Intercalation behavior of L-ascorbic acid into layered double hydroxides

The intercalation Of L-ascorbic acid (ASA) into three kinds of layered double hydroxides, such as Mg-Al, Mg-Fe and Zn-Al LDHs, has quantitatively been investigated by the calcination-rehydration (reconstruction) and coprecipitation methods. The amount of ASA intercalated was considerably different by the LDH systems that was estimated to be ca. 0.40 mol/mol-M3+ for the Mg-Al and Mg-Fe systems by the reconstruction method. The Zn-Al system was hardly restored to the LDH structure by the rehydration reaction with the intercalation of ASA. ASA was also intercalated into the Mg-Al and Zn-Al LDHs by the coprecipitation method, while the intercalation of NO3- was observed in the Mg-Fe LDH. The basal spacing of the solid products were expanded to d(003)=0.84 (Mg-Al) and 0.86 (Mg-Fe) nm by the reconstruction method, 0.97 (Mg-Al) and 1.06 (Zn-Al) nm by the coprecipitation method, respectively, suggesting that ASA was intercalated into the LDHs. A large fraction of ASA was intercalated as reduced form after the light and heat resistance tests of the ASA/LDHs. This result confirmed that ASA was stabilized by the intercalation of the LDHs interlayer space. Furthermore, the intercalated ASA was easily deintercalated from the LDH interlayer space by the ion exchange method using CO32-. It is expected that LDHs will be good host materials for safe storage of vitamins. (C) 2006 Elsevier B.V. All rights reserved.