Effect of Fe 3+ ions present in the structure of poly(acrylic acid)/montmorillonite composites on their thermal decompos
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Effect of Fe3+ ions present in the structure of poly(acrylic acid)/ montmorillonite composites on their thermal decomposition Piotr Natkan´ski • Piotr Kus´trowski Anna Białas • Janusz Surman
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Received: 16 October 2012 / Accepted: 26 April 2013 / Published online: 21 May 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract Poly(acrylic acid)/montmorillonite (MMT) composites with various polymer contents were synthesized by in situ polymerization technique. The structure of obtained materials was characterized by powder X-ray diffraction and infrared spectroscopy (FTIR). It was found that only a limited amount of hydrogel could be introduced between the clay layers. The remaining part of polymer was deposited on the external surface of clay particles. The introduction of the polymer modifier significantly increased the adsorption capacity of MMT in the elimination of Fe3? ions from aqueous solution. The thermal behavior of the samples before and after the Fe3? adsorption was examined by thermogravimetry and differential thermal analysis. Moreover, the composition of gaseous products evolved during decomposition was determined by FTIR. The materials after Fe3? adsorption exhibited different thermal stability in oxidizing atmosphere than the fresh samples. Fe3? cations, forming FeOx species during thermal treatment, appeared to be effective catalysts of polymer oxidation. Keywords Polymer–clay composites Montmorillonite Cation adsorption Thermal stability
Introduction Modification of clay structure has attracted great attention due to the possibility of obtaining promising materials to new applications. Various materials based on clay minerals, are extensively used in many fields of life and industry as P. Natkan´ski P. Kus´trowski (&) A. Białas J. Surman Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krako´w, Poland e-mail: [email protected]
nanocomposite fillers, thickeners in paints, oil-base drilling mud, adsorbents of heavy metals, and organic pollutants as well as catalysts (e.g., for Fischer–Tropsch synthesis, catalytic cracking, Friedel–Crafts reaction, combustion of volatile organic compounds, oxidation of H2S) [1–10]. One of the most often investigated and abundant layered aluminosilicate is montmorillonite (MMT), belonging to the smectite group. In the MMT structure, the sheet containing Al3? in octahedral coordination with O2- and OHions is sandwiched between two sheets with Si4? in tetrahedral coordination with O2- ions. The layers are interconnected by sharing O2- at polyhedral corners and edges [11]. The partial substitution of Al3? cations by lower valency ions (mainly Mg2?) leads to the generation of negative charge on the clay layers, which is neutralized by hydrated, exchangeable cations (e.g., Ca2?, Mg2?, Na?, K?) located in the interlayer spaces. Such a structure causes that the interlamellar space of the natural clay can be functionalized through the replacement of interlayer ions by other species, for instan
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