Cobalt nanoparticle formation in the pores of hyper-cross-linked polystyrene: Control of nanoparticle growth and morphology

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 dimethylf ormamide (DMF), followed by thermolysis at 200 degrees C, results in the fo rmation of discrete Co nanoparticles. The concentration and characteristics of such nanoparticles were investigated by X-ray fluorescence (XRF) spectr oscopy, ferromagnetic resonance (FMR) spectroscopy, and transmission electr on microscopy (TEM). The FMR data here confirm the formation of spherical n anoparticles. 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 na noparticles up to 15 nm across. Regulated nanoparticle growth over a wide r ange of Co concentrations is attributed to nanoscale HPS cavities, which se rve to physically restrict the size of growing particles.