Clean Synthesis And Structure Of Layered Double Hydroxides With Intercalated Selective Theoretical Study

In this paper, a clean route for the synthesis of hydrotalcites using the magnesia and the sodium aluminate liquor has been investigated, and the possibility of utilizing the waste liquors has also been studied. The range of Mg/Al mole ratios in the reaction mixtures, the reaction time and other factors to influence the formation of the hydrotalcites have been discussed. It has been shown that the Mg/Al ratio in the reaction mixtures plays an important role in hydrotalcites formation. When the Mg/Al ratio in the reaction mixtures is between 1.0 and 2.0, pure hydrotalcite-like materials can be obtained. The results indicate that the high crystallinity of MgO is beneficial to the formation of the hydrotalcites. The Mg/Al ratios in the products are all in the range 2 to 3. And the higher the Mg/Al in the synthesis mixtures, the lower the Mg/Al ratio in the products, which shows that Mg-rich reaction systems is favor Al substitution in the brucite-like layer. It has also been proved that the waste liquor can be fully reused. In a word, the route is very clean and friendly to the environment.The interactions of the intercalated anions with the cationic sheets in magnesium aluminum layered double hydroxides have been investigated using the ASED-MO method (including atomic repulsion energy). The energy changes, nature of bonding and charge transfer have been studied during the formation of the layered structure with different anions, based on the model of Mg6Al2(OH)i6X.H2O. The calculated results have shown that both Coulombic and hydrogen bonding interactions exist in the layered structure, and the strength of hydrogen bonding interaction is connected with the charge distribution of the anion and its orientation in space. Furthermore, it indicates that the variation in acid-base property of the layers affected by the intercalated charge distribution of the intercalated anion.In addition, the intercalation of benzoate and 1,2-, 1,3- or 1,4- benzenedioate ions into LDHs by reaction of calcined Mg/Al and Zn/Al LDHs with solutions of theorganic acids have been investigated in this paper. Selective reaction was observed in competitive experiments involving pairs of acids. The mechanism of these shape-selective intercalation reactions has been studied by using an ab initio (HF/6-31G) method within the G94w program. It has been shown that the nature of the LDHs, the charge density of the guest, the shape of the guest, the charge density of oxygen atoms in the guest and the solvent can influence the selectivity of the intercalation reaction.