Preparation Of Bimetallic Nano-catalysts In Spherical Poly Electrolyte Brushes By In-situ Reduction Reaction And Their Catalytic Activity

Metal nanoparticles have been widely used due to their high surface-to-volume ratio and catalytic activity.However,due to the potential synergistic effect of bimetallic catalysts,the catalytic performance of the bimetallic catalysts may be even higher than that of single metals.In recent years,they have attracted extensive attention from researchers.However,due to the higher interfacial energy,the nano-sized metal particles should be immobilized by suitable stabilizers or carriers to avoid coagulation.In this paper,nano-bimetallic Ag-Pd catalysts were prepared by in-situ reduction using spherical polyelectrolyte brushes(SPB)as carier under two different conditions.One is through one-step reduction to obtain Ag-Pd nano-catalyst and the carrier is PS-PNIPA microgel,which consists of polystyrene(PS)core and crosslinked poly N-isopropylacrylamide(PNIPA)shell.Another one is through layer-by-layer self-assembly to obtain Ag-Pd nano-catalysts and the carrier is PS-PAA spherical polyelectrolyte brush with PS core and polyacrylic acid(PAA)chain.Finally,the catalytic activity of bimetallic Ag-Pd nanoparticles was studied by UV spectrophotometer and the comparison of catalytic activity of Ag-Pd nanoparticles and monometal nanoparticles was carried out.The main conclusions were as follows:PS-PNIPA microgels and PS-PAA spherical polyelectrolyte brushes are good carriers for loading nano-metal particles.The prepared particles have the characteristics of small particle size(<10 nm),narrow particle size distribution and stable storage.The metal nanoparticles were mainly distributed on the PNIPA networks around the PS cores,and the metal particles were directly embedded in the PNIPA network structure.The thermosensitivity of PNIPA with metal nanoparticles was unchang.The diameter of the Ag,Pd,and Ag-Pd nanoparticles immobilized in the PNIPA networks were 8.1±0.5 nm,4.2±0.4 nm,and 5.4±0.8 nm,respectively.The diameter of the Ag,Pd,Ag-Pd nanoparticles prepared by PS-PAA spherical brush were 3.1±0.8 nm,2.3±0.5 nm,and 2.6±0.6 nm,respectively.The catalytic reaction of metal nanoparticles was studied through the reduction of p-nitrophenol.The rate constants of Ag-Pd,Ag,Pd,and mechanically mixed Ag-Pd nanoparticles prepared by PS-PNIPA microgels were 1.2×10-1 L/m2·s?4.6×10-2 L/m2·s?9.2×10-2 L/m2·s and 7.0×10-2 L/m2·s respectively.It could draw a conclusion that the catalytic activity of Ag was lower than that of Pd,and the catalytic activity of mechanical mixing Ag-Pd particles was between Ag and Pd,while the Ag-Pd bimetallic nano-catalyst showed enhanced catalytic activity due to the synergistic effect.And the catalytic activity could be modulated by the volume transition of PNIPA.The rate constants of Ag and Ag-Pd particles prepared by PS-PAA spherical brushes were 6.6×10-2 L/m2·s and 2.4×10-1 L/m2·s,respectively.It could be easily found that the catalytic activity of metal nanoparticles immobilized in PS-PAA higher than those nanoparticles located in the PNIPA,which was caused by the properties of carriers.