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

Abstract

English: 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

Afrikaans: ‘n Reeks grootmaat- asook nano-grootte metaal heksasianoferraat partikels (KMy[Fe(CN)6]z·qH2O, M = Fe, Co, Ni en Cu) is voorberei met behulp van ‘n gesamentlike presipitasie en omgekeerde emulsie reaksie, onderskeidelik. Dit is gevind dat die opbrengs afhanklik is van die Pauling elektronegatiwiteit, σM, van die metaal M. Transmissie elektron mikroskopie het getoon dat die nano-grootte metaal heksasianoferrate se gemiddelde groottes tussen 46 en 124 nm varieer. Daar is veelvuldige CN pieke in die 1900 – 2200 cm-1 gebied van die infrarooi spektroskopie gevind van die voorbereide koördinasieverbindings, wat die gemengde oksidasietoestande van die verskillende metale in die heksasianoferrate bevestig het. X-straal foto-elektron spekstroskopie is gebruik om die verhouding tussen die metale asook die verhouding van elke oksidasietoestand teenwoordig van die veerskillende metale te bepaal. Die vergelyking van resultate tussen infrarooi spektroskopie en X-straal foto-elektron spektroskopie het insig in die elektron verspreiding, ladingsoordrag en mate van koördinasie in hierdie verbindings gelewer. Die termiese gravimetriese ontledings het massaverlies by verwarming in drie groepe verdeel. Tot en met ~200 °C, is eksterne water molekules verdamp, tussen 200 °C en 300 °C is interkalêre (interne) water molekules verdamp en vanaf ~300 °C het die ontbinding van die organiese bindings plaasgevind. Hierdie word deur differensiaal skanderings kalorimetriese en fourier getransformeerde infrarooi spektroskopiese opnames bevestig wat geneem is na elke verwarmingsgedeelte. Kobalt heksasianoferraat is gebruik om elektrodes te modifiseer deur óf ‘n fisiese laagvorming óf deur elektrodeponering van die oppervlak van ‘n glasagtige koolstof werkselektrode. Koolstof puree gemodifiseerde elektrodes is ook voorberei. Die elektrochemiese reaksie van die gemodifiseerde elektrodes is in blanko water en asetonitriel oplossings onderskeidelik getoets. Die invloed op die vinnige elektronoordraende verbinding ferroseen is ook ondersoek. Hierdie elektrodes is ook getoets vir hul elektrokatalitiese oksidasie van hidrasien.