Comparative study on adsorption of cationic and anionic dyes by nanomagnetite supported on biochar derived from Eichhornia crassipes and Phragmites australis stems

Abstract Nanomagnetite supported on biochar derived from Eichhornia crassipes (MECB) and Phragmites australis (MPAB) stems were successfully synthesized by simultaneous carbonization, magnetization, and activation processes. The as-synthesized adsorbents were characterized and tested for their adsorption ability toward methylene blue (MB) and reactive blue 19 (RB 19). The results indicated that MECB was more effective than MPAB in terms of higher adsorption capacity of 88.89 mg/g for MB and 72.56 mg/g for RB 19 compared to 44.78 mg/g and 39.36 mg/g of MPAB, respectively. The adsorption of MB onto MECB and MPAB was best described by the pseudo-second-order kinetic and Langmuir isotherm models. In contrast, the pseudo-first order kinetic and Freundlich isotherm models were the most suitable models for describing the adsorption of RB 19. The thermodynamic analysis confirmed that the adsorption of the dyes onto the produced adsorbents was spontaneous and endothermic. The adsorption mechanism was identified to be related to electrostatic interaction, ion exchange, π–π stacking interaction, n–π interaction, hydrogen bonding, and pore-filling. The recycling and leaching studies proved that the prepared adsorbents exhibited high reusability and stability. This work showed that MECB and MPAB could serve as promising reusable adsorbents in removing dyes from aqueous solutions.