Direct synthesis of different metal hexacyanoferrate nanoparticles in reverse microemulsions by using a ferrocyanide functionalized surfactant

Reverse microemulsions (RME) formed by the functionalized surfactant cetyltrimetyl ammonium ferrocyanide (CTAFeII) were used as reaction media to synthesize different metal hexacyanoferrates (MHCF). By just adding diluted solutions of CoCl2, NiCl2, CuCl2 or FeCl3 to the RME, spherical nanoparticles of CoHCF, NiHCF, CuHCF and FeHCF were obtained respectively. Bare RME and RME containing nanoparticles were measured by small angle X-ray scattering. The results obtained by the fits performed with the Teubner and Strey model show no significant difference in the periodicity (dTS) and in the correlation length (ξTS), which suggests that the synthesis process does not affect the RME structure. Micrographs obtained by transmission electron microscopy confirm that the nanoparticles are consistently spherical with an average size of 4 nm for CoHCF and CuHCF, and 6 nm for NiHCF and FeHCF. The average value of the lattice parameter obtained by X-ray diffraction is completely agrees with the values reported in the literature for this type of coordination compounds. The surfactant CTAFeII opens the possibility to obtain nanoparticles of other coordination compounds by using a cationic surfactant in their functionalized form.