Thermal analysis of MgFe-Cl Layered doubled hydroxide (LDH) directly synthetized and produced “via memory effect”

Abstract

Abstract Layered doubled hydroxides (LDHs) are known to be an interesting class of 2D layered materials, with a wide range of possible composition and a flexible structure suitable for topochemical reactions. Thus, LDHs have been applying in different fields, such as catalysis, energy storage and all the applications in which a high exchange capability (of both cations and anions) is required. For remediation purpose, a MgFe-Cl LDH $${[({\mathrm{Mg}}_{0.66}^{2+}{\mathrm{Fe}}_{0.33}^{3+}{\left(\mathrm{OH}\right)}_{2}]}^{0.33+}{({\mathrm{Cl}}_{0.33}^{-})}^{0.33-}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mo>[</mml:mo> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>Mg</mml:mi> <mml:mrow> <mml:mn>0.66</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> <mml:msubsup> <mml:mi>Fe</mml:mi> <mml:mrow> <mml:mn>0.33</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> <mml:msub> <mml:mfenced> <mml:mi>OH</mml:mi> </mml:mfenced> <mml:mn>2</mml:mn> </mml:msub> <mml:mo>]</mml:mo> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mn>0.33</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mo>(</mml:mo> <mml:msubsup> <mml:mi>Cl</mml:mi> <mml:mrow> <mml:mn>0.33</mml:mn> </mml:mrow> <mml:mo>-</mml:mo> </mml:msubsup> <mml:mo>)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>0.33</mml:mn> <mml:mo>-</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> (MFC in the following) could be a promising candidate to capture the toxic CrO 4 2− from water, in exchange with the Cl − in an efficient way. The synthesis of this compound might seem simple, consisting of a coprecipitation reaction, and actually, it is strongly affected by the environmental carbon dioxide able to replace the Cl − with the more stable CO 3 2− . To avoid this problem, LDHs could be also prepared with a rehydration of their calcinated oxide (memory effect). In this work were prepared two samples of MFC: one via coprecipitation (MFC-1 in the following) and one via “memory effect” (MFC-mem in the following). Both the compounds were characterized by means of X-ray powder diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR) and differential thermal analysis-thermogravimetry (DTA-TG) coupled with evolved gas analysis. The results demonstrated that the synthesis of pure MFC is very difficult, and only a minimum contamination of carbon dioxide led to the formation of the carbonate LDH in a massive way. It was also demonstrated that Mg-Fe LDHs in the presence of carbonate could catalyse the formation of the formic acid (HCOOH) at low temperature (&lt; 300 °C).

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