Congo red dye removal using modified banana leaves: Adsorption equilibrium, kinetics, and reusability analysis

Congo red (CR) dye is a synthetic azo dye expansively used in the textile industry, is discharged to aquatic environments, and is toxic to humans and aquatic flora. The performance of cationic amino-modified banana leaves (CMBL) for CR dye sequestration was evaluated first time in this study. The surface modification of CMBL was analyzed using Scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectrum and compared with raw banana leaves powder (RBL). The optimum condition for CR dye adsorption using CMBL was optimized using Central Composite Design (CCD) by investigating four critical operating parameters: contact time, pH, RBL/CMBL doses, and initial CR dye concentrations. The proposed model (quadratic) was acceptable due to the high values of correlation coefficients R2 (0.96) and adjusted R2 (0.92). The CMBL exhibited maximum removal efficiency of 76.82% towards CR dye at pH 3 compared to RBL, i.e., 19.63%. Electrostatic interaction and hydrogen bonding were the primary removal mechanisms for the CR dye adsorption process using CMBL. Freundlich isotherm and pseudo-second-order kinetic model exhibited a strong correlation for experimental data and reported a correlation coefficient (R2) of more than 0.99. In addition, CMBL showed excellent reusability for the adsorption of CR dye even after three consecutive adsorption-desorption experiments.