Thermal and spectroscopic studies on the decomposition of [Ni{di(2-aminoethyl)amine}2]- and [Ni(2,2′:6′,2′′-terpyridine)2]-Montmorillonite intercalated composites
Introduction
Incorporation of organic or inorganic cationic compounds into layered structures like Montmorillonite (Mnt) clay can result in microporous materials having definite gallery height depending upon the size and shape of the cations [1], [2], [3], [4], [5], [6], [7], [8]. Organic cations like tetraalkylammonium ions are intercalated into smectites during the preparation of chromatographic materials for separation of mixtures of gases [9], [10], [11], [12], [13]. But the organo-Mnt clay composites, in general, exhibit limited thermal stability due to decomposition of the organic moiety at comparatively low temperature (<200°C) [14] and hence these composites may not be useful in systems where a comparatively higher temperature (>200°C) is involved. On the other hand, metal complexes containing suitable organic ligands exhibit comparatively higher thermal stability which is further enhanced upon intercalation into Mnt [15], [16], [17]. Therefore, suitable metal complexes may be superior to cationic organic molecules as intercalating species in developing microporous Mnt clay composites with higher thermal stability. The aim of the present work is to investigate the intercalation of two bulky three-dimensional cationic metal-complexes, i.e., [Ni(den)2]Cl2 and [Ni(tpy)2](ClO4)2 (where den=di(2-aminoethyl) amine and tpy=2,2′:6′,2′′-terpyridine) with Na-Mnt and to evaluate the thermal stability of the intercalated products by thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analysis (DTA) supplemented by X-ray diffraction (XRD) and infrared (IR) spectroscopy.
Section snippets
Materials and methods
Montmorillonite clay, collected from M/S Neelkanth Sodaclays and Pulverisers, Jodhpur, India, contained silica sand, iron oxide etc. as impurities, and was purified by the sedimentation method [18]. The <2 μm fraction was collected. The oxide composition of the clay was SiO2: 49.42; Al2O3: 20.02; Fe2O3: 7.43; TiO2: 1.55; CaO: 0.69; MgO: 2.82; Na2O: 0.09; LOI: 17.91 and others 0.07%. The clay was converted to the Na-exchanged form by stirring in 2 M NaCl solution for about 78 h and then washed and
DTA, TG and DTG studies
The DTA–TG–DTG curves of Na- and Ni-Mnt are shown in Fig. 1. Na- and Ni-Mnt each shows the first and second endothermic peaks in the DTA curve in the temperature ranges 50–150°C and 480–520°C. These correspond to dehydration from the interlayer water and dehydroxylation of the clay, respectively. The TG and DTG curves show two mass loss stages. In the first stage up to about 150°C, Na- and Ni-Mnt show mass loss of about 14 and 17%, respectively, and correspond to loss of water from the
Conclusions
Thermal stability of the intercalated [Ni{Di(2-aminoethyl)amine}2]-Montmorillonite (I) and [Ni(2,2′:6′,2′′terpyridine)2]-Montmorillonite (II) composites, studied by thermal(TG, DTA, DTG) analyses substantiated by XRD and IR spectroscopy, are about 50 and 150°C higher compared to melting/decomposition of their respective free metal complex salts. Metal complex with aromatic backboned ligands gets higher thermal stability than that containing aliphatic one upon intercalation into Mnt and this may
Acknowledgements
The authors are grateful to the Director, RRL Jorhat, for encouragement and permission to publish the paper. Thanks are also due to Dr. P.C. Borthakur, Head, Material Science Division, RRL Jorhat, for his keen interest and support. The authors also thank Prof. A.T. Baker, University of Technology, Sydney, Australia, for providing the metal-complex and crystallographic data.
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