Simple synthesis of three primary colour nanoparticle inks of Prussian blue and itsanalogues

Abstract

Historic Prussian blue (PB) pigment is easily obtained as aninsoluble precipitate in quantitative yield from an aqueous mixture ofFe3+ and [FeII(CN)6]4− (Fe2+ and [FeIII(CN)6]3−). It has been found that the PB pigment is inherently an agglomerate of 10–20 nm nanoparticles,based on powder x-ray diffraction (XRD) line broadenings and transmission electronmicroscopy (TEM) images. The PB pigment has been revived as both organic-solvent-solubleand water-soluble nanoparticle inks. Through crystal surface modification with aliphaticamines, the nanoparticles are stably dispersed from the insoluble agglomerate into usualorganic solvents to afford a transparent blue solution. Identical modification with[Fe(CN)6]4− yields water-soluble PB nanoparticles. A similar ink preparation is applicable toNi-PBA and Co-PBA (nickel and cobalt hexacyanoferrates). The PB (blue), Ni-PBA(yellow), and Co-PBA (red) nanoparticles function as three primary colour inks.