Growth Mechanisms of Mesoscale Prussian Blue Analogue Particles in Modifier-free Synthesis

The growth mechanism of mesoscale, 100–500 nm, Prussian blue analogue (PBA) particles synthesized via a modifier-free coprecipitation method was investigated. A series of Co2+ and Ni2+ analogues, RbjCok[M(CN)6]l·nH2O (M = Cr, Fe, Co) and RbjNik[M(CN)6]l·nH2O (M = Cr, Fe, Co) are compared, along with the parent Prussian blue and the Cu2+ analogue, rubidium copper hexacyanoferrate. The study finds that growth mechanisms differ among this closely related family of compounds. On the one hand, ex situ transmission electron microscopy and in situ ionic conductivity and DLS analyses indicate the Cu2+ and Ni2+ analogues grow by a traditional heterogeneous precipitation process, whereby nucleated particles grow by addition of ions from solution. On the other hand, the Co2+ analogues and the parent rubidium ferric ferrocyanide grow by aggregation of precursor particles followed by annealing into crystalline mesoscale particles. Understanding of the growth mechanisms is useful for designing routes to mesoscale coordination polymer structures and heterostructures.