Polystyrene-b-poly(acrylic acid) nanospheres for the synthesis of size-controlled cobalt nanoparticles encapsulated inside hollow carbon spheres

Metal particle agglomeration is known to be one of the factors responsible for the reduction in catalytic activity (even selectivity) when metal particles are supported on carbon. In this study, an approach using functional groups attached to a polymeric support was used to reduce metal agglomeration. Herein, we report on the preparation of polystyrene (PS) (d = 350 nm) and asymmetric polystyrene-b-poly(acrylic acid) (PS-b-PAA) nanospheres (8% and 12% PAA loadings; d = 274 nm and 343 nm) to make cobalt/polymer complexes. The CoxOy nanoparticles were supported on the PS and PS-b-PAA templates (5%, 10% and 15% Co loading), and then the CoxOy/template was coated with resorcinol–formaldehyde (RF). Thermal removal of the templates and annealing of the RF at 600 °C for 2 h gave the CoxOy@HCS materials. At a nominal Co loading of 5%, the PS template produced CoxOy@HCS materials that contained small Co particles (6.1 nm) while at higher Co loadings (10%, 15%) large and irregularly shaped Co nanoparticles (d > 20 nm) were formed. In contrast, PS-b-PAA gave CoxOy@HCS with small, highly dispersed Co nanoparticles (d < 10 nm) at loadings between 5 and 15%. The three polymeric nanospheres and the CoxOy/polymer and CoxOy@HCS materials were all characterized using SEM, TEM, TGA and FTIR spectroscopy. The use of functionalized polymer templates thus allows small Co particles to be easily transferred from the template to the RF to give CoxOy@HCS, even when using high-temperature (600 °C) synthesis conditions.