The preparation and characterisation of nano-metal hexacyanoferrates with a potential catalytic application

A series of bulk and nano-sized metal hexacyanoferrates (KMy[Fe(CN)6]z·qH2O, M = Fe, Co, Ni and Cu) were prepared by a co-precipitation and reverse emulsion reaction, respectively. The yields obtained were dependant on the Pauling scale electronegativity, σM, of the metal M. Transmission electron microscopy showed that nano-sized metal hexacyanoferrates had an average size between 46 and 124 nm. Multiple CN peaks in the 1900 – 2200 cm-1 area of the infrared spectroscopy of the prepared coordination compounds confirmed mixed oxidation states of the different metals in the metal hexacyanoferrates. X-ray photoelectron spectroscopy was used to determine the ratio between the metals as well as the ratio of each oxidation state present of the different metals. The comparison of results between infrared spectroscopy and X-ray photoelectron spectroscopy gave insight into the electron distribution, charge transfer and degree of covalency within these compounds. The thermal gravimetric analyses indicated that mass loss upon heating are categorised into three groups: up to ~200 °C, external water is evaporated, ~200 to ~300 °C intercalated (internal) water is lost and from ~300 °C onwards decomposition of the organic binder occurs. This is confirmed by differential scanning calorimetry and comparative Fourier transformed infrared spectroscopy recorded after each heating stage. Cobalt hexacyanoferrate was used to modify electrodes by either physical coating or by electrodeposition of a glassy carbon working electrode, carbon paste modified electrodes were also prepared. The electrochemical response of the modified electrodes were tested in a blank water and acetonitrile solution. The electrochemical behaviour in water/KCl of cobalt hexacyanoferrateselectrodeposited modified glassy carbon electrode (GCED), showed an electrochemically reversible (∆E = 0 mV) but chemically irreversible (ipa/ipc < 1) FeII/FeIII couple. The modified glassy carbon electrodes revealed no CoII/CoIII couples, which implies that the compounds crystallised in the insoluble form. The influence on the fast electron transfer compound ferrocene was also investigated. These electrodes were also tested for their electrocatalytic oxidation of hydrazine. The heterogeneous hydrogenation of 1-octene was tested to determine the viability and practicality of metal hexacyanoferrate compounds as heterogeneous catalytic material. It was determined, during these preliminary catalysis experiments, that more than one product formed during the hydrogenation of 1- octene, exhibiting that metal hexacyanoferrates has the potential to be used as heterogeneous catalysts