Reversible intercalation of ammonia molecules into a layered double hydroxide structure without exchanging nitrate counter-ions

A zinc/aluminum LDH was precipitated with recycled ammonia from a chemical vapor deposition reaction. The LDH presented a crystalline phase with basal distance of 8.9 angstrom, typical for nitrate-containing LDHs, and another phase with a basal distance of 13.9 angstrom. Thermal treatment at 150 degrees C eliminated the phase with the bigger basal distance leaving only the anhydrous nitrate-intercalated LDH structure with 8.9 angstrom. Intense N-H stretching modes in the FTIR spectra suggested that the expansion was due to intercalation of ammonia in the form of [NH(4)(NH(3))(n)](+) species. When additional samples were precipitated with pure ammonia, the conventional LDH nitrate structure was obtained (8.9 angstrom basal distance) at pH = 7, as well as a pure crystalline phase with 13.9 angstrom basal distance at pH = 10 due to ammonia intercalation that can be removed by heating at 150 degrees C or by stirring in acetone, confirming a unusual sensu stricto intercalation process into a LDH without exchanging nitrate ions. (C) 2010 Elsevier Inc. All rights reserved.