Green-Made Nanocomposite Strips Toxic Methylene Blue Dye from Water in Under an Hour

A team of researchers in Malaysia and its international collaborators has unveiled a hybrid nanocomposite that strips one of the world’s most stubborn textile pollutants, methylene blue, from water with remarkable speed and efficiency. The material, dubbed GA@SnO2-AC, combines gallic acid, a naturally occurring phenolic acid, with tin oxide nanoparticles anchored on activated carbon. In batch experiments, the adsorbent removed up to 98.64 percent of the dye under optimized conditions, and the team reports that the process reached equilibrium within roughly two hours, with the bulk of the uptake occurring in the first thirty minutes. The work, published in Polymer Bulletin, offers a potentially economical route for treating dye-laden industrial effluent, an environmental problem that the textile sector alone generates in volumes estimated at around 200 billion litres of wastewater each year.

The motivation behind the study is stark. Synthetic dyes are produced on a colossal scale, with the global output of dyes estimated at 650,000 tonnes and roughly 100,000 commercial varieties available. Between 10 and 15 percent of dye production is released into wastewater streams, where the vivid pigments block sunlight from penetrating aquatic ecosystems, choking photosynthesis and endangering aquatic life. Methylene blue, used in coloring cotton, wool and paper as well as in medical applications, carries a catalogue of human health risks including eye irritation, skin sensitization, respiratory disorders, abdominal complaints and even Heinz body formation. Because dye molecules can bioaccumulate and pass up the food chain through trophic biomagnification, the researchers argue that removing them at the source is critical for both ecosystem and public health.

What sets the new adsorbent apart is its green synthesis route. The team prepared the material hydrothermally, first precipitating tin oxide from tin(II) chloride dihydrate with sodium hydroxide, then calcining the precipitate at 300 degrees Celsius. Gallic acid was stirred into the tin oxide, activated carbon was added, and finally a fermented maize extract solution served as a non-toxic cross-linking agent to bind the components together. This approach avoids the hazardous chemicals typical of conventional nanocomposite preparation. Gallic acid was chosen for its proven stability, biocompatibility and its ability to bind metal ions, while the activated carbon provides an enormous internal surface area. The researchers note that no previous investigation has tested this particular three-component hybrid for methylene blue uptake, establishing the novelty of the work.

Characterization confirmed the composite’s credentials. Brunauer-Emmett-Teller analysis revealed a specific surface area of 486.86 square metres per gram with a pore volume of 0.2689 cubic centimetres per gram and an average pore diameter of about 2.2 nanometres, consistent with a mesoporous type IV isotherm. X-ray diffraction matched the tin oxide phase against the standard JCPDS reference card 21-2150, while Fourier-transform infrared spectroscopy identified hydroxyl, carbonyl and Sn-O-Sn vibrational bands that provide the chemical handles for dye binding. Thermogravimetric analysis showed a total weight loss of only 19.11 percent up to 800 degrees Celsius, indicating robust thermal stability. Scanning electron microscopy revealed an irregular, crystal-like morphology with large pores, and energy-dispersive X-ray analysis confirmed the successful deposition of carbon-rich gallic acid and activated carbon on the tin oxide framework.

Batch adsorption tests mapped how the process responds to its operating variables. Removal surged within the first thirty minutes as abundant surface sites captured dye molecules, then slowed as those sites saturated, with equilibrium reached between 120 and 180 minutes. Raising the initial dye concentration from 30 to 70 milligrams per litre increased the equilibrium capacity from 60 to 108.44 milligrams per gram at 298 kelvin. Increasing the adsorbent dose from 30 to 80 milligrams lifted removal from 51.45 to 97.93 percent, although the capacity per gram fell as sites became underutilized. Temperature worked against the process: as conditions warmed from 298 to 338 kelvin, removal slipped from 97.93 to 95.18 percent, confirming the exothermic character of the uptake. Acidity proved decisive, with removal climbing from 72.06 percent at pH 2 to 97.93 percent at pH 11, a behavior explained by the material’s point of zero charge of 6.0, below which protonated surfaces repel the positively charged dye cations.

Modeling of the equilibrium data pointed to a monolayer adsorption mechanism. The Langmuir isotherm gave the best fit, with a regression coefficient of 0.9761 and a maximum adsorption capacity of 95.24 milligrams per gram at 298 kelvin. The dimensionless separation factor ranged from 0.6880 to 0.7280, below unity and therefore indicating a favorable process. Kinetic analysis showed the pseudo-second-order model best described the uptake, suggesting chemisorption involving electrostatic interactions, while intraparticle diffusion plots were non-linear, revealing a multi-step process with mass transfer across both external and internal surfaces. Dubinin-Radushkevich energies between roughly 1.1 and 2.2 kilojoules per mole pointed to physisorption as the dominant transport mechanism.

Thermodynamics reinforced the picture of a spontaneous, exothermic system. The enthalpy change of minus 23.1196 kilojoules per mole confirmed heat release during adsorption, while the entropy change of minus 0.0442 kilojoules per mole per kelvin indicated decreasing randomness at the solid-liquid interface as dye molecules settled onto the surface. Gibbs free energy values were negative across the studied temperature range, from minus 9.9540 to minus 8.6286 kilojoules per mole between 298 and 328 kelvin, confirming that the process proceeds spontaneously and remains feasible under realistic operating temperatures.

The team then turned to statistical optimization using a central composite design within response surface methodology, varying pH, contact time, dye concentration and adsorbent dosage simultaneously. Analysis of variance identified pH, initial concentration and dosage as significant factors, with a model F-value of 63.69 and a p-value below 0.0001. The quadratic model achieved a coefficient of determination of 0.9835, and a lack-of-fit test was non-significant, validating the fit. Three-dimensional response surfaces showed, for example, that raising the dose from 30 to 60 milligrams lifted removal from 93.56 to 95.84 percent, while increasing concentration from 30 to 70 milligrams per litre cut removal from 93.56 to 57.33 percent. Numerical optimization converged on a pH of 11.0, a contact time of 48 minutes, a dye concentration of 58 milligrams per litre and a dosage of 50 milligrams, achieving a desirability of 1 and a predicted removal of 98.64 percent. Experimental validation delivered 98.13 percent, an excellent match between prediction and reality.

Practical considerations rounded out the assessment. Regeneration tests using 0.1 molar ethanol as eluent showed the composite retaining 86.66 percent removal efficiency after five adsorption-desorption cycles, with the gradual decline attributed to incomplete dye release from the surface. A cost analysis found the hybrid material cheaper to produce than commercial activated carbon, which has been reported at approximately 259.5 US dollars per unit basis in earlier literature. The authors argue that the combination of rapid kinetics, high capacity, reusability and low production cost makes GA@SnO2-AC a credible candidate for industrial deployment, potentially in adsorption units for factories generating dye-contaminated water, with the resin regenerable and the water restorable.

The study’s broader significance lies in demonstrating that green chemistry and rigorous statistical design can converge on a water treatment solution that is simultaneously effective, economical and environmentally benign. By pairing a plant-derived cross-linker and a common phenolic acid with inexpensive activated carbon and tin oxide, the researchers have produced an adsorbent whose performance rivals or exceeds many previously reported materials, whose capacities in the literature range from 3.785 to 371.7 milligrams per gram. The team suggests that future work could extend the platform to other cationic organic and inorganic contaminants, widening its reach across the water treatment sector. For an industry under mounting pressure to clean up its effluent, the message is that high-performance remediation need not come at a punishing environmental or financial price.

Subject of Research: Adsorptive removal of methylene blue dye from water using a hybrid gallic acid-tin oxide-activated carbon nanocomposite

Article Title: Rapid adsorptive and optimization of batch process for removal of methylene blue using hybrid GA@SnO2-AC composite materials

Article References: Adeoye, J. B., Lau, S. Y., Tan, Y. H., Tan, Y. Y., Chiong, T., Mubarak, N. M., Khalid, M., & Ng, J. T. W. (2026). Rapid adsorptive and optimization of batch process for removal of methylene blue using hybrid GA@SnO2-AC composite materials. Polymer Bulletin, 83(12), Article 680. https://doi.org/10.1007/s00289-026-06745-3

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06745-3

Keywords: methylene blue, adsorption, nanocomposite, gallic acid, tin oxide, activated carbon, water treatment, response surface methodology, green synthesis, isotherm, kinetics, thermodynamics