Sustainable removal of congo red from tannery effluents using sugarcane bagasse-derived cellulose/bentonite...

The discharge of dye-containing effluents from tannery industries poses a serious environmental challenge due to their toxicity, persistence, and resistance to conventional treatment processes. Among these pollutants, congo red (CR), an anionic azo dye widely used in the textile and leather industries, requires efficient removal strategies. In this study, a low-cost and eco-friendly Cellulose/Bentonite composite (CB-comp) was developed for CR removal from tannery wastewater, combining cellulose extracted from sugarcane bagasse with acid-activated Moroccan bentonite, promoting agro-industrial waste valorization while enhancing structural properties. Characterization using X-ray Fluorescence Spectroscopy (XRF), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, and of the point of zero charge (pH_PZC) determination confirmed successful composite formation, with partial cellulose intercalation increasing the specific surface area from 78 to 177 m²/g. Batch adsorption experiments showed optimal CR removal at pH 4 using 30 mg of adsorbent, achieving a maximum adsorption capacity of 167.25 mg/g, significantly higher than raw bentonite (95.72 mg/g). Adsorption equilibrium and kinetics followed the Langmuir isotherm and pseudo-second-order model, while thermodynamic analysis indicated a spontaneous and endothermic process. Density functional theory (DFT) and molecular dynamics (MD) simulations revealed adsorption governed by n-π interactions, electrostatic attraction, and hydrogen bonding. The composite retained over 75% efficiency after five regeneration cycles and achieved 98% CR removal from real tannery wastewater, demonstrating its potential as a sustainable adsorbent for industrial effluent treatment.