Gold Nanoparticles Stabilized By Amphiphilic Polymers With Different Morphology As Heterogeneous Catalysts

A series of organo-soluble spherical gold nanoparticles （AuNPs） were preparedthrough the reduction of HAuCl4by NaBH4in the presence of amphiphilichyperbranched polymers that had a hydrophilic hyperbranched polyethylenimine coreand a hydrophobic shell formed by many fattyacidamide chains. For comparison, thecorresponding linear polymeric analog derived from linear polyethylenimine was alsoused to prepare the organo-soluble AuNPs.The obtained AuNPs were characterized by transmission electron microscopy. Itwas found that higher feed ratio of polymer to HAuCl4and utilization of polymerswith higher CX density usually resulted in smaller AuNPs with relatively lowerpolydispersity. Except of the polymer having the pronounced low molecular weight,the molecular weight and the morphology of the amphiphilic polymers had almost noobvious effect on the size of the formed AuNPs. If there are double bonds in thehydrophobic shell formed by fattyacidamide chains, the AuNPs will have bettersolubility and can be dissolved in a variety of organic solvents.These organo-soluble AuNPs could be used as efficient catalysts for the biphasiccatalytic reduction of4-nitrophenol by NaBH₄. Their apparent rate coefficients hadcorrelation with the molecular weight of the used amphiphilic polymers, but were lessrelevant to the morphology of these polymers. These organo-soluble AuNPs could beconveniently recovered and reused many times. The morphology of the cappingpolymers had obvious effect on the lifetime of the AuNPs catalysts in the catalyticreduction of4-nitrophenol. Except of the pronounced low molecular weighthyperbranched polymer, the other hyperbranched ones with relatively high molecularweight rendered the AuNPs to have bigger turnover number values than their linearanalog.