Mónika Sipiczki

Synthesis and properties of CaAl-layered double hydroxides of hydrocalumite-type

CaAl-layered double hydroxides (CaAl-LDHs) with various carbonate ion contents are essentially formed in Bayer liquors during the causticisation step in alumina production. Under well-defined conditions hemicarbonate is formed, which is beneficial in the process of retrieving both Al(OH)4− and OH− ions. In the current work, Ca2Al-LDHs with various carbonate contents were prepared by the co-precipitation procedure and the products were dried in different ways. Structural information was obtained by a variety of methods, such as X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Elemental maps were constructed through a combination of SEM images and EDX measurements. The targeted CaAl-hydrocalumites were successfully synthesised. It was found that the method used for drying did not influence the basal spacing although it significantly altered the particle sizes.

Synthesis and characterisation of alkaline earth-iron(III) double hydroxides

Double hydroxides containing alkaline earth and iron(III) ions were synthesised by the co-precipitation method. The solid materials obtained were characterised by a range of instrumental methods (powder X-ray diffractometry, thermogravimetry, scanning electron microscopy, energy dispersive X-ray fluorescence spectrometry, elemental maps, and infrared spectroscopy). It was found that the Ca(II)Fe(III), Mg(II)Fe(III), and Ba(II)Fe(III) double hydroxides had layered structures, while Sr(II)Fe(III) had not. The optimum conditions for synthesis of Ca(II)Fe(III)-layered double hydroxides (materials to be used in further studies) were also elaborated.

Water Types and Their Relaxation Behavior in Partially Rehydrated CaFe-Mixed Binary Oxide Obtained from CaFe-Layered Double Hydroxide in the 155–298 K Temperature Range

Heat-treated CaFe-layered double hydroxide samples were equilibrated under conditions of various relative humidities (11%, 43% and 75%). Measurements by FT-IR and dielectric relaxation spectroscopies revealed that partial to full reconstruction of the layered structure took place. Water types taking part in the reconstruction process were identified via dielectric relaxation measurements either at 298 K or on the flash-cooled (to 155 K) samples. The dynamics of water molecules at the various positions was also studied by this method, allowing the flash-cooled samples to warm up to 298 K.

Preparation, Characterisation and Some Reactions of Organocatalysts Immobilised Between the Layers of a CaFe-Layered Double Hydroxide

Five- and six-membered cyclic α-amino acid anions with secondary nitrogen in the ring (l-prolinate and dl-pipecolinate) were immobilised in Ca3Fe-L(ayered)D(ouble)H(ydroxide) by the dehydration-rehydration method. The resulting organic–inorganic hybrids were characterised by various instrumental methods (powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray fluorescence with elemental mapping, and analytical techniques for determining the iron as well as the organic contents) and molecular modelling. The immobilised organocatalysts were tested in the cross-aldol dimerization-condensation reaction between benzaldehyde and acetone and found to be active and enantioselectivity in the dimerization was also observed.

Carbon nanotube-layered double hydroxide nanocomposites

Preparation of multiwalled carbon nanotube-layered double hydroxide (MWCNT-LDH) nano-composites by (i) the co-precipitation of LDH components and pristine or surface-treated MWCNT or (ii) the delamination of LDH and application of the layer-by-layer technique has been attempted. For MWCNT, two types of surface treatment were used, either the surface was hydroxylated and deprotonated or wrapped in a tenside (dodecylbenzenesulfonate, DBS). LDH was delaminated by N,N-dimethylformamide. The obtained materials were characterized by X-ray diffractometry (XRD), and by scanning and transmission electron microscopies (SEM and TEM). Element distribution was mapped with help of the X-ray energy dispersive spectroscopy (XEDS) available as an extension of the scanning electron microscope. MWCNT could not be sandwiched between the layers of LDH by any of the methods employed; however, tenside-treated bundles of MWCNT could be wrapped in LDH thus forming a nanocomposite.