Preferential Intercalation In Layered Double Hydroxides And Mechanism Study

In this thesis, Mg-Al LDHs and Zn-Al LDHs have been used as host materials, while 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, or 3,5- pyridinedicarboxylate have been used as guest materials. Intercalation of 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, or 3,5- pyridinedicarboxylate into the LDHs was carried out by the reconstruction method. The result has indicated that Mg-Al LDHs exhibit preferential intercalation reactions with isomeric pyridinedicarboxylate anions. The preference order of each organic acid intercalated in the Mg-Al LDHs has been found to be in the order: 2,3-pyridinedicarboxylate ≈ 2,5-pyridinedicarboxylate > 2,4-pyridinedicarboxylate > 3,5-pyridinedicarboxylate > 3,4-pyridinedicarboxylate > 2,6-pyridinedicarboxylate. The structures of the intercalates formed by reaction of six guests with Mg-Al LDHs were characterized by X-ray diffraction, infrared, and thermogravimetry techniques. 2,3-, 2,5-, 2,4-, 3,5- pyridinedicarboxylate can be intercalated into Mg-Al LDHs, but 3,4-, 2,6- pyridinedicarboxylate are hardly intercalated into Mg-Al LDHs and most likely on the external surface of the LDHs crystallites. The intercalation of isomers of pyridinedicarboxylate anions into Zn-Al LDHs was also observed. The preference order of each organic acid intercalated in the Zn-Al LDHs differs from that of Mg-Al LDHs. It seems that the nature of the LDHs can affect the intercalation preferences.In order to develop a greater understanding of the factors influencing the preferential intercalation and the reaction mechanism, we have performed quantum chemical calculations on the organic guest ions using an ab initio (HF/6-31G) method by G98w. According to the guest size and the charge density of the oxygens of the guest, 2,3- and 2,5- pyridinedicarboxylate are the most highly favoured, and the lower symmetry structures and larger molecular sizes of 2,4- and 3,5-pyridinedicarboxylate can influence them intercalate into the interlayer of LDHs, but 3,4- and 2,6- pyridinedicarboxylate are very difficult to be intercalated into LDHs. In addition, the reaction kinetics of intercalation reaction was also studied. The intercalation reaction is a fast reaction, but it takes some time for the products to form ordered crystallinity.In addition, the regeneration and repeat intercalation of Zn-Al LDO with 1,4-benzenedicarboxylate and Mg-Al LDO with 2,5-pyridinedicarboxylate have been studied. It has been shown that these metal mixed oxides own a preferable property of regeneration and repeat intercalation. Furthermore, the maximum of pyridinedicarboxylate anions absorbed on the Mg-Al LDO was studied. The pyridinedicarboxylate anions reacted with Mg-Al LDO were exchanged by CO32-. This process provides high exchange efficiency, and can attain the aim of separation organic isomer.