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

[摘要] English: A series of bulk and nano-sized metal hexacyanoferrates (KMy[Fe(CN)6]z·qH2O, M = Fe, Co, Ni andCu) were prepared by a co-precipitation and reverse emulsion reaction, respectively. The yieldsobtained were dependant on the Pauling scale electronegativity, σM, of the metal M. Transmissionelectron microscopy showed that nano-sized metal hexacyanoferrates had an average size between 46and 124 nm. Multiple CN peaks in the 1900 �?2200 cm-1 area of the infrared spectroscopy of theprepared coordination compounds confirmed mixed oxidation states of the different metals in the metalhexacyanoferrates. X-ray photoelectron spectroscopy was used to determine the ratio between themetals as well as the ratio of each oxidation state present of the different metals. The comparison ofresults between infrared spectroscopy and X-ray photoelectron spectroscopy gave insight into theelectron distribution, charge transfer and degree of covalency within these compounds. The thermalgravimetric 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 differentialscanning calorimetry and comparative Fourier transformed infrared spectroscopy recorded after eachheating stage. Cobalt hexacyanoferrate was used to modify electrodes by either physical coating or byelectrodeposition of a glassy carbon working electrode, carbon paste modified electrodes were alsoprepared. The electrochemical response of the modified electrodes were tested in a blank water andacetonitrile solution. The electrochemical behaviour in water/KCl of cobalt hexacyanoferrateselectrodepositedmodified glassy carbon electrode (GCED), showed an electrochemically reversible(∆E = 0 mV) but chemically irreversible (ipa/ipc < 1) FeII/FeIII couple. The modified glassy carbonelectrodes revealed no CoII/CoIII couples, which implies that the compounds crystallised in the insolubleform. The influence on the fast electron transfer compound ferrocene was also investigated. Theseelectrodes were also tested for their electrocatalytic oxidation of hydrazine.The heterogeneous hydrogenation of 1-octene was tested to determine the viability and practicality ofmetal 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

[发布机构] University of the Free State