Reticular Synthesis of Covalent Organic Frameworks for Carbon Dioxide Adsorption

Reticular Synthesis of Covalent Organic Frameworks for Carbon Dioxide Adsorption | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL Chinese Journal of Chemistry This is a preprint and has not been peer reviewed. Data may be preliminary. 25 September 2025 V1 Latest version Share on Reticular Synthesis of Covalent Organic Frameworks for Carbon Dioxide Adsorption Authors : Fuxiang Wen 0000-0001-6061-7174 and Ning Huang 0000-0002-7021-8705 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.175879152.22892919/v1 Published Chinese Journal of Chemistry Version of record Peer review timeline 394 views 190 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The ongoing increase in atmospheric carbon dioxide (CO 2 ) concentration has become a pressing issue that requires immediate attention to mitigate the substantial global warming and the associated environmental crisis. Sorbent-based CO 2 capture offers a promising approach to addressing the problems. However, an efficient capture process requires materials to have high CO 2 capacity, fast kinetics, good selectivity, and long-term stability under operating conditions. Guided by reticular chemistry, which enables the linking of molecular building blocks into crystalline frameworks through strong bonds, covalent organic frameworks (COFs) have demonstrated great potential as efficient CO 2 adsorbents due to their high porosity, tailor-made pore environment, and excellent stability. Considering the significant progress in this field, this review provides the basic design principles of COFs, summarizes recent de novo and post-synthetic modification methods for designing suitable COFs for CO 2 capture, and discusses the challenges and prospects. Cite this paper: Chin. J. Chem. 2024 , 42 , XXX—XXX. DOI: 10.1002/cjoc.202400XXX Reticular Synthesis of Covalent Organic Frameworks for Carbon Dioxide Adsorption Fuxiang, Wen, Ning, Huang* State Key Laboratory of Silicon and Advanced Semiconductor Materials, Department of Polymer Science and Engineering, Zhejiang University, 310058, Hangzhou, China Carbon capture | Covalent organic frameworks | Porous polymer | Reticular chemistry | 2D Nanomaterials Comprehensive Summary The ongoing increase in atmospheric carbon dioxide (CO 2 ) concentration has become a pressing issue that requires immediate attention to mitigate the substantial global warming and the associated environmental crisis. Sorbent-based CO 2 capture offers a promising approach to addressing the problems. However, an efficient capture process requires materials to have high CO 2 capacity, fast kinetics, good selectivity, and long-term stability under operating conditions. Guided by reticular chemistry, which enables the linking of molecular building blocks into crystalline frameworks through strong bonds, covalent organic frameworks (COFs) have demonstrated great potential as efficient CO 2 adsorbents due to their high porosity, tailor-made pore environment, and excellent stability. Considering the significant progress in this field, this review provides the basic design principles of COFs, summarizes recent de novo and post-synthetic modification methods for designing suitable COFs for CO 2 capture, and discusses the challenges and prospects. In 2005, Yaghi and co-workers developed the first example of COFs, and in the past two decades, advanced the development of this field by exploring the structural and functional diversity of COFs. For example, Furukawa and Yaghi reported the first experimental study of CO 2 adsorption in COFs in 2009, opening the following works on applying COFs to CO 2 adsorption. In 2015, Jiang, Huang, and co-workers reported a series of post-synthetic modification methods to modify COFs toward CO 2 adsorption. The pore environment of COFs was modified by the famous click reactions and the well-developed ring-opening reaction, thus enhancing the CO 2 capture performance of these COFs. Lotsch and co-workers reported another post-synthetic modification method to modify the pore properties of COFs. They doped the COFs with metal salts and achieved a high CO 2 capture performance. The direct synthesis of COFs with CO 2 -philic sites could also help to fabricate COFs with high adsorption uptake. In 2017, Jiang, Huang, and co-workers constructed a novel ionic COFs from ionic building units and applied it to CO 2 capture. Besides 2D COFs, Fang and co-workers designed a series of 3D COFs and applied them to CO 2 adsorption. In 2024, Yaghi, Zhou, and co-workers reached a milestone. They reported a new COF-based CO 2 adsorbent that could achieve direct CO 2 capture from the air with exceptional uptake capacity, high cyclic stability, and fast kinetics. Contents 1. Introduction Page No. 2. Synthesis of COFs Page No. 2.1. Building unit 2.2. Linkage 2.3 Topology 2.4 Post-synthetic modification Page No. 3. Design COFs for CO 2 capture 3.1 Suitable building unit 3.2 Special linkage 3.3 Pre-designed topology 3.4 Post-synthetic modification Page No. 4. Conclusions and Perspectives Page No. 1. Introduction As industrialization and social development rapidly proceed, the escalating anthropogenic carbon dioxide (CO₂) emissions crisis has emerged as one of the most pressing challenges facing modern society. With global atmospheric CO₂ concentration surpassing 420 ppm in 2022, urgent action is required to mitigate the associated climate change impacts, including rising sea levels, extreme climatic events, and ecosystem disruption. [1-2] Although renewable energy technologies offer long-term solutions to reduce CO 2 emissions, the current energy mix and the intermittent nature of solar, wind, and other power necessitate complementary strategies for large-scale CO₂ capture and utilization methods. [3-6] Among various carbon capture technologies, sorbent-based methods have gained prominence due to their modular scalability, tunable selectivity, and reduced energy penalties. [7-8] Central to the advancement of these technologies are porous materials—materials characterized by high surface areas and tailored pore architectures, which have demonstrated exceptional promise in achieving efficient CO₂ adsorption and storage. [9-11] Various porous materials have been examined in this field, including zeolites, [12] porous carbons, [11] and metal-organic frameworks (MOFs). [2, 13-14] Although these porous solids, compared with aqueous amine solutions, rely mostly on physical adsorption of CO 2 , they suffer from different drawbacks. [15] Zeolites are highly hydrophilic and easily saturated with water, which reduces their CO 2 capture performance. Porous carbons exhibit low CO 2 / N 2 selectivity, small low-pressure working capacity, disability to perform pore engineering, and disordered pore width. More recently, MOFs have emerged as a new star of next-generation porous materials for CO 2 adsorption owing to their high porosity, tailor-made pore structures, and the hybrid nature of comprising metal-containing nodes and organic linkers. However, MOFs might lose their structural integrity under harsh conditions due to the low bond energy of the coordination bond. [16] Developing new porous materials seems to offer a new solution toward practical CO 2 capture. Figure 1. Representative building units for fabricating COFs for CO 2 capture. Covalent organic frameworks (COFs) are a class of crystalline porous polymers that are constructed from lightweight elements such as C, H, O, and N. [17-20] Under the guidance of reticular chemistry, various building blocks are linked through covalent bonds to form well-defined structures with intrinsic porosity, tunable functionality, and high stability via the de novo synthetic processes. [19, 21] Meanwhile, the properties of COFs could be easily modified by various post-synthetic modification methods, during which the framework structure of the COFs is retained. [22] These properties promote COFs promising for CO₂ capture, and COFs have made significant progress in this field over the past decades. [16, 23-26] In consideration of the past impressive development, summarizing the structural design principles of COFs for CO 2 capture and revealing the underlying structure-function relationship would help develop next-generation COF-based CO 2 adsorbents. In this review, the design strategies toward efficient COF-based CO 2 sorbents and the related progress were summarized. The structural information, including the building units, linkages, and topologies of the COFs, was highlighted, and some efficient post-synthetic modification methods were also included, trying to decode the structure-function relationship during the CO 2 capture process. Finally, the challenges and prospects are discussed, outlining several future directions of applying COFs towards practical CO 2 sorption. 2. Reticular synthesis of COFs Reticular chemistry enables the linking of molecular building units to make crystalline open frameworks through strong bonds. The first two COFs, COF-1 and COF-5, were reported in 2005, after which the concept of reticular chemistry was expanded to synthesi- ze COFs. [17] Since COFs are composed of pure organic components, their properties can be designed and manipulated by the well-developed organic chemistry via de novo synthesis or post-synthetic modifications. [21, 27] During the de novo synthesis, the building units, linkages, and topologies constitute the fundamental information of COFs materials and determine their properties. The formation of the high-order COFs relies on the rigid backbone of the building units and the relatively reversible linkages formed during the polymerization reaction. [21, 28] The combination of various building units with different geometries and different reactive sites would generate numerous COFs with different crystalline networks. [29] The structure of these networks could be simplified into different topologies. [21, 29-30] Meanwhile, the properties of the COFs could be significantly changed by introducing different functional species through post-synthetic modification methods, making COFs exhibit various advantages in gas separation and storage, [30-32] catalysis, [33-36] sensing, [37] and other fields. [38-43] 2.1. Building units The geometry of the building units plays an important role in determining the final structure of the COFs. For example, the combination of the planar building units would mostly generate 2D extended networks, while the combination of some building units that hold special geometry, like the orthogonal geometry, would produce 3D extended networks. [21, 29-30] In addition, the formation of the well-defined structure of COFs requires the building units to hold relatively rigid backbones in which the reactive sites hold distinct geometry and are distributed in specific positions. In this regard, most of the building units consist of benzene rings or fused rings. The well-developed organic chemistry provides sufficient Figure 2. Typical linkages for COFs synthesis. tools for the design and synthesis of these monomers. The geometry of the building units and the reactive sites can be predesigned. Different functional groups could also be attached to the skeleton of the building units to regulate their properties. [19] For example, as shown in Figure 1, various building units have been designed and applied to synthesize COFs for CO 2 capture. 2.2. Linkage Linkages represent the linking modes between the building units. To construct the crystalline frameworks, selecting suitable reactions is important. Guided by dynamic covalent chemistry, the reversible reactions between the building units during the polymerization process provide sufficient opportunities for the proofreading and error-checking procedure and guarantee the formation of the ordered frameworks under thermodynamic control. The linkages between the building units decide their relative positions, thus helping to determine the final topology of COFs. Various linkages have been developed since 2005, and some of them are listed in Figure 2. Apart from their function in structure formation, linkages also have a huge impact on the function of the COFs. Some linkages, like the 1,4-dioxin linkage and the phenazine, exhibited extraordinary chemical and thermal stability under harsh conditions, [44-45] while some linkages, like the imidazole linkage, could supply additional affinitive sites for CO 2 adsorption. [46] 2.3. Topology Topology describes the simplified network structure of COFs, depicting the pore shape and the relative position of the building units. One of the most significant properties of COFs is their porosity, which is derived from the special alignment of the rigid building units. One building unit connects with another, extends in a 2D or 3D manner, and creates open networks during the polymerization. As the building units that hold similar geometry could be simplified as the same block model, these networks could be simplified as special topological structures. [29] In this way, although there are infinite combinations of building units and reactive sites, the number of topologies is limited. The polymerization process could be simplified and illustrated by the topology diagram. As shown in Figure 3, the combination of [ C 3 + C 3 ] generates hexagonal COFs, while the combination of [ C 4 + C 2 ] generates tetragonal COFs. Based on such a topology diagram, a variety of 2D and 3D networks could be constructed easily. Figure 3. Selective topology diagrams for designing COFs. 2.4. Post-synthetic modification Although the restricted geometry of the building units and the reversible linkages make the crystallization of COFs possible under optimal conditions, some situations would not generate the crystalline frameworks. The functional groups may not be compatible with the synthetic conditions, and the bulky moieties may interfere with the formation of the crystalline structures. [47] In this regard, some post-synthetic modification methods have been developed to solve these problems. As COFs hold large open spaces toward the outer environment, which permits various substrates to go into the pores and react with the frameworks via covalent or non-covalent binding, different functionalities could be imposed on the pristine COFs, and the chemical and physical properties of COFs could be tuned. Over the past years, considerable efforts have been put into this field and have achieved great progress. [22, 27] Table 1. Summary of the representative COFs for CO 2 adsorption. VM-COF 1258 1.0 273 K, 1 bar 4.90 32 COF-JLU6 1450 3.1 273 K, 1 bar 2.93 33 COF-JLU7 1392 3.3 273 K, 1 bar 3.43 PZ-COF-1 845 1.6 273 K, 1 bar 3.04 45 PZ-COF-2 1130 2.4 273 K, 1 bar 4.06 TBICOF 1424 2.5 273 K, 1 bar 3.08 46 ND-COF-1 794 1.6 273 K, 1 bar 2.24 49 ND-COF-2 879 1.5 273 K, 1 bar 2.12 COF-5 1670 2.7 273 K, 1 bar 1.34 50 COF-103 3530 1.2 273 K, 1 bar 1.73 CAA-COF-1 841 1.3 273 K, 1 bar 5.72 51 CAA-COF-2 723 1.9 273 K, 1 bar 2.72 M-COF 761 1.4 273 K, 1 bar 3.23 52 T-COF 587 0.8 273 K, 1 bar 4.04 53 ESM-COF-1 722 0.9 273 K 1 bar 4.64 54 ESM-COF-2 876 1.6 273 K, 1 bar 3.85 TDCOF-5 2497 2.6 273 K, 1 bar 2.09 55 cage-COF-1 1237 1.1 273 K, 1 bar 1.96 56 TPA-COF-3 557 2.0 273 K, 1 bar 2.07 57 TPA-COF-6 1535 2.6 273 K, 1 bar 2.10 Car-TPA-COF 1334 2.3 273 K, 1 bar 2.79 58 COF-N18 1262 1.4 273 K, 1 bar 4.45 59 COF- N 2 7 840 1.4 273 K, 1 bar 4.45 ACOF-1 1176 0.9 273 K, 1 bar 4.02 60 COF-JLU2 415 1.0 273 K, 1 bar 4.93 61 TFPPz–MPA–COF 897 0.9 273 K, 1 bar 1.49 62 TFPPz–BD(OMe) 2 –COF 224 1.3, 1.6 273 K, 1 bar 1.34 COF-Z1 513 1.4, 1.7 273 K, 1 bar 1.08 63 COF-Z2 549 1.4, 1.8 273 K, 1 bar 0.95 M-COF-1 903 0.9 273 K, 1 bar 2.85 64 M-COF-2 741 0.9 273 K, 1 bar 3.24 COF-OH 1589 1.8 273 K, 1 bar 3.92 65 COF-F 1441 1.8 273 K, 1 bar 2.50 TH-COF-1 684 1.1 273 K, 1 bar 2.91 66 Cz-COF 871 2.0 273 K, 1 bar 2.50 67 Tz-COF 1439 2.1 273 K, 1 bar 3.50 COF-H1 510 1.3 273 K, 1 bar 1.50 68 Pa-Tp 781 3.0 273 K, 1 bar 3.43 70 DB 10% -Pa-Tp 877 4.4 273 K, 1 bar 4.83 DB 25% -Pa-Tp 602 3.6 273 K, 1 bar 3.65 DB 50% -Pa-Tp 581 4.2 273 K, 1 bar 2.40 DB-Tp 916 4.3 273 K, 1 bar 2.49 COF-IL 291 1.7, 2.2 273 K, 1 bar 4.73 71 PyTTA-BFBIm-iCOF 1532 2.3 273 K, 1 bar 4.02 72 3D-ionic-COF-1 966 0.9 273 K, 1 bar 3.66 73 3D-ionic-COF-2 880 0.8 273 K, 1 bar 3.02 3D-IL-COF-1 517 0.8 298 K, 1 bar 1.20 74 3D-IL-COF-2 653 1.1 298 K, 1 bar 1.73 3D-IL-COF-3 870 1.2 298 K, 1 bar 1.12 3D-HNU5 864 1.0 273 K, 1 bar 2.80 75 COF-115 1387 1.2, 2.9 298 K, 1 bar 1.65 76 BBO-COF 1 891 1.3 273 K, 1.2 bar 3.42 77 BBO-COF 2 1106 1.8 273 K, 1.2 bar 2.55 CD-COF-PPZ 494 0.6 273 K, 1 bar 2.77 79 HEX-COF 1 1214 1.1 273 K, 1 atm 4.55 80 DL-COF-1 2259 1.4 273 K, 1 bar 6.07 81 DL-COF-2 2071 1.3 273 K, 1 bar 4.96 3D-CageCOF-1 1040 0.6, 0.9 273 K, 1 bar 4.64 82 3D-Py-COF 1290 0.6 273 K, 1.08 bar 3.49 83 TPE-COF-II 2168 1.2 273 K, 1 bar 5.30 84 PT-COF 1791 1.8 273 K, 1 bar 2.16 85 PY-COF 1220 1.8 273 K, 1 bar 3.32 PT 2 B-COF 2367 1.8, 2.4 273 K, 1 bar 1.93 PY 2 B-COF 1984 1.8, 2.4 273 K, 1 bar 2.89 3D-ceq-COF 1149 1.0, 1.6 273 K, 1 bar 4.07 86 JUC-568 1433 1.9 273 K, 1 bar 4.38 87 SP-CA-COF-IM 1551 1.0 273 K, 1 bar 2.47 88 SP-CA-COF-AM 1557 1.0 273 K, 1 bar 3.75 [MeOAc] 50 -H 2 P-COF 754 1.8 273 K, 1 bar 2.00 89 [AcOH] 50 -H 2 P-COF 866 1.8 273 K, 1 bar 2.66 [EtOH] 50 -H 2 P-COF 784 1.9 273 K, 1 bar 2.82 [EtNH 2 ] 50 -H 2 P-COF 1044 1.9 273 K, 1 bar 3.57 [HO 2 C] 25% -H 2 P-COF 786 2.2 273 K, 1 bar 2.18 90 [HO 2 C] 50% -H 2 P-COF 673 1.9 273 K, 1 bar 3.04 [HO 2 C] 75% -H 2 P-COF 482 1.7 273 K, 1 bar 3.57 [HO 2 C] 100% -H 2 P-COF 364 1.4 273 K, 1 bar 3.95 COF-HNU3 2027 2.6 273 K, 1 bar 2.95 92 TAPT-BP 2+ -COF 474 3.3 273 K, 1 bar 2.55 93 TAPT-BP-COF 593 3.9 273 K, 1 bar 2.02 [HO] 25% -Py-COFs 1977 2.2 273 K, 1 bar 2.08 94 [HO] 50% -Py-COFs 2153 2.2 273 K, 1 bar 2.59 [Et 4 NBr] 25% -Py-COFs 1014 2.0 273 K, 1 bar 2.72 [Et 4 NBr] 50% -Py-COFs 879 1.6 273 K, 1 bar 3.74 ATFG-COF 520 0.6, 1.3 273 K, 1 bar 3.93 102 Zn@ATFG-COF 162 N/A 273 K, 1 bar 3.40 Li@ATFG-COF 242 N/A 273 K, 1 bar 3.58 AB-COF 1125 1.3 273 K, 1 bar 3.38 Zn@AB-COF 1120 N/A 273 K, 1 bar 4.68 Li@AB-COF 998 N/A 273 K, 1 bar 4.33 3. Design COFs for CO 2 capture Over the past decades, many COFs have been reported and applied to different applications. Some of them have been applied to adsorb CO 2 and exhibited exceptional performance, which makes them competitive candidates for industrial carbon capture and, more attractively, help to realize the net-zero emission goal (Table 1). [16, 48-49] Like other porous solids, the adsorption of CO 2 in COFs relies on the following basic concept. As CO 2 is non-polar but has an intrinsic quadrupole moment, any moieties that induce polarity are desirable for efficient CO 2 capture. In addition, introducing non-polar interactions (like creating a confined space for CO 2 ) and incorporating chemisorption processes by bringing in amine species into the pores also facilitate the CO 2 adsorption. The following section will present an overview of designing COFs for CO 2 adsorption and try to decode their structure-function relationship. 3.1. Design suitable building units Designing proper building units is crucial and efficient for fabricating desired COFs for CO 2 adsorption. As mentioned above, selecting suitable building units could create confined spaces for CO 2 adsorption, especially under low pressure. The first experimental work that applied COFs to CO 2 adsorption dates back to 2009. Yaghi et al. reported seven COFs and systematically explored their CO 2 adsorption properties. [50] These COFs were categorized into three groups. Group 1 contained two 2D COFs (COF-1 and COF-6) with small 1D pores about 0.9 nm. Group 2 comprised three 2D COFs with larger 1D pores (2.7 nm for COF-5, 1.6 nm for COF-8, and 3.2 nm for COF-10), and Group 3 included two 3D COFs with a 3D middle size of about 1.2 nm. At higher temperature and pressure (298 K, 55 bar), the CO 2 uptake of these COFs decreased in the sequence of COF-102 (1200 mg g −1 ) > COF-103 (1190 mg g −1 ) > COF-10 (1010 mg g −1 ) > COF-5 (870 mg g −1 ) > COF-8 (630 mg g −1 ) >COF-6 (310 mg g −1 ) > COF-1 (230 mg g −1 ), following the sequence of their Brunauer-Emmett-Teller (BET) surface area. While at lower temperature and pressure (273 K, 1bar), COF-6 exhibited superior performance over other COFs, demonstrating the favorable effect of creating con- Figure 4. Comparison of the CO 2 capture performance of 66 COFs with their pore size. The data were collected from Table 1, and the colors were solely used to discriminate the CO 2 adsorption capacity of these COFs. fined space for CO 2 adsorption. Such phenomena could also be found in other works. [51-54] Figure 4 shows a comparison of CO 2 uptake capacity for different COFs with different pore diameters, suggesting a pore size less than 2 nm to be preferred for CO 2 adsorption at 273 K and 1bar. found in other works. The unique geometry of the building units could be beneficial for CO 2 capture. Generally, in 2D COFs, the close stacking of 2D layers would make some affinitive sites less accessible than their 3D counterparts. In this way, El-Kaderi et al. designed a special 2D COF, TDCOF-5, with boronate ester linkages by reacting 1,4-benzenediboronic acid with hexahydroxytriptycene. [55] In contrast to the normally used planar units that assemble into closely stacked structures due to the strong π-π interactions in 2D COFs, the non-planar triptycene unit would make the boron sites more accessible to guest molecules. This was proved by the larger d-spacing (7.41 Å) between the 2D layers (the normal d-spacing for 2D COFs was 3-4 Å). Besides, the BET surface area of TDCOF-5 was determined as 2497 m 2 g -1 . These features made it a potential CO 2 capture material. At 273 K and 1 bar, TDCOF-5 could adsorb 2.09 mmol g -1 CO 2 . Wang et al. also designed and synthesized a prism-like cage-based building unit to synthesize COFs. [56] Due to the unique geometry of such components, the obtained COF was found to exhibit ABC stacking mode, forming trigonal channels along the c-axis and resulting in a reduction of pore size to 1.1 nm. Such a 3D-like 2D extended structure offered special affinity to CO 2 molecules, and cage-COF-1 reached a CO 2 uptake of 1.96 mmol g -1 at 273 K and 1 bar. Considering the intrinsic quadrupole moment of CO 2 , integrating heteroatoms into the skeleton of the building units would improve the CO 2 adsorption performance of COFs. Different heteroatoms, including N, [57-59] O, [60-64] F, [65] S, [66-67] Cl, [51] etc., have been proven to be beneficial to CO 2 capture. For example, Liu et al. synthesized two COFs, named ACOF-1 and COF-JLU2, with a similar pore size of about 1 nm and investigated their CO 2 capture performance. [60-61] ACOF-1 was synthesized by co-condensation of 1,3,5-triformylbenzene and hydrazine hydrate, while COF-JLU2 was synthesized by co-condensation of 1,3,5-triformylphloroglucinol (Tp) and hydrazine hydrate. The BET surface area of ACOF-1 and COF-JLU2 was 1176 m 2 g -1 and 470 m 2 g -1 . However, due to the higher content of O, COF-JLU2 exhibited a higher Q st of 31 kJ mol -1 compared with 27.6 kJ mol -1 of ACOF-1, making COF-JLU2 exhibit a higher CO 2 uptake of 4.93 mmol g -1 than 4.02 mmol g -1 of ACOF-1 at 273 K and 1 bar. (Figure 5) Meanwhile, the CO 2 / N 2 selectivity of Figure 5. (a) Synthetic diagram of ACOF-1. (b) CO 2 adsorption curve of ACOF-1 at 273 K and 298 K. Reproduced with permission from ref. 60. Copyright 2014, Royal Society of Chemistry. (c) Synthetic diagram of COF-JLU2. (d ) CO 2 adsorption curve of COF-JLU2 at 273 K and 298 K. Reproduced with permission from ref. 61. Copyright 2015, Wiley-VCH. COF-JLU2 was determined to be 77 at 273 K, which was higher than 40 for ACOF-1. In fact, not only the content of heteroatoms in COFs but also the distribution of these heteroatoms impacts their CO 2 capture performance. Zou et al. reported two COFs, termed COF-H1 and COF-H2, from a novel tetratopic 2,3,5,6-tetrakis(4-aminophenyl) pyrazine unit and two ditopic aromatic aldehydes with different positions of the hydroxyl groups. [68] The porosity of these two COFs was estimated by nitrogen adsorption, and COF-H1 held a BET surface area of 510 m 2 g -1 and a pore size of 1.3 nm, while COF-H2 was 625 m 2 g -1 and 1.2 nm, which made COF-H2 seem to be more favorable for CO 2 adsorption according to the previous empirical findings. However, at 273 K, 1 bar, COF-H1 exhibited a capacity of 1.50 mmol g -1 and COF-H2 held a capacity of 1.29 mmol g -1 , which demonstrated that the o-dihydroxyl groups in COF-H1 had a higher affinity to CO 2 compared with the p-dihydroxyl groups in COF-H2. Gu et al. also found a similar result during water harvesting from the air. [69] These results highlight the important role of controlling the distribution of functional groups within COFs. Creating an ionic pocket within COFs introduces an electrostatic interaction toward the CO 2 molecule and would improve their CO 2 capture ability. [70-71] Jiang et al. designed and synthesized a cationic linker, named 5,6-bis(4-formylbenzyl)-1,3-dimethyl-benzimidazolium bromide, and obtained PyTTA-BFBIm-iCOF after reacting with 4,4’,4’ ’,4’ ’ ’-(pyrene-1,3,6,8-tetrayl) tetraaniline (Figure 6). [72] PyTTA-BFBIm-iCOF was found to hold an unconventional reversed AA-stacking mode, which alternately orientated the cationic units to both sides of its pore walls. Such an open ionic interface within the framework endowed PyTTA-BFBIm-iCOF with unusual electrostatic function, making it a promising candidate for CO 2 adsorption. Compared with its neutral analog, PyTTA-TPhA-COF, with a CO 2 uptake of 1.48 mmol g -1 , PyTTA-BFBIm-iCOF exhibited a much higher CO 2 uptake of 4.02 mmol g -1 at 273 K and 1 bar. Later, Dong et al. also applied such a concept to synthesize an ionic COFs by introducing a monomer with ionic liquid (IL) side chains and achieved a high CO 2 uptake of 4.73 mmol g -1 at 273 K and 1 bar. [71] Fang et al. reported a similar phenomenon in 3D COFs. [73] Interestingly, Fang et al. reported an ionothermal synthesis method by using ILs as a solvent. After the reaction, ILs could be left within the pores of these COFs and facilitate the adsorption of CO 2 . [74] Figure 6. (a) Synthetic diagram of PyTTA-BFBIm-iCOF. (b) Top and side views of the simulated reversed slipped AA-stacking mode of PyTTA-BFBIm-iCOF. (c) CO 2 (circles) and N 2 (triangles) adsorption curves of PyTTA-BFBIm-iCOF at 273 K (red) and 298 K (blue). Reproduced with permission from ref. 72. Copyright 2017, Wiley-VCH. 3.2. Choose special linkages Different linkages have been developed to synthesize COFs, and these linkages have a profound influence on the crystallinity, porosity, stability, and affinity to CO 2 of COFs. Since the previous works have proved that it is constructive to create a confined space for CO 2 adsorption. [75] Under this empirical principle, the azine linkage is found to be attractive to manufacture COFs with small apertures due to the small size of the hydrazine hydrate molecule. As shown in Figure 7, Wan et al. synthesized a tailor-made azine-linked COFs, T-COF, via the polycondensation reaction between 2, 4, 6-trimethoxybenzene-1, 3, 5-tricarbaldehyde and hydrazine hydrate. [53] T-COF owned a microporous structure, and its porosity was estimated by nitrogen adsorption. Although the BET surface area of T-COF was only 587 m 2 g -1 , T-COF exhibited a high CO 2 uptake of 4.04 mmol g -1 due to its small pore size of 0.8 nm and the presence of abundant N and O heteroatoms. Figure 7. (a) Synthetic diagram of T-COF. (b) Top views of the simulated AA-stacking mode of T-COF. (c) CO 2 adsorption curves of T-COF at 273 K (red) and 298 K (black). Reproduced with permission from ref. 53. Copyright 2022, Royal Society of Chemistry. The linkage of COFs could also provide additional interactions with the CO 2 molecule to strengthen the CO 2 capture performance of the COFs, as the majority of the linkages contain heteroatoms. [27] Yaghi et al. reported a nitrone-linked COF, COF-115, by reacting terephthaladehyde with a multidentate hydroxylamine monomer. [76] The zwitterionic nature of the nitrone linkage in COF-115 was expected to provide more favorable interactions with CO 2 compared with the imine-linked COF with the same pore size and similar BET surface area. As expected, the CO 2 uptake of COF-115 was 1.65 mmol g -1 at 298 K and 1 bar, while it was only 1.16 mmol g -1 for the imine-linked COF. Some works on the other linkages, like the benzobisoxazole linkage, [77] the benzimidazole linkage, [46] the dioxin linkage, [44] the cyanurate linkage, [78] etc., also proved that a special linkage could enhance the CO 2 uptake capacity of COFs. Besides, linkage could also create ionic pockets within COFs. Feng et al. developed a spiroborate-linked COF via the thermodynamically controlled transesterification reaction between hydroxy groups and trimethyl borate (B(OMe) 3 ) (Figure 8). [79] The spiroborate linkage was anionic and required counterions to balance its negative charges, which also offered special insight to explore the influence of these counterions. The co-condensation of γ-cyclodextrin (γ-CD) with B(OMe) 3 in the presence of LiOH under microwave-assisted solvothermal conditions generated CD-COF-Li with an anionic spiroborate linkage with Li + as the counterion. Replacing LiOH with piperazine (PPZ) or dimethyl amine (DMA) as proton acceptors under similar conditions would generate CD-COF-PPZ and CD-COF-DMA with related counterions. These COFs were found to hold the same backbone, and only the counterions were different. The BET surface area was 760 m 2 g -1 for CD-COF-Li, 494 m 2 g -1 for CD-COF-PPZ, and 934 m 2 g -1 for CD-COF-DMA, and they displayed similar pore size. However, CD-COF-PPZ with the lowest BET surface area reached the highest CO 2 uptake of 2.77 mmol g -1 at 273 K and 1 bar, proving the ionic environment could also impact the CO 2 capture capacity of COFs and the floating protonated PPZ ions within the pore of CD-COF-PPZ supplied special affinity towards CO 2 molecules. Figure 8. (a) Synthetic diagram of CD-COFs. (b) Effects of various counterions on CO 2 / N 2 selectivity, Q st values, and CO 2 uptake of CD-COF-Li, CD-COF-DMA, and CD-COF-PPZ. (c) Illustration of the preferred adsorption of CO 2 over N 2 in CDCOFs. ). Reproduced with permission from ref. 79. Copyright 2017,Wiley-VCH. 3.3. Control the topology The topology diagram offers a direct way toward COFs with a small confined space for CO 2 . According to the topology diagram, Figure 9. (a) Synthetic diagram of HEX-COF 1. (b) Nitrogen isotherm of HEX-COF 1 at 77 K. (c) CO 2 adsorption curve of HEX-COF 1 at 273 K (filled circles) and 298 K (open circles). Reproduced with permission from ref. 80. Copyright 2016, Royal Society of Chemistry. if the distance between the two vertices is defined as L , the pore size of the 2D triangular, tetragonal, and hexagonal lattice would be about 1/\(\sqrt{3}\) L , L , and \(\sqrt{3}\) L , respectively. [21] Therefore, the [ C 6 + C 2 ] combination opens a good way to fabricate COFs with small pores. In 2016, Smaldone et al. reported an azine-linked COF, HEX-COF 1, based on the co-condensation of hydrazine hydrate with a six-fold symmetric hexphenylbenzene (HEX) monomer (Figure 9). [80] The pore size of HEX-COF 1 was determined to be 1.1 nm, and the BET surface area of HEX-COF 1 was measured as 1214 m 2 g -1 . These features made HEX-COF 1 a suitable CO 2 adsorbent. The CO 2 adsorption property of HE-COF 1 was measured at 273K and 1 bar. HEX-COF 1 showed an excellent sorption capability of 4.55 mmol g -1 . While differing from 2D COFs, 3D COFs supplied another approach to construct a small confined space. [81] In 3D COFs, the building units are extended in a 3D mode without the close stacking of the building units, making the open framework less stable. However, the large space of these 3D COFs allowed interpenetration of the networks, which not only made the framework more stable but also reduced the pore size. [30-31, 82] Wang et al. reported the synthesis of a 3D COF, named 3D-Py-COF, with the pts topology (Figure 10). [83] 3D-Py-COF exhibited a good BET surface area of 1290 m 2 g -1 and a small aperture of 0.6 nm, which was suitable for CO 2 capture. At 273 K and 1.08 bar, 3D-Py-COF reached a high CO 2 uptake capacity of 3.49 mmol g -1 . The adsorption selectivity for CO 2 / N 2 mixtures (15/85 molar ratio) of 3D-Py-COF as a function of pressure was calculated. The selectivity of CO 2 over N 2 showed a smooth increase between 0 and 1.08 bar and reached 22.2 at 1.08 bar. Figure 10. (a) Synthetic diagram of 3D-Py-COF. (b) N 2 isotherm of 3D-Py-COF at 77 K. (c) CO 2 and N 2 adsorption curve of 3D-Py-COF at 273 K. Reproduced with permission from ref. 83. Copyright 2016, American Chemical Society. The topology diagram also provides an insightful way to construct defective COFs with unreacted functional groups. These functional groups contain heteroatoms that could serve as additional CO 2 adsorption sites. Loh et al. reported the synthesis of a defective COF, named TPE-COF-II, through a [2+4] pathway by simply tuning the solvents during the solvothermal synthesis. [84] Compared with the ideal [4+4] product, TPE-COF-II exhibited a higher BET surface area, a similar pore size distribution, and additional unreacted aldehyde groups, which implied TPE-COF-II would be preferred for CO 2 capture. In expectation, the [2+4] TPE-COF-II exhibited a higher CO 2 uptake of 5.30 mmol g -1 than 3.06 mmol g -1 of its [4+4] counterpart at 273 K and 1 bar. Such defective COFs could also be synthesized by a geometry-mismatch [4+3] topology diagram. Loh et al. developed a [4+3] topology diagram to construct a sub-stoichiometric COF with unreacted amine groups. [85] Unlike the normal complementary polycondensation mode, which formed a fully condensed 2D framework, such [4+3] combination would generate a frustrated 2D network due to their geometry mismatch. The obtained PT-COF and PY-COF were assigned to hold the bex topology with some unreacted amine groups hanging onto the pore wall of the COFs. The CO 2 uptake capacity of PT-COF and PY-COF was 2.16 mmol g -1 and 3.32 mmol g -1 at 273 K and 1 bar, verifying their good affinity to CO 2 molecules. In contrast to creating stacking structure in 2D COFs, the building units in 3D COFs are extended in a 3D mode, making the active sites more accessible to the CO 2 molecule. [86-87] He et al. developed a 3D COF with the ceq topology utilizing a D 3h -symmetric triangular prism vertex with a planar triangular linker. This as-synthesized 3D COF was named 3D-ceq-COF and found to display a two-fold interpenetrated structure (Figure 11). [86] Interestingly, Fang et al. also reported the synthesis of a 3D COF, named JUC-568, with the ceq topology from the same building units as 3D-ceq-COF, while JUC-568 was found to be non-interpenetrated. [87] The BET surface area of 3D-ceq-COF and JUC-568 was 1149 m 2 g -1 and 1433 m 2 g -1 . However, the pore size of them was different owing to their different interpenetrated structure. 3D-ceq-COF exhibited two main peaks at 1.0 nm and 1.6 nm, and JUC-568 exhibited one peak at 1.9 nm. Both COFs were applied to CO 2 adsorption, and the CO 2 uptake of 3D-ceq-COF and JUC-568 was 4.07 mmol g -1 and 4.38 mmol g -1 . He et al. systematically investigated the interaction between the CO 2 molecule and the framework using density functional theory calculations. They found that the exposed phenyl groups and the triazine rings in the 3D framework have stronger interaction with CO 2 than their stacked counterparts. More importantly, the geometry of the triptycene-based building units made the two adjacent electron-rich imine bonds form a special pocket for the CO 2 molecule and exhibit a higher adsorption energy of CO 2 than the individual and the stacked imine bonds. Figure 11. (a) Synthetic diagram of 3D-ceq-COF and the corresponding simplified two-fold interpenetrated ceq net. (b) N 2 isotherm of 3D-ceq-COF at 77 K. (c) Gas adsorption curves of 3D-ceq-COF. Reproduced with permission from ref. 86. Copyright 2021, American Chemical Society. 3.3. Post-synthetic modification of COFs The aqueous solution of amine has already been developed for capturing CO 2 at low concentrations due to its high CO 2 affinity. Therefore, integrating amine species into COFs provides a new opportunity toward high-performance COF-based adsorbents. In Figure 12, Zhao et al. reported a one-step post-synthetic modification method to reduce the imine linkage to the amine linkage. [88] The transformation was achieved by treating the parent SP-CA-COF-IM with NaBH(OAc) 3 , which was found to yield a remarkable conversion rate and could efficiently convert the imine bond into the amine bond. Surprisingly, after the reduction, the crystalline structure of SP-CA-COF-IM was well-retained, and the BET surface area of SP-CA-COF-AM was also comparable to SP-CA-COF-IM (1557 m 2 g -1 for SP-CA-COF-AM and 1551 m 2 g -1 for SP-CA-COF-IM). Inspired by these features, the authors further tested the CO 2 uptake capacity of the two COFs. At 273K and 1 bar, the CO 2 uptake capacity of SP-CA-COF-IM and SP-CA-COF-AM was 2.47 and 3.75 mmol g -1 , which proved the higher affinity of the amine linkage over the imine linkage. Figure 12. (a) Synthetic diagram of SP-CA-COF-IM and SP-CA-COF-AM. (b) N 2 isotherm of SP-CA-COF-IM and SP-CA-COF-AM at 77 K. (c) CO 2 adsorption curves of SP-CA-COF-IM and SP-CA-COF-AM. Reproduced with permission from ref. 88. Copyright 2023, Royal Society of Chemistry. Beyond the linkage transformation, various functionalities could also be facilely attached to the skeleton of COFs via post-synthetic modifications. [89-93] For example, Jiang et al. performed the famous click reaction to anchor a variety of functional groups, including ethyl, acetate, hydroxyl, carboxylic acid, and amino groups, onto the pore wall of an imine-linked COFs with a low capacity in CO 2 adsorption (Figure 13). [89] Although the surface area of the resulting COFs would decrease after the modification, their interaction with CO 2 would also change due to the reduced pore sizes and the introduced functional groups. The CO 2 uptake of these modified COFs varied, and most of them exhibited higher performance than the original COFs. [EtNH 2 ] 50 -H 2 P-COF, in which the proper content of amine species was introduced, especially exhibited a high CO 2 uptake capacity of 3.57 mmol g -1 at 273 K and 1 bar, which was 3-fold of the parent [HC≡C] 50 -H 2 P-COF. Figure 13. (a) Synthetic diagram of pore surface engineering of imine-linked COFs with various functional groups via click reactions. (b) Pore structures of COFs with different functional groups (gray, C; blue, N; red, O). (c) CO 2 adsorption capacity of the COFs at 273 (red) and 298 K (blue) and 1 bar. Reproduced with permission from ref. 89. Copyright 2015, American Chemical Society. Besides, Jiang et al. reported another pore surface modification method, which relied on the transformation of the hydroxyl groups into the carboxylic acid groups via a ring-opening reaction. [90] Although the BET surface area of the modified COF also decreased, the incorporation of a higher density of carboxylic acid groups would result in higher CO 2 uptake capacity, which meant the structural benefits of this post-synthetic modification compensated for the loss of porosity. As a result, the [HO 2 C] 100% -H 2 P-COF exhibited a CO 2 uptake capacity of 4.09 mmol g -1 , which was 2.8-fold of the [HO] 100% -H 2 P-COF. More importantly, they applied the ideal absorbed solution theory (IAST) to calculate the selectivity of CO 2 over N 2 . For the CO 2 / N 2 mixture with 15% CO 2 and 85% N 2 at 298 K and 100 kPa, [HO 2 C] 100% -H 2 P-COF exhibited a selectivity of 77, whereas [HO] 100% -H 2 P-COF exhibited a selectivity of only 8. Similarly, the post-synthetic modification method could also integrate ionic units into the COFs. Gao et al. presented a post-synthetic modification method to immobilize ionic units on the channel wall of the COFs. [94] The modification was accomplished via the Williamson ether reaction between the hydroxyl groups and (2-bromoethyl)triethylammonium bromide. After the evaluation, the [Et 4 NBr] 50% -Py-COF possessed the best CO 2 uptake capacity of 3.74 mmol g -1 at 273 K and 1 bar. More importantly, the counterions within the ionic COFs could also be exchanged via ion-exchange, which provided a facile strategy to modify their CO 2 adsorption performance. [95-97] Incorporation of metal ions into the skeleton of COFs also helps to improve their affinity to CO 2 . [98-101] Lotsch et al. reported two isostructural COFs based on 1,3,5-triformyl benzene (AB-COF) and 1,3,5-triformylphloroglucinol (ATFG-COF) and hydrazine building units. [102] The structure of AB-COF and the ATFG-COF held the same structure as the previous ACOF-1 and COF-JLU2, while exhibiting relatively lower CO 2 uptake capacity at 273 K and 1 bar. To enhance their gas sorption capacities, they chemically modified the pore environment of the COFs by metal-doping. After the modification, the metal loading of the resulting Zn@ATFG-COF, Li@ATFG-COF, Zn@AB-COF, and Li@AB-COF was determined to be 8%, 1%, 0.6%, and 0.8%. Compared with the pristine ATFG-COF, Zn@ATFG-COF and Li@ATFG-COF exhibited lower CO 2 uptake capacity due to the severely reduced BET surface area, while in comparison with AB-COF, Zn@AB-COF and Li@AB-COF showed higher CO 2 uptake capacity. Zn@AB-COF especially, exhibited a high CO 2 uptake of 4.68 mmol g -1 at 273 K and 1 bar (AB-COF was 3.38 mmol g -1 ). Similar phenomena were reported by Zhao et al (Figure 14). [103] The Py-1P COF was doped with different metal salts. After doping, the CO 2 uptakes were increased by 67.9%, 89.5%, and 25% in Fe 3+ -doped, Cr 3+ -doped, and In 3+ -doped Py-1P, respectively. More interestingly, they found unusual CO 2 sorption isotherms featuring one or more tunable hysteresis steps after metal salt doping. By synchrotron X-ray diffraction, spectroscopic and computational studies, they proposed that such phenomena originate from the insertion of CO 2 between the metal ion and the N atom of the imine bond on the inner pore surface of the COFs as the CO 2 pressure reaches threshold values and can be adjusted through controlling the amount of water adsorbed on the metal ion or altering the counterion around the metal center. Figure 14. (a) Synthetic diagram of the metal ion-doped 2D COFs. (b) CO 2 adsorption curves of pure and metal ion-doped Py-1P COFs. Reproduced with permission from ref. 103. Copyright 2023, National Academy of Sciences. It is important to capture CO 2 under low concentration, especially directly from the air. Efficient capture of CO 2 from the air requires materials that can selectively and efficiently adsorb CO 2 under low CO 2 concentrations. To achieve this goal, Yaghi et al. proposed a series of post-synthetic methods to incorporate multiple amine groups into their tailor-made COFs and obtained several COFs with exceptional performance. [104-106] The main point of these methods was creating a stable framework precursor and then introducing amine species into the precursors to modulate their CO 2 uptake capacity. In 2022, they synthesized the first example, COF-609, which was made by crystallization of one COF with the imine linkage, followed by the cycloaddition procedure on the linkage, converting it into the base-stable tetrahydroquinoline linkage, and finally introduced the amine species by substituting the -Cl groups with tris(3-aminopropyl)amine units. [104] After such conversion, COF-609 could adsorb 0.304 mmol g -1 CO 2 at 298 K and 0.4 mbar, exhibiting a 1360-fold increase compared with the pristine COF, which only adsorbed 0.00022 mmol g -1 under the same conditions. After the proof-of-concept work, they further designed two new COFs, termed COF-709 and COF-999, with different skeletons and reached better CO 2 adsorption performance than COF-609. COF-709 was synthesized by crystallization of an imine COF, followed by linkage oxidation to form a stable amide-linked framework, and finally installed the amine species by aromatic nucleophilic substitution between -SH and -F groups. [105] COF-709 could adsorb 0.44 mmol g -1 at 298 K and 0.4 mbar and 1.24 mmol g -1 under 75% relative humidity at 298 K and 0.4 mbar, and exhibited good cyclic stability after 10 adsorption-desorption cycles. Different from COF-609 and COF-709, the skeleton of COF-999 was synthesized through the direct Knoevenagel condensation between the building units, forming the stable olefin-linked framework (Figure 15). [106] The reduction of the azide groups in the precursors formed the -NH 2 groups, and treating the reduced samples with aziridine could introduce the amine species within the pores to obtain the aiming COF-909. COF-909 could adsorb 0.96 mmol g -1 at 298 K and 0.4 mbar CO 2 and 2.09 mmol g -1 under 75% relative humidity at 298 K and 0.4 mbar. More importantly, COF-999 retained its performance after more than 100 adsorption-desorption cycles under practical outdoor tests. Figure 15. (a) Synthetic diagram of COF-999. (b) Gas adsorption curves COF-999 at 298 K. (c) Magnified view of the CO 2 sorption isotherm highlighting the uptake at the ambient CO 2 pressure (0.4 mbar). (d) CO 2 uptake under 400 ppm of CO 2 with 0%, 25%, 50% and 75% RH. Reproduced with permission from ref. 106. Copyright 2024, Springer Nature. 4. Conclusions and Perspectives In summary, despite the development of renewable energy technologies having made great progress, the increasing atmospheric CO 2 concentration requires other complementary technologies, like sorbent-based technology, to be implemented and help to address the urgent global CO 2 emission crisis. As one of the recently developed porous solids, COFs own intrinsic porosity, structural diversity, and high durability, which would undoubtedly render them promising candidates to capture and store CO 2 . Although COFs have achieved significant progress in this field over the last decades and exhibited their potential to be invested in to realize industrial carbon capture, there is still a long way to go to realize this goal. Many efforts have been put into designing and synthesizing COFs with high CO 2 adsorption capacity and high selectivity over other gases, while most of them focus on introducing CO 2 -philic sites into the frameworks via the de novo synthetic method or the post-synthetic modification to modify their pore environments. Few works concentrate on manipulating the stacking mode of COFs. The stacking mode of COFs could not only impact the pore size of COFs, but also change the distance of the functional groups between the nearby extended layer structures, offering special affinity to CO 2 . Besides, the morphology of COFs could also influence their separation properties. For example, creating hierarchically porous structures supplies large pores to guarantee the fast diffusion of guest gases, while the small pores promote the separation of CO 2 over other gases. In addition to introducing a suitable pore environment to bind CO 2 , constructing COFs with a high specific surface area also facilitates high CO 2 uptake. In this regard, compared with 2D COFs with layered structures and one-dimensional channels, 3D COFs hold more void space and interconnected pore structures, which enable them to obtain a high surface area, and enable the active sites within their open frameworks to be accessed. Nevertheless, there are only limited works applied 3D COFs to capture CO 2 up to now. Compared with 2D COFs, the crystallization of 3D COFs is more difficult and requires more rigid and precise conditions, resulting in most of the reported COFs being 2D COFs. Since more and more works on 3D COFs have been reported in recent years, more efforts should be made to apply 3D COFs to capture CO 2 . More investigations, especially the real-life tests on selectively adsorbing CO 2 over other gases, should be completed. Most reported works focus on the selective adsorption of CO 2 over N 2 . Some other gases, particularly H 2 O vapor, would compete with CO 2 and severely interfere with the carbon capture process. Meanwhile, despite the robustness of the covalent bond endowing COFs with high thermal stability, the chemical stability of different COFs varies due to their different compositions, pore structures, and crystallinities, etc. Some COFs may exhibit high stability and maintain their structural integrity after soaking in different solvents, while for real-life applications, the capture stability under the operating conditions of COFs should also be considered. The experimental findings supply important information toward future design of COFs for CO 2 capture, while the tedious laboratory work is inevitable to find suitable material. 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M.; Alawad, M. O.; Gagliardi, L.; Sauer, J.; Yaghi, O. M. Carbon dioxide capture from open air using covalent organic frameworks. Nature 2024 , 635 , 96-101. Left to Right: Fuxiang Wen, Ning Huang Fuxiang Wen received his B. S. from the Department of Polymer Science and Engineering, Zhejiang University (China) in 2021. He is currently a PhD candidate under the supervision of Prof. Ning Huang in the Department of Polymer Science and Engineering at Zhejiang University. His research focuses on designing and synthesizing novel covalent organic frameworks and other complex systems Ning Huang is a professor in the Department of Polymer Science and Engineering, Zhejiang University. He received his BS degree from Shandong University in 2009 and his PhD degree from Institute of Molecular Sciences (Japan) in 2015. From 2016 to 2019, he worked as a postdoctoral researcher at Japan Advanced Institute of Science and Technology, Texas A&M University, and National University of Singapore. In 2019, he started a faculty position at Zhejiang University. His research includes the design, synthesis, and function exploration of crystalline two-dimensional polymers, including covalent organic frameworks and metal-organic frameworks. Entry for the Table of Contents Reticular Synthesis of Covalent Organic Frameworks for Carbon Dioxide Adsorption Fuxiang, Wen, Ning, Huang* Chin. J. Chem. 2024 , 42 , XXX—XXX. DOI: 10.1002/cjoc.202400XXX This review provides the basic design principles of COFs, summarizes recent de novo and post-synthetic modification methods for designing suitable COFs for CO 2 capture, and discusses the challenges and prospects. 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Collection Chinese Journal of Chemistry Keywords 2d nanomaterials carbon capture covalent organic frameworks porous polymer reticular chemistry Authors Affiliations Fuxiang Wen 0000-0001-6061-7174 Zhejiang University Department of Polymer Science and Engineering View all articles by this author Ning Huang 0000-0002-7021-8705 [email protected] Zhejiang University Department of Polymer Science and Engineering View all articles by this author Metrics & Citations Metrics Article Usage 394 views 190 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Fuxiang Wen, Ning Huang. Reticular Synthesis of Covalent Organic Frameworks for Carbon Dioxide Adsorption. Authorea . 25 September 2025. DOI: https://doi.org/10.22541/au.175879152.22892919/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. 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