Royal Society of Chemistry(RSC) Advances published a study which found that green coconut husk waste could remove 95.5% of Congo red dye from water within 80 minutes. The researchers modified the coconut-derived lignin by adding nitrogen-containing groups, creating what they called aminated lignin. Under the best conditions tested, only 0.025 grams of the material was needed to treat a 20 ppm dye solution at pH 5. The findings point to a way of giving agricultural waste a useful role in wastewater treatment.
Manufacturing a water-cleaning material from coconut husk waste
The process started with green coconut husk waste, which contains lignin, a complex organic polymer that binds plant cells together, providing rigidity, structural support, and waterproofing to wood and bark. According to the study, the researchers first extracted alkali lignin from coconut fibre. They named this starting material coconut fibre alkali lignin(CFAL).Then the researchers altered the lignin to make it better at interacting with dye molecules in water. They used a chemical process called a Mannich reaction, which treats the lignin with diethylamine, formaldehyde and acetic acid. The mixture was heated to 65°C for four hours while being stirred.This process produced aminated lignin, known as AmL. Tests confirmed that nitrogen-containing groups had been added to the material. The modified lignin had a nitrogen content of 6.83%.
Coir fibre extracted from coconut husk. Image Credit: Wikipedia
The modified coconut waste performed better than the untreated one
The researchers compared AmL with the original CFAL instead of testing the modified material in isolation. In this way, they compared whether changing the lignin had actually improved its ability to remove dye from water.The study focused on Congo red, an anionic dye that can be found in industrial wastewater. The team investigated the materials in different conditions, including changes in the acidity of the water, the amount of adsorbent used and the concentration of the dye solution.AmL always performed better in dye removal than CFAL. The results indicated that adding the nitrogen-containing groups had made the coconut-derived material more effective at capturing Congo red from water.
What happened during the 80-minute treatment
The strongest result came under the study’s best conditions. AmL removed 95.5% of Congo red from a 20 ppm solution within 80 minutes. The test used 0.025 grams of the modified lignin at pH5.The researchers linked this performance mainly to the amine groups introduced during the modification process. These groups helped the material attract the dye molecules, which are negatively charged. There was also hydrogen bonding between the dye and the material that helped bring them together.Temperature also played a role in the process. The maximum removal efficiency of AmL was up to 95.5% at 303 K (30 °C). When the temperature increased to 323 K, the efficiency dropped to 85.5%.The researchers therefore described the adsorption process as exothermic. In simple terms, higher temperatures did not favour the removal of Congo red in these experiments.
Could the coconut-based material be used more than once
The researchers also looked at whether the material could be reused. After AmL had captured the dye, they regenerated it and put it through another treatment cycle.AmL retained 83.4% of its dye-removal efficiency after 4 adsorption and desorption cycles. The original CFAL showed a larger decline during repeated use, falling from 87.5% removal in the first cycle to 72.1% by the fourth.The researchers associated AmL’s stronger reusability with the amine groups on the material. These groups provided binding sites that remained useful during the regeneration process. That meant the modified lignin was not limited to a single use in the lab tests.
What could this mean for coconut waste recycling
The study brings together two separate environmental problems of agricultural waste and polluted water. Instead of leaving coconut husk waste as a material that needs to be discarded or managed, the researchers used one of its natural components as the starting point for a water-treatment material.The researchers discovered that aminated lignin has potential as a cost-effective and environmentally sustainable option for wastewater treatment because it comes from renewable biomass. Its ability to retain 83.4% removal efficiency after four cycles also showed that it could be reused in the lab tests.The results were obtained under controlled conditions, so more research would be needed before the material could be considered for large-scale industrial wastewater treatment. Even so, the findings show what can happen when an agricultural waste material is given a different purpose.Green coconut husk may normally be treated as waste, but its lignin can be recovered, modified and used to tackle a common wastewater pollutant. In this study, that approach produced a material that removed 95.5% of Congo red within 80 minutes while also showing the ability to work through repeated treatment cycles.
