Spatial Confinement Of Sub-nanometer Noble Metal Nanoparticles In Yolk-shell Magnetic Nanocomposites As Heterogenous Catalysts

It is quite important to develop catalysts with high efficiency,high stability and easy recoverability for the chemical ind lytic activity of noble metal nanoparticles and facile recoverbility of magnetic support.However,the aggregation among noble metal nanparticles caused by their high surface energy may lead to deactivation during catalytic reactions.Therefore,we report rational design of magnetic yolk-shell nanocatalysts with an inner movable Fe₃O₄ core and a hollow crosslinked polymer shell confining mulitple dispersible noble metal nanoparticles in itself and their catalytic performances.The hollow crosslinked polymer shell not only spatially isolates noble metal nanoparticles to avoid the loss and aggregation of noble metal nanoparticles,and also provides the diffusion routes for reactants from both inside and outside the shell to enhance catalytic activity of noble metal nanoparticles confined with the shell.Firstly,the electrostaic interaction-driven polymerization strategy was develop to construct pH-responsive poly?4-vinylpyridine-co-divinylbenzene??P?4-VP-DVB??shell on the surface of Fe₃O₄@SiO₂,and the width of P?4-VP-DVB?shell is about 20 nm.Subsequently,The method of in-situ reduction was used to synthesize Au nanoparticles confined within the structure of P?4-VP-DVB?.The acid reaction system casued by the addition of HAuCl4 leads to swelling of P?4-VP-DVB?polymer and AuCl4-anions are absorbed in the structure of the polymer.While the alkaline reaction systemcaused by the addition of NaBH4 results in the collapse of P?4-VP-DVB?polymer,and Au nanoparticles were reducted simultaneously.ustries.Metal-based magnetic nanocatalysts have attracted much attention due to high cataThe high-activity of Fe₃O₄@void@P?4-VP-DVB?/Au nano-catalyst could be ascribed to the the sub-nano-sized Au particles,about 1.5 nm.The high stability could be ascribed to the confinement of Au nanocrystals uniformly into P?4-VP-DVB?shell against aggregation and even loss of active sites during catalytic transformations.Meanwhile,P?4-VP-DVB?shell can control the size of Au nanopticles due to the abundant pyridine functional groups.Secondly,Fe₃O₄@void@Thermally crosslinked-poly?3,4-ethoxylene dioxy thiophene?/Pt?Fe₃O₄@void@TC-PEDT/Pt?yolk-shell nanopaticles were synthesized through a series of methods including simultaneous oxidation-reduction method,sacrifial templating method,thermally crosslinking process.The high-activity of Fe₃O₄@void@TC-PEDT/Pt nano-catalyst could be ascribed to the the sub-nano-sized Pt particles,about 2 nm.The high stability could be ascribed to the confinement of Pt nanocrystals uniformly into TC-PEDOT ultrathin shell against aggregation and even loss of active sites during catalytic transformations.The high cross-linked of TC-PEDOT ultrathin shell could be ascribed to the carbonization of polymer shell against burst during catalytic transformations.The inner cavity of yolk-shell structure could realize bidirectional diffusion of substrate and product.The catalysts were used in the reduciton of nitroaromatic compounds and exhibited good catalytic activity,high stability and magnetic recyclability.