The effect of synthesis temperature on the formation of hydrotalcites in Bayer liquor : a vibrational spectroscopic analysis

The seawater neutralisation process is currently used in the Alumina industry to reduce the pH and dissolved metal concentrations in bauxite refinery residues, through the precipitation of Mg, Al, and Ca hydroxide and carbonate minerals. This neutralisation method is very similar to the co-precipitation method used to synthesise hydrotalcite (Mg6Al2(OH)16CO3•4H2O). This study looks at the effect of temperature on the type of precipitates that form from the seawater neutralisation process of Bayer liquor. The Bayer precipitates have been characterised by a variety of techniques, including X-ray diffraction, Raman spectroscopy and infrared spectroscopy. The mineralogical composition of Bayer precipitates largely includes hydrotalcite, hydromagnesite, and calcium carbonate species. XRD determined that Bayer hydrotalcites that are synthesised at 55 °C have a larger interlayer distance, indicating more anions are removed from Bayer liquor. Vibrational spectroscopic techniques have identified an increase in hydrogen bond strength for precipitates formed at 55 °C, suggesting the formation of a more stable Bayer hydrotalcite. Raman spectroscopy identified the intercalation of sulfate and carbonate anions into Bayer hydrotalcites using these synthesis conditions.

A vibrational spectroscopic study of hydrated Fe3+ hydroxyl-sulphates; polymorphic minerals butlerite and parabutlerite

Raman and infrared spectra of two polymorphous minerals with the chemical formula Fe3+(SO4)(OH)•2H2O, monoclinic butlerite and orthorhombic parabutlerite, are studied and the spectra assigned. Observed bands are attributed to the (SO4)2- stretching and bending vibrations, hydrogen bonded water molecules, stretching and bending vibrations of hydroxyl ions, water librational modes, Fe-O and Fe-OH stretching vibrations, Fe-OH bending vibrations and lattice vibrations. The O-H...O hydrogen bond lengths in the structures of both minerals are calculated from the wavenumbers of the stretching vibrations. One symmetrically distinct (SO4)2- unit in the structure of butlerite and two symmetrically distinct (SO4)2- units in the structure of parabutlerite are inferred from the Raman and infrared spectra. This conclusion agrees with the published crystal structures of both mineral phases.

Vibrational spectroscopic study of the mineral tsumebite Pb2Cu(PO4,SO4) (OH)

The mineral tsumebite Pb2Cu(PO4)(SO4)(OH), a copper phosphate-sulfate hydroxide of the brackebuschite group has been characterised by Raman and infrared spectroscopy. The brackebuschite mineral group are a series of monoclinic arsenates, phosphates and vanadates of the general formula A2B(XO4)(OH,H2O), where A may be Ba, Ca, Pb, Sr, while B may be Al, Cu2+,Fe2+, Fe3+, Mn2+, Mn3+, Zn and XO4 may be AsO4, PO4, SO4,VO4. Bands are assigned to the stretching and bending modes of PO43- and HOPO3 units. Hydrogen bond distances are calculated based upon the position of the OH stretching vibrations and range from 2.759 Å to 3.205 Å. This range of hydrogen bonding contributes to the stability of the mineral.

A vibrational spectroscopic study of the mixed anion mineral sanjuanite Al2(PO4)(SO4)(OH)•9H2O

The mineral sanjuanite Al2(PO4)(SO4)(OH)•9H2O has been characterised by Raman spectroscopy complimented by infrared spectroscopy. The mineral is characterised by an intense Raman band at 984 cm-1, assigned to the (PO4)3- ν1 symmetric stretching mode. A shoulder band at 1037 cm-1 is attributed to the (SO4)2- ν1 symmetric stretching mode. Two Raman bands observed at 1102 and 1148 cm-1 are assigned to (PO4)3- and (SO4)2- ν3 antisymmetric stretching modes. Multiple bands provide evidence for the reduction in symmetry of both anions. This concept is supported by the multiple sulphate and phosphate bending modes. Raman spectroscopy shows that there are more than one non-equivalent water molecules in the sanjuanite structure. There is evidence that structural disorder exists, shown by the complex set of overlapping bands in the Raman and infrared spectra. At least two types of water are identified with different hydrogen bond strengths. The involvement of water in the sanjuanite structure is essential for the mineral stability.

Synthesis and characterisation of hybrid gold/polymer nanoparticles for bioassay application

A bioassay technique, based on surface-enhanced Raman scattering (SERS) tagged gold nanoparticles encapsulated with a biotin functionalised polymer, has been demonstrated through the spectroscopic detection of a streptavidin binding event. A methodical series of steps preceded these results: synthesis of nanoparticles which were found to give a reproducible SERS signal; design and synthesis of polymers with RAFT-functional end groups able to encapsulate the gold nanoparticle. The polymer also enabled the attachment of a biotin molecule functionalised so that it could be attached to the hybrid nanoparticle through a modular process. Finally, the demonstrations of a positive bioassay for this model construct using streptavidin/biotin binding. The synthesis of silver and gold nanoparticles was performed by using tri-sodium citrate as the reducing agent. The shape of the silver nanoparticles was quite difficult to control. Gold nanoparticles were able to be prepared in more regular shapes (spherical) and therefore gave a more consistent and reproducible SERS signal. The synthesis of gold nanoparticles with a diameter of 30 nm was the most reproducible and these were also stable over the longest periods of time. From the SERS results the optimal size of gold nanoparticles was found to be approximately 30 nm. Obtaining a consistent SERS signal with nanoparticles smaller than this was particularly difficult. Nanoparticles more than 50 nm in diameter were too large to remain suspended for longer than a day or two and formed a precipitate, rendering the solutions useless for our desired application. Gold nanoparticles dispersed in water were able to be stabilised by the addition of as-synthesised polymers dissolved in a water miscible solvent. Polymer stabilised AuNPs could not be formed from polymers synthesised by conventional free radical polymerization, i.e. polymers that did not possess a sulphur containing end-group. This indicated that the sulphur-containing functionality present within the polymers was essential for the self assembly process to occur. Polymer stabilization of the gold colloid was evidenced by a range of techniques including, visible spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and Raman spectroscopy. After treatment of the hybrid nanoparticles with a series of SERS tags, focussing on 2-quinolinethiol the SERS signals were found to have comparable signal intensity to the citrate stabilised gold nanoparticles. This finding illustrates that the stabilization process does not interfere with the ability of gold nanoparticles to act as substrates for the SERS effect. Incorporation of a biotin moiety into the hybrid nanoparticles was achieved through a =click‘ reaction between an alkyne-functionalised polymer and an azido-functionalised biotin analogue. This functionalized biotin was prepared through a 4-step synthesis from biotin. Upon exposure of the surface-bound streptavidin to biotin-functionalised polymer hybrid gold nanoparticles, then washing, a SERS signal was obtained from the 2-quinolinethiol which was attached to the gold nanoparticles (positive assay). After exposure to functionalised polymer hybrid gold nanoparticles without biotin present then washing a SERS signal was not obtained as the nanoparticles did not bind to the streptavidin (negative assay). These results illustrate the applicability of the use of SERS active functional-polymer encapsulated gold nanoparticles for bioassay application.

A profluorescent azaphenalene nitroxide for nitroxide-mediated polymerization

A novel nitroxide-mediated polymerization (NMP) control agent; 1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalen-2-yloxyl (TMAO), was used in the free-radical polymerization of styrene. The conversion of styrene during NMP was studied using FT-Raman spectroscopy and the effectiveness of TMAO as a NMP control agent was assessed by GPC analysis. Fidelity of the TMAO-alkoxyamine end-group on the synthesized polymers was confirmed by GPC, UV-Vis and fluorescence spectroscopic analyses. Comparison to the well known NMP control agent, TEMPO was made. TMAO showed control of molecular weight approaching that of TEMPO. Attempts to improve the properties of TMAO as an NMP control agent by synthesizing an analogue with bulkier substituents around the nitroxide did not generate the target molecule but demonstrated some of the interesting chemistry of the azaphenalene ring system

Are the ‘cave’ minerals archerite (K,NH4)H2PO4 and biphosphammite (K,NH4)H2PO4 identical? A molecular structural study

The molecular structure of the mineral archerite ((K,NH4)H2PO4) has been determined and compared with that of biphosphammite ((NH4,K)H2PO4). Raman spectroscopy and infrared spectroscopy has been used to characterise these ‘cave’ minerals. Both minerals originated from the Murra-el-elevyn Cave, Eucla, Western Australia. The mineral is formed by the reaction of the chemicals in bat guano with calcite substrates. Raman and infrared bands are assigned to H2PO4-, OH and NH stretching vibrations. The Raman band at 981 cm-1 is assigned to the HOP stretching vibration. Bands in the 1200 to 1800 cm-1 region are associated with NH4+ bending modes. The molecular structure of the two minerals appear to be very similar, and it is therefore concluded that the two minerals are identical.

Molecular Structure of the mineral woodhouseite CaAl3(PO4,SO4)2(OH)6

The mineral woodhouseite CaAl3(PO4,SO4)2(OH)6 is a hydroxy phosphate-sulphate mineral belonging to the beudantite subgroup of alunites, and has been characterised by Raman spectroscopy, complimented with infrared spectroscopy. Bands at various wavenumbers were assigned to the different vibrational modes of woodhouseite, which were then associated to the molecular structure of the mineral. Bands were primarily assigned to phosphate and sulphate stretching and bending modes. Two symmetric stretching modes for both phosphate and sulphate supported the concept of non-equivalent phosphate and sulphate units in the mineral structure. Bands in the OH stretching region enabled hydrogen bond distances to be calculated.

A vibrational spectroscopic study of the mineral hinsdalite (Pb,Sr)Al3(PO4)(SO4)(OH)6

The objective of this research is to determine the molecular structure of the mineral hinsdalite using vibrational spectroscopy. The mineral hinsdalite (Pb,Sr)Al3(PO4,SO4)2(OH)6 is a hydroxy phosphate-sulphate mineral belonging to the beudantite subgroup of alunites. The mineral is interesting because it contains two oxyanions, phosphate and sulphate, which is unusual. The formation of hinsdalite offers a mechanism for the removal of phosphate from the environment. The mineral has been characterised by Raman spectroscopy and infrared spectroscopy. The spectra are then related to the molecular structure of the mineral. Bands at various wavenumbers are assigned to the different vibrational modes of hinsdalite, which were then associated to the molecular structure of the mineral. Bands were primarily assigned to phosphate and sulphate stretching and bending modes. The Raman spectrum is characterised by an intense sharp band at 982 cm-1 with a component band at 997 cm-1 assigned to the ν1 (PO4)3- symmetric stretching modes. Two symmetric stretching modes for both phosphate and sulphate supported the concept of non-equivalent phosphate and sulphate units in the mineral structure. Bands in the OH stretching region enabled hydrogen bond distances to be calculated. Hinsdalite is characterised by disordered phosphate/sulphate tetrahedra and non-equivalent phosphate units are observed in the vibrational spectrum of hinsdalite.