Synthesis and characterisation of layered double hydroxides and their application for water purification

Layered doubly hydroxides (LDHs) also known as hydrotalcites or anionic clays are a group of clay minerals that have shown promise for the removal of toxic anions from water through both anion exchange and a process known as the reformation effect. This project has involved the preparation and characterisation of LDH materials as well as the investigation of their ability to remove selected anions from aqueous solutions by the reformation effect. The LDH materials were successfully prepared from magnesium, aluminium, zinc and chromium chloride salts using the co-precipitation method. Samples were characterised using powder X-ray diffraction (XRD) and thermogravimetry (TG) to confirm the presence of LDHs. Powder XRD revealed a characteristic LDH structure for all LDH samples. Thermal Analysis showed decomposition usual occurred through a three or four step process as expected for LDHs. Preliminary investigations of the removal of sulfate, nitrate and fluoride by an Mg/Al LDH were carried out, and the products were characterised using XRD and TG which showed that an LDH material similar to the original hydrotalcite was formed after reformation. A Zn/Al LDH was investigated as a potential sorbent material for the removal of iodine and iodide from water. It was found that the LDH was a suitable adsorbent which is able to remove almost all of the iodine present in the test solutions. Again, the products were characterised by XRD, TG and evolved gas mass spectrometry (EGMS) in an attempt to better understand the iodine removal process. Powder XRD showed successful reformation of the LDH structure and TG/EGMS showed that only a small amount of iodine species were lost during thermal decomposition. Finally, the mineral stichtite a Mg/Cr LDH was successfully synthesised and investigated using XRD, TG and EGMS. Unfortunately, due to lack of time it was not possible to identify any new uses for the mineral stichtite in the current project

Removal of iodine using LDH technology

This project has investigated the removal of iodine species from wastewater using LDH technology. This research focused on initial laboratory scale experiments to assess the suitability of this methodology as a cost effective means of treating water contaminated with radioiodine from industrial and medical wastes

Removal of boron species by layered double hydroxides : a review

Boron, which is an essential element for plants, is toxic to humans and animals at high concentrations.\ud Layered double hydroxides (LDHs) and thermally activated LDHs have shown good uptake of a range of boron species in laboratory scale experiments when compared to current available methods, which are for the most part ineffective or prohibitively expensive. LDHs were able to remove anions from water by anion exchange, the reformation (or memory) effect and direct precipitation. The main mechanism of\ud boron uptake appeared to be anion exchange, which was confirmed by powder X-ray diffraction (XRD)\ud measurements. Solution pH appeared to have little effect on boron sorption while thermal activation did not always significantly improve boron uptake. In addition, perpetration of numerous LDHs with varying boron anions in the interlayer region by direct co-precipitation and anion exchange have been reported by a number of groups. The composition and orientation of the interlayer boron ions could be identified with reasonable certainty by applying a number of characterisation techniques including: powder\ud XRD, nuclear magnetic resonance spectroscopy (NMR), X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy. There is still considerable scope for future research on the application of LDHs for the removal of boron contaminants

Thermogravimetric analysis of selected layered double hydroxides

Thermogravimetric analysis (TG) and powder X-ray diffraction (PXRD) were used to study some selected\ud Mg/Al and Zn/Al layered double hydroxides (LDHs)\ud prepared by co-precipitation. A Mg/Al hydrotalcite was\ud investigated before and after reformation in fluoride and\ud nitrate solutions. Little change in the TG or PXRD patterns\ud was observed. It was proposed that successful intercalation\ud of nitrate anions has occurred. However, the absence of any\ud change in the d(003) interlayer spacing suggests that fluoride anions were not intercalated between the LDH layers. Any fluoride anions that were removed from solution are most likely adsorbed onto the outer surfaces of the hydrotalcite. As fluoride removal was not quantified it is not possible to confirm that this has happened without further experimentation. Carbonate is probably intercalated into the interlayer of these hydrotalcites, as well as fluoride or nitrate. The carbonate most likely originates from either incomplete decarbonation during thermal activation or adsorption from the atmosphere or dissolved in the deionised water. Small and large scale co-precipitation syntheses of a Zn/Al LDH were also investigated to determine if there was any change in the product. While the small scale experiment produced a good quality LDH of reasonable purity; the large scale synthesis resulted in several additional phases. Imprecise measurement and difficulty in handling the large quantities of reagents appeared to be sufficient to alter the reaction conditions causing a mixture of phases to be formed

Label-free identification of Erythropoietin isoforms by surface enhanced Raman spectroscopy

We present a sensitive label-free surface enhanced Raman spectroscopy (SERS) method for the discrimination between the recombinant and endogenous human Erythropoietin (EPO) isoforms. The proposed methodology comprises a lectin-functionalised extractor chip for the extraction of the recombinant human EPO (rhuEPO) and the endogenous EPO (enEPO) from blood plasma. The disulfide bond molecular structure of the purified isoforms was modified to chemisorb the biomolecules onto a SERS substrate in a unified orientation, thus maximizing the reproducibility and sensitivity of the SERS measurements. The acquired SERS spectra of the EPO isoforms showed diagnostic Raman bands that allowed for the discrimination between rhuEPO and enEPO. The method was also used for the SERS quantification of rhuEPO and enEPO down to 0.1 pM and 0.5 pM, respectively. The SERS determination of the protein isoforms was cross validated against ELISA. The new SERS method has strong potential for the rapid screening of rhuEPO doping in athletes and for the therapeutic drug monitoring of rhuEPO treatment in cancer patients.</p

Iodide removal using LDH technology

The presence of radioactive iodine (radioiodine) in drinking water is a significant health hazard that originates from nuclear medicine and atomic energy industries. The application of LDHs to the removal of iodine offers potential for iodine capture and entrapment. Mg/Al and Zn/Al layered double hydroxides (LDHs) have been prepared and have been evaluated for the sorption of iodide in some small-scale batch experiments. All LDHs were prepared by the co-precipitation method and characterised by a range of techniques including powder X-ray diffraction, transmission electron microscopy and elemental analysis. Adsorption experiments were carried out at high iodide concentrations up to 1000 ppm and no control or pH or atmospheric carbonate commonly used in most studies. The highest iodide uptake of approximately 71% was observed using a 3:1 Zn/Al LDH thermally activated to 500 °C, however, a 3:1 Mg/Al LDH exhibited similar results. LDHs potentially offer a technology for the removal of iodine from aqueous media

Leaching of iodide (I−) and iodate (IO3−) anions from synthetic layered double hydroxide materials

Several studies have previously demonstrated that layered double hydroxides (LDHs) show considerable potential for the adsorption of radioiodine from aqueous solution; however, few studies have demonstrated that these materials are able to store radioactive I-131 for an acceptable period. The leaching of iodide (I-) and iodate (IO3-) form Mg/Al LDHs has been carried out. Contact time appeared to be a more significant variable for the leaching of iodate (IO3-) compared to that of iodide (I-). Experimental results are fitted to the pseudo second order model, suggesting that diffusion is likely to be the rate-limiting step. The presence of carbonate in the leaching solution appeared to significantly increase the leaching of iodide (I-) as did the presence of chloride to a lesser extent. The maximum amount of iodate (IO3-) leached using ultrapure water as the leaching solution was 21% of the iodate (IO3-) originally present. The corresponding result for iodide (I-) was even lower at 3%. (C) 2016 Elsevier Inc. All rights reserved

Vibrational spectroscopic study of the sulphate mineral glaucocerinite (Zn,Cu)10Al6(SO4)3(OH)32⋅18H2O – a natural layered double hydroxide

We have studied the molecular structure of the mineral glaucocerinite (Zn,Cu)5Al3(SO4)1.5(OH)16�9(H2O) using a combination of Raman and infrared spectroscopy. The mineral is one of the hydrotalcite supergroup of natural layered double hydroxides. The Raman spectrum is characterised by an intense Raman band at 982 cm�1 with a low intensity band at 1083 cm�1. These bands are attributed to the sulphate symmetric and antisymmetric stretching mode. The infrared spectrum is quite broad with a peak at 1020 cm�1. A series of Raman bands at 546, 584, 602, 625 and 651 cm�1 are assigned to the m4 (SO4)2� bending modes. The observation of multiple bands provides evidence for the reduction in symmetry of the sulphate anion from Td to C2v or even lower symmetry. The Raman band at 762 cm�1 is attributed to a hydroxyl deformation mode associated with AlOH units. Vibrational spectroscopy enables aspects of the molecular structure of glaucocerinite to be determined

A vibrational spectroscopic study of the silicate mineral pectolite – NaCa2Si3O8(OH)

The mineral pectolite NaCa2Si3O8(OH) is a crystalline sodium calcium silicate which has the potential to be used in plaster boards and in other industrial applications.\ud \ud Raman bands at 974 and 1026 cm−1 are assigned to the SiO stretching vibrations of linked units of Si3O8 units. Raman bands at 974 and 998 cm−1 serve to identify Si3O8 units. The broad Raman band at around 936 cm−1 is attributed to hydroxyl deformation modes. Intense Raman band at 653 cm−1 is assigned to OSiO bending vibration. Intense Raman bands in the 2700–3000 cm−1 spectral range are assigned to OH stretching vibrations of the OH units in pectolite. Infrared spectra are in harmony with the Raman spectra. Raman spectroscopy with complimentary infrared spectroscopy enables the characterisation of the silicate mineral pectolite