Adsorption of azo dyes onto environmentally friendly bacterial cellulose/kappa-carrageenan hydrogel: Isotherm and kinetic studies

Abstract

Bacterial cellulose (BC)/kappa carrageenan (κ-C) hydrogel was synthesized via in-situ method by inoculating the κ-C into the Acetobacter xylinum cell culture medium. The structural features of the hydrogel was characterized using Fourier Transform Infrared Spectroscopy. The presence of both biopolymers in the hydrogel was confirmed by the O–H stretching of BC at 3390 cm⁻¹ and the sulfate group (-SO₃) of κ-C at 1226 cm⁻¹. Scanning electron microscope images of the hydrogel showed A 3-D network of fibrils with high porosity. The enhanced swelling capacity of the hydrogel in water at pH 7 is due to the combined number of hydrophilic groups from BC and κ-C. The conductivity of the hydrogel increased with increasing κ-C due to the increased number of sulfate groups (-SO₃). The hydrogel had the ability to adsorb organic dyes; Congo red, Crystal violet and Methylene blue from neutral water at 27 °C. All the dyes fitted the pseudo second order kinetic model and followed both the Langmuir and the Freundlich adsorption isotherms indicating monolayer adsorption on heterogeneous surfaces. The ΔG^o_ad was negative indicating spontaneous physisorption for the three dyes. The prepared hydrogel being environmentally friendly also showed an improved ability to adsorb the organic dyes.