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Various amino acids were intercalated into Mg−Al layered double hydroxides (LDHs) as interlayer anions. The goal of this approach was to create an interlayer environment that was attractive to formamide, because of hydrogen bonding, so that penetration of formamide would lead to delamination. Some of the amino acid intercalates were successfully delaminated in formamide, but others were not. The intercalates that could not be delaminated had a high amino acid content, exceeding 15−20% of the charge occupation rate. At that rate, closely packed amino acids were likely to be tightly connected to one another and to the host layers via hydrogen bonds, and therefore formamide presumably could not open or penetrate the interlayers in large volume. In contrast, there was not a clear lower threshold for charge occupation of amino acid; even LDH intercalates with charge occupations of less than 1% underwent delamination. Finally, M2+-Al LDH systems other than the Mg−Al system also underwent delamination.

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Abstract--Historically, the decarbonation of Mg-A1-CO3 hydrotalcite-like compounds (HTlc) has been thought to occur between 400* and 500"C. The present work demonstrates that when HTlcs having the maximum AI content, AU(A1 + Mg) = 0.33, are heated to 5000C, 20-30% of the carbonates remain. The evolution of the remaining carbonates was observed as two maxima, at 600 and 900~ At these temperatures, AI ions go into MgO, and spinel (MgA1204) forms. Therefore, the carbonates are released as the A1 ions migrate.At a lower A1 content, AI/(A1 + Mg) = 0.25, CO2 evolution is almost complete at 500"12. This HTlc has no maximum of CO2 evolution above 5000C. Lower charge densities, due to lower A1 contents, lead to lower amounts of remaining carbonate anions.

Calcined hydrotalcite-like compounds (HTlcs) can be reconstructed to their original structure by exposure to an aqueous solution, provided that the original HTlcs contain volatile interlayer anions. In the present study, repetitive treatment consisting of calcination at 400 °C and subsequent reconstruction in an aqueous solution was carried out for Mg-Al-CO 3 HTlcs. Gradual changes in these HTlcs during repetitions of the treatment were observed. The quantity of interlayer carbonate anions decreased as the treatment was repeated. This finding indicates that the HTlcs were not completely reconstructed and that some Al was extracted from the structure during treatments, because the quantity of interlayer anions is proportional to Al content in HTlcs. The extracted Al increased with repetitions of the treatment, and spinel (MgAl 2 O 4 ), whose Al content is much higher than HTlcs, was eventually detected after several repetitions as a consequence of segregation of the extracted Al phase. The spinel obtained by the repetitive treatments was highly crystalline and comparable to spinel obtained by calcination of Mg-Al coprecipitates above 1000 °C.

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Layered double hydroxides (LDHs) have long been thought to have low selectivity for NO 3 -. In contrast, it has recently been reported that LDHs with certain compositions show high selectivity for NO 3 -. The reason for the high selectivity has been unclear, although the ion sieve effect has been proposed as a possible mechanism. Moreover, small LDHs have been reported to show good anion exchanging ability. Given this background, a systematic study was conducted using Mg-Al LDHs with two different crystallinities. High-crystallinity LDHs with lager particle sizes clearly showed selectivity changes that de-