Removal of silver nanoparticles by mussel-inspired Fe 3 O 4 @ polydopamine core-shell microspheres and its use as efficient catalyst for methylene blue reduction.

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 Fe3 O4 @polydopamine (Fe3 O4 @PDA) nanocomposite can be used for efficient removal and recovery of AgNPs. Adsorption of AgNPs over Fe3 O4 @PDA was confirmed by TEM, FT-IR, XRD, TGA and magnetic property. The adsorption efficiency of AgNPs by Fe3 O4 @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-Fe3 O4 @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-Fe3 O4 @PDA promised good recyclability for at least 8 cycles and acid resistant with good stability.