Graphene Oxide Strips Toxic Dye From Water in Just Minutes, Study Finds

A vivid pink dye that has long troubled waterways around the world may have met its match in one of the thinnest materials ever made. In a study published in Environmental Science and Pollution Research, researchers at the Thapar Institute of Engineering and Technology in Patiala, India, report that graphene oxide and reduced graphene oxide, two oxygen-modified forms of graphene, can strip more than 99 percent of Rhodamine B from water, with equilibrium reached in as little as ten minutes. The work, led by Anshu Tyagi with colleagues Bhupendra Chudasama and Amjad Ali, combines careful batch adsorption experiments with spectroscopic characterization, kinetic and isotherm modeling, quantum-chemical calculations, and a plant-based toxicity test, offering one of the more complete portraits yet of how these carbon nanomaterials capture a stubborn cationic dye.

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

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

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

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

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

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

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

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

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

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

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

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

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38167-z

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