共价有机框架（covalent organic frameworks，COFs）是一类结晶多孔聚合物，其允许有机单元从原子层面精确整合成具有周期性骨架和有序纳米孔道的延伸结构。COFs的一个重要特征是它们是可设计的，也就是说，可以控制构筑基元的几何形状和尺寸以指导结构周期性的拓扑演变。构筑基元的多样性和共价连接的拓扑方案使 COFs成为结构控制和功能设计的新兴材料平台，非常有望用来解
2）将 COF多孔、大比表面积的优势与磁性材料易于磁分离的特点结合起来，合成了一种含有高比例 COF的磁性固相萃取剂，并将其用于富集环境水样中的有机污染物。通过简单的策略将 COF（TpPa-1）接枝到表面修饰的 Fe3O4纳米颗粒（Fe3O4 NPs）上，制备了新型花束状磁性多孔纳米复合材料。磁性 TpPa-1（由1,3,5-triformylphloroglucinol（Tp）和 p-phenylenediamine（Pa-1）合成的 COF）材料包含核-壳型磁性纳米颗粒簇和相互连接的多孔 TpPa-1纳米纤维。由于这种特殊的形貌，它具有更大的比表面积、更高的孔隙率和超磁性，使其成为富集痕量分析物的理想吸附剂。在高效液相色谱分析之前，通过磁性固相萃取（MSPE）环境样品中痕量多环芳烃（PAHs）评估其性能。结果表明，磁性 TpPa-1材料对于这类有机化合物具有很强的富集能力。
3）考虑到 COFs结构的多样性和可定制性，COFs材料被认为是有机半导体材料分子设计的诱人平台。它们的能带结构和物理化学特性可以通过定制构筑基元来轻松调节。我们通过分子设计和精确构筑定向制备了三种高效的可见光光催化剂，并深入探索了影响光催化剂性能的结构因素及其 COFs光催化降解有机污染物的机理。
利用 1,3,5-triformylphloroglucinol（Tp）和 melamine（MA）合成内嵌有 C3N4构建模块的 COF，将其作为一种高效可见光响应型无金属光催化剂。将促发光催化性能的三个因素巧妙地整合到 COF骨架中，其中三嗪单元作为光活性中心，环酮单元作为吸电子基团，共轭结构作为光电子转移平台。这种缺电子-给电子单元交错排列的 COF对于降解有机污染物表现出卓越的可见光光催化能力。研
利用相同的醛和三种不同的含氮官能团单体合成了一系列亚胺键连接的COFs，研究了前体中化学组成和结构的变化对所得 COFs光电性能的转变，并随之对光催化降解能力的影响。研究结果表明，可见光光催化性能随着活性中心密度和骨架中的共轭程度的增加而增强，这将为其结构和物理化学性质的系统微调提供有力依据，从而拓宽了 COFs在光催化领域中的应用。
利用高稳定的 TTB-TTA（4,4',4''-(1,3,5-triazine-2,4,6-triyl) tribenzaldehyde TTB）和 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline（TTA）合成的 COF）包覆金属有机框架（metal-organic framework，MOF）构建了一系列新型的金属有机框架/共价有机框架（MOF/COF）杂化材料。这类杂化材料继承了 MOF和COF结晶度高、比表面积大、可见光响应强和带隙可调的优势。将 NH2-MIL-125(Ti)引入到杂化材料中，可以调控它们的光电和氧化还原特性，同时形成的异质结可以有效地促进电荷分离，从而显著地提高了材料的光催化性能。因此，NH2-MIL-125(Ti)/TTB-TTA复合物具有极高的甲基橙（MO）光降解动力学常数，其速率分别高于母体 NH2-MIL-125(Ti)和 TTB-TTA的 9倍和 2倍。这种通用的分子-材料平台可以实现 COF分子工程和 MOF类型筛选双重调控模式，在许多领域都能得到应用。
Covalent organic frameworks (COFs) are a class of crystalline porous polymer that allows the atomically precise integration of organic units into extended structures with periodic skeletons and ordered nanopores. One important feature of COFs is that they are designable; that is, the geometry and dimensions of the building blocks can be controlled to direct the topological evolution of structural periodicity. The diversity of building blocks and covalent linkage topology schemes make COFs an emerging materials platform for structural control and functional design, which are promising for handling environmental issues. This dissertation focuses on the design and preparation of COFs and their applications in enrichment and photocatalytic degradation of organic pollutants. It consists of the following three sections.
The first part describes the properties of COFs, the progresses in the fields of magnetic solid-phase extraction (MSPE) and photocatalysis, and the application prospects of COFs in MSPE and photocatalysis.
In the second part, combining the advantages of porous and large specific surface area of COFs with the magnetic separation of magnetic materials, a magnetic solid-phase extraction material with a high proportion of COF is synthesized for enrichment of organic pollutants in environmental water samples. A facile strategy for the fabrication of novel bouquet-shaped magnetic porous nanocomposite via grafting a COF (TpPa-1) onto the surface-modified Fe3O4 nanoparticles (Fe3O4 NPs) was reported. The magnetic TpPa-1(a COF synthesized from 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa-1)) contains clusters of core-shell magnetic nanoparticles and interconnected porous TpPa-1 nanofibers.
Due to this particular morphology, it possesses larger specific surface area, higher porosity, and supermagnetism, making it an ideal sorbent for enrichment of trace analytes. Its performance was evaluated by the magnetic solid-phase extraction (MSPE) of trace polycyclic aromatic hydrocarbons (PAHs) from environmental samples prior to high-performance liquid chromatographic analysis. The results indicated that the magnetic TpPa-1 possessed superior enrichment capacity of such organic compounds.
In the third part, given the structural diversity and tailorability, COFs were regarded as an appealing platform for the molecular design of organic semiconductors. The band structure and physicochemical properties can be easily tuned by tailoring the building blocks. We synthesized three visible-light-driven covalent organic framework photocatalysts via molecular design and precise construction, and further explored the structural factors affecting the photocatalytic performance and the photocatalytic mechanism for the organic pollutants degradation.
A COF inlaid with C3N4 building block was synthesized from 1,3,5-triformylphloroglucinol (Tp) and melamine (MA), which was employed as a high-performance metal-free photocatalyst with visible light response. Three functional factors inducing photocatalytic ability were artfully integrated in the COF skeleton, where triazine units served as photoactive centers, cyclic ketone units as electron-withdrawing moieties, and conjugated structure as a photoelectron shift platform, respectively. This COF with segregated donor-acceptor alignments exhibits an excellent visible-light photocatalytic capacity for organic pollutant decomposition.
Our findings demonstrate that by the judicial design of the molecular structure of polymers, it is possible to precisely regulate their band gap structures and optoelectronic properties, thus creating an enhanced photocatalytic performance.
We synthesized a series of imine-linked COFs from the same aldehyde and three different monomers of nitrogen-containing functional groups, and investigated the translation of chemical and structural variation in the precursors to photoelectric properties of the resulting COFs, with the consequent influence on photocatalytic degradation. We found that the visible-light photocatalytic performances were enhanced with increasing density of active centers and conjugation degree in the networks, which provide a forceful basis for the systematic fine-tuning of their structural and physicochemical properties thus broadening the applications of COFs in photocatalysis.
Series of novel metal-organic framework/covalent organic framework (MOF/COF) hybrid materials were constructed by encapsulating metal-organic framework（ MOF） with highly stable TTB-TTA (a COF synthesized from 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde(TTB)and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (TTA)) layer, inheriting their merits of high crystallinity, large surface area, outstanding visible-light response and tunable band gaps. The introduction of NH2-MIL-125(Ti) into the hybrid materials could modulate their optical, electronic and redox properties, and promote the charge separation owing to the formation of heterojunction, thus resulting in an enhanced photocatalytic performance for organic pollutant decomposition. As such,NH2-MIL-125(Ti)/TTB-TTA composite has a much higher photodegradation kinetic of methyl orange (MO) which is over 9 and 2 times the rates of parent NH2-MIL-125(Ti) and TTB-TTA, respectively. This versatile molecular-material platform can achieve dual adjusting modes consisting of a COF molecular engineering and a MOF type screening strategy, which will be applicable to a wide range of fields.