Dendrimer intercalation in layered double hydroxides

Abstract

New organic/inorganic (O/I) hybrid assemblies based on Layered Double Hydroxide (LDH) with polyamide amine dendrimer (PAMAM, generation −0.5 and generation +0.5) were prepared by two different routes using either the direct coprecipitation at constant pH or the anion exchange procedure in double surfactant S+S− phases. The obtained materials were characterized by means of powder X-ray diffraction, thermal gravimetric analysis associated with mass spectrometry, and Fourier-transform infrared spectroscopy. X-ray powder diffraction pattern of the O/I LDH assembly exhibit characteristic profiles of LDH-based materials with basal spacing depending on the nature of the dendrimer. Indeed, for both synthetic procedures, interleaved PAMAM −0.5 gives rise to an interlayer space in agreement with a perpendicular molecular arrangement against the layer of the host structure. For PAMAM+0.5, considering its spherical dimension, a much smaller basal spacing was observed. This observation was interpreted as shrinkage of the molecule to accommodate the interlayer LDH gap, which was rendered possible by the bond angle twisting within PAMAM−0.5. FTIR spectra confirm the presence of both moieties inside both Zn2Al/PAMAM G−0.5 and Zn2Al/PAMAM G+0.5 assemblies. Finally, thermal analysis associated with mass spectrometry confirm this composition, and in situ temperature XRD data reveal that the highly constrained arrangement for the generation +0.5 is not accompanied by a gain in thermal structural stability; in fact, the assembly prepared from PAMAM −0.5 is more stable. Both O/I PAMAM LDH assemblies constitute well-defined materials which are candidate for catalytic applications.