Adsorptive removal of Congo red from aqueous solution using a chitosan-g-poly (acrylic acid-co-itaconic acid) hydrogel: equilibrium, kinetics and thermodynamics
Abstract
Textile effluent carrying Congo red (CR) is hard to treat, because the dye is highly soluble, chemically stable and toxic at low concentration. Here a hydrogel was prepared by graft copolymerising acrylic acid (AA) and itaconic acid (IA) onto chitosan, giving CH-g-poly(AA-co-IA), with potassium persulfate as initiator and N,N′-methylenebisacrylamide as crosslinker. It was examined by FTIR, XRD and FESEM, then tested on CR in batch mode. Uptake was strongly pH dependent: removal peaked at pH 3 (91.6 %) and fell to 14.2 % at pH 10, placing the protonated amine groups of the chitosan backbone at the centre of the binding step. A dose of 2 g L−1 removed more than 90 % of the dye from a 50 mg L−1 solution, and equilibrium was reached at about 210 min. Kinetic data were described best by the pseudo-second-order equation (R2 = 0.9974 by non-linear fitting, 0.9991 in linear form); the intraparticle diffusion plot was multilinear, with a fast diffusion-controlled stage followed by a much slower approach to equilibrium. Equilibrium data followed the Freundlich model (R2 = 0.9981, n = 2.20) more closely than the Langmuir model, which indicates an energetically heterogeneous surface; the Langmuir capacity was 100.7 mg g−1 at 298 K. The mean free energy from the Dubinin–Radushkevich model was 11.5 kJ mol−1. Thermodynamic parameters (ΔH° = +22.92 kJ mol−1, ΔS° = +88.74 J mol−1 K−1, ΔG° = −2.61 to −6.14 kJ mol−1) describe a spontaneous, endothermic and entropy-driven process.
Keywords:
Congo red, chitosan, grafted hydrogel, itaconic acid, adsorption isotherm, thermodynamics
References
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5. Ben Slama, H.; Chenari Bouket, A.; Pourhassan, Z.; Alenezi, F.N.; Silini, A.; Cherif-Silini, H.; et al. Diversity of synthetic dyes from textile industries, discharge impacts and treatment methods. Applied Sciences 2021, 11 (14), 6255. https://doi.org/10.3390/app11146255
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10. Hua, Z.; Pan, Y.; Hong, Q. Adsorption of Congo red dye in water by orange peel biochar modified with CTAB. RSC Advances 2023, 13 (18), 12502-12508. https://doi.org/10.1039/D3RA01444D
11. Aramesh, N.; Bagheri, A.R.; Bilal, M. Chitosan-based hybrid materials for adsorptive removal of dyes and underlying interaction mechanisms. International Journal of Biological Macromolecules 2021, 183, 399-422. https://doi.org/10.1016/j.ijbiomac.2021.04.158
12. Pal, P.; Pal, A.; Nakashima, K.; Yadav, B.K. Applications of chitosan in environmental remediation: a review. Chemosphere 2021, 266, 128934. https://doi.org/10.1016/j.chemosphere.2020.128934
13. Agha, H.M.; Jawad, A.H. A review on the influence of crosslinking and grafting processes on the adsorptive performance of chitosan biopolymer for dyes removal. Next Bioengineering 2025, 1, 100007. https://doi.org/10.1016/j.nxbio.2025.100007
14. Yin, S.; Yuan, W.; Zhao, L.; Niu, Y.; Guo, J. Chitosan hydrogels for antibiotic remediation and dye removal: a review. Gels 2026, 12 (8), 658. https://doi.org/10.3390/gels12080658
15. Patel, R.; Trivedi, R.; Raj, M.; Raj, L. Graft copolymerization of chitosan with various monomers: a comprehensive review. Polymer Bulletin 2025, 82 (17), 11551-11591. https://doi.org/10.1007/s00289-025-06002-z
16. Phonlakan, K.; Meetam, P.; Chonlaphak, R.; Kongseng, P.; Chantarak, S.; Budsombat, S. Poly(acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid)-grafted chitosan hydrogels for effective adsorption and photocatalytic degradation of dyes. RSC Advances 2023, 13 (44), 31002-31016. https://doi.org/10.1039/D3RA05596E
17. Choi, H.; Park, J.; Lee, J. Sustainable bio-based superabsorbent polymer: poly(itaconic acid) with superior swelling properties. ACS Applied Polymer Materials 2022, 4 (6), 4098-4108. https://doi.org/10.1021/acsapm.2c00021
18. Sangeetha, E.; Narayanan, A.; Dhamodharan, R. Super water-absorbing hydrogel based on chitosan, itaconic acid and urea: preparation, characterization and reversible water absorption. Polymer Bulletin 2022, 79 (5), 3013-3030. https://doi.org/10.1007/s00289-021-03641-w
19. Mohammadzadeh Pakdel, P.; Peighambardoust, S.J.; Arsalani, N.; Aghdasinia, H. Safranin-O cationic dye removal from wastewater using carboxymethyl cellulose-grafted-poly(acrylic acid-co-itaconic acid) nanocomposite hydrogel. Environmental Research 2022, 212, 113201. https://doi.org/10.1016/j.envres.2022.113201
20. Sayyar, Z.; Mohammadzadeh Pakdel, P.; Peighambardoust, S.J. Oral delivery of Sunitinib malate using carboxymethyl cellulose/poly(acrylic acid-itaconic acid)/Cloisite 30B nanocomposite hydrogel as a pH-responsive carrier. BMC Biotechnology 2024, 24 (1), 70. https://doi.org/10.1186/s12896-024-00883-0
21. Penyan, W.L.; Jasim, L.S. Preparation and characterization of a novel pH-sensitive pectin-grafted-poly(acrylic acid-co-itaconic acid)/MWCNTs-COOH hydrogel composite for adsorption and controlled release of diclofenac sodium. Carbon Letters 2024, 34 (5), 1413-1429. https://doi.org/10.1007/s42823-024-00702-8
22. Lagergren, S. Zur Theorie der sogenannten Adsorption gelöster Stoffe. Kungliga Svenska Vetenskapsakademiens Handlingar 1898, 24 (4), 1-39.
23. Ho, Y.S.; McKay, G. Pseudo-second order model for sorption processes. Process Biochemistry 1999, 34 (5), 451-465. https://doi.org/10.1016/S0032-9592(98)00112-5
24. Weber, W.J., Jr.; Morris, J.C. Kinetics of adsorption on carbon from solution. Journal of the Sanitary Engineering Division (ASCE) 1963, 89 (2), 31-59. https://doi.org/10.1061/JSEDAI.0000430
25. Chien, S.H.; Clayton, W.R. Application of Elovich equation to the kinetics of phosphate release and sorption in soils. Soil Science Society of America Journal 1980, 44 (2), 265-268. https://doi.org/10.2136/sssaj1980.03615995004400020013x
26. Langmuir, I. The adsorption of gases on plane surfaces of glass, mica and platinum. Journal of the American Chemical Society 1918, 40 (9), 1361-1403. https://doi.org/10.1021/ja02242a004
27. Freundlich, H. Über die Adsorption in Lösungen. Zeitschrift für Physikalische Chemie 1906, 57U (1), 385-470. https://doi.org/10.1515/zpch-1907-5723
28. Temkin, M.I.; Pyzhev, V. Kinetics of ammonia synthesis on promoted iron catalysts. Acta Physicochimica URSS 1940, 12, 217-222.
29. Dubinin, M.M.; Radushkevich, L.V. Equation of the characteristic curve of activated charcoal. Proceedings of the Academy of Sciences of the USSR, Physical Chemistry Section 1947, 55, 331-333.
30. Wang, J.; Guo, X. Adsorption isotherm models: classification, physical meaning, application and solving method. Chemosphere 2020, 258, 127279. https://doi.org/10.1016/j.chemosphere.2020.127279
31. Wang, J.; Guo, X. Adsorption kinetic models: physical meanings, applications, and solving methods. Journal of Hazardous Materials 2020, 390, 122156. https://doi.org/10.1016/j.jhazmat.2020.122156
32. Al-Ghouti, M.A.; Da'ana, D.A. Guidelines for the use and interpretation of adsorption isotherm models: a review. Journal of Hazardous Materials 2020, 393, 122383. https://doi.org/10.1016/j.jhazmat.2020.122383
33. Lima, E.C.; Hosseini-Bandegharaei, A.; Moreno-Piraján, J.C.; Anastopoulos, I. A critical review of the estimation of the thermodynamic parameters on adsorption equilibria. Wrong use of equilibrium constant in the Van't Hoof equation for calculation of thermodynamic parameters of adsorption. Journal of Molecular Liquids 2019, 273, 425-434. https://doi.org/10.1016/j.molliq.2018.10.048
34. Tran, H.N. Improper estimation of thermodynamic parameters in adsorption studies with distribution coefficient KD (qe/Ce) or Freundlich constant (KF): considerations from the derivation of dimensionless thermodynamic equilibrium constant and suggestions. Adsorption Science & Technology 2022, 2022, 5553212. https://doi.org/10.1155/2022/5553212
35. Thamer, B.M.; Aldalbahi, A.; Moydeen A., M.; El-Newehy, M.H. In situ preparation of novel porous nanocomposite hydrogel as effective adsorbent for the removal of cationic dyes from polluted water. Polymers 2020, 12 (12), 3002. https://doi.org/10.3390/polym12123002
36. Farasati Far, B.; Naimi-Jamal, M.R.; Jahanbakhshi, M.; Keihankhadiv, S.; Baradarbarjastehbaf, F. Enhanced methylene blue adsorption using single-walled carbon nanotubes/chitosan-graft-gelatin nanocomposite hydrogels. Scientific Reports 2024, 14, 19217. https://doi.org/10.1038/s41598-024-69969-1
37. Omidi, S.; Kakanejadifard, A. Eco-friendly synthesis of graphene-chitosan composite hydrogel as efficient adsorbent for Congo red. RSC Advances 2018, 8 (22), 12179-12189. https://doi.org/10.1039/C8RA00510A
38. Ferfera-Harrar, H.; Benhalima, T.; Sadi, A. Development of functional chitosan-based superabsorbent hydrogel nanocomposites for adsorptive removal of Basic Red 46 textile dye. Polymer Bulletin 2022, 79 (8), 6141-6172. https://doi.org/10.1007/s00289-021-03795-7
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Mojar, Q. K. (2026). Adsorptive removal of Congo red from aqueous solution using a chitosan-g-poly (acrylic acid-co-itaconic acid) hydrogel: equilibrium, kinetics and thermodynamics. Journal of Integral Sciences, 9(2), 63-73. https://doi.org/10.37022/jis.v9i2.155
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