水滑石类层状化合物插层选择性及机理的研究
作者：莫丹
院校:北京化工大学
关键字:镁铝水滑石;锌铝水滑石;吡啶二甲酸异构体阴离子;选择性插层;机理;再生
学位：硕士
专业:应用化学
摘要:
本论文主要以镁铝及锌铝水滑石为主体，吡啶二甲酸异构体（2,3-, 2,4-, 2,5-, 2,6-, 3,4- 和3,5- 吡啶二甲酸）为有机阴离子客体，采用焙烧复原法研究了水滑石类层状化合物与吡啶二甲酸异构体阴离子的插层反应。研究表明：镁铝水滑石对吡啶二甲酸异构体阴离子存在着明显的选择性，有机酸异构体优先进入层间的顺序是：2,3-吡啶二甲酸≈2,5-吡啶二甲酸>2,4-吡啶二甲酸>3,5-吡啶二甲酸>3,4-吡啶二甲酸>2,6-吡啶二甲酸，XRD、IR和TG分析结果进一步说明2,3-, 2,5-, 2,4- 及3,5- 吡啶二甲酸阴离子能够进入水滑石层间，而3,4- 和2,6- 吡啶二甲酸阴离子未进入层间，而是吸附在水滑石表面。锌铝水滑石对吡啶二甲酸异构体阴离子也表现出一定的插层选择性，但有机酸阴离子的优先插入量顺序有所变化，这说明由于LDHs层板组成的改变，导致了其插层选择性的不同。 本论文还采用Gaussian-98软件包中ab initio 分子轨道法（HF/6-31G）计算了吡啶二甲酸异构体阴离子的分子结构，并结合实验数据从微观作用的角度分析了插层过程中主体与客体的相互作用，从而确定插层过程中的选择性的影响规律及插层机理。结果表明，吡 啶二甲酸异构体阴离子电子结构及几何结构，决定了2,3-, 2,5- 吡啶二甲酸阴离子最易进入水滑石层间，2,4-, 3,5- 吡啶二甲酸阴离子受空间位阻影响而略难进入水滑石层间，而3,4- 和2,6-吡啶二甲酸阴离子由于极性较大，与介质作用力大，从而不易进入水滑石层间。反应动力学初步研究表明，LDHs与吡啶二甲酸的插层反应能够快速进行，但所得产物需要一定时间才能形成有序的晶体结构。 在上述研究的基础上，本论文还以锌铝复合氧化物和镁铝复合氧化物为主体，对苯二甲酸和2,5-吡啶二甲酸为客体，分别将锌铝复合氧化物与对苯二甲酸及镁铝复合氧化物与2,5-吡啶二甲酸进行多次煅烧及重复插层反应。研究结果表明，这两种双金属复合氧化物均具有良好的再生及重复插层使用性能。 此外，还研究确定了镁铝复合氧化物对吡啶二甲酸的最大吸附反应量，并利用 CO32－将与镁铝复合氧化物反应了的吡啶二甲酸阴离子交换出来，此方法具有较高的交换效率，可达到最终分离有机异构体的目的。
Abstract:
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.