Gold nanoparticles stabilized by amphiphilic hyperbranched polymers for catalytic reduction of 4-nitrophenol

Abstract Amphiphilic hyperbranched polymers (Hx-PEI-PEG) with polyethylene glycol (PEG) chains and low-molecular-weight polyethylenimine (PEI) conjugated to commercial aliphatic hyperbranched polyesters (Boltorn Hx) were used to stabilize gold nanoparticles (AuNPs) at the interlayer between the core and the shell. It was found that low generations of Hx-PEI-PEG such as H20-PEI-PEG and H30-PEI-PEG cannot effectively stabilize AuNPs. However, H40-PEI-PEG was both the reduction agent and the stabilizer for the formation of AuNPs, which was confirmed from the solution color change and UV–vis absorption spectra. Spherical nanosized AuNPs (below 10 nm) with narrow particle size distributions were observed from the TEM images. The H40-PEI-PEG-stabilized AuNPs solution could be shelf-stored at room temperature for more than 1 month. In addition, H40-PEI-PEG-stabilized AuNPs showed high catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP).