Chemical modification of zinc hydroxide nitrate and Zn–Al-layered double hydroxide with dicarboxylic acids

A zinc hydroxide nitrate (ZHN), Zn5(OH)8(NO3)2⋅2H2O, and a layered double hydroxide (LDH), Zn/Al-NO3 were doped with 0.2 mol% of Cu2+ during alkaline chemical precipitation. Both compounds were intercalated with adipate (−OOC(CH2)4COO−), azelate (−OOC(CH2)7COO−), and benzoate (C6H5COO−) ions through ion exchange reactions. Solid state 13C nuclear magnetic resonance spectroscopy showed only one signal of carboxylic carbon for adipate and azelate intercalated into LDH, indicating that the carboxylic ends of both acids were equivalent, whereas the signal split when the intercalation was into the ZHN matrix. The electron paramagnetic resonance (EPR) spectrum of copper in octahedral cation sites of LDH layers showed a Hamiltonian parameter ratio g‖/A‖=170 cmg‖/A‖=170 cm and, after intercalation of adipate, the change was not significant: g‖/A‖=174 cmg‖/A‖=174 cm. This result indicates that the carboxylate ions did not coordinate with copper centers. Nonetheless, the intercalation of azelate increased the ratio to g‖/A‖=194 cmg‖/A‖=194 cm, similar to the spectra of ZHN modified with adipate, g‖/A‖=199 cmg‖/A‖=199 cm, and azelate, g‖/A‖=183g‖/A‖=183 and 190 cm, which are associated with the coordination of copper by weak carboxylate anion ligands. Copper occupies octahedral or tetrahedral sites in ZHN layers, and the EPR spectra indicate that the dicarboxylate anions reacted preferentially with octahedral sites, whereas benzoate reacted with both sites.

Graphical abstractPossible arrangements of (a) adipate and (b) azelate ions between the layers of layered double hydroxides and (c) adipate, (d) azelate, and (e) benzoate ions in zinc hydroxide nitrate.Figure optionsDownload full-size imageDownload as PowerPoint slide