Effects of pH and concentration on ability of Cl− and NO3− to intercalate into a hydrotalcite-like compound during its synthesis

In this study, we confirmed that the characteristics of anion intercalation into the interlayer of a hydrotalcite-like compound (HT) during synthesis are similar to those of the anion-exchange reaction of HTs as well as the reconstruction reaction of HTs from Mg-Al oxide. We demonstrated that (i) Cl−, which has a higher charge density than NO3−, more easily reacted with Mg and Al species to form HT structure, resulting in greater intercalation of Cl− into the HT interlayer; and (ii) for HTs with lower Mg: Al molar ratios, OH−, which has a higher charge density than Cl− and NO3−, was more likely to interact with Mg and Al species to form HT structure, blocking the intercalation of Cl− and NO3−. Furthermore, we showed that high concentrations of Cl− and NO3− in solution regulated their intercalation into the HT interlayer. The high activity of Cl− and NO3− in solution would facilitate the anions’ reactions with Mg and Al species to form HTs, resulting in a high degree of anion intercalation into the interlayer of HTs.