Magnetic Nanocomposites Derived from Hollow ZIF-67 and Core-Shell ZIF-67@ZIF-8: Synthesis, Properties, and Adsorption of Rhodamine B

Two types of magnetic nanocomposites, Co-carbon composite (Co@C) and Zn/Co-carbon composite (Zn/Co@C), were synthesized by one-step calcinations of hollow Co-ZIF (ZIF-67) and Zn/Co-ZIF (ZIF-67@ZIF-8) (ZIF = zeolitic imidazolate framework), as well as applied as adsorbents in the reduction of Rhodamine B (RhB). The prepared composites were carefully analyzed by SEM, TEM-EDXS (EDXS = energy-dispersive X-ray specroscopy), XRD, SQUID, and nitrogen adsorption/desorption measurements. Co@C and Zn/Co@C showed the maximum adsorption capacities of 48 mgg(-1) and 101.93 mgg(-1), respectively, toward RhB. The adsorption isotherms of RhB on the Zn/Co@C nanocomposites were well fitted with the Langmuir model, and the pseudo-second-order model accurately describes the adsorption kinetic process for the adsorption of RhB on the materials. The results show that the composite materials of Zn/Co@C possess higher porosity and magnetic properties and exhibit higher adsorption capacity, convenient separation ability, along with good reusability of the adsorbent. The theoretical calculations also clarify that RhB on the distorted Co-Zn surface is much more stable than that on Co(111), in good agreement with the experimental observations.