Synthesis Of Magnetic Hierarchical Core-shell Structured Pd Nanocatalysts And Their Application In Catalysis

Pd nanoparticles（NPs）have outstanding catalytic performance for many kinds of reactions such as pollutants degradation,C-C coupling reactions and hydrogenation reactions.However,Pd NPs tend to aggregate and are hard to be separated due to their high surface energy and small size.Therefore,supported Pd catalysts have been developed to solve these problems.Recently the core-shell structured multifunctional nanocomposites have been investigated because they possess not only the unique physical and chemical properties of nanomaterials but also excellent properties of cores and shells.As a significant member of multifunctional nanocomposites,magnetic hierarchical core-shell structured Pd nanocatalysts,which consist of a core of inner modified magnetic NPs,transition layer of Pd,and a porous outer shell,have attracted considerable attention in heterogeneous catalysis.In addition,with the increasing shortage of energy and environmental pollution,green chemistry has become an inevitable trend in the development of modern chemical industry.It is of great practical significance to develop a supported Pd photocatalyst that can be used under visible light irradiation at room temperature.Herein,twokindsofmagnetichierarchicalcore-shellPdnanocatalysts,Fe₃O₄@PDA-Pd@[Cu₃（btc）₂]and h-NiZnFe₂O₄@PDA-Pd@[Cu₃（btc）₂],have been prepared,and their structures and properties were characterized with TEM、XRD、VSM、UV-vis DRS and XPS,etc.Then,their catalytic activity and recyclability were studied.The main contents are as follows:1.A series of magnetic hierarchical core-shell structured Fe₃O₄@PDA-Pd@[Cu₃（btc）₂]（n）nanocomposites with different[Cu₃（btc）₂]shell thickness have been fabricated via a facile layer-by-layer assembly method（n=the number of[Cu₃（btc）₂]assembly cycles）.The prepared Fe₃O₄@PDA-Pd@[Cu₃（btc）₂]（n=5）nanocomposite shows ultrahigh catalytic activity for the reduction of 4-nitrophenol(a Knor of 28800 min^-1g^-1)and the Suzuki cross coupling reactions(a TOF reached up to 32667 h^-1).Meanwhile the nanocomposite could be conveniently separated by magnet and reused at least 8 runs with high yields for both the reactions.The catalyst possesses outstanding catalytic performances mainly because the integration of[Cu₃（btc）₂]with Fe₃O₄@PDA-Pd that combines the advantages of each component could exhibit synergistically enhanced catalytic performances.2.Fe₃O₄@PDA-Pd@[Cu₃（btc）₂]（n=5）nanocomposite shows excellent photocatalytic activity for the Suzuki reaction in EtOH/H₂O at the room temperature.The TOF value can reach up to247.5 h^-1.Moreover,the Fe₃O₄@PDA-Pd@[Cu₃（btc）₂]（n=5）catalyst could be reused at least 8times with high yields obtained.Its excellent photocatalytic properties are mainly attributed to the broad visible light absorption ability and efficient separation of photoelectron-hole pairs,and its unique hierarchical core-shell structure can stabilize the Pd NPs to exhibit excellent reusability.3.A series of magnetic hollow hierarchical core-shell structured h-Ni ZnFe₂O₄@PDA-Pd@[Cu₃（btc）₂]（n）nanocatalysts with different shell thickness were prepared（n=the time of the coated[Cu₃（btc）₂]）.The prepared h-NiZnFe₂O₄@PDA-Pd@[Cu₃（btc）₂]（7）shows ultrahigh photocatalytic activity for the Suzuki reaction of in EtOH/H₂O at room temperature.The TOF value can reach up to 413.7 h^-1.Moreover,the h-NiZnFe₂O₄@PDA-Pd@[Cu₃（btc）₂]（7）could be simply separated with an external magnet and reused 8 times with excellent yields obtained.Compared with Fe₃O₄@PDA-Pd@[Cu₃（btc）₂]（n=5）,h-NiZnFe₂O₄@PDA-Pd@[Cu₃（btc）₂]（7）possesses higher catalytic performances mainly because hollow hierarchical core-shell structure can not only effectively prolong the action time of the irradiated light for the multiple reflections but also promote the separation of the photogenerated carrier.