The dynamic process in the formation of Tyr/LDH nanohybrids

The dynamic intercalation process of tyrosine (Tyr) into layered double hydroxide (LDHs) by co-precipitation method was investigated by powder X-ray diffractometry, Fourier transform infrared spectroscopy, specific surface area measurements, pore size distributions as well as thermal analysis. The nanohybrids were found to have an expanded layered structure indicating that amino acid anions were intercalated into the gallery space. Two kinds of arrangements such as mono- or bilayers of the tyrosinate anions could be deduced from the XRD patterns. The arrangement changed from monolayer to bilayer, then again to monolayer with increasing aging time of the synthesis solution. The diffraction intensity increased then decreased with aging time, because of the variation in the orientation and ordering of the particles. TG analysis and the varying M2+/M-3+ results revealed that the amount of tyrosinate anions in the gallery first decreased then increased with the increase of aging time. In addition, the morphology results showed that the degree of ordering also increased then decreased with aging time. On all accounts, the intercalation of the tyrosinate anions was a typical dynamic process. At the beginning numerous biomolecules entered the gallery space, giving rise to increased basal spacings and BET surface areas. Later the increase of aging time led to the escape of amino acid anions from the gallery space, hence to the decrease of basal spacing and surface areas. (c) 2006 Elsevier B.V. All rights reserved.