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

Abstract 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 A, typical for nitrate-containing LDHs, and another phase with a basal distance of 13.9 A. Thermal treatment at 150 °C eliminated the phase with the bigger basal distance leaving only the anhydrous nitrate-intercalated LDH structure with 8.9 A. Intense N–H stretching modes in the FTIR spectra suggested that the expansion was due to intercalation of ammonia in the form of [NH4(NH3)n]+ species. When additional samples were precipitated with pure ammonia, the conventional LDH nitrate structure was obtained (8.9 A basal distance) at pH=7, as well as a pure crystalline phase with 13.9 A basal distance at pH=10 due to ammonia intercalation that can be removed by heating at 150 °C or by stirring in acetone, confirming a unusual sensu stricto intercalation process into a LDH without exchanging nitrate ions.