Selective Co(II) Adsorption Using Hollow ZIF-8 Nanostructures with Embedded Fe₃O₄ Nanoparticles

In this study, we developed a magnetic hollow metal–organic framework (Fe 3 O 4 /HZIF-8) nanocomposite by modifying ZIF-8 nanocrystals with magnetic Fe 3 O 4 nanoparticles at room temperature. The resulting Fe 3 O 4 /HZIF-8 nanostructured composite was used as an absorbent for Co(II) elimination. Due to the functionalization of Fe 3 O 4 nanoparticles and the hollow structure of ZIF-8, the prepared absorbent showed a maximum adsorption capacity of 155.8 mg g –1 within 4 h and could be easily separated from the matrix using magnetization. Additionally, the absorbent exhibited a wide pH tolerance range from pH 2.0 to 9.0 and maintained excellent selectivity for Co(II) adsorption in simulated wastewater. The experimental data was well described by the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model. The ultraviolet–visible spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) studies further indicated that complexation reactions dominated the adsorption of Co(II). Thereby, the nanostructured hollow MOF could be performed as a high-performance absorbent for pollutant removal. This work sheds light on the nanostructured design and uptake mechanism study of the metal ions and radionuclide removal.