Clean Water and Sanitation (SDG 6), Climate Action (SDG 13)
Azo dye removal using eco-friendly bacterial cellulose/kappa-carrageenan hydrogel: isotherm and kinetic studies Jacinta Botleng 1 , Tejesvi Patel 1 , Roselyn Lata 1 , Robert Chang 1 , David Rohindra 1* 1 Discipline of Chemistry, School of Agriculture Geography Environment Oceans and Natural Sciences, The University of the South Pacific, Suva, Fiji. E-mail: david.rohindra@usp.ac.fj Azo dyes, commonly used in industries, pose severe environmental and health risks due to their toxicity and persistence in water [1, 2] . Several azo dyes and their degradation products, such as aromatic amines, are known to be carcinogenic and mutagenic, posing risks to human health. Organic dyes cannot be metabolized by the body and accumulates in living organisms, creating disorders such as cancer, damage to functional organs and in extreme cases death [3] . This study aligns with SDG 6 by developing an eco-friendly bacterial cellulose(BC)/kappa-carrageenan(κ-C) hydrogel for dye removal. The hydrogel, synthesized via in-situ method using Acetobacter xylinum, was characterized by FTIR and SEM, confirming its highly porous 3D fibrillar structure. Enhanced swelling capacity resulted from the combined hydrophilic groups of BC and κ-C, while increased κ-C content improved conductivity due to additional sulfate groups. The hydrogel effectively adsorbed toxic azo dyes from water, including Congo Red, Crystal Violet, and Methylene Blue. Adsorption followed a pseudo-second-order kinetic model and aligned with Langmuir and Freundlich isotherms, suggesting monolayer adsorption on heterogeneous surfaces. The -ΔG° confirmed spontaneous physisorption. This biodegradable and non-toxic hydrogel offers an eco-friendly, sustainable solution for wastewater treatment, addressing water pollution and promoting cleaner water resources in line with SDG 6. Key words: Adsorption models, Kinetics, Isotherms, Free Energy, Organic Dyes References 1. T. Benhalima, W. Chicha and H. Ferfera-Harrar, “Sponge-like biodegradable polypyrrole-modified biopolymers for selective adsorption of basic red 46 and crystal violet dyes from single and binary component systems.,” International Journal of Biological Macromolecules , p. 127532, 2023. 2. D. Wishart, Y. Feunang, A. Marcu, A. Guo, K. Liang, R. Vázquez-Fresno, T. Sajed, D. Johnson, C. Li, N. Karu and Z. Sayeeda, “HMDB 4.0: the human metabolome database for 2018.,” Nucleic acids research , pp. D608-D617, 2018. 3. T. Benhalima, H. Ferfera-Harrar, N. Saha and P. Saha, “Fe3O4 imbuing carboxymethyl cellulose/dextran sulfate nanocomposite hydrogel beads: an effective adsorbent for methylene blue dye pollutant,” Journal of Macromolecular Science , Part A, pp. 442-461, 2023.
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