Intercalation of Hydrotalcites with Hexacyanoferrate(II) and (III)-a ThermoRaman Spectroscopic Study

Raman spectroscopy using a hot stage indicates that the intercalation of hexacyanoferrate(II) and (III) in the interlayer space of a Mg,Al hydrotalcites leads to layered solids where the intercalated species is both hexacyanoferrate(II) and (III). Raman spectroscopy shows that depending on the oxidation state of the initial hexacyanoferrate partial oxidation and reduction takes place upon intercalation. For the hexacyanoferrate(III) some partial reduction occurs during synthesis. The symmetry of the hexacyanoferrate decreases from Oh existing for the free anions to D3d in the hexacyanoferrate interlayered hydrotalcite complexes. Hot stage Raman spectroscopy reveals the oxidation of the hexacyanoferrate(II) to hexacyanoferrate(III) in the hydrotalcite interlayer with the removal of the cyanide anions above 250 °C. Thermal treatment causes the loss of CN ions through the observation of a band at 2080 cm-1. The hexacyanoferrate (III) interlayered Mg,Al hydrotalcites decomposes above 150 °C

Thermal decomposition of the hydrotalcite Zn6Al2CO3(OH)16.4H2O – a Thermogravimetric analysis and hot stage Raman spectroscopic study

A combination of thermogravimetry and hot stage Raman spectroscopy has been used to study the thermal decomposition of the synthesised zinc substituted takovite Zn6Al2CO3(OH)16.4H2O. Thermogravimetry reveals seven mass loss steps at 52, 135, 174, 237, 265, 590 and ~780 degrees Celsius. MS shows that the first two mass loss steps are due to dehydration, the next two to dehydroxylation, the mass loss step at 265 degrees Celsius to combined dehydroxylation and decarbonation. The two higher mass loss steps are attributed to decarbonation. Raman spectra of the hydroxyl stretching region over the 25 to 200 degrees Celsius temperature range, enable identification of bands attributed to water stretching vibrations, MOH stretching modes and strongly hydrogen bonded CO32- -water bands. CO32- symmetric stretching modes are observed at 1077 and 1060 cm-1. One possible model is that the band at 1077 cm-1 is ascribed to the CO32- units bonded to one OH unit and the band at 1092 cm-1 is due to the CO32- units bonded to two OH units from the Zn-takovite surface. Thermogravimetric analysis when combined with hot stage Raman spectroscopy forms a very powerful technique for the study of the thermal decomposition of minerals such as hydrotalcites

Synthesis and characterisation of iron doped boehmite nanofibres, nanotubes and nanosheets

The modification of nanostructured materials is of great interest due to controllable and unusual properties inherent in such materials. In this paper, iron doped boehmite nanofibres, nanotubes and nanosheets with varying iron content have been prepared through low temperature hydrothermal treatment in the presence of poly (ethylene oxide) surfactant. The combination of transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and N2 adsorption were employed to characterize the resulting nanostructures. TEM images showed that the resulting nanostructures are predominantly nanofibres when iron content is less than 5 % (mol/mol); in contrast nanosheets were formed when iron doping was above 5%. Nanotubes instead of nanofibres and iron rich particles were observed in samples with 20 % added iron. XRD showed that the iron doped nanostructures are boehmite (x100216-AlOOH), with EDX analysis indicating the maximum iron content in the boehmite nanostructures is about 4.3%. Nitrogen adsorption results indicate a lowering of the surface area for the iron doped phase in comparison to that of undoped boehmite nanofibres. Further study is required to determine the magnetic and optical properties of the iron doped boehmite nanostructures for their prospective applications. A detailed characterization of the iron doped nanofibres is presented

Thermal decomposition of metatorbernite - A controlled rate thermal analysis study

The mineral metatorbernite, Cu[(UO2)2(PO4)]2•8H2O, has been studied using a combination of energy dispersive X-ray analysis, X-ray diffraction, dynamic and controlled rate thermal analysis techniques. X-ray diffraction shows that the starting material in the thermal decomposition is metatorbernite and the product of the thermal treatment is copper uranyl phosphate. Three steps are observed for the dehydration of metatorbernite. These occur at 138 degrees Celsius with the loss of 1.5 moles of water, 155 degrees Celsius with the loss of 4.5 moles of water, 291 degrees Celsius with the loss of an additional 2 moles of water. These mass losses result in the formation of four phases namely meta(II)torbernite, meta(III)torbernite, meta(IV)torbernite and anhydrous hydrogen uranium copper pyrophosphate. The use of a combination of dynamic and controlled rate thermal analysis techniques enabled a definitive study of the thermal decomposition of metatorbernite. While the temperature ranges and the mass losses vary from author to author due to the different experimental conditions, the results of the CRTA analysis should be considered as standard data due to the quasi-equilibrium nature of the thermal decomposition process

Raman and infrared spectroscopic study of the basic copper chloride minerals: implications for the study of the copper and brass corrosion and "bronze disease"

The vibrational spectra of both synthetic and natural atacamite and clinoatacamite are compared with natural paratacamite, have been obtained at 298 using a combination of FTIR and Raman microscopy. The vibrational spectra of the minerals are different, in line with differences in crystal structure and composition. The vibrational spectra of paratacamite are different from that of both atacamite and clinoatacamite. Paratacamite is not polymorphic with atacamite but rather is a separate phase. Some similarity in the Raman spectra of the polymorphs exists, particularly in the OH stretching region, but characteristic differences in the OH deformation regions are observed. These differences may be used to characterize the minerals. Differences are also observed in the chloride stretching and deformation regions. The implication from the study of these minerals is that copper, brass and bronze objects of archaeological, antiquarian and medieval significance can be studied by the use of Raman spectroscopy. Indeed the restoration of these types of articles can be aided by the application of Raman spectroscopy to the study of the degradation products from paintings of antiquity

Surface modification of alumina nanofibres for the selective adsorption of alachlor and imazaquin herbicides

The effective removal of pollutants using a thermally and chemically stable substrate that has controllable absorption properties is a goal of water treatment. In this study, the surfaces of thin alumina (γ-Al2O3) nanofibres were modified by the grafting either of two organosilane agents, 3-chloro-propyl-triethoxysilane (CPTES) and octyl-triethoxysilane (OTES). These modified materials were then trialed as absorbents for the removal of two herbicides, alachlor and imazaquin from water. The formation of organic groups during the functionalisation process established super hydrophobic sites on the surfaces of the nanofibres. This super hydrophobic group is a kind of protruding adsorption site which facilitates the intimate contact with the pollutants. OTES grafted substrate were shown to be more selective for alachlor while imazaquin selectivity is shown by the CPTES grafted substrate. Kinetics studies revealed that imazaquin was rapidly adsorbed on CPTES-modified surfaces. However, the adsorption of alachlor by OTES grafted surface was achieved more slowly

Thermal decomposition of the composite hydrotalcites of iowaite and woodallite

The thermal stability and thermal decomposition pathways for synthesized composite iowaite /woodallite have been determined using thermogravimetry analysis in conjunction with evolved gas mass spectrometry. Dehydration of the hydrotalcites occurred over a range of 56-70 °C. The first dehydroxylation step occurred at around 255 °C and, with the substitution of more iron (III) for chromium (III) this temperature increased to an upper limit of 312 °C. This trend was observed throughout all decomposition steps. The release of carbonate ions as carbon dioxide gas initialised at just above 300 °C and was always accompanied by loss of hydroxyl units as water molecules. The initial loss of the anion in this case the chloride ion was consistently observed to occur at about 450 °C with final traces evolved at 535 to 780 °C depending of the Fe:Cr ratio and was detected as HCl (m/Z = 36). Thus for this to occur, hydroxyl units must have been retained in the structure at temperatures upwards of 750 °C. Experimentally it was found difficult to keep CO2 from reacting with the compounds and in this way the synthesized iowaite-woodallite series somewhat resembled the natural minerals