Hybrid materials based on a layered zinc hydroxide solid and gallic acid: Structural characterization and evaluation of the controlled release behavior as a function of the gallic acid content

摘要

The formation of hybrid compounds from gallic acid immobilized into a layered zinc hydroxide is reported. Elemental analysis, X-Ray diffraction, X-ray thermo-diffraction analysis, FT-IR spectroscopy, scanning electron microscopy, and X-Ray photoelectron spectroscopy allowed to identify clear differences between the hybrid materials obtained depending on the gallate anion content within the inorganic matrix. The elemental analysis showed a reduction in the zinc content while a lower d-value was exhibited in the XRD pattern for the material with the highest gallate anion content. With these results was evidenced a structural transformation from a Zn-5(OH)(8)(NO3)(2)center dot 2H(2)O type phase to a layered Zn-3(OH)(4)(NO3)(2) type phase when the gallate anions entirely replaced the nitrate anions. The formation of the latter phase at room temperature has not previously been reported. The final hybrid compound with a formula of Zn-3(OH)(4)(C7H6O5)(2), shows an interlayer space of 7.7 angstrom in comparison to 7.0 angstrom for the Zn-3(OH)(4)(NO3)(2) phase, which suggests an arrangement of the organic molecule with a parallel orientation to the y-axis. The X-ray diffraction patterns as a function of temperature showed that a completed incorporation of the gallate anion into the material increased over a 200 degrees C range (from 150 to 350 degrees C), the temperature for the decomposition of the layered phase to ZnO. The organic-inorganic materials synthesized using gallic acid as a guest and a layered zinc hydroxide as a host matrix can act as controlled delivery and storage systems. The release of gallate anions was found to be concentration-dependent with a release mechanism described by the Elovich and Freundlich models.