The removal of silver nanoparticles (AgNPs) from water is highly needed because of their increasing use and potential risk to the environment due to their toxic effects. Catalysis over AgNPs has received significant attention because of their highly catalytic performance. However, their use in practical applications is limited due to high cost and limited resources. Here, we present for the first time that the mussel-inspired Fe3O4@polydopamine (Fe3O4@PDA) nanocomposite can be used for efficient removal and recovery of AgNPs. Adsorption of AgNPs over Fe3O4@PDA was confirmed by TEM, FT-IR, XRD, TGA and magnetic property. The adsorption efficiency of AgNPs by Fe3O4@PDA was investigated as a function of pH, contact time, ionic strength and concentration of AgNPs. The kinetic data were well fitted to a pseudo-second order kinetic model. The isotherm data were well described by Langmuir model with a maximum adsorption capacity of 169.5 mg/g, which was higher than those by other adsorbents. Notably, the obtained AgNPs-Fe3O4@PDA exhibited highly catalytic activity for methylene blue reduction by NaBH4 with a rate constant of 1.44 × 10−3/s, which was much higher than those by other AgNPs catalysts. The AgNPs-Fe3O4@PDA promised good recyclability for at least 8 cycles and acid resistant with good stability.

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Here, we reported a novel one-step hydrothermal route for the facile synthesis of 1,6-hexanediamine functionalized magnetic chitosan microspheres (AF-MCTS), which were characterized by TEM, FT-IR and XPS to look into its morphology, surface functional groups, and adsorption mechanism of Cr(VI) from the aqueous solution. Cr(VI) adsorption on AF-MCTS as a function of contact time, Cr(VI) concentration, pH, and ionic strength was investigated. The adsorption process follows the Langmuir isotherm model and pseudo-second-order kinetic model. The AF-MCTS exhibited high performance for Cr(VI) removal with very fast adsorption rate (reaching equilibrium within 5 min) and high adsorption capacity (208.33 mg/g), which was 1.1 to 12 times that of other chitosan-based adsorbents. Cr(VI) adsorption onto AF-MCTS was an endothermic and spontaneous process. The recovery and reuse of AF-MCTS was demonstrated 11 times without obvious decrease in adsorption capacity. Mechanism study suggested that –OH rather than –NH2 groups in AF-MCTS were the electron donors for reducing Cr(VI) to Cr3+. Consumption or addition of H+ could trigger the reversible supramolecular coordination between Cr3+ and chitosan. Given the easy preparation, low cost, and remarkable performance, AF-MCTS composite is expected to show promising potential for the practical application in removing toxic Cr(VI) from aqueous media.