Anion Exchange Reaction Potentials as Approximate Estimates of the Relative Thermodynamic Stabilities of Mg/Al Layered Double Hydroxides Containing Different Anions

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• 作者：Belavalli E. Prasad ; P. Vishnu Kamath ; K. Vijayamohanan
• 刊名：Langmuir
• 出版年：2011
• 出版时间：November 15, 2011
• 年：2011
• 卷：27
• 期：22
• 页码：13539-13543
• 全文大小：766K
• 年卷期：v.27,no.22(November 15, 2011)
• ISSN：1520-5827

文摘

Coatings of hydrotalcite-like nitrate-intercalated Mg/Al layered double hydroxides are electrochemically deposited on a Pt electrode by electrogeneration of base by reduction of a mixed metal nitrate aqueous solution. As-prepared coatings are stable to workup and function as rugged electrodes. The voltammetric response generated by anion exchange of intercalated nitrate for dissolved anions from solution under equilibrium conditions is employed to estimate the thermodynamic stabilities of the Mg/Al layered double hydroxides comprising different anions relative to the nitrate-containing phase. Among monovalent anions, the most stable is the fluoride-containing LDH (螖G掳 = 鈭?8.7 kJ molp>鈥?p>) relative to the nitrate-containing LDH. The stability in aqueous phase decreases as Fp>鈥?/sup> > Clp>鈥?/sup> > Brp>鈥?/sup> > NO₂p>鈥?/sup> > NO₃p>鈥?/sup>, whereas, among divalent anions, SO₄p>2鈥?/sup> (螖G掳 = 鈭?.7 kJ molp>鈥?p>) > CO₃p>2鈥?/sup> (螖G掳 = 14.3 kJ molp>鈥?p>). The results of monovalent ions match well with the Miyata series, whereas the divalent anion series is at variance with the commonly held belief that carbonate-LDHs are more stable than sulfate-LDHs.