Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 114, Issue 24, Pages 10768-10774Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp103115q
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Funding
- National Nature Science Foundation of China [20477024, 20677037, 20877053]
- key subject of Shanghai Municipality [S30109]
- ARC Centre of Excellence for Functional Nanomaterials
- Australia Research Council under its Centre of Excellence Scheme
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We reinvestigated dehydration and dehydroxylation of hydrotalcite and four other hydrotalcite-like compounds (HTlcs) with the combined thermogravimetry/differential thermal analysis/mass spectrometry (TG-DTA-MS) technique. The observations indicate that HTlcs undergo dehydration first and then dehydroxylation, followed by or overlapping with decomposition of interlayer anions. The detail deconvolution of MS curves of m/z = 18 reveals that both dehydration and dehydroxylation occurs in two consecutive steps. Dehydration of crystalline water molecules starts on the surface and edge in the first step, and then continues to the interlayer water. Both steps are influenced by the nature of the interlayer anions and layer cations. For the first time, we have assigned two dehydroxylation steps to two types of hydroxyl groups in the HT lattice, i.e. OH (M(II)(3)) and OH (M(II)(2)M(III)). The thermal stability of these two hydroxyl groups is principally determined by the nature of the cations. According to this research, the thermal stability of hydroxyl groups in HTlcs is OH-(Ca-3) (similar to 480 degrees C) > OH (Mg2Al) (similar to 410 degrees C) > OH (Mg2Fe) (similar to 350 degrees C) approximate to OH-(Mg-3) (300-370 degrees C) approximate to OH (Ca2Al) (similar to 330 degrees C) approximate to OH-(Ca2Fe) (similar to 290 degrees C) at a ramping rate of 2 degrees C/min.
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