Development of a Novel Core–Shell Magnetic Fe₃O₄@CMC@ZIF-8-OH Composite with Outstanding Rubidium-Ion Capacity

A novel core–shell magnetic composite, Fe₃O₄@CMC@ZIF-8-OH, was innovatively prepared using zeolitic imidazolate frameworks (ZIF-8) functionalized with carboxymethyl cellulose (CMC), Fe₃O₄, and phenol via wet impregnation dispersion and hydrothermal reaction techniques. Rubidium ions (Rb⁺ ions) can be conveniently collected from an aqueous solution due to the contribution of Fe₃O₄ magnetic properties. The adsorption capacity of Rb⁺ ions can be obviously increased because of the phenolic hydroxyl group existing on ZIF-8 with high surface area and water-resistant performance. The as-synthesized novel composites were examined using N₂ adsorption–desorption, scanning electron microscopy combined with an energy-dispersive X-ray system, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, etc. The results revealed that the Fe₃O₄, phenol, and CMC were assembled in the ZIF-8 structure. Rb⁺ ions have a high adsorption rate and an extraordinary uptake capacity onto Fe₃O₄@CMC@ZIF-8-OH, which is preferential to the other adsorbents reported in the literature. The saturated composite was simply recovered by flushing with an ammonium nitrate solution. Even at the fifth sorption cycle, values of more than 91% adsorption efficiency were achieved for Rb⁺ ions. Generally, Fe₃O₄@CMC@ZIF-8-OH might be capable of capturing rubidium ions from water, which would be applied on a large scale if more engineering data are supported.