| Abstract [eng] |
Layered double hydroxides (LDH), also known as hydrotalcite-like compounds and anionic clays, are a widely studied class of layered inorganic materials. These compounds can be synthesized using several different methods, but the formation of a well-defined layered structure requires appropriate synthesis conditions, particularly the pH value. The structural properties of LDHs, such as crystallinity, particle size and interlayer spacing determines their ability to incorporate anions into the interlayer. Mg2Al1, Zn2Al1, Cu2Al1, Co2Fe1 and Ni2Fe1 LDHs were synthesized using the co-precipitation method. Kinetic studies were performed by varying the synthesis pH over the range of 8 to 12 to determine the optimal conditions for sample formation. Obtained XRD results showed that synthesis pH significantly affects not only the LDH formation, but also the formation of secondary impurity phases. Because different metal cations precipitate at different pH values, the optimal synthesis pH depends on the nature of the metal ions used. The M2+/M3+ ratio in the samples was determined using ICP-OES. Anion exchange reactions were performed on the synthesized LDH samples. The introduction of chloride anions into the interlayer space confirmed that carbonate anions are not easily replaced due to their high stability and strong interactions with the layers. Anion exchange successfully occurs when higher salt concentrations are used, as confirmed by FTIR spectra and the shift of diffraction peaks towards lower 2θ angles. During the intercalation of organic salicylate and sulfadiazine anions into the LDH structure, coordination interactions and adsorption on the layered structure were observed. Salicylate anions were successfully incorporated into the interlayer space of Mg2Al1, Zn2Al1, Co2Fe1 and Ni2Fe1 samples, whereas sulfadiazine was intercalated only into Co2Fe1 and Ni2Fe1. The synthesized and anion-exchanged LDH samples were characterized in terms of phase composition, structural and morphological properties, crystallographic parameters, as well as surface area and pore structure characteristics. The obtained results show that the properties of LDH strongly depend on synthesis conditions and the nature of the intercalated anions. |
