Synthesis of monodisperse composite poly(N-isopropylacrylamide) microgels incorporating dispersive Pt nanoparticles with high contents

A facile synthesis of monodisperse composite poly(N-isopropylacrylamide) (PNIPAM) microgels incorporating dispersive Pt nanoparticles with high contents was proposed using an in situ method in which platinum ions were reduced in the presence of PNIPAM microgels. The high contents of dispersive Pt nanoparticles were achieved in a reduction process where a concentrated Pt ion solution suspending PNIPAM gels was injected into a diluted solution of sodium borohydride (NaBH4). Cross-sectional TEM image and energy dispersive X-ray spectroscopy (EDX) for the composite microgels with a high Pt content showed that the major part of Pt nanoparticles formed in the reduction process was localized in the periphery of the PNIPAM microgels. The amount of Pt nanoparticles incorporated into the composite microgels could be enhanced by a decrease in the number of PNIPAM microgels in the in situ reduction method. A highest incorporation at the Pt content of 46 wt% much higher than that previously reported was attained with maintaining their Pt particle sizes less than 5 nm when the concentration of PNIPAM gels was adjusted to a low concentration of 7.7 × 10−2 wt% in the reduction process. It could also be confirmed with dynamic light scattering that sizes of the Pt-PNIPAM composite microgels were sharply decreased with an increase in temperature from 25 °C to 40 °C. In principle, the present method is applicable to the incorporation of other metals than Pt. The applicability was confirmed in additional experiments in which hydrogen tetrachloroaurate (III) was reduced in the presence of PNIPAM microgels.