Magnetic metal-organic frameworks/carbon dots as a multifunctional platform for detection and removal of uranium

Herein, a design of multifunctional hybrid adsorbent made of a magnetic core and a zeolite imidazolate framework (ZIF-8) shell embedded with carbon dots (CDs) is synthesized to combine detection with separation and recycling of uranium from aqueous solution. The adsorbents retain the strong superparamagnetic behavior of Fe3O4 nanoparticles and similar luminescence of carbon dots. Interestingly, the adsorbents not only exhibit obviously fluorescence response for U(VI) but also enhance U(VI) adsorption performance via assisting with the loaded-carbon dots. The adsorption processes of U(VI) on Fe3O4-CMC@ZIF-8 and Fe3O4-CMC@ZIF-8@CDs well fit with the pseudo-second-order model. The maximum U(VI) adsorption amount of Fe3O4-CMC@ZIF-8@CDs is high as 606.06 mg/g at pH = 4.0 and T = 298 K with Langmuir model, which is obviously higher than that of Fe3O4-CMC@ZIF-8 (564.97 mg/g). Particularly, BET, FTIR and XPS results show that the improvement of adsorption properties on Fe3O4-CMC@ZIF-8@CDs is mainly ascribed to the large specific surface area and abundant nitrogen/oxygen functional groups on the surface, suggesting that the main interaction mechanisms are diffusion and coordination. The design for hybrid materials provides a convenient way to achieve a multifunctional adsorbent with detection, separation and recycling properties for uranium.