Removal of Binary Dye Mixtures (Methylene Blue/Congo Red) Using a Plant-Waste Reinforced Hydrogel: Competitive Adsorption and Mechanism Study
Abstract
The discharge of synthetic dyes into aquatic systems is a serious environmental problem, so efficient and low cost adsorbents have been developed. A new plant-waste reinforced (PWR) hydrogel was synthesised from agricultural biomass (rice husk and banana peel cellulose) cross-linked with polyvinyl alcohol and glutaraldehyde for the simultaneous removal of methylene blue (MB) and congo red (CR) from aqueous solutions in single and binary systems. The synthesised hydrogel was well characterised by FTIR, XRD, FESEM, TEM, BET surface area (SBET = 86.42 m2/g, Vpore = 0.534 cm3/g) and zeta potential (pHpzc = 4.8) tests. The influence of solution pH, adsorbent dose, initial dye concentration, contact time and temperature on dye removal was thoroughly studied. In single systems, the removal efficiencies of PWR-hydrogel were 97.2% for MB and 95.8% for CR at optimised circumstances (pH 8 for MB, pH 2 for CR, dose 2.5 g/L, 120 min). In the binary system, due to competitive adsorption, the uptake decreased to 38.5 and 35.8 mg/g for MB and CR, respectively, which indicates antagonistic interactions. Adsorption kinetics matched the pseudo-second-order model (R2 > 0.998), and equilibrium data fitted the Langmuir isotherm (qmax = 98.7 mg/g for MB, 100.0 mg/g for CR). The thermodynamic analysis showed that the process was endothermic and spontaneous. Spectroscopic data confirmed that the main adsorption mechanisms were electrostatic attraction, hydrogen bonds and pi-pi stacking interactions. The PWR-hydrogel displayed outstanding reusability over five cycles, keeping above 85% removal efficiency, emphasising its promise as a sustainable and inexpensive adsorbent for treating dye-laden wastewater.
Keywords:
Plant-waste hydrogel, Binary dye mixture, Methylene blue, Congo red, Competitive adsorption, Adsorption mechanism, Wastewater treatment
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References
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22. Recyclable 3D-printed composite hydrogel con-taining rice husk biochar for organic contaminants adsorption in tap water. ACS Appl. Polym. Mater. 6, 355–367 (2024).
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24. Jute stick-derived cellulose-based hydrogel: synthe-sis, characterization, and methylene blue removal from aqueous solution. ACS Omega 8, 43749–43762 (2023).
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28. Comparative performance of fruit peel materials for methylene blue dye adsorption. Int. J. Environ. Sci. Technol. 21, 13459–13474 (2024).
29. Studying removal of anionic dye by prepared highly adsorbent surface hydrogel nanocomposite as an applicable for aqueous solution. Sci. Rep. 14, 11120 (2024).
30. High-capacity dye adsorption by low-cost combo hydrogel: kinetic, thermodynamic, and regenera-tion study. J. Inorg. Organomet. Polym. Mater. 35, 1423–1438 (2025).
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33. Experimental and modeling studies for the simulta-neous removal of anionic dyes in single and binary systems using activated clay. Sci. Rep. 15, 1024 (2025).
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35. Evaluation of the dye extraction using designed hydrogels for further applications towards water treatment. Gels 10, 248 (2024).
36. Efficient removal of Eosin B and Bismarck Brown dyes through microwave-assisted synthesis of pec-tin- and pullulan-based hydrogel. Polym. Bull. 82, 2345–2366 (2025).
37. Preparation of hydrogel adsorbents with functional sulfone groups for removal of cationic dyes from aqueous solution. J. Polym. Res. 32, 112 (2025).
38. Efficient removal anionic dyes in water using cati-onic crosslinked poly(N-vinyl imidazole) nanocom-posite hydrogel. Colloid Polym. Sci. 303, 567–582 (2025).
39. Biofunctional hydrogel adsorbents for sustainable downstream dye purification and circular wastewa-ter management. Front. Chem. Eng. 8, 1895352 (2026).
40. Development of a regenerable kappa-carrageenan/clay hydrogel for sustainable cationic dye removal. J. Solut. Chem. 54, 221–240 (2025).
41. Synthesis, characterization, and properties of PVA/jackfruit peel CMC/GO/kaolin composite hy-drogels. Gels 11, 626 (2025).
42. Sustainable adsorption of methylene blue using untreated date pits and banana peels: kinetics, iso-therms, and characterization. Water Pract. Tech-nol. 20, 2792–2810 (2025).
43. Low-cost and sustainable bioadsorbent from ba-nana peel for methylene blue removal. BioRe-sources 20, 10640–10660 (2025).
44. Unveiling the removal performance of banana peel biochar and rice husk nanoparticles for crystal vio-let and methylene blue dyes from aqueous media. RSC Adv. 15, 3291 (2025).
45. Kinetic, isotherm, and thermodynamic studies of the adsorption of dye from aqueous solution by propylene glycol adipate-modified cellulose aerogel. Colloids Surf. A 605, 125368 (2020).
46. Facile construction of lignin-based network com-posite hydrogel for efficient adsorption of methyl-ene blue from wastewater. Cellulose 30, 8849–8865 (2023).
47. Environmental Advances: Hydrogel-based adsorb-ents for dye-contaminated wastewater treatment. Environ. Adv. 15, 100488 (2024).
48. Cellulose-based hydrogel for adsorptive removal of cationic dyes from aqueous solution: isotherms and kinetics. RSC Adv. 13, 4757–4774 (2023).
49. [Methylene blue and rhodamine B dyes’ efficient removal using biocarbons developed from waste. Molecules 29, 4132 (2024).
50. Issue 11, 2023: Advances in dye adsorption using waste-derived adsorbents. Environ. Sci. Water Res. Technol. 9, 3392–3408 (2023).
2. Liu, Y., Nie, Y., Wang, J., Wang, J., Wang, X., Chen, S., Zhao, G., Wu, W., Lu, J. (2022). Fabrication of multifunctional biomass-based aerogel with 3D hierarchical porous structure from waste reed for the synergetic adsorption of dyes and heavy metal ions. Chem. Eng. J. 446, 137089.
3. Majamo, S.L., Amibo, T.A., Bedada, D.B. (2024). Experimental investigation on adsorption of me-thylene blue dye from waste water using corncob cellulose-based hydrogel. Sci. Rep. 14, 4560.
4. Le, H.V., Dao, N.T., Bui, H.T., Kim, I.T., La, D.D. (2023). Bacterial cellulose aerogels derived from pineapple peel waste for the adsorption of dyes. ACS Omega 8, 33412–33425.
5. Qiu, C., Wang, J., Xu, L., Wang, D. (2022). High-efficient double-cross-linked biohybrid aerogel bio-sorbent prepared from waste bamboo paper and chitosan for wastewater purification. J. Clean. Prod. 338, 130615.
6. Srirangapatna Umesh, A., Kumar, S.R., Meenakshi, S. (2024). Enhanced adsorption: reviewing the po-tential of reinforcing polymers and hydrogels with nanomaterials for methylene blue dye removal. Surf. Interfaces 42, 103490.
7. Mussa, Z.H., Al-Qaim, F.F., Jawad, A.H., Scholz, M. (2023). A comprehensive review on adsorption of methylene blue dye using leaf waste as a bio-sorbent. Environ. Monit. Assess. 195, 395.
8. Li, P., Zhang, J., Yang, Y., Liu, Q. (2024). Prepara-tion of efficient adsorbent for methylene blue and Congo red by co-hydrothermal of red mud with food waste compost. Desalin. Water Treat. 319, 100445.
9. Wan, X., Zhan, Y., Long, Z., Zeng, G., He, Y. (2022). Chitosan-based dual network composite hydrogel for efficient adsorption of methylene blue dye. Int. J. Biol. Macromol. 210, 404–414.
10. Kubra, M.J., Islam, M.M., Rahman, M.L., Alam, M.A. (2025). Eco-friendly lignin/N,N-dimethyl acrylamide hydrogel with carrageenan and polyvinyl pyrrolidone for amphoteric adsorption of methylene blue and Congo red. Int. J. Biol. Macromol. 285, 138243.
11. Jiang, M., Ye, K., Lin, J., Zhang, X., Ye, W., Zhao, S., Van der Bruggen, B. (2023). Modified beta-cyclodextrin hydrogel for selective adsorption and desorption for cationic dyes. Colloids Surf. A 661, 130916.
12. Grigoras, C.G., Simion, A.I., Gavrilescu, M. (2022). Performance of dye removal from single and binary component systems by adsorption on composite hydrogel beads derived from fruits wastes en-trapped in natural polymeric matrix. Gels 9, 795.
13. Zhang, M., Wu, Y., Li, J., Wu, H. (2025). Adsorp-tion behaviors and mechanisms of polyvinyl alco-hol/xanthan gum/graphene oxide porous hydrogel for methylene blue and congo red. Int. J. Biol. Mac-romol. 287, 138445.
14. Qin, W.H., Li, Q., Wu, X.Y. (2024). High capacity and selective adsorption of Congo red by cellu-lose-based aerogel with mesoporous structure. Int. J. Biol. Macromol. 258, 128884.
15. Li, Z., Hanafy, H., Zhang, L., Sellaoui, L., Netto, M.S., Oliveira, M.L.S., Seliem, M.K., Dotto, G.L., Bonilla-Petriciolet, A., Li, Q. (2020). Adsorption of congo red and methylene blue dyes on an ashitaba waste and a walnut shell-based activated carbon from aqueous solutions. Chem. Eng. J. 388, 124263.
16. Su, H.Z., Wang, Y., Liu, H., Lu, J. (2024). Fabrica-tion of physically multi-crosslinked sodium algi-nate/carboxylated-chitosan/montmorillonite-base aerogel modified by polyethyleneimine for the effi-cient adsorption of organic dye and Cu(II) con-taminants. Sep. Purif. Technol. 329, 125186.
17. Labena, A., Abdelhamid, A.E., Amin, A.S., Ahmed, N.M., Zakaria, M.Y. (2021). Removal of methylene blue and congo red using adsorptive membrane impregnated with dried Ulva fasciata and Sargas-sum dentifolium. Plants 10, 384.
18. Liu, H., Zhang, J., Chen, R., Hou, J. (2025). Efficient removal of anionic dye congo red by Chito-san/Poly(dimethyl diallyl ammonium chloride-co-acrylamide) composite hydrogel. Int. J. Biol. Mac-romol. 290, 138790.
19. Kloster, M., Muraca, D., Luna, J.A. (2025). Chito-san/sodium alginate aerogels showing effective ad-sorption of anionic Congo Red and cationic Me-thylene Blue dyes for sustainable water treatment. Int. J. Biol. Macromol. 286, 138340.
20. Aly, A.R., Sayed, M.A., Ibrahim, A.R. (2024). Upcy-cling of sugar refining mud solid waste as a novel adsorbent for removing methylene blue and Congo red from wastewater. RSC Adv. 14, 8738–8751.
21. Bora A, Karak N. Biobased hydrogel reinforced with wastepaper-derived modified cellulose nano-fiber as an efficient dye remover from wastewater. Journal of Polymer Research. 2023 Dec;30(12):452.
22. Recyclable 3D-printed composite hydrogel con-taining rice husk biochar for organic contaminants adsorption in tap water. ACS Appl. Polym. Mater. 6, 355–367 (2024).
23. Thermodynamic, kinetic, and isotherm studies of Direct Blue 86 dye absorption by cellulose hy-drogel. Sci. Rep. 13, 5934 (2023).
24. Jute stick-derived cellulose-based hydrogel: synthe-sis, characterization, and methylene blue removal from aqueous solution. ACS Omega 8, 43749–43762 (2023).
25. Cellulose based pH-sensitive hydrogel for highly efficient dye removal in water treatment. Cellulose 29, 4199–4215 (2022).
26. Modified rice husk polymeric hydrogel as biode-gradable adsorbent for the effective removal of or-ganic pollutant methylene blue dye. Indian J. Chem. Technol. 31, 215–224 (2024).
27. Starch/rice husk ash based superabsorbent com-posite: high methylene blue removal efficiency. Iran. Polym. J. 26, 361–370 (2020).
28. Comparative performance of fruit peel materials for methylene blue dye adsorption. Int. J. Environ. Sci. Technol. 21, 13459–13474 (2024).
29. Studying removal of anionic dye by prepared highly adsorbent surface hydrogel nanocomposite as an applicable for aqueous solution. Sci. Rep. 14, 11120 (2024).
30. High-capacity dye adsorption by low-cost combo hydrogel: kinetic, thermodynamic, and regenera-tion study. J. Inorg. Organomet. Polym. Mater. 35, 1423–1438 (2025).
31. Agricultural and food wastes derived cellulose hy-drogels for water reservoirs and dye sorption. Po-lym. Bull. 83, 4561–4580 (2026).
32. Highly efficient removal of adsorbed cationic dyes by dual-network chitosan-based hydrogel. PubMed (2024).
33. Experimental and modeling studies for the simulta-neous removal of anionic dyes in single and binary systems using activated clay. Sci. Rep. 15, 1024 (2025).
34. Adsorption mechanisms of hydrogels for heavy metal and organic dyes removal: a short review. Mater. Today Sustain. 23, 100447 (2023).
35. Evaluation of the dye extraction using designed hydrogels for further applications towards water treatment. Gels 10, 248 (2024).
36. Efficient removal of Eosin B and Bismarck Brown dyes through microwave-assisted synthesis of pec-tin- and pullulan-based hydrogel. Polym. Bull. 82, 2345–2366 (2025).
37. Preparation of hydrogel adsorbents with functional sulfone groups for removal of cationic dyes from aqueous solution. J. Polym. Res. 32, 112 (2025).
38. Efficient removal anionic dyes in water using cati-onic crosslinked poly(N-vinyl imidazole) nanocom-posite hydrogel. Colloid Polym. Sci. 303, 567–582 (2025).
39. Biofunctional hydrogel adsorbents for sustainable downstream dye purification and circular wastewa-ter management. Front. Chem. Eng. 8, 1895352 (2026).
40. Development of a regenerable kappa-carrageenan/clay hydrogel for sustainable cationic dye removal. J. Solut. Chem. 54, 221–240 (2025).
41. Synthesis, characterization, and properties of PVA/jackfruit peel CMC/GO/kaolin composite hy-drogels. Gels 11, 626 (2025).
42. Sustainable adsorption of methylene blue using untreated date pits and banana peels: kinetics, iso-therms, and characterization. Water Pract. Tech-nol. 20, 2792–2810 (2025).
43. Low-cost and sustainable bioadsorbent from ba-nana peel for methylene blue removal. BioRe-sources 20, 10640–10660 (2025).
44. Unveiling the removal performance of banana peel biochar and rice husk nanoparticles for crystal vio-let and methylene blue dyes from aqueous media. RSC Adv. 15, 3291 (2025).
45. Kinetic, isotherm, and thermodynamic studies of the adsorption of dye from aqueous solution by propylene glycol adipate-modified cellulose aerogel. Colloids Surf. A 605, 125368 (2020).
46. Facile construction of lignin-based network com-posite hydrogel for efficient adsorption of methyl-ene blue from wastewater. Cellulose 30, 8849–8865 (2023).
47. Environmental Advances: Hydrogel-based adsorb-ents for dye-contaminated wastewater treatment. Environ. Adv. 15, 100488 (2024).
48. Cellulose-based hydrogel for adsorptive removal of cationic dyes from aqueous solution: isotherms and kinetics. RSC Adv. 13, 4757–4774 (2023).
49. [Methylene blue and rhodamine B dyes’ efficient removal using biocarbons developed from waste. Molecules 29, 4132 (2024).
50. Issue 11, 2023: Advances in dye adsorption using waste-derived adsorbents. Environ. Sci. Water Res. Technol. 9, 3392–3408 (2023).
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30/07/2026
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Kmal, H. K. “Removal of Binary Dye Mixtures (Methylene Blue/Congo Red) Using a Plant-Waste Reinforced Hydrogel: Competitive Adsorption and Mechanism Study”. International Journal of Pharmacognosy and Chemistry, Vol. 7, no. 2, July 2026, pp. 29-36, doi:10.46796/ijpc.v7i2.938.
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