摘要/Abstract
共价有机框架(covalent organic framework, COF)是一种由轻质元素(C、H、O和N)以共价键的形式连接组成的结晶多孔聚合物, 由于其具有规则的孔道、可修饰的骨架以及良好的稳定性而被广泛应用于不同的领域. 尤其是将含氮的功能基团连接到COF的骨架中, 可以为其吸附特定的染料提供丰富的活性位点. 基于此, 本工作成功制备了一种酰胺功能化的二维共价有机框架材料(JUC-578), 通过一系列的表征证明了该材料具有高的结晶度、均一规整的形貌以及开放的一维介孔孔道. 更重要的是, 发现JUC-578可以选择性地吸附阳离子染料, 并且可以多次循环利用. 这主要归因于骨架中的氮作为电子给体与缺电子的染料之间的静电作用以及其他弱相互作用(氢键、偶联作用等). 与此同时, JUC-578高的结晶度和有序的孔道也是实现可逆吸附染料非常重要的因素.
关键词: 多孔材料, 共价有机框架, 晶体结构, 酰胺功能化, 染料吸附
Organic dyes are widely applied for cloth dyeing process, paper printing, cosmetics, and food processing industries. The toxicity of industrial dyes poses serious threats to water and human health. Thus, several methods such as adsorption, degradation, and photocatalytic oxidation or reduction have been proposed to remove dyes from water. Among them, with low cost and high adsorption efficiency, porous materials become the most common materials to remove organic dyes from aqueous solutions. Notably, covalent organic frameworks (COFs) are a kind of novel crystalline porous polymers with regular pores, modifiable frameworks, high specific areas and excellent stability. Because of their outstanding properties, COFs have been used in many fields, such as gas adsorption and separation, heterogeneous catalysis, semiconductors and sensors. Especially the introduction of the nitrogen-containing functional groups to the COF skeletons provides abundant active sites to adsorb specific dyes in the field of dye adsorption. Inspired by this, a novel amide-functionalized two-dimensional COF (termed as JUC-578) was successfully prepared through Schiff-based condensation reaction of 4,4'-diaminobenzanilide (DABA) and 1,3,5-benzenetricarboxaldehyde (BT). A series of characterizations proved that JUC-578 has high crystallinity, uniform morphology and opening one-dimensional mesoporous pores. Especially the morphology of JUC-578, which was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), showed a clear spherical structure with uniform morphology distribution and smooth surface. Moreover, we studied the reversible adsorption of JUC-578 on dyes from aqueous solutions by UV-Vis spectrophotometry. The results show that JUC-578 can selectively adsorbed cationic dyes and the structure remained stable after cycling, which was attributed to the electrostatic interaction between the electron donor nitrogen in the skeleton and the electron-deficient dyes as well as other weak interactions (hydrogen bonding, coupling, etc.). Meanwhile, the crystallinity and ordered pores of JUC-578 are also important factors for reversible dye adsorption. These results indicate that COFs as functionalized porous materials have great potential in dealing with environmental problems.
Key words: porous material, covalent organic framework, crystal structure, amide-functionalized, dye adsorption
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