Dynamics of inter- and de-intercalation of fluorescent probes and mechanisms of polymorphic transformations in a class of layered double hydroxides -

Abstract

We present a new method for the synthesis of layered double hydroxides (LHDs) based on a reaction-diffusion framework, which consists of diffusing two initially separated co-precipitates into a gel matrix. The obtained precipitates are characterized by numerous techniques such as XRD, TGA, DSC, EDX, ssNMR, Raman, FT-IR and elemental mapping. This novel method is also adapted to study the kinetics of intercalation and de-intercalation of some anionic and cationic fluorescent probes, such as Rhodamine B and HPTS, using in situ steady state fluorescence. The activation energies of intercalation-de-intercalation of the dyes are computed. Moreover, the incorporation of these dyes into the cavities of the LDHs and their expulsion from their interlayer region is confirmed via XRD, fluorescence microscopy and ssNMR. Furthermore, we report the synthesis and self-assembly of CdAlA-HT. This hydrotalcite assumes a flowery-like shaped microstructure. Electron tomography performed on these microstructures reveals an interior structure consisting of many individual and connected nano-sheets resulting in voids and channels. On the other hand, we are able to shed light, using SEM and elemental mapping, on the mechanism of the polymorphic transformation of this cadmium-aluminum LDH to the brucite-like β-Cd(OH)2, whereby the flowery-like LDH dissolves, expels the aluminum cations from the crystal lattice and reappears in the form of nano-spheres of the brucite compound. Finally, we show that this novel LDH can have two potential applications: the photo-degradation of organic compounds (polysaccharide mixture) and the photo-reduction of CO2 in the gas phase, both under visible light.