A soft, water-swollen material made from cellulose, gelatin, and citric acid can pull a stubborn blue dye out of polluted water—and still remove more than eighty-five percent of it after being used again and again. Wastewater from textile dyeing can carry methylene blue, a stable dye and a major source of pollution.

That pollution threatens both the environment and human health. Several treatment methods exist, but they can require strict conditions, remain unstable, or cost a great deal. Adsorption is easier and more economical, as long as it does not create new pollutants.

The challenge is that some common materials used to capture pollutants are expensive to produce and may cause secondary pollution. So the search is for a dye-catching material that is effective, low-cost, and environmentally friendly. Earlier cellulose-based membranes had problems: one had weak structure and captured only twenty-five milligrams of dye per gram, while another reached seven hundred sixty-nine milligrams per gram.

Its goal was to remove methylene blue from wastewater, so the hydrogel’s adsorption performance was investigated in detail across time, dosage, pH, temperature, and initial concentration. The material was examined as it swelled under different salt levels and acidity levels, then the best version was tested under different conditions for capturing the dye.

The material was made by dissolving cellulose and gelatin in water, then combining the two solutions. Citric acid was added afterward. Think of it like mixing two kinds of threads before tying some of them together: one thread provides many places for dye to stick, while the other helps form a connected, supportive mesh.

The three hydrogel versions differed in their gelatin content, and the results showed that dye-capture capacity decreased as the gelatin content increased. The likely reason is that more gelatin means less cellulose in the same amount of material, leaving fewer charged sites available for holding the dye.

The material rapidly captures the dye at first, then slows and levels off after about three hundred minutes. Increasing its water swelling goes along with less dye held, pointing to a trade-off between expansion and the chemical sites that trap the dye.

The experimental dye-capture capacity reached 941.25 milligrams per gram, nearly matching the model’s predicted maximum of 943.40 milligrams per gram. The results fit a picture in which the dye settles into a single full layer of available sites, rather than continuing to pile up without limit.

When compared with the other materials listed in the study, the hydrogel had a higher maximum capacity for capturing methylene blue than all of them. That comparison suggests the material can compete strongly with the other dye-catching materials listed in the literature, achieving the highest maximum capacity among those compared.

After repeated dye-capture and release, the hydrogel still removed more than eighty-five percent of the methylene blue from water. Its performance fell, but it remained effective after reuse. Some dye was difficult to release because parts of the material held it more firmly after capture.

Even so, the hydrogel continued to remove methylene blue from water after repeated use. The study concludes that the hydrogel has a porous structure, good heat stability, and sensitivity to acidity and salt levels—features that suit it to dye adsorption.

The study reports a maximum equilibrium adsorption capacity of 943.15 milligrams per gram, and describes the capture as spontaneous, heat-releasing, and occurring in a single layer of dye. Most importantly outside the laboratory, the material still removed eighty-five percent of the dye after three reuse cycles, making it a possible environmentally friendly, efficient, and stable option for treating dye wastewater.

The hydrogel combines accessible ingredients with strong dye capture and reuse, pointing toward a simpler, less wasteful way to treat colored wastewater.