Designed Synthesis And Catalytic Properties Of Carbon Based Magnetic Nanocomposite Materials

The supported noble-metal nanocomposite catalysts attract extensive attention in chemical industry,due to their high activity and recyclable property in the liquid-phase catalysis.Magnetic supported noble-metal nanocomposite catalysts could be separated from the reaction systems easily with assistance of exterior magnetic field,which made them to be one of the most important catalyst materials.Among these metarials,various carbon-based magnetic nanocomposites were developed to support the noble-metal nanocatalysts with the high chemical and thermal stability,and outstanding solvent resistance property of the carbon metarials.It is clear that,without active functional groups in the carbon stuctures,these composite supports usually fail to immobilize the noble-metal nanoparticles?NMNPs?effectively.To overcome the problem,a traditional method is modifying the surfaces of the carbon metarials by organic ligands,it is almost impossible to control the distribution,and the weak connections between NMNPs and the supports can not maintain these small particles monodisperse and stability,which limits their applications.Based on the above considerations,nitrogen-containing polmer shells were encapsulated on the surfaces of Fe₃O₄ nanoclusers through a simple electrostatic assist polymerization reaction,after that,the polymer shells were in situ pyrolyzed to be nitrogen doped carbon metarials.On this basis,a variety of high-efficiency and stable carbon-based magnetic noble-metal nanocomposite catalysts were constructed with different structures in this paper.Based on electrostatic adsorption mechanism,with the attraction between NH₄⁺cation adsorbed on the surfaces of Fe₃O₄/Polyacrylic acid?Fe₃O₄/PAA?nanoclusers and3-Aminophenol-Formaldehyde?APF?resin intermediates,and with the layer-by-layer self-assembly method under the assist of NH₄⁺,Fe₃O₄@APF nanospheres were synthesized successfully with different thicknesses of APF resin shell.The correspongding Fe₃O₄@Nitrogen-containing Carbon?Fe₃O₄@N-Carbon?nanospheres were obtained by subsequently thermal treatment.An in situ reduction process was chosen to prepare Fe₃O₄@N-Carbon@Pt nanocomposite catalysts with the coordination interaction between lone pair electrons in N atoms on carbon structures of Fe₃O₄@N-Carbon nanospheres and unoccupied orbitals in Pt atoms.The nanocomposite catalysts revealed excellent catalytic activities for the reduction of 4-nitroaniline?4-NA?,4-nitrophenol?4-NP?and2-nitroaniline?2-NA?;controllable magnetic separation property;good cyclic catalysis performance.With the coordination interaction between N atoms on APF resin shells and Au nanoparticles and electrostatic adsorption of the amino resins,highly dispersed Au nanoparticles with average particle size of 3.47 nm and ultrathin APF resin shells with thickness of about 2 nm were successively deposited on the surfaces of Fe₃O₄@APF nanospheres,and after the in situ pyrolysis,the Fe₃O₄@N-Carbon@Au@N-Carbon nanocomposite catalysts were obtained.Compared with the Fe₃O₄@APF@Au nanocomposites?with Au nanoparticles on surfaces?and Fe₃O₄@APF@Au@APF nanocomposites?without termal treatment?in reduction reaction of 4-NP,the Fe₃O₄@N-Carbon@Au@N-Carbon nanocomposite catalysts possessed outstanding stability,which even been reused for 20 times,the structure was well preserved.The Au nanoparticles on the two other nanocomposites were agglomerated and flown away.The nanocomposite catalysts revealed excellent catalytic activities for the reduction of 4-NP,2-nitrophenol?2-NP?,4-NA and 2-NA.Fe₃O₄/PAA nanoclusers were coated with a double-layered silica@Resorcinol-3-Aminophenol-Formaldehyde?SiO₂@RF/APF?shell through a one-pot process.After a series of treatments that containing in situ Au nanoparticles immobilization,APF resin coating process,thermal treatment and etching reaction,the yolk-shell Fe₃O₄@Void@N-Carbon@Au@N-Carbon nanocomposite catalysts were prepared successfully.Compared with the Fe₃O₄@SiO₂@RF/APF@Au nanocomposites?with Au nanoparticles on surfaces?and Fe₃O₄@SiO₂@RF/APF@Au@APF nanocomposites?withouttermaltreatment?inreductionreactionof4-NP,the Fe₃O₄@Void@N-Carbon@Au@N-Carbon nanocomposite catalysts possessed outstanding stability with conversion above 96%in 20 cycles,which even been reused for 20 times,the carbon shell structure and Au nanoparticles were well preserved.Compared with Fe₃O₄@SiO₂@N-Carbon@Au@N-Carbon nanocomposites,the Fe₃O₄@Void@N-Carbon@Au@N-Carbon nanocomposite catalysts revealed higher catalytic activities for the reduction of 4-NP,2-NP and 4-NA,due to the double-diffusion property of yolk-shell structural composite catalysts.