Abstract
We studied the kinetics of intercalation of a fluorescent probe (rhodamine B (RhB)) during the formation of hierarchal microspheres of cadmium-aluminum layered double hydroxide (CdAlA LDH) and its de-intercalation upon transformation from the LDH phase into the cadmium hydroxide beta phase (Cd(OH)(2)) using a reaction-diffusion framework (RDF) where the hydroxide anions diffuse into an agar gel matrix containing the proper salts-fluorescent probe mixture. In this framework, we achieved the stabilization of the CdAlA LDH, which is known to be thermodynamically unstable and transforms into Cd(OH)(2) and Al(OH)(3) in a short period. RDF is advantageous as it allows with ease the extraction of the cosynthesized polymorphs and their characterization using X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), solid-state nuclear magnetic resonance (SSNMR), Fourier transform infrared (FT-IR), and energy dispersive X-ray (EDX). The kinetics of inter/de-intercalation is studied using in situ steady-state fluorescence measurements. The existence of RhB between the LDH layers and its expel during the transition into the beta phase are examined via fluorescence microscopy, XRD, and SSNMR. The activation energies of intercalation and de-intercalation of RhB are determined and show dependence on the cationic ratio of the corresponding LDH. We find that the energies of de-intercalation are systematically higher than those of intercalation, indicating that the dyes are stabilized due to the probe-brucite sheets interactions. SSNMR is used to shed light on the mechanism of intercalation and stabilization of RhB inside the layers of the LDH.