Decoration of ZIF-8 on polypyrrole nanotubes for highly efficient and selective capture of U(VI)

Metal−organic frameworks (MOFs) combined with adsorptive materials have proven their prospect for radionuclide sequestration. To achieve more void space of MOFs as active sites for U(VI) capture, ZIF-8 (zeolitic imidazolate framework-8) nanoparticles were decorated on the polypyrrole (PPy) nanotubes (denoted as PPy/ZIF-8) via an easy and green method. X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy were applied to evaluate the effectiveness of the preparation of PPy/ZIF-8. This novel PPy/ZIF-8 was evaluated for the capture of U(VI) from the simulated wastewater. Based on the Langmuir model, the adsorption capacity was 534.0 mg/g at pH 3.5, which surpassed many other MOF-based adsorbents. The kinetic analysis disclosed that 90 min was enough for PPy/ZIF-8 to reach the adsorption equilibrium. In addition, the introduction of polypyrrole nanotubes endowed PPy/ZIF-8 high adsorption performance in a relatively wide pH range from 3.0 to 7.0. The superior adsorption performance was predominately traceable to the coordination of U(VI) with pyrrolic –NH– groups and Zn terminal hydroxyl groups based on the systematic spectroscopy characterization. PPy/ZIF-8 also showed excellent selectivity and regeneration ability. The excellent adsorption performance endows this novel composite a promising scavenger for the purification of U(VI)-polluted wastewater.