Stability and catalysis activity of amphiphilic silver nanoparticles stabilized by modified hyperbranched polymer

Silver nanoparticles protected by modified hyperbranched polymer (amphiphilic hyperbranched polyglycerol, mHPG) were prepared and dispersed in base fluids with different polarities to form nanofluids. The effect of temperature on the preparation of silver nanoparticles was also studied. The stability of the water/toluene-based silver nanofluids and the improvement of the thermal conductivity of the silver nanofluids with different concentrations (0.05–0.5 wt%) and temperatures (25–50 °C) are discussed. The silver nanoparticles were used as quasi-homogeneous catalysts for the catalytic reduction of 4-nitrophenol (4-NP) and rhodamine B (RhB). The experimental results showed that the silver nanoparticles prepared at 25 °C can be stably dispersed in the base-fluid with different polarity for more than 3 months. The thermal conductivity enhancement of silver nanofluids improved significantly with the rise of mass fraction of silver nanoparticles and temperature. The thermal conductivity of the silver nanofluid with 0.5 wt% Ag@mHPG was improved by up to 80 % at 50 °C. The silver nanoparticles show good catalytic activity and reusability. The maximum reaction rate constants ( k ) were estimated to be 0.347 min −1 for RhB reduction and 0.114 min −1 for 4-NP reduction. The catalyst was separated readily and the conversion efficiency for 4-NP reduction was over 89 % after five cycles. The silver nanoparticles and nanofluids stabilized by modified hyperbranched polyglycerol could be promising for a wide range of applications in the thermal management systems used as working fluids to improve heat transfer and in quasi-homogeneous catalysis. The changes of relative content for silver nanoparticles in nanofluids with storage time; catalytic reduction of organic dyes with NaBH 4 using Ag@mHPG as catalyst in aqueous medium. • Silver nanoparticles protected by mHPG have excellent stability in different base fluids. • Silver nanoparticles protected by mHPG significantly improved the thermal conductivity of nanofluids. • Good catalytic activity and reusability for the reduction of 4-nitrophenol and rhodamine B.