Selective and efficient adsorption of anionic dyes by core/shell magnetic MWCNTs nano-hybrid constructed through facial polydopamine tailored graft polymerization: Insight of adsorption mechanism, kinetic, isotherm and thermodynamic study

Abstract

It is a big challenge to design advanced adsorbents that have high adsorption capacity and excellent selectivity to efficiently remove organic dyes from complex environmental systems. Herein, by utilizing the adhesion property of polydopamine (PDA) and its crosslinking reaction with polyethyleneimine (PEI), a novel core/shell magnetic MWCNTs/Fe3O4@(PDA + PEI) nano-hybrid that carries superior adsorption performance of dyes was constructed through facile polydopamine tailored graft polymerization. In such hierarchical structure, the inner shell of Fe3O4 nanoparticles and outer shell of (PDA + PEI) contributed to the abundant active adsorption sites, large specific surface area (126 m2/g) and high saturation magnetization value (10.91 emu/g). As a result, the prepared adsorbent exhibited highly selective adsorption performance toward multiple anionic dyes, including MB, CR, and MO with maximum adsorption capacity of 1449, 1006, and 935 mg/g at 298.15 K, respectively. It was found that the main adsorption mechanism was attributed to the hydrogen bonding and electrostatic interaction. The kinetics data fitted well with the pseudo-second-order model, and both the Langmuir and Freundlich isotherm models presented well fit to the isotherm data. The investigation of thermodynamic study indicated that the adsorption of anionic dyes onto core/shell magnetic MWCNTs/Fe3O4@(PDA + PEI) nano-hybrid was spontaneous and endothermic. More importantly, the adsorbent presented excellent regeneration property after multiple adsorption-desorption cycles and prominent stability in harsh environments, especially in the alkaline condition. Therefore, these results revealed the promising applications of hierarchical MWCNTs/Fe3O4@(PDA + PEI) nano-hybrid in water remediation.