Adsorption behaviour of Congo red dye onto ZnFe₂O₄ and its carbon nanotube-modified composite

Sorption is a key process in effluent treatment, particularly for addressing the coloured wastewater produced by the dyeing and bleaching industries. In this study, zinc ferrite (ZnFe₂O₄, ZF) and zinc ferrite-carbon nanotube composite (ZFCNT) were synthesized and evaluated for their ability to adsorb Congo red dye (CR-dye) from aqueous solutions. The prepared adsorbents were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) surface area analyses. BET and TGA analyses confirmed the enhanced surface and thermal properties of the materials; ZF and ZFCNT exhibited surface areas of 29.52 and 35.70 m²/g, respectively, and retained 98.55% and 95% of their original mass at 600 °C, indicating excellent thermal stability. The adsorption parameters examined included pH, agitation time, dye concentration, adsorbent dose, and temperature. Maximum adsorption occurred at pH 3 for both materials, and equilibrium was rapidly reached within 30 min. ZF and ZFCNT showed high adsorption capacities of 617.30 mg/g and 408.10 mg/g, respectively. Kinetic analysis indicated that the process followed a pseudo-second-order model, suggesting chemisorption as the dominant removal mechanism. Thermodynamic analysis showed that the adsorption was endothermic and spontaneous with increased entropy. These results clearly demonstrate the high efficiency and fast kinetics of ZF and ZFCNT in CR-dye removal from aqueous dye-containing solutions. KEY WORDS: Adsorption, Congo red, Zinc ferrite, Zinc ferrite/Carbon nanotube composite Bull. Chem. Soc. Ethiop. 2026, 40(3), 593-612. DOI: https://dx.doi.org/10.4314/bcse.v40i3.8