Facile synthesis of shell-core structured Fe₃O₄@ACS as recyclable magnetic adsorbent for methylene blue removal

A series of magnetic activated carbon nanospheres (MACSs) were synthesized via a simple one-step hydrothermal and pyrolysis method. The characterization results confirm that the shell-core structured MACSs were formed because of Fe3O4 nanoparticles (Fe3O4NPs) mostly dispersed on the surface of activated carbon nanospheres. This structure can not only effectively prevent the agglomeration of activated carbon, but can provide a sufficient magnetism for recycle via the magnetic assisted separation technology. Batch tests for methylene blue (MB) removal show that an excellent adsorption capacity of 192.64 mg g−1 at 298 K can be obtained on MACS-700, which can be kept up to 156.4 mg g−1 even after five cycles. The adsorption isotherm and kinetics results show that the adsorption behavior can be well described by Langmuir isotherm model and the experimental data fit better for the pseudo-second-order kinetic model. It demonstrate that the adsorption rate of MB mainly controlled by chemical-adsorption, meanwhile, effects of external mass transfer and intra particle diffusion also can be found.