Fabrication of core-shell α-MnO2@polydopamine nanocomposites for the efficient and ultra-fast removal of U(vi) from aqueous solution

The development of functional nanoparticles with ultra-fast and high adsorption capacities is an important strategy for wastewater treatment. Here, alpha-MnO2@polydopamine nanocomposites (alpha-MnO2@PDAs) were synthesized by coating alpha-MnO2 nanowires with polydopamine and were used to remove U(VI) from solutions. The alpha-MnO2@PDAs possessed a large surface area (22.8 m(2) g(-1)), excellent dispersibility, and abundant surface functional groups. The adsorption of U(VI) was clearly influenced by pH rather than ionic strength, which suggested inner-sphere surface complexation. The adsorption could reach equilibrium within 5 min, and the kinetics was well fitted by the pseudo-second-order model. The maximum adsorption capacity determined from the Langmuir model at 298 K and different pH values was in the order of pH 5.0 (383.14 mg g(-1)) > 8.0 (213.22 mg g(-1)) > 3.0 (158.73 mg g(-1)), which indicated that the alpha-MnO2@PDAs could still remove U(VI) efficiently at a pH of 8, which is close to the pH of natural water. Spectroscopic analyses suggested that favourable adsorption occurred on active binding sites, e.g., phenolic O-H and amide functional groups. The higher removal efficiency of the alpha-MnO2@PDAs for U(VI) was due to electrostatic attraction and surface complexation. Moreover, the practical applicability of the alpha-MnO2@PDAs in the treatment of real wastewater was confirmed by their high adsorption capacity for U(VI) from natural or synthetic water.