Impregnation of hyper-cross-linked polystyrene (HPS) by either Co 2 (CO) 8 in 2-propanol or the [Co(DMF) 6 ] 2+ [Co(CO) 4 ] -2 complex in dimethylformamide (DMF), followed by thermolysis at 200 °C, results in the formation of discrete Co nanoparticles. The concentration and characteristics of such nanoparticles were investigated by X-ray fluorescence (XRF) spectroscopy, ferromagnetic resonance (FMR) spectroscopy, and transmission electron microscopy (TEM). The FMR data here confirm the formation of spherical nanoparticles. At relatively low concentrations of Co, the magnitude of the FMR line width reveals that the mean Co nanoparticle diameter is about 2 nm, which agrees closely with the mean particle diameter discerned by TEM. An increase in Co content higher than 8 wt % is accompanied by an increase in mean particle diameter due to an increase in the population of large Co nanoparticles up to 15 nm across. Regulated nanoparticle growth over a wide range of Co concentrations is attributed to nanoscale HPS cavities, which serve to physically restrict the size of growing particles.

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