Hyperbranched polymer-protected gold nanoparticles well-dispersed in different organic solvents: preparation and their catalytic applications to 4-nitrophenol reduction

A series of spherical gold nanoparticles (AuNPs) stabilized by amphiphilic hyperbranched polymers, which have a hydrophilic hyperbranched polyethylenimine core and a hydrophobic shell formed by many long acidamide chains such as saturated palmitamide, octadecanamide, and unsaturated oleamide chains, were prepared by chemical reduction. The effect of the kinds and the ratio of the aliphatic chain in amphiphilic polymers, the amount of the amphiphilic polymers, and the storage time on their size, solubility, and stability in chloroform, toluene, petroleum ether, and n-butyl acetate was investigated by TEM, UV-vis. The results revealed that a high-concentration polymer with a double bond can greatly improve the organic solubility and stability of the AuNPs in the toluene, petroleum ether, and n-butyl acetate. All the AuNPs in different solvents could be used as highly efficient catalysts for the biphasic catalytic reduction of 4-nitrophenol. The effect of the concentration of AuNPs and the capping polymers, the volume of organic phase, and temperature on the turnover number (TON) values of AuNPs is also studied. Their TON values could be enhanced by the AuNPs capped with more polymers or selecting a good solvent. The maximum TON values of the AuNPs in different solvents are about 5040 which has never been reported in the heterogeneous catalytic reduction of 4-nitrophenol.