College of Chemistry, Beijing Normal University, China.
Dalton Trans. 2011 Oct 14;40(38):9835-43. doi: 10.1039/c1dt10982k. Epub 2011 Aug 23.
The structural control involving staging formation was studied in the nanocomposites of macrocyclic tetraazacrown ether carboxylic acid derivative (TECA) and layered double hydroxide (LDH) obtained by an osmotic swelling/restoration process. After NO(3)-type MgAl-LDH was osmotically swollen in formamide, TECA was added, leading to a restoration of the LDH sheets and formation of TECA-LDH nanocomposites. In the wet state, the structure of the composites was homogenous, and the basal spacings of ∼2.0 or 1.8 nm were not changed by the water-washing process that removed formamide and caused the replacement of NO(3)(-) by CO(3)(2-). However, in the drying process, both the orientation of TECA in the interlayer and the formed staging structure varied with the TECA content. The TECA orientation changed from horizontal to tilted/twisted and finally to vertical with interlayer TECA density. The staging structure occurred for samples with both TECA and small inorganic guests coexisting in the interlayer. Third-staging, second-staging, and homogenous structures were observed at TECA/LDH weight ratios of low (0.125 and 0.25), medium (0.5) and large (1 and 2) values, respectively. The decrease of negative charge of TECA ions from -4 to -1 led to the co-existence of small ions (NO(3)(-)) with TECA in the gallery and the formation of a NO(3)(-)-containing staging structure, even at a high TECA/LDH ratio of 2. The study of the influence of CO(3)(2-) on the composite structure indicates that a TECA/CO(3)(2-) ion exchange progressed reversibly and the staging structure formed is thermodynamically stable, depending mainly on the chemical composition of the interlayer guests. The staging formation could be explained by the Daumas-Hérold model, which differs markedly from the Rüdorff model previously proposed for the LDH system. The treatment in formamide of the composite such as T2L+Na(2)CO(3) with staging structure shows that the transformation process is reversible, and these kinds of composites may be used as an adsorbent for some harmful organic solvents.
采用渗透溶胀/恢复过程制备大环四氮杂冠醚羧酸衍生物（TECA）和层状双氢氧化物（LDH）的纳米复合材料，研究了涉及成核形成的结构控制。在甲酰胺中对 NO(3)-型 MgAl-LDH 进行渗透溶胀后，加入 TECA，导致 LDH 片层恢复并形成 TECA-LDH 纳米复合材料。在湿态下，复合材料的结构是均匀的，层间距约为 2.0 或 1.8nm，通过水洗过程不会发生变化，该过程去除了甲酰胺并使 NO(3)(-)被 CO(3)(2-)取代。然而，在干燥过程中，层间 TECA 的取向和形成的成核结构都随 TECA 含量而变化。TECA 的取向从水平变为倾斜/扭曲，最后变为垂直，层间 TECA 密度增加。在层间共存 TECA 和小无机客体的情况下发生分级结构。在 TECA/LDH 重量比为低（0.125 和 0.25）、中（0.5）和高（1 和 2）时，分别观察到三级、二级和均匀结构。TECA 离子的负电荷从-4 减少到-1 导致小离子（NO(3)(-))与 TECA 共存于夹层中，并形成含 NO(3)(-)的成核结构，即使在 TECA/LDH 比为 2 的情况下也是如此。研究 CO(3)(2-)对复合结构的影响表明，TECA/CO(3)(2-)离子交换是可逆的，形成的成核结构热力学稳定，主要取决于夹层客体的化学成分。成核形成可以用 Daumas-Hérold 模型来解释，该模型与之前提出的用于 LDH 系统的 Rüdorff 模型明显不同。对具有成核结构的复合材料（如 T2L+Na(2)CO(3)）进行甲酰胺处理表明，转化过程是可逆的，这些类型的复合材料可用作一些有害有机溶剂的吸附剂。
