Layered double hydroxides (LDH) are a class of synthetic clays that contain cationic layers similar to brucite [Mg(OH)\(_{2}\)]. An anion in the interlayer provides charge balance. Layered hydroxides are highly susceptible to modification in both the cationic and anionic layers, and their synthesis offers the possibility of obtaining materials with desired properties. The objective of this study is to synthesize Mg\(_{3}\)Al\(_{1}\)(OH)\(_{Y}\), Mg\(_{3-X}\)Ag\(_{X}\)Al\(_{1}\)(OH)\(_{Y}\), and Mg\(_{3}\)Al\(_{1-X}\)Cr\(_{X}\)(OH)\(_{Y}\) and to investigate the structure and properties of the resulting materials.
Mg/Al LDHs are synthesized by the co-precipitation method. Metal nitrate solutions, mixed in the required proportions, are slowly dropped into a sodium carbonate solution at the required pH which is adjusted with sodium hydroxide solution, followed by aging of the synthesised material at 80 ℃. LDH with Cr is synthesised in the same manner, only replacing part of the aluminium nitrate with a solution of Cr(NO\(_{3}\))\(_{3}\) or CrO\(_{3}\). The synthesis of LDH with Ag is carried out using pre-made Mg/Al LDH, which is submerged in AgNO\(_{3}\) solution and stirred at temperatures ranging from 80 to 100°C for 15 minutes. The temperature is maintained by a hydrothermal reactor and a hot plate.
The substitution of Al³⁺ ions by Cr³⁺ ions in the cationic layer was successful, as evidenced by XRD data showing that no additional phases were formed during the reaction, regardless of the Cr source. Conversely, the substitution of Mg²⁺ ions by Ag⁺ ions proved unsuccessful, as silver failed to incorporate into the structure and instead precipitated as elemental silver.