Selective adsorption of Congo red and Cu(II) from complex wastewater by core-shell structured magnetic carbon@zeolitic imidazolate frameworks-8 nanocomposites

Abstract Efficient and convenient removal of organic dyes and heavy metals from complex wastewater is still a challenge for human health and ecosystem remediation. Novel adsorbent, Fe3O4@Carbon@ZIF-8 with specific core-shell structure was synthesized by layer-by-layer self-assembly. The hydrophilic carbonaceous shell acts as both a linker and stabilizer between Fe3O4 and ZIF-8. The characteristics of self-made adsorbent were comprehensively identified by numerous characterization methods. The adsorption kinetics, isotherms and the influence of various reacting parameters on its adsorption capacity of Congo red (CR) and Cu(II) were systematically investigated. Compared with other reported adsorbents, the maximum adsorption capacities of Fe3O4@Carbon@ZIF-8 towards CR (806.45 mg g−1) and Cu(II) (234.74 mg g−1) were much higher. Moreover, the adsorption process followed pseudo-second-order kinetics and Langmuir isotherm models. Selective adsorption of CR was investigated in the presence of cationic and anionic dyes, and the same as Cu(II) in the existence of competitive ions, which revealed that it was appropriate for selective adsorption toward CR and Cu(II) in complex wastewater. On the basis of FT-IR and XPS analyses, electrostatic interaction, hydrogen bonding, π-π bonding and ion exchange were involved in the mechanism of adsorption. Fe3O4@Carbon@ZIF-8 is suitable for practical application because of its good stability and reusability.