govern metal adsorption on oxidized carbons.

The point of zero charge reinforced this picture. Using potentiometric titration under argon with sodium chloride electrolytes at three ionic strengths, the team determined pHpzc values of 3.58 for AC450-A and 2.94 for AC600-N. Below these thresholds the surfaces are protonated and positively charged; above them, carboxylic and phenolic groups deprotonate, generating negatively charged sites that attract cationic iron species. Suspension pH measurements, both below 4.0, confirmed the strongly acidic character imparted by the citric acid treatment, and scanning electron microscopy showed AC450-A as a rough, cracked, defect-rich surface while AC600-N appeared denser and more homogeneous, with EDX detecting calcium in the latter, likely concentrated from the natural mineral fraction of the shells after high-temperature carbonization.

Batch adsorption experiments across the pH 2 to 10 range revealed strongly pH-dependent behaviour. At pH 2, apparent removal was modest, roughly 5.2 milligrams per gram for AC450-A and 6.3 for AC600-N, because protonated surfaces and a flood of competing hydrogen ions shut down binding sites. As pH rose above the points of zero charge, deprotonation opened the door to electrostatic attraction and complexation. The highest apparent removal, 23 to 26 milligrams per gram for AC450-A and 27 to 31 for AC600-N, occurred at pH 9 to 10. Crucially, the authors caution that these high-pH values cannot be read as true adsorption capacities: at alkaline pH, ferrous iron hydrolyzes, and in the presence of dissolved oxygen it oxidizes to Fe(III), which precipitates as sparingly soluble hydroxides. Because no adsorbent-free precipitation blanks were run, adsorption, oxidation, hydrolysis and precipitation could not be quantitatively separated, and the results are framed honestly as overall iron removal.

Kinetic modelling added an empirical layer. The pseudo-second-order model of Ho and McKay clearly outperformed the Lagergren pseudo-first-order equation, with coefficients of determination reaching 0.997 for AC450-A and 0.999 for AC600-N, and calculated equilibrium capacities closely matching experimental values at most concentrations. The team, however, resists over-interpretation: a good fit to a pseudo-second-order equation is not proof of chemisorption, and the kinetic data were interpreted alongside the spectroscopic and surface-charge evidence rather than in isolation. Equilibrium data were fitted with four isotherm models, and the Langmuir equation won decisively, with R-squared values up to 0.998 for AC450-A and 0.999 for AC600-N. Model-derived monolayer capacities rose with temperature, from 4.47 to 6.76 milligrams per gram for AC450-A and from 4.62 to 9.27 for AC600-N between 20 and 40 degrees Celsius, and separation factors between zero and one confirmed favourable uptake across the entire concentration range.

Thermodynamics painted a nuanced picture. Gibbs free energies were negative at all three temperatures for both carbons, confirming spontaneous retention, but the van’t Hoff analysis yielded an apparent endothermic enthalpy of about +32.6 kilojoules per mole for AC450-A against a strongly exothermic -95.9 kilojoules per mole for AC600-N, with entropy changes of +207.9 and -217.2 joules per mole-kelvin respectively. With only three temperatures and limited linearity, the authors treat these numbers cautiously, refusing to assign a mechanism from them alone. The same discipline applies to the Dubinin-Radushkevich adsorption energies, which were explicitly not used to distinguish physical from chemical binding, a refreshing departure from common practice in the adsorption literature.

The broader significance of the work lies in its integrated approach and its honesty. Rather than chasing a headline capacity number, the study demonstrates that iron removal by these walnut-shell carbons is governed by a pH-dependent interplay of surface chemistry, iron speciation and thermal history, and that a carbon with almost no BET surface area can still perform meaningfully if its surface is rich in the right oxygen functionalities. The trade-off is clear: AC450-A preserves the carboxyl-rich chemistry that favours metal binding, while AC600-N gains carbonization, thermal stability and a modestly larger surface. For regions like Moldova, where walnut cultivation generates vast shell residues, the work offers a template for converting agricultural waste into water-treatment materials using a benign, food-grade acid. The authors note that model single-solute solutions were used, and that regeneration, competitive adsorption and performance in real waters remain open questions, but the foundation is laid: sometimes the smartest adsorbent is not the most porous one, but the one whose surface chemistry is preserved with care.

Subject of Research: Citric acid-modified activated carbons from walnut shells for Fe(II) adsorption from aqueous solutions

Article Title: Preparation and characterisation of citric acid-modified activated carbons for the adsorption of Fe(II) ions from aqueous solutions

Article References: Ceban, I., Vicol, C., & Mihet, M. (2026). Preparation and characterisation of citric acid-modified activated carbons for the adsorption of Fe(II) ions from aqueous solutions. Results in Engineering, 32, Article 113432. https://doi.org/10.1016/j.rineng.2026.113432

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113432

Keywords: activated carbon, walnut shells, citric acid modification, Fe(II) adsorption, water treatment, heavy metals, biomass valorisation, point of zero charge, Langmuir isotherm, adsorption kinetics, surface functional groups, Republic of Moldova

The team’s approach centers on a familiar workhorse of industrial chemistry: gamma-phase aluminum oxide, commonly written as γ-Al2O3. This porous ceramic material is cheap, mechanically robust, chemically stable, and easy to shape into pellets that can be packed into treatment columns. On its own, however, alumina is not particularly good at grabbing nitrate. Its surface carries charge characteristics that favor certain ions over others, and nitrate, a relatively weakly hydrated and mobile anion, does not bind strongly enough to bare alumina to enable efficient extraction from real water. The researchers therefore set out to transform the surface chemistry of the pellets by grafting onto them organic molecules that would actively attract and hold nitrate ions.

The key innovation lies in the modifiers themselves. The group synthesized phosphonate-based quaternary ammonium compounds in a two-step reaction and then used them to functionalize the alumina surface. Quaternary ammonium groups are permanently positively charged, which makes them natural anchors for negatively charged anions such as nitrate. Phosphonic acid groups, meanwhile, bind tenaciously to metal oxide surfaces like alumina, forming stable linkages that keep the modifier in place through repeated use. By combining these two functional elements in a single molecule, the chemists created a self-anchoring, positively charged coating that turns each pellet into a nitrate-hunting surface. This dual-function design is what distinguishes the work from simpler approaches that merely coat adsorbents with loosely attached cationic species.

The performance data show that the strategy works. When the modified pellets were exposed to water containing 50 milligrams of nitrate per liter, a concentration representative of heavily contaminated sources, uptake rose rapidly to about 3.3 milligrams of nitrate per gram of adsorbent within the first hour. The adsorption then slowed and reached a plateau of roughly 3.45 milligrams per gram after 120 minutes. That rapid initial phase matters in practice, because it suggests that a treatment column packed with these pellets could strip a large fraction of nitrate from flowing water in a short contact time. The plateau indicates that the available binding sites had become saturated, defining the practical working capacity of the material under those conditions.

To characterize the full range of the adsorbent’s capability, the researchers fitted their equilibrium data to the Langmuir isotherm model, a standard framework that describes adsorption onto a finite number of uniform binding sites. The resulting Langmuir capacities ranged from 9.7 to 13.2 milligrams of nitrate per gram, depending on which modifier was used. The highest value, 13.2 milligrams per gram, was achieved with pellets modified using a compound abbreviated C2TMABr, a quaternary ammonium species with a short ethyl spacer. This modifier dependence is scientifically interesting because it shows that the molecular architecture of the grafted layer, not just its overall positive charge, controls how accessible and effective the binding sites are. It also gives future researchers a design lever: by tuning the organic chain between the phosphonate anchor and the ammonium head group, selectivity and capacity can be adjusted.

Real water is never a clean solution of a single contaminant, and the study directly confronted this complication. Natural waters contain a cocktail of competing anions, including chloride, sulfate, bicarbonate, and phosphate, all of which can crowd out nitrate at the positively charged binding sites. The experiments showed that these competing ions did reduce nitrate uptake, but not equally. Sulfate, a doubly charged anion, exerted a substantially stronger inhibitory effect than chloride, which carries only a single negative charge. This behavior is consistent with electrostatic theory, since divalent ions are attracted more strongly to cationic sites and bind with higher affinity. The finding is important for anyone planning to deploy the material in the field, because sulfate-rich waters, which are common in agricultural catchments where gypsum and other sulfate salts leach from soils, would demand either larger adsorbent inventories or a pretreatment step.

Perhaps the most practically significant result concerns regeneration. A major weakness of many adsorption technologies is that the spent adsorbent becomes a disposal problem in itself, or loses performance after only a few use cycles. The German team demonstrated that a simple brine wash solves this. Regenerating the pellets with a sodium chloride solution of 16.13 millimoles per liter restored about 95 percent of the initial adsorption performance after just 30 minutes. The mechanism is straightforward: a high concentration of chloride ions floods the surface and displaces the bound nitrate, releasing it into the regenerant solution and freeing the binding sites for another round. The concentrated nitrate-laden brine could then be managed separately, concentrating the contaminant into a much smaller volume than the original water stream.

The durability of the material over repeated cycles is equally encouraging. The C2TMABr-modified adsorber was subjected to ten consecutive adsorption and desorption cycles, and over the final seven of those cycles it retained 93 percent, with an uncertainty of plus or minus 2 percent, of its initial capacity. That stability implies that the phosphonate anchor holds the modifier firmly to the alumina surface even under the ionic stress of repeated brine washes, and that the quaternary ammonium sites themselves are not degraded by the regeneration chemistry. For a real-world treatment system, this kind of cycle stability is what separates a laboratory curiosity from a technology that can operate economically for months or years between media replacements.

It is worth being clear about what the material does and does not deliver. The nitrate capacities reported here, in the range of roughly 10 to 13 milligrams per gram, are moderate rather than record-breaking. Some specialized anion exchangers and engineered sorbents report higher capacities in idealized laboratory conditions. What the alumina pellets offer instead is a compelling combination of properties: they are dense, mechanically robust, and easy to separate from treated water, avoiding the fine-particle handling problems that plague powdered adsorbents; they can be regenerated with cheap table salt rather than aggressive chemicals; and they maintain their performance over many cycles. In water treatment engineering, that combination of separability, regenerability, and stability often matters more to overall cost than raw capacity alone.

The study arrives at a moment when regulators worldwide are tightening nitrate limits and water utilities are searching for treatment options that sit between expensive membrane processes and biological denitrification, which requires careful control of microbial communities. Adsorptive removal with regenerable media occupies an attractive middle ground: it is simple to operate, works at ambient temperature, and concentrates the contaminant for downstream management. The work of Gützlaff, Kutschin, Bräutigam, and Schacher shows that rational surface chemistry, in this case the marriage of phosphonate anchoring groups with quaternary ammonium binding sites on a robust ceramic support, can turn an ordinary industrial material into a targeted nitrate scavenger. The next steps for the field will involve testing the pellets in natural water matrices with their full complement of competing ions and organic matter, scaling the synthesis of the modifiers, and integrating the media into continuous-flow column systems. If those challenges are met, phosphonate-functionalized alumina pellets could become a practical tool in the effort to keep nitrate out of the water people drink and the ecosystems that depend on clean rivers and groundwater.

Subject of Research: Adsorptive nitrate removal from water using phosphonate-quaternary ammonium surface-modified γ-Al2O3 pellets

Article Title: Surface-modification of γ-Al 2 O 3 pellets with organic phosphonic acids-quaternary ammonium compounds for adsorptive nitrate removal from water

Article References: Gützlaff, J. P. E., Kutschin, T., Bräutigam, P., & Schacher, F. H. (2026). Surface-modification of γ-Al2O3 pellets with organic phosphonic acids-quaternary ammonium compounds for adsorptive nitrate removal from water. PLOS Water, 5(8), e0000586. https://doi.org/10.1371/journal.pwat.0000586

Image Credits: AI Generated

DOI: 10.1371/journal.pwat.0000586

Keywords: nitrate removal, water treatment, adsorption, γ-Al2O3, phosphonic acid, quaternary ammonium, surface modification, regeneration, Langmuir isotherm, anion selectivity, drinking water, PLOS Water

The molecule, named N1,N4-bis((1H-benzo[d]imidazol-2-yl)methyl)cyclohexane-1,4-dicarboxamide, or BCHDA, was assembled by coupling 2-aminomethylbenzimidazole with cyclohexane-1,4-dicarboxylic acid in pyridine, using triphenyl phosphite as a dehydrating agent. The reaction produced a white solid in 44 percent yield with a melting point of 310 degrees Celsius. Its structure was confirmed through elemental analysis, FT-IR and UV-visible spectroscopy, proton and carbon-13 NMR, high-resolution mass spectrometry and single-crystal X-ray diffraction. The proton NMR revealed a roughly 7:1 mixture of cis and trans isomers around the central cyclohexane ring, a detail the team tracked carefully through the characteristic resonances of the axial and equatorial hydrogens.

What makes BCHDA special is its architecture. Where most previously studied benzimidazole inhibitors carry a single fused aromatic ring, BCHDA carries two, linked through amide bridges to a cyclohexane core. Each benzimidazole unit is rich in electron-donating nitrogen atoms, and the amide groups add further oxygen and nitrogen donor sites. In principle, this gives the molecule multiple anchoring points for bonding to an iron surface, along with an extended conjugated pi-electron system capable of sharing electron density with vacant metal d-orbitals. The researchers set out to test whether this dual-ring design translates into superior protection.

The electrochemical evidence was unambiguous. Using potentiodynamic polarization in 0.5 molar sulfuric acid, the team found that adding BCHDA suppressed both the anodic dissolution of iron and the cathodic evolution of hydrogen gas. The corrosion potential shifted by less than 85 millivolts relative to the blank solution, the accepted signature of a mixed-type inhibitor acting on both halves of the corrosion reaction. At the highest concentration tested, 10 to the minus 3 molar, and at 298 kelvin, the corrosion current density fell so dramatically that the calculated inhibition efficiency reached 99.13 percent. Efficiency rose with concentration but declined with temperature, dropping to 92.80 percent at 328 kelvin at the same dose, a pattern consistent with partial desorption of the inhibitor film as thermal agitation increases.

Electrochemical impedance spectroscopy told a matching story. The Nyquist plots showed depressed capacitive semicircles whose diameters grew steadily with inhibitor concentration, reflecting a rising charge-transfer resistance at the metal-electrolyte interface. The data fitted well to a two-time-constant equivalent circuit, with one relaxation process assigned to the dielectric response of the adsorbed inhibitor film and the other to charge transfer across the double layer. From the impedance measurements the team derived a maximum inhibition efficiency of 94.32 percent at 10 to the minus 3 molar and 298 kelvin. The small discrepancy with the Tafel-derived figure arises because the two techniques probe different aspects of the corrosion process, one under finite overpotential and the other near open circuit, yet both showed the same concentration-dependent trend.

Adsorption analysis showed that the surface coverage data followed the Langmuir isotherm almost perfectly, indicating monolayer adsorption on energetically equivalent sites with negligible interaction between adsorbed molecules. The standard free energy of adsorption came out near minus 40 kilojoules per mole, right at the boundary between physical and chemical adsorption, while the adsorption enthalpy of minus 72.23 kilojoules per mole pointed clearly toward dominant chemisorption. The negative adsorption entropy indicated that the molecules become more ordered as they assemble into a protective layer at the metal-solution interface. Arrhenius analysis added further support, with activation energies for the inhibited systems exceeding those of the blank acid, confirming that the adsorbed film acts as a genuine kinetic barrier.

Direct imaging sealed the case. Scanning electron micrographs of polished steel showed a smooth surface marked only by polishing lines. After 24 hours in uninhibited sulfuric acid the surface was ravaged by cracks, pits and irregular corrosion products. In acid containing BCHDA the damage was dramatically reduced, with the 10 to the minus 3 molar sample retaining the smoothest morphology. Energy-dispersive X-ray analysis quantified the difference: iron content on the surface fell from 98.73 percent on polished steel to 56.35 percent after uninhibited acid exposure, but recovered to 71.52 percent in the presence of the inhibitor, while oxygen from oxide corrosion products dropped from nearly 40 percent to about 13 percent. Crucially, carbon and nitrogen signals appeared on the protected surfaces, direct fingerprints of adsorbed BCHDA molecules.

To understand why the molecule works so well, the team turned to density functional theory at the B3LYP/6-311+G(d,p) level, computing descriptors for both the neutral molecule and its protonated form, which predominates in sulfuric acid. The neutral species showed a HOMO energy of minus 6.09 electron-volts, a small frontier orbital gap of 1.74 electron-volts and a high electrophilicity index, all markers of a molecule well suited to donating and accepting electron density at a metal surface. Protonation widened the gap to 3.06 electron-volts and reduced the electron-donating capacity, yet the protonated form remained strongly surface-active. Natural bond orbital analysis revealed powerful intramolecular charge-transfer interactions, including a sigma-to-lone-pair stabilization of 43.04 kilocalories per mole in the neutral molecule and a pi-to-pi-star delocalization of 45.23 kilocalories per mole in the protonated species, confirming that the conjugated framework stays electronically robust under acidic conditions.

Molecular dynamics simulations on a four-layer iron (110) slab in aqueous sulfuric acid provided the final molecular-scale picture. The neutral BCHDA molecule bound to the surface with an interaction energy of minus 185 kilocalories per mole, lying nearly parallel to the metal to maximize contact between its pi-system and the iron atoms. The protonated form, though slightly weaker at minus 160 kilocalories per mole, still adsorbed spontaneously through a synergistic combination of electrostatic attraction to the sulfate-charged surface and residual donor-acceptor bonding through unprotonated nitrogen sites. Together, the experiments and simulations reveal a dual-mode mechanism: rapid electrostatic coverage by protonated molecules followed by durable chemisorption of neutral ones through nitrogen and oxygen lone pairs and aromatic pi-electrons. The authors argue that this integrated experimental-theoretical strategy offers a blueprint for rationally designing the next generation of corrosion inhibitors, positioning bis-benzimidazole derivatives as promising candidates for protecting steel in some of the harshest acidic environments industry can produce.

Subject of Research: Corrosion inhibition of mild steel in sulfuric acid by a bis-benzimidazole diamide derivative

Article Title: Experimental and computational studies on the corrosion inhibition of Bisbenzimidazole diamide derivative on mild steel in acidic media

Article References: Kumar, A., Jain, R., Kumar, S., Sanyukta, Shabnam, Vashisht, H., Baxi, S., Mahiya, K., Mathias, G. E., Anadebe, V. C., Olasunkanmi, L. O., & Ebenso, E. E. (2026). Experimental and computational studies on the corrosion inhibition of Bisbenzimidazole diamide derivative on mild steel in acidic media. Discover Electrochemistry, 3(1), Article 86. https://doi.org/10.1007/s44373-026-00175-6

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00175-6

Keywords: corrosion inhibition, mild steel, benzimidazole, sulfuric acid, electrochemical impedance spectroscopy, potentiodynamic polarization, density functional theory, molecular dynamics, Langmuir isotherm, chemisorption, SEM-EDX, protective film

The logic behind the design draws on two well-established strands of environmental chemistry. Geopolymers, first described by Joseph Davidovits in 1991, are aluminosilicate materials formed by alkali activation of precursors such as metakaolin, and they have repeatedly shown promise as adsorbents for dissolved metals. Biosorption, meanwhile, exploits the dense array of functional groups on microbial cell walls, which can bind metal ions through complexation and exchange. The challenge has always been practicality: free-floating microbial biomass is difficult to handle, separate and reuse in real treatment systems. Immobilization solves that problem by anchoring the cells onto a solid carrier, and the new study demonstrates that a geopolymer can serve as that carrier through simple passive contact rather than elaborate chemical grafting.

To understand what makes JEONS5 tick, the team subjected the material to a battery of analytical techniques. Zeta potential measurements mapped the surface charge of the composite across the relevant pH range, while Fourier-transform infrared spectroscopy identified the chemical groups available for binding, including hydroxyl, amine, carbonyl, C–N, Si–O and Al–O functionalities. Scanning electron microscopy paired with energy-dispersive X-ray spectroscopy revealed the morphology of the fungal cells integrated into the geopolymer matrix and confirmed the presence of lead after uptake. X-ray diffraction, X-ray fluorescence and X-ray photoelectron spectroscopy rounded out the picture, allowing the researchers to track how the surface chemistry of the hybrid changed as it captured Pb2+ ions from solution.

Batch experiments established the operating conditions for maximum performance. At a pH of 5.0 and a modest sorbent dosage of just 0.04 grams, the material removed more than 95 percent of lead from a solution containing 100 milligrams of Pb2+ per liter. That dosage figure is notable in itself, because it means only a small quantity of the composite is needed to treat a given volume of contaminated water, which directly affects the cost and footprint of any future treatment process. The team also found that uptake was essentially independent of temperature, suggesting the binding interaction is not strongly thermally activated and that performance should hold steady across a range of ambient conditions.

Speed is where the material truly stands out. Equilibrium was reached in roughly 30 minutes, and more than 75 percent of the total lead uptake occurred within the first five minutes of contact. For water treatment engineers, that kind of kinetics matters enormously: rapid uptake translates into shorter contact times, smaller reactor volumes and higher throughput in continuous systems. The kinetic data fit a pseudo-second-order model well, a pattern typically interpreted as indicating that the rate-limiting step involves chemical interactions between the metal ions and the binding sites rather than simple diffusion to the surface.

Equilibrium data, meanwhile, were best described by the Langmuir isotherm model, which assumes a finite number of uniform binding sites on the sorbent surface. From that fit the team calculated a maximum uptake capacity of 1.05 × 10⁻³ moles per gram, equivalent to 217.56 milligrams of lead per gram of material. That figure places JEONS5 among the more capable biosorbents reported for lead, and the authors attribute the capacity to the joint activity of the geopolymer framework and the fungal cells, each contributing distinct binding chemistry to the composite.

Because real treatment plants rarely operate in batch mode, the researchers also tested the material in a fixed-bed column configuration, the geometry most commonly used in industrial adsorption. The column showed a breakthrough point at 20 minutes and an exhaustion point at 350 minutes, defining the window during which the bed delivers treated water below the target concentration. The shape of the breakthrough curve was fairly well captured by Chu’s simplistic model, a modern analytical tool for fixed-bed adsorption data, which gives engineers a way to predict column performance without resorting to computationally intensive simulations.

Perhaps the most consequential result concerns reuse. Regeneration tests showed that JEONS5 retained sorption and desorption efficiencies above 90 percent through its first ten loading and unloading cycles, and even at the end of the twentieth cycle the material still delivered 50 percent of its original sorption efficiency. Reusability is the economic linchpin of any adsorbent technology, since a material that must be replaced after a handful of cycles quickly becomes more expensive than conventional alternatives. Twenty usable cycles, with the possibility of recovering the captured lead during desorption, points toward a genuinely practical process rather than a laboratory curiosity.

The mechanistic picture that emerges from the spectroscopic evidence is one of multiple pathways operating in parallel. The authors conclude that lead capture proceeds through surface complexation, in which Pb2+ coordinates directly with functional groups on the composite; ion exchange, in which lead displaces other cations from the geopolymer framework; and electrostatic interactions, in which the charged surface attracts the metal ions. This redundancy is a strength, because a sorbent that relies on a single mechanism can be vulnerable to changes in water chemistry, whereas a multi-pathway material should perform more robustly across diverse contaminated waters.

The study, funded by the Scientific and Technological Research Council of Türkiye under project number 123Y131, arrives amid growing pressure to find low-cost, low-waste methods for heavy metal remediation. Lead exposure remains a serious public health concern worldwide, with no known safe blood level, and contaminated water is a major exposure route. A sorbent that combines abundant raw materials, a simple passive immobilization step, rapid kinetics, a high capacity and demonstrated reusability addresses several of the barriers that have kept biosorption technologies out of mainstream practice. The researchers argue that JEONS5 has enormous potential for treating Pb2+-contaminated aquatic systems, and the next test for the material will be demonstrating that performance on real industrial effluents, where competing ions and organic matter complicate the chemistry far beyond the clean laboratory solutions used in this study.

Subject of Research: A geopolymer-immobilized fungal biosorbent for removing toxic lead ions from contaminated water

Article Title: Geopolymer fungal cell integration achieved through passive immobilization: a new sustainable candidate to effectively remove toxic lead contamination

Article References: Geopolymer fungal cell integration achieved through passive immobilization: a new sustainable candidate to effectively remove toxic lead contamination. (n.d.). https://doi.org/10.1007/s10653-026-03515-y

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03515-y

Keywords: geopolymer, Neurospora, biosorption, lead removal, heavy metal remediation, water treatment, immobilized cells, hybrid sorbent, adsorption kinetics, Langmuir isotherm, fixed-bed column, sustainable materials

The material itself is a clever piece of green chemistry. Gelatin, a protein derived from collagen, and alginate, a polysaccharide extracted from brown seaweed, are both abundant, biodegradable, and rich in functional groups that can interact with dissolved pollutants. By cross-linking the two polymers, the researchers created a stable film that resists dissolving in water, a common failure mode for purely biopolymer adsorbents. Embedded within this matrix are particles of montmorillonite, a naturally occurring swelling clay whose negatively charged layers normally attract cations rather than the anionic dye molecules that dominate reactive dye effluents.

That is where the surfactant comes in. Treating the clay with tetradecyltrimethylammonium bromide, a cationic surfactant known as TTAB, swaps the naturally occurring counterions between the clay layers for long, positively charged alkylammonium chains. This organophilic modification transforms the clay interior into an environment that welcomes anionic species such as RR120, whose sulfonate groups are drawn electrostatically to the quaternary ammonium sites. The result is a hybrid in which the clay supplies high-affinity binding sites while the surrounding biopolymer network holds everything together in a form that can be handled, recovered, and ultimately degraded.

The most consequential design decision, however, was architectural. The team had previously reported a bulk version of the same composite, but diffusion through thick granular adsorbents is slow: dye molecules must wind through tortuous internal pores before reaching binding sites buried deep within the material. By casting the composite as a thin film, the researchers dramatically shortened the diffusion pathways. Less time spent traveling means less internal mass-transfer resistance, and more of the material’s binding capacity becomes accessible within a practical contact time. It is a reminder that in adsorption science, geometry can matter as much as chemistry.

Batch experiments mapped out how the system behaves under varying conditions. Equilibrium adsorption capacity rose with contact time, initial dye concentration, and temperature, but fell as solution pH increased. That pH dependence is chemically coherent: under acidic conditions the adsorbent surface carries a more positive charge, strengthening the electrostatic pull on the anionic dye, while at higher pH, hydroxide ions compete with dye molecules for cationic sites and the surface charge shifts unfavorably. The positive temperature effect points to an endothermic adsorption process, in which thermal energy helps dye molecules overcome barriers to reaching and anchoring at active sites.

To dissect the mechanism, the researchers fitted their kinetic data to three classical models: pseudo-first-order, pseudo-second-order, and intraparticle diffusion. The analysis indicated that uptake was governed by a combination of surface adsorption and intraparticle diffusion, meaning that dye molecules both bind rapidly at external sites and gradually penetrate the film interior. At equilibrium, the Langmuir isotherm described the data best, implying monolayer adsorption onto a finite set of energetically equivalent sites, with a maximum adsorption capacity of 46.79 milligrams of dye per gram of composite. Regeneration tests using 0.5 molar sodium chloride showed moderate reusability, with chloride ions displacing bound dye and allowing the film to be cycled again.

The study’s second act is what elevates it beyond a conventional adsorption paper. Rather than relying solely on laborious one-factor-at-a-time experiments, the team trained several machine-learning algorithms on their experimental dataset and asked which could best predict adsorption capacity from the operating variables. Among the candidates evaluated, an optimized gradient boosting model emerged as the clear winner, achieving a coefficient of determination of 0.9606 on the test set and a root-mean-square error of just 1.4265 milligrams per gram. Gradient boosting works by building an ensemble of weak predictive models, typically shallow decision trees, each trained to correct the residual errors of its predecessors, and it has become a favorite for small-to-medium experimental datasets in environmental engineering because it captures nonlinear interactions without enormous data volumes.

With a trustworthy model in hand, the researchers used it to search the operating space for the conditions that would maximize dye uptake. The algorithm pointed to a contact time of 356 minutes, an initial dye concentration of 277 milligrams per liter, a pH of 2.8, and a temperature of 41 degrees Celsius. The crucial test came next: the team ran actual batch experiments at those predicted optima and measured an adsorption capacity of 45.23 plus or minus 0.05 milligrams per gram, a relative prediction error of only 0.91 percent. That level of agreement between simulation and experiment is the kind of result that turns a modeling exercise into a genuine engineering tool.

The broader significance is twofold. First, the work demonstrates that biodegradable, low-cost adsorbents need not sacrifice performance, particularly when smart design choices such as thin-film geometry and surfactant intercalation are deployed to overcome the classic weaknesses of biopolymer systems. Second, it shows that machine learning can compress the optimization workflow for water treatment processes: instead of exhaustively mapping every combination of time, concentration, pH, and temperature in the lab, researchers can train a model on a manageable dataset and let the algorithm navigate toward the optimum, reserving experiments for validation. Similar approaches are spreading rapidly across adsorption science, from biochar design for heavy metal capture to carbon materials for carbon dioxide separation.

Challenges remain before such films could see real-world deployment. The moderate reusability observed with salt regeneration suggests that long-term cycling performance would need improvement, and real textile effluents carry a far messier cocktail of salts, surfactants, and competing organics than a synthetic dye solution. Still, the study offers a compelling template: a biodegradable polymer-clay hybrid engineered for fast mass transfer, a classical mechanistic framework that explains why it works, and a machine-learning layer that tells operators exactly how to run it. As textile industries face tightening discharge standards and growing scrutiny of azo dye toxicity, strategies that combine sustainable materials with data-driven optimization are likely to move from the laboratory bench toward the treatment plant, and this thin-film composite with its gradient boosting guidepost is a vivid example of what that transition can look like.

Subject of Research: Machine learning optimization of Reactive Red 120 dye biosorption onto a biodegradable gelatin/alginate–montmorillonite thin-film composite

Article Title: Machine learning for optimizing Reactive Red 120 biosorption onto cross-linked gelatin/alginate-TTAB-montmorillonite composite

Article References: Machine learning for optimizing Reactive Red 120 biosorption onto cross-linked gelatin/alginate-TTAB-montmorillonite composite. (n.d.). https://doi.org/10.1007/s11356-026-38211-y

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38211-y

Keywords: Reactive Red 120, biosorption, machine learning, gradient boosting, gelatin, alginate, montmorillonite, TTAB, thin-film composite, textile wastewater, adsorption, Langmuir isotherm

The research, published in the journal Discover Soil by Francesca Pedron and Gianniantonio Petruzzelli of Italy’s National Research Council’s Institute of Research on Terrestrial Ecosystems in Pisa, tackles a question that has been largely ignored: what happens to a soil’s ability to trap cobalt long after compost spreading has stopped? Most studies of organic amendments focus on soils that are actively being treated. The Italian team instead examined soils from a single Tuscan farm where compost applications had ceased either five or ten years earlier, comparing them with a neighboring field that had never received compost at all.

Cobalt occupies an unusual position among trace metals. In tiny amounts it is essential, serving as the metallic core of vitamin B12 and supporting crop growth, but above certain thresholds it becomes harmful to plants, disrupting nutrient transport within cells and producing symptoms such as leaf yellowing, premature leaf drop, reduced photosynthesis, and stunted biomass. It enters soil from natural events such as volcanic eruptions and forest fires, and from human activities including mining, smelting, road traffic, and the manufacture of cobalt-containing alloys and chemicals. Material flow analyses indicate that its dispersion in the environment is increasing as demand for batteries and green technologies accelerates, and recent machine-learning maps of European soils have revealed rising cobalt concentrations in some agricultural areas.

Whether that rising cobalt actually threatens crops and groundwater depends on a set of chemical reactions collectively called sorption, the transfer of dissolved metal ions from soil water onto solid soil surfaces. A soil with strong sorptive capacity holds cobalt immobilized, keeping it away from plant roots and aquifers. A soil with weak sorption lets the metal remain in solution, where it can be taken up by crops or leached away. The researchers hypothesized that compost-induced changes in soil organic matter and acidity would persist long enough to maintain enhanced cobalt sorption for a decade or more, and their experiments were designed to test exactly that.

The three soils came from the plough layer of a farm in the Province of Pisa, in a flat alluvial plain with a Mediterranean climate. Two of them had received green compost, produced from garden trimmings, crop residues, and other plant waste, for eight consecutive years at a rate of five megagrams of dry matter per hectare per year. On one plot, applications stopped ten years before sampling; on another, five years before. The third plot had never been treated. Texture, iron content, and total cobalt concentration were nearly identical across all three soils, but the chemical fingerprints of compost were unmistakable. Organic matter had risen from 1.15 percent in the untreated soil to 2.08 percent in the ten-year-old plot and 3.13 percent in the five-year-old one, while pH had shifted from a slightly acidic 6.25 to near-neutral values around 7.0. Cation exchange capacity, a measure of the soil’s ability to hold positively charged ions, climbed in parallel.

Those differences translated directly into cobalt retention. In laboratory batch experiments, the team shook one-gram soil samples with cobalt nitrate solutions of increasing concentration for twelve hours at controlled temperatures, then measured how much metal disappeared from solution. Fitting the resulting curves to the Langmuir isotherm model revealed maximum sorption capacities of 222 millimoles per kilogram in the five-year soil and 196 in the ten-year soil, against just 141 in the untreated control. The shape of the isotherms, an L-type pattern, showed that at low cobalt concentrations sorption rose almost linearly, indicating that high-affinity binding sites dominate initially; only as those sites fill do weaker domains take over, flattening the curve toward a plateau.

The mechanism behind this enhanced retention lies in the chemistry of compost-derived organic matter. Humified materials introduce abundant carboxyl, phenolic, and hydroxyl functional groups that form stable complexes with divalent cations such as cobalt. The near-neutral pH produced by composting amplifies the effect in two ways: it reduces competition between cobalt ions and hydrogen ions for reactive surfaces, and it encourages the deprotonation of those functional groups, making them more negatively charged and chemically reactive. Experiments that varied the ionic strength of the background solution added a further clue. Sorption in the untreated soil dropped by 40 to 48 percent as ionic strength increased, a signature of weak, electrostatically held outer-sphere complexes. In the compost-amended soils the decline was far smaller, 18 to 22 percent in the five-year soil and 28 to 36 percent in the ten-year one, pointing to a predominance of inner-sphere complexes, in which cobalt coordinates directly and strongly with organic and mineral surfaces.

Thermodynamic analysis reinforced the picture. Across temperatures from 298 to 318 kelvin, the Gibbs free energy of sorption was negative in all soils, confirming a spontaneous process, but the values were most favorable in the compost-amended plots. Enthalpy changes were positive, indicating an endothermic process that likely reflects the energy cost of partially dehydrating cobalt ions and forming specific surface complexes, and entropy changes were negative, consistent with metal ions becoming immobilized on ordered surface sites. The distribution coefficient, a ratio that summarizes how strongly a soil partitions cobalt between solid and solution phases, told the same story: differences among the soils were largest at low cobalt concentrations, precisely the range most relevant to real agricultural contamination, and converged only as high-affinity sites approached saturation.

Perhaps the most striking evidence came from desorption experiments, in which previously loaded soils were challenged with a harsh 0.5 molar calcium chloride solution designed to displace loosely held metal. In the untreated soil, between 1.6 and 24 percent of the sorbed cobalt was released, depending on loading. In the ten-year compost soil the released fraction ranged from 1.2 to 18 percent, and in the five-year soil from just 0.6 to 11 percent. At low cobalt loadings, desorption was minimal in all soils, confirming that the first metal ions to arrive occupy high-affinity sites and are effectively locked in place. The cobalt that resisted even this aggressive extraction can reasonably be considered non-bioavailable, meaning it is unlikely to reach plants or soil microorganisms.

The authors are careful to note the limits of their work. The compost’s own cobalt content was never measured because Italian law does not require it, so a complete mass balance was impossible, although total soil cobalt did not differ among the three plots, suggesting the compost added no detectable metal. Laboratory conditions, with fixed temperatures and equilibration times, cannot fully reproduce the complexity of field soils, including microbial activity, and the results apply specifically to the soils studied rather than to all soil types. Long-term effects will also depend on compost composition, climate, and farming practices. Even so, the central finding stands: in Mediterranean soils, where organic matter decomposes slowly enough to persist for decades, a single decade of composting left a chemical legacy that still suppressed cobalt mobility ten years later. As cobalt demand surges with the ecological transition, the study suggests that the humble practice of returning organic waste to farmland is not merely a fertility tool but a long-term instrument for keeping a critical, and potentially toxic, metal out of the food chain.

Subject of Research: Long-term cobalt sorption and desorption behavior in aged compost-amended Mediterranean agricultural soils

Article Title: Cobalt sorption in aged compost-amended soils

Article References: Pedron, F., & Petruzzelli, G. (2026). Cobalt sorption in aged compost-amended soils. Discover Soil, 3(1), Article 109. https://doi.org/10.1007/s44378-026-00273-2

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00273-2

Keywords: cobalt, compost, soil organic matter, sorption, desorption, Langmuir isotherm, heavy metals, soil chemistry, Mediterranean soils, bioavailability, trace metal contamination, sustainable soil management

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 study, published in the journal Discover Soil, examined surface soils from an ongoing long-term experiment established in 2015 under a soybean-wheat cropping system. The researchers compared five nutrient management treatments: an unfertilized control, soil test crop response-based fertilizer application (STCR), integrated nutrient management combining 75 percent recommended fertilizer with 25 percent farmyard manure, fully organic nutrient management, and conservation agriculture with recommended NPK plus 90 percent crop residue retention. The experimental soil was a classic Vertisol, a fine clayey, montmorillonitic Typic Haplustert containing 52 percent clay, slightly alkaline at pH 7.8, and initially very low in available phosphorus at just 5.74 kilograms per hectare by Olsen’s method.

What makes Vertisols so difficult for phosphorus management is their mineralogy and chemistry. These soils are dominated by smectitic clays that swell and shrink with moisture, and they carry appreciable calcium carbonate along with abundant exchangeable calcium. In alkaline, calcareous conditions, phosphate ions are adsorbed onto clay surfaces and precipitated as relatively insoluble calcium-phosphate minerals. The result is that only a small fraction of applied fertilizer phosphorus remains available for crop uptake during the growing season, making phosphorus deficiency a major constraint on productivity across tropical and subtropical agriculture.

To quantify how a decade of different management had altered this behavior, the team equilibrated soil samples with a series of potassium dihydrogen phosphate solutions ranging from 0 to 100 milligrams of phosphorus per kilogram, prepared in 0.01 molar calcium chloride at a 1:10 soil-to-solution ratio. After six days of equilibration, the amount of phosphorus retained by each soil was fitted to the Langmuir adsorption isotherm, a model that yields two key parameters: the sorption maximum, which describes how much phosphorus the soil can hold, and the bonding energy constant, which describes how tightly that phosphorus is gripped. The model performed superbly, with coefficients of determination of 0.99 across all treatments, confirming its suitability for characterizing phosphorus retention in these soils.

The differences between treatments were striking. The phosphorus adsorption maximum ranged from 394 to 527 micrograms per gram. The highest values appeared under the STCR treatment and the control, both at 527 micrograms per gram, with conservation agriculture close behind at 526. The lowest value by far was recorded under fully organic management at 394 micrograms per gram, followed by integrated nutrient management at 457. The bonding energy constant told an even sharper story, falling from 0.55 milliliters per microgram under STCR to just 0.10 under organic management. In other words, the organic soil not only held less phosphorus overall but held what remained far more loosely, leaving a larger share free to move into soil solution where roots can access it.

Derived quantities reinforced the pattern. The maximum phosphorus buffering capacity, which measures a soil’s ability to resist changes in solution phosphorus concentration, ranged from 278.13 liters per kilogram under STCR down to 40.57 under organic management. The standard phosphorus requirement, defined as the amount of phosphorus that must be sorbed to maintain a solution concentration of 0.2 milligrams per liter, the threshold generally considered adequate for most crops, followed the same trend: 57.39 milligrams per kilogram under STCR against only 7.33 under organic management. Practically, this means the organic soil needed roughly one-eighth as much phosphorus input to keep solution levels adequate, a dramatic improvement in potential fertilizer-use efficiency.

Sequential fractionation, following the classic Chang and Jackson scheme, revealed where the phosphorus actually resided. Calcium-bound phosphorus dominated every treatment, reflecting the inherent calcareous nature of Vertisols, but its share varied enormously. Under the control it accounted for 92.3 percent of the total phosphorus pool, whereas under organic farming it dropped to about 70.7 percent. Meanwhile, aluminum-bound phosphorus rose from roughly 3 to 4 percent under control and STCR to about 14.2 percent under organic management, and iron-bound phosphorus climbed from 2 to 4 percent to between 8.5 and 10 percent under organic and conservation systems. The combined pool of relatively labile fractions, including soluble, aluminum-bound, iron-bound, and available phosphorus, increased from about 7.7 percent in the control to 29.3 percent under organic farming, nearly a fourfold shift toward plant-accessible forms.

The mechanism behind this transformation lies in soil organic matter chemistry. As farmyard manure and crop residues decompose, they release low-molecular-weight organic acids and dissolved organic carbon that compete with phosphate ions for adsorption sites on clay and mineral surfaces. These compounds also chelate calcium and iron ions in solution, reducing the precipitation reactions that convert soluble phosphorus into insoluble calcium phosphates. Organic inputs simultaneously stimulate microbial communities and phosphatase enzymes that mineralize organic phosphorus into plant-available inorganic forms. The chemical data mirrored these processes: organic carbon reached 1.21 percent under organic management and 1.15 percent under conservation agriculture, compared with 0.64 percent in the control, while available phosphorus under organic treatment soared to 80.0 kilograms per hectare against 9.53 in the control. Soil pH also dipped slightly under organic and integrated management, from 8.09 in the control to around 7.87, consistent with organic acid release during decomposition.

The implications extend well beyond a single research farm. Because phosphorus is a finite, mined resource with rising costs and significant environmental risks when it accumulates excessively and runs off into waterways, any management system that reduces fixation losses carries both economic and ecological weight. The authors suggest that standard phosphorus requirement measurements could be used to tailor fertilizer recommendations to a soil’s actual buffering characteristics, avoiding over-application in lightly buffering soils and under-application in strongly fixing ones. Integrated nutrient management and conservation agriculture, by building organic carbon and moderating phosphorus retention, offer sustainable pathways for the Vertisol-based cereal and pulse systems that feed much of Central India.

The researchers caution that their findings come from a single long-term experiment at one Vertisol location, and that validation across diverse Vertisol regions, cropping systems, and climates would strengthen the conclusions. Even so, the message is compelling: a decade of patient organic inputs and residue retention measurably rewired the phosphorus chemistry of some of the world’s most phosphorus-hungry soils, converting locked-up reserves into forms that crops can actually use. For farmers wrestling with the twin burdens of fertilizer cost and declining soil fertility, the black soils of Bhopal suggest that the cheapest phosphorus may be the kind already in the ground, waiting to be released.

Subject of Research: Long-term effects of nutrient management on phosphorus sorption and fractionation in calcareous Vertisols

Article Title: Long-term nutrient management influences phosphorus sorption, buffering capacity, and fractionation in Vertisols of Central India

Article References: Davel, P., Gurav, P. P., Vinaykumar, L. N., Meena, B. P., Biswas, A. K., Shirale, A. O., Jain, R. C., Srivastava, S., Vishwakarma, A. K., Das, H., Shinogi, K. C., Yadav, D. K., & Shibin, M. (2026). Long-term nutrient management influences phosphorus sorption, buffering capacity, and fractionation in Vertisols of Central India. Discover Soil, 3(1), Article 174. https://doi.org/10.1007/s44378-026-00325-7

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00325-7

Keywords: phosphorus sorption, Vertisols, Langmuir isotherm, phosphorus fractionation, organic farming, conservation agriculture, integrated nutrient management, soil fertility, buffering capacity, Central India, soil organic carbon, nutrient use efficiency

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