Research On The Construction And Properties Of Magnetic Recyclable Nanocomposites Based On Fe 3 O 4

Noble metal nanoparticles exhibit excellent catalytic activity in many different reactions such as hydrogenation,dehydrogenation,and oxidation.However,when the particle size decreases to nanoscale,two drawbacks usually appear:（1）the aggregation caused by high surface energy usually lead to the decrease in catalytic activity;（2）it is difficult to separate and recycle nanoparticles from reaction solution because of their small size.Anchoring metal nanoparticles on magnetic supports is an effective method for solving these disadvantages.Based on the above consideration,we carried out the following two experiments:（1）Fe₃O₄@polypyrrole（PPy）hollow capsules were prepared by hard-template method.Fe3O4@PPy/Pd composites were constructed by in-situ reduction technique,and there morphologies and structures were characterized.The magnetic properties of the materials were investigated.Their catalytic performance was evaluated by reduction of 4-nitrophenol（4-NP）with sodium borohydride as reducing agent.The experimental results indicated that the hollow capsules structure had a higher specific surface area and lower density.The as-prepared catalysts exhibited high catalytic activity towards the reduction of 4-NP,and the reaction rate constant increased with the increase of Pd nanoparticle loading.The magnetic hollow capsules not only solved the basic problem of catalyst separation and recovery,but also increased the loading of Pd nanoparticles.This method provides an experimental basis for the construction of magnetic hollow capsule catalysts.（2）Fe₃O₄/Pd@PPy composites with core-shell structure were constructed by one-stepmethod using pyrrole as reducing agent.The morphologies and structures of the composites were investigated.the catalytic activity and stability of Fe₃O₄/Pd@PPy were evaluated by reduction of the 4-NP with sodium borohydride.The composite displayed good magnetic separation property.The introduction of PPy enhanced the stability of materials and improved the dispersion of Pd nanoparticles.Compared with Fe₃O₄/Pd composite,Fe₃O₄/Pd@PPy showed superior stability and better recyclability.The method provided one-step approach for constructing magnetic materials coated with noble metal nanocatalysts.