Au-Ag bimetallic nanoparticles decorated multi-amino cyclophosphazene hybrid microspheres as enhanced activity catalysts for the reduction of 4-nitrophenol

Highly dispersed Au-Ag bimetallic nanoparticles were facilely synthesized on the multi-amino poly(cyclotriphosphazene-co-polyethyleneimine) (PCP) microspheres through in situ co-reduction method and then used as catalysts for the reduction of 4-nitrophenol (4-NP). Characterization results showed that the as-synthesized PCP microspheres possessed regular spherical morphology and relatively smooth surface, which could be well modified by highly dispersed Au-Ag bimetallic nanoparticles with size of 2–4 nm. For the reduction of 4-NP, it was found that the as-synthesized PCP@Au-Ag composites showed much better catalytic activity than PCP microspheres supported monometallic counterparts, which could be ascribed to a synergistic effect between Au and Ag in Au-Ag bimetals . For the PCP@Au-Ag catalysts, the rate constant k and intrinsic activity parameter κ of the reaction could be up to 2.87 × 10 −3 s −1 and 144 s −1  g −1 , respectively, and the conversion of the 4-NP could still reach 83% after six cycles. In addition, the possible catalytic mechanism of PCP@Au-Ag composites towards the reduction of 4-AP was also proposed.