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Open AccessArticle

Effect of Isomorphous Substitution on the Thermal Decomposition Mechanism of Hydrotalcites

by Sergio Crosby 1,†, Doanh Tran 2,†, David Cocke 2,†, El-Shazly M. Duraia 1,3,† and Gary W. Beall 1,4,*,†
Department of Chemistry and Biochemistry, Texas State University, 601 University Drive, San Marcos, TX 78666, USA
Department of Chemical Engineering, Lamar University, 4400 South MLK, Beaumont, TX 77705, USA
Physics Department, Faculty of Science, Suez Canal University, Ismailia 41522, Egypt
Physics Department, Faculty of Science, King Abdulaziz University, Jeddah, 21589, Saudi Arabia
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Materials 2014, 7(10), 7048-7058;
Received: 17 July 2014 / Revised: 1 September 2014 / Accepted: 22 September 2014 / Published: 17 October 2014
Hydrotalcites have many important applications in catalysis, wastewater treatment, gene delivery and polymer stabilization, all depending on preparation history and treatment scenarios. In catalysis and polymer stabilization, thermal decomposition is of great importance. Hydrotalcites form easily with atmospheric carbon dioxide and often interfere with the study of other anion containing systems, particularly if formed at room temperature. The dehydroxylation and decomposition of carbonate occurs simultaneously, making it difficult to distinguish the dehydroxylation mechanisms directly. To date, the majority of work on understanding the decomposition mechanism has utilized hydrotalcite precipitated at room temperature. In this study, evolved gas analysis combined with thermal analysis has been used to show that CO2 contamination is problematic in materials being formed at RT that are poorly crystalline. This has led to some dispute as to the nature of the dehydroxylation mechanism. In this paper, data for the thermal decomposition of the chloride form of hydrotalcite are reported. In addition, carbonate-free hydrotalcites have been synthesized with different charge densities and at different growth temperatures. This combination of parameters has allowed a better understanding of the mechanism of dehydroxylation and the role that isomorphous substitution plays in these mechanisms to be delineated. In addition, the effect of anion type on thermal stability is also reported. A stepwise dehydroxylation model is proposed that is mediated by the level of aluminum substitution. View Full-Text
Keywords: hydrotalcite; thermal decomposition; dehydroxylation; charge density; isomorphous substitution hydrotalcite; thermal decomposition; dehydroxylation; charge density; isomorphous substitution
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Crosby, S.; Tran, D.; Cocke, D.; Duraia, E.-S.M.; Beall, G.W. Effect of Isomorphous Substitution on the Thermal Decomposition Mechanism of Hydrotalcites. Materials 2014, 7, 7048-7058.

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