New Antimony Substituted Mg-Al Layered Double Hydroxides
Abstract:No antimony hydroxide has been previously reported not only in solid state but also in aqueous solution, surely due to the fact that the formation of antimony oxide, Sb2O3, is thermodynamically more favorable than that of the hydroxide phase, Sb(OH)3. According to the pH dependent solubility diagram of Sb2O3, antimony (III) hydroxide may not exist as a definite compound but be proposed as a hydrated monomeric molecular species, Sb(OH)3(aq), which is in equilibrium with Sb2O3, under a condition of very small ionic strength. This is probably the reason why no Sb3+-containing layered double hydroxide, LDH, has been reported as yet. In the present study, an attempt has been made to prepare new Sb3+-LDH by substituting the Al3+ in octahedral site partially with Sb3+ upto approximately 10%. From the X-ray diffraction analysis, we found that the lattice constants (a = 3.075 Å, c = 23.788 Å) of the pristine, Mg-Al LDH, increased gradually upto those (a = 3.087 Å, c = 24.167 Å) of Sb-LDH (8%-substituted). Beyond 10%, the Sb substitution does not lead to any further increases of lattice constants but the impurity Sb2O3 phase is formed. It is, therefore, concluded that the solubility limit of Sb3+ in LDH would be around 10%. In addition, we were able to determine the chemical formula of Sb-substituted LDHs as follows, Mg4Al1−xSbxOH10(CO3)1/2·H2O(x = 0∼0.08) on the basis of energy dispersive X-ray spectroscopy.
Document Type: Research Article
Publication date: October 1, 2008
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