Synthesis of polyethyleneimine modified CoFe2O4-loaded porous biochar for selective adsorption properties towards dyes and exploration of interaction mechanisms

A novel adsorbent of polyethyleneimine modified magnetic porous biochar from waste bamboo powder was synthesized and applied to the selective removal of Congo red (CR) in wastewater. The adsorbents were characterized by multiple methods, and the adsorption properties of CR from single, binary and simulated textile wastewater were investigated. The kinetics showed that the adsorption process conformed to Elovich model and the rate-controlling step was determined by multiple stages. In addition, the adsorption isotherms indicated that CR adsorption was well fitted to Freundlich model, and thermodynamic parameters depicted the endothermic nature and the spontaneous process. The maximum adsorption capacity of the adsorbent was 435.9 mg/g, and adsorption amount reached 899.44 mg/g at pH = 3. The adsorption mechanism of CR involved electrostatic interaction and hydrogen bonding. Additionally, the influences of the presence of anionic methyl orange (MO) and cationic methylene blue (MB) on CR adsorption and the interaction mechanisms between the dyes manifested that the removal of CR slightly inhibited by MO while significantly promoted by MB was respectively due to the competition and synergy. Furthermore, the high efficiency of the novel adsorbent for CR from simulated textile wastewater and the excellent reusability indicated the adsorbent has great potentials in the practical application of wastewater treatment.