Enhanced decontamination of cationic and anionic dye from aqueous solutions using Hybrid ultrasonicated eggshell...

This study explored the synthesis of a green hybrid ultrasonicated eggshell biochar adsorbent (HUEBA) for the decontamination of cationic methylene blue (MB) and anionic methyl orange (MO). The hybrid material's morphological structure and physicochemical properties were examined using SEM, TEM, BET, FTIR, XRD, and point of zero charge techniques. Batch adsorption studies in decontamination of dye pollutants at varying dosages, pH, concentrations, temperatures, and time were performed. The produced material demonstrated outstanding performance against the sorption of MB and MO, achieving 85.49 and 53.45%, respectively, at an equilibration time of 2 h. Response surface methodology (RSM) optimization demonstrated satisfactory predictability for MB removal efficiency, with the importance of the model's validity confirmed through analysis of variance (p < 0.05) and R² value of 0.99. Optimized conditions (236 mg/100 mL adsorbent dosage and 233 min adsorption time) resulted in over 99.9% decontamination of the initial 61 mg/L of MB dye. The validation of the sorption process with numerical isotherm models demonstrated Langmuir recorded a better fit than Freundlich at R² of 0.9888 and 0.9939 mg/g with MB and MO, respectively. Moreover, the monolayer sorption capacities were 99.80 and 73.53 mg/g. The kinetics studies fitted the pseudo-second order and Elovich model against both dyes, revealing chemisorption processes. The thermodynamic studies exhibited exothermic, spontaneous, favourable and random for the sorption of both dye pollutants. The postulated mechanism of decontamination of MB and MO revealed electrostatic interaction, π-π electron stacking and hydrogen bridging. Hence, it is an outstanding material for decontaminating organic pollutants from wastewater systems.