Synthesis and Characterization of [Zn-Al] Layered Double Hydroxides: Effect of the Operating Parameters

In this study, [Zn-Al] layered double hydroxides (LDHs) were prepared using the coprecipitation method at constant pH. The synthesis parameters (including the aging time, synthesis pH, nature of the alkali, concentration of metallic salts, and the cationic molar ratio R=Zn/Al) were varied in order to elucidate their effect on the properties of the obtained materials. Different characterization techniques, namely X-ray diffraction, Fourier transform infrared, thermogravimetric analysis-differential thermogravimetry, transmission electron microscopy, energy-dispersive X-ray, inductively coupled plasma, and photoluminescence, were used in this study. It was found that obtaining well-crystallized LDHs requires (i) an aging time of 24h and (ii) a synthesis pH value in the range 8-12. Our results also show that the concentration of the cationic metallic salts has no influence on the structural properties of the LDHs. The use of NH4OH as alkali for adjusting the pH value during the synthesis favors the formation of nitrated LDH phases while NaOH gives rise to carbonated ones. Moreover, it was found that irrespective of the molar cationic ratio used (between 1 and 5), [Zn-Al] LDHs could be obtained. The sample synthesized at R=2 exhibited the best crystallinity.