Preparation, Characterisation, and Application of a Chitosan–Zeolite Adsorbent for Efficient Congo Red Dye Removal from Aqueous solutions

Abstract

The presence of synthetic dyes such as Congo red (CR) in wastewater, particularly from the textile industries, poses serious threats to both the environment and human health. These dyes are not only toxic and potentially carcinogenic but are also chemically stable, making them difficult to break down using conventional treatment methods such as coagulation, oxidation, or biological processes. In this study, a chitosan–zeolite adsorbent (CZA) was developed and investigated for the removal of CR from aqueous solutions. The adsorbent was synthesised using a simple mixing method and thoroughly characterised using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface area analysis. The results confirmed the successful formation of CZA, with relevant functional groups, a semi-crystalline structure, and a porous structure with a surface area of 34.01 m²/g. Batch adsorption experiments were conducted to study the influence of parameters such as pH, contact time, temperature, and adsorbent dosage on dye removal efficiency. The highest dye removal efficiency of 98.4% was achieved using 1.0 g of CZA under optimum conditions of a pH 2, a contact time of 120 min, and 25°C. The adsorption data were analysed using isotherm and kinetic models. Among the isotherm models evaluated, the Langmuir model provided the best fit (  = 0.9980), indicating monolayer adsorption with a maximum adsorption capacity ( ) of 89.29 mg/g. Kinetic modelling showed that the adsorption followed the pseudo-second-order model (  = 0.9966), suggesting that chemisorption was the dominant mechanism. Overall, this study demonstrates that the CZA exhibits high adsorption efficiency and has considerable potential for application in the treatment of dye-contaminated wastewater.