Covalent Organic Frameworks for Carbon Dioxide Capture from Air

Solubility-Driven Ligand Design of Zn(II) Complexes for Enhanced CO2 Capture in Methanol

Diacetyl-2-(4-methyl-3-thiosemicarbazonato)-3-(2-hydrazinatopyridine)(methanol) zinc(II) (ZnL10(MeOH)) and related structures use metal-ligand cooperativity to capture atmospheric CO2 under ambient conditions. However, the low solubility in protic solvents limits their practical use in direct air capture systems. This study reports the synthesis, characterization, and CO2 binding affinity of a series of new alkylthiocarbamato-hydrizinato(pyridine) ZnLn(MeOH) complexes (n = 1-9) and assesses the solubility and CO2 binding affinity of each complex. Replacement of the thiosemicarbazonato functional group with alkylthiocarbamato groups leads to increased Lewis acidity and CO2 binding affinity relative to ZnL10(MeOH). Additionally, the solubility of the complexes increased as a function of the alkylthiocarbamato group. In comparison to the structurally related thiosemicarbazonato complex, ZnL11(MeOH), the solubility of the ZnL1(MeOH) to ZnL9(MeOH) complexes was more than 100 times higher, accompanied by excellent binding affinities. The CO2 equilibrium binding constant (K1) showed an increase from 33,600 ± 1700 for ZnL1(MeOH) to 69,000 ± 7900 for ZnL8(MeOH) with the addition of the backbone phenyl group. Overall, the study revealed that the total amount of CO2 captured per unit volume is influenced by both the CO2 binding constant (K1) and the solubility of the complex, with the solubility being the dominant factor.

In Pursuit of Carbon Neutrality: Progresses and Innovations in Sorbents for Direct Air Capture of CO2

Direct air capture (DAC) is of immense current interest, as a means to facilitate CO2 capture at low concentrations (∼400 ppm) directly from the atmosphere, with the aim of addressing global warming caused by excessive anthropogenic CO2 production. Traditionally, DAC of CO2 has relied on amine scrubbing and metal carbonate /hydroxide solutions. However, recent years have seen notable progress in DAC sorbents, with key advancements aimed at improving efficiency, capacity, and regenerability while reducing energy consumption. This review delivers an exhaustive analysis of contemporary developments in DAC sorbents, addressing the innovations in material design and consequent performance enhancement. The limitations of the sorbents have also been discussed, with future perspectives for improving sustainable CO2 capture strategies. We anticipate that this overview will help lay the groundwork for further development and large-scale implementation of sustainable sorbents and cutting-edge technologies toward attaining carbon neutrality.

Covalent Organic Framework Membranes: Synthesis Strategies and Separation Applications

Covalent organic frameworks (COFs) have emerged as highly promising materials for membrane separations due to their high porosity, tunable pore sizes, ordered crystalline structures, and exceptional chemical stability. With these features, COF membranes possess greater selectivity and permeability than conventional materials, making them the preferred choice in various fields, including membrane separations. Fascinating research endeavors have emerged encompassing fabrication strategies for COF-based membranes and their diverse separation applications. Hence, this review summarizes the latest advancements in COF synthesis, including COF powders and continuous COF-based membranes and their applications in separation membranes. Special consideration was given to regulation strategies for the performance optimization of COF membranes in separation applications, such as pore size, hydrophilicity/hydrophobicity, surface charge, crystallinity, and stability. Furthermore, applications of COF membranes in water treatment, metal ion separation, organic solvent nanofiltration, and gas separation are comprehensively reviewed. Finally, the research results and future prospects for the development of COF membranes are discussed. Future research may be focused on the following key directions: (1) single-crystal COF fabrication, (2) cost-effective membrane preparation, (3) subnanometer pore engineering, (4) advanced characterization techniques, and (5) AI-assisted development.

Unraveling Dimensional Tuning: From 2D to 3D in Covalent Organic Frameworks for Enhanced 2e- Oxygen Reduction Reaction

Covalent organic frameworks (COFs) with a two-dimensional (2D) topology have recently emerged as promising catalyst systems for the electrosynthesis of hydrogen peroxide (H2O2) from oxygen (O2). However, designing 2D catalysts to achieve higher H2O2 selectivity presents a significant challenge because of the extensive layer stacking and the aggregated active sites located in the basal planes. It results in lower atom utilization, which requires attention. In this study, we present two functionally similar COFs: one with a 2D rhombus topology (2D@BT_TPA-COF) and another with a three-dimensional (3D) noninterpenetrated pts topology (3D@BT_TPA-COF). Both COFs were utilized for the 2e- oxygen reduction reaction (2e- ORR). Tunning the dimensionality from 2D to 3D resulted in an increase in H2O2 selectivity from approximately ∼56% to approximately ∼96% (at 0.4 V) and a rise in the turnover frequency (TOF) from 0.05 to 0.08 s-1 at 0.3 V. Nonaggregated active site distribution over 3D topology, featuring higher active site exposure, provides better access to the O2/electrolyte and facilitates electron transfer leading to higher 2e- ORR activity and selectivity compared to the 2D counterpart.

Efficient photoresponsive one-dimensional covalent organic framework as oxidase-like enzyme for ultrasensitive detection of antioxidants

Natural polyphenolic antioxidants are widely present in foods such as fruits and vegetables, meanwhile applied in food processing and storage to prevent the formation of harmful compounds. While excessive antioxidants lead to negative impacts on human health. Hence, it is crucial to accurately detect antioxidant levels in order to enhance the overall nutritional content and food safety. Herein, a novel one-dimensional covalent organic framework (COF-Por-DPP) was constructed using 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin and 4,4'-(2,6-pyrazinediyl)bisbenzaldehyde. The unique photoresensitive properties and topological structures endowed COF-Por-DPP excellent oxidase-like activity. The COF-Por-DPP based colorimetric assay was established for three antioxidants (gallic acid, tannic acid and caffeic acid). Moreover, this method was used to analyze real samples and a hydrogel sensor was constructed, which demonstrated good accuracy and practicability.

Integrated Capture and Electrocatalytic Conversion of CO2: A Molecular Electrocatalysts Perspective

The ever-increasing concentration of atmospheric CO2, primarily driven by anthropogenic activities, has raised urgent environmental concerns, spurring the development of carbon capture and utilization (CCU) technologies. This review focuses on the integrated capture and electrochemical conversion of CO2 (ICECC), a promising approach that combines carbon capture with its direct electroreduction into value-added products. By eliminating energy-intensive steps such as CO2 release, compression, and transportation, ICECC offers a more energy-efficient and cost-effective alternative to conventional CCU methods. In this review, particular attention is given to molecular electrocatalysts, which offer high tunability and selectivity in electrochemical CO2 reduction reaction (eCO2RR). The role of capturing agents, including both external and dual-functional molecular systems, is critically examined to understand their influence on CO2 binding and catalytic efficiency. Whereas ICECC has significant potential, research in this area remains underexplored compared to conventional CO2 reduction methods. The review discusses the mechanistic insights into ICECC processes, highlighting key challenges and potential future research directions for improving catalyst design, enhancing capture efficiency, and scaling up ICECC technologies. These developments can make ICECC a critical component in achieving carbon neutrality and addressing climate change.

Structural Regulation of Three-Dimensional Covalent Organic Frameworks for Efficient Photoredox Catalysis toward Atom Transfer Radical Polymerization

Covalent organic frameworks (COFs) have emerged as a thriving class of photocatalysts in various chemical transformations. However, the utilization of COFs as photoredox catalysts for atom transfer radical polymerization is rarely known. Herein, we designed and synthesized a series of phenazine-based functional 3D COFs with the dia topology. Structural regulation over interpenetration folds and energy levels of COFs was implemented through the substituent effects. These COFs can work as effective photoredox catalysts toward atom transfer radical polymerization. Notably, DADP-CF3-COF with trifluoromethyl group exhibits much higher catalytic activity than other COFs, allowing the efficient synthesis of polymers with controllable molecular weights, low dispersity, and high conversion. This work not merely realizes the structural regulation of 3D COFs through substituent effects, but also exhibits brilliant prospects for the utilization of COFs as efficient catalysts in a bunch of challenging chemical transformations.

Phase Change-Mediated Capture of Carbon Dioxide from Air with a Molecular Triamine Network Solid

The efficient removal of CO2 from exhaust streams and even directly from air is necessary to forestall climate change, lending urgency to the search for new materials that can rapidly capture CO2 at high capacity. The recent discovery that diamine-appended metal-organic frameworks can exhibit cooperative CO2 uptake via the formation of ammonium carbamate chains begs the question of whether simple organic polyamine molecules could be designed to achieve a similar switch-like behavior with even higher separation capacities. Here, we present a solid molecular triamine, 1,3,5-tris(aminomethyl)benzene (TriH), that rapidly captures large quantities of CO2 upon exposure to humid air to form the porous, crystalline, ammonium carbamate network solid TriH(CO2)1.5·xH2O (TriHCO2). The phase transition behavior of TriH converting to TriHCO2 was studied through powder and single-crystal X-ray diffraction analysis, and additional spectroscopic techniques further verified the formation of ammonium carbamate species upon exposing TriH to humid air. Detailed breakthrough analyses conducted under varying temperatures, relative humidities, and flow rates reveal record CO2 absorption capacities as high as 8.9 mmol/g. Computational analyses reveal an activation barrier associated with TriH absorbing CO2 under dry conditions that is lowered under humid conditions through hydrogen bonding with a water molecule in the transition state associated with N-C bond formation. These results highlight the prospect of tunable molecular polyamines as a new class of candidate absorbents for high-capacity CO2 capture.

Enhanced Removal of Ultratrace Levels of Gold from Wastewater Using Sulfur-Rich Covalent Organic Frameworks

In view of the increasing global demand and consumption of gold, there is a growing need and effort to extract gold from alternative sources besides conventional mining, e.g., from water. This drive is mainly due to the potential benefits for the economy and the environment as these sources contain large quantities of the precious metal that can be utilized. Wastewater is one of these valuable sources in which the gold concentration can be in the ppb range. However, the effective selective recovery and recycling of ultratrace amounts of this metal remain a challenge. In this article, we describe the development of a covalent imine-based organic framework with pores containing thioanisole functional groups (TTASDFPs) formed by the condensation of a triazine-based triamine and an aromatic dialdehyde. The sulfur-functionalized pores served as effective chelating agents to bind Au3+ ions, as evidenced by the uptake of more than 99% of the 9 ppm Au3+ solution within 2 min. This is relatively fast kinetics compared with other adsorbents reported for gold adsorption. TTASDFP also showed a high removal capacity of 245 mg·g-1 and a clear selectivity toward gold ions. More importantly, the material can capture gold at concentrations as low as 1 ppb.

Direct Electroreduction of Low-Concentration CO2: Progress and Perspective

The conversion of CO2 into carbon-based fuels and chemicals via the electrocatalytic CO2 reduction reaction (CO2RR) offers an attractive route to reducing the CO2 emission for carbon neutrality. Currently, high-purity CO2 gas has been widely used as the feedstock for most of the CO2RR studies, while CO2 sources with a typically low concentration impose the extra cost for CO2 capture and purification steps. The direct utilization of low-concentration CO2 for the CO2RR is a promising approach to substantially address this problem. In this Perspective, we first highlight the prominent advantages of direct electroreduction of low-concentration CO2. Then we focus on the summary of several important design strategies for CO2RR in diluted CO2 and gas impurities-containing CO2 atmosphere. Finally, we propose personal outlooks on future challenges and some opportunities for this fascinating research field.

Porous Organic Polymers for CO2 Capture and Catalytic Conversion

Overuse of fossil fuels and anthropogenic activities have led to excessive emissions of carbon dioxide, leading to global warming, and measures to reduce atmospheric carbon dioxide concentrations are needed to overcome this global challenge. Therefore, exploring an environmentally friendly strategy for capturing airborne CO2 and converting it into high-value-added chemicals offers a promising pathway toward "carbon neutrality". In recent years, porous organic polymers have attracted much attention for carbon capture and the catalytic conversion of carbon dioxide because of their high specific surface area, high chemical stability, nanoscale porosity, and structural versatility, which make them easy to functionalize. In this review, we introduce the preparation methods for various POPs, the types of POPs adsorbed during carbon dioxide capture, and the progress in the use of POPs for the photocatalytic and chemicatalytic conversion of carbon dioxide, with a special discussion on the influence of adsorption type on the efficiency of catalytic conversion. Finally, we propose a prospective direction for the subsequent development of this field.

Advancements of astaxanthin production in Haematococcus pluvialis: Update insight and way forward

The global market demand for natural astaxanthin (AXT) is growing rapidly owing to its potential human health benefits and diverse industry applications, driven by its safety, unique structure, and special function. Currently, the alga Haematococcus pluvialis (alternative name H. lacustris) has been considered as one of the best large-scale producers of natural AXT. However, the industry's further development faces two main challenges: the limited cultivation areas due to light-dependent AXT accumulation and the low AXT yield coupled with high production costs resulting from complex, time-consuming upstream biomass culture and downstream AXT extraction processes. Therefore, it is urgently to develop novel strategies to improve the AXT production in H. pluvialis to meet industrial demands, which makes its commercialization cost-effective. Although several strategies related to screening excellent target strains, optimizing culture condition for high biomass yield, elucidating the AXT biosynthetic pathway, and exploiting effective inducers for high AXT content have been applied to enhance the AXT production in H. pluvialis, there are still some unsolved and easily ignored perspectives. In this review, firstly, we summarize the structure and function of natural AXT focus on those from the algal H. pluvialis. Secondly, the latest findings regarding the AXT biosynthetic pathway including spatiotemporal specificity, transport, esterification, and storage are updated. Thirdly, we systematically assess enhancement strategies on AXT yield. Fourthly, the regulation mechanisms of AXT accumulation under various stresses are discussed. Finally, the integrated and systematic solutions for improving AXT production are proposed. This review not only fills the existing gap about the AXT accumulation, but also points the way forward for AXT production in H. pluvialis.

Building a Co-Salen-Immobilized Porous Organic Polymer Catalyst for CO2 Cycloaddition

The CO2-epoxide addition to cyclic carbonate is of great significance but usually requires high temperatures and CO2 pressures. Herein, a spirobifluorene-based porous organic polymer catalyst is designed with a Co-salen complex immobilized on the backbone (ST-CoSalen-POP) to enable CO2 fixation under mild conditions. ST-CoSalen-POP possesses a high Co-loading content (9.35 wt%), a large pore volume, and high CO2 adsorption capacity. This catalyst achieves a 96% yield in the cycloaddition of CO2 with epoxides at 25 °C and 0.1 MPa CO2 pressures. Moreover, ST-CoSalen-POP also offers the advantages of wide adaptability over epoxide substrates and high structural stability for three consecutive cycles. This study presents a novel catalytic approach for promoting CO2 fixation, offering a significant advancement in the efficient synthesis of fine chemicals.

Impact of Postsynthetic Modification on the Covalent Organic Framework (COF) Structures

Covalent organic frameworks (COFs) have emerged as a versatile class of materials owing to their well-defined crystalline structures and inherent porosity. In the realm of COFs, their appeal lies in their customizable nature, which can be further enhanced by incorporating diverse functionalities. Postsynthetic modifications (PSMs) emerge as a potent strategy, facilitating the introduction of desired functionalities postsynthesis. A significant challenge in PSM pertains to preserving the crystallinity and porosity of the COFs. In this study, we aim to investigate the intricate interplay between PSM strategies and the resulting crystalline and porous structures of the COFs. The investigation delves into the diverse methodologies employed in PSMs, to elucidate their distinct influences on the crystallinity and porosity of the COFs. Through a comprehensive analysis of recent advancements and case studies, the study highlights the intricate relationships among PSM parameters, including reaction conditions, precursor selection, and functional groups, and their impact on the structural features of COFs. By understanding how PSM strategies can fine-tune the crystalline and porous characteristics of COFs, researchers can harness this knowledge to design COFs with tailored properties for specific applications, contributing to the advancement of functional materials in diverse fields. This work not only deepens our understanding of COFs but also provides valuable insights into the broader realm of PSM strategies for other solid materials.

From Fundamentals to Synthesis: Covalent Organic Frameworks as Promising Materials for CO2 Adsorption

Covalent organic frameworks (COFs) are highly crystalline polymers that possess exceptional porosity and surface area, making them a subject of significant research interest. COF materials are synthesized by chemically linking organic molecules in a repetitive arrangement, creating a highly effective porous crystalline structure that adsorbs and retains gases. They are highly effective in removing impurities, such as CO2, because of their desirable characteristics, such as durability, high reactivity, stable porosity, and increased surface area. This study offers a background overview, encompassing a concise discussion of the current issue of excessive carbon emissions, and a synopsis of the materials most frequently used for CO2 collection. This review provides a detailed overview of COF materials, particularly emphasizing their synthesis methods and applications in carbon capture. It presents the latest research findings on COFs synthesized using various covalent bond formation techniques. Moreover, it discusses emerging trends and future prospects in this particular field.

Direct air capture of CO2 for solar fuel production in flow

Direct air capture is an emerging technology to decrease atmospheric CO2 levels, but it is currently costly and the long-term consequences of CO2 storage are uncertain. An alternative approach is to utilize atmospheric CO2 on-site to produce value-added renewable fuels, but current CO2 utilization technologies predominantly require a concentrated CO2 feed or high temperature. Here we report a gas-phase dual-bed direct air carbon capture and utilization flow reactor that produces syngas (CO + H2) through on-site utilization of air-captured CO2 using light without requiring high temperature or pressure. The reactor consists of a bed of solid silica-amine adsorbent to capture aerobic CO2 and produce CO2-free air; concentrated light is used to release the captured CO2 and convert it to syngas over a bed of a silica/alumina-titania-cobalt bis(terpyridine) molecular-semiconductor photocatalyst. We use the oxidation of depolymerized poly(ethylene terephthalate) plastics as the counter-reaction. We envision this technology to operate in a diurnal fashion where CO2 is captured during night-time and converted to syngas under concentrated sunlight during the day.

Diketopyrrolopyrrole-Activated Dynamic Condensation Approach to Narrow-Band Gap Vinylene-Linked Covalent Organic Frameworks

Vinyl units intrinsically featuring less steric, nonpolarity, and unsaturated character, are well-known π-bridge used in the synthesis of high-performance semiconducting materials. Two-dimensional (2D) vinylene-linked covalent organic frameworks (COFs) represent a promising class of π-conjugated structures, however, the range of available monomers for the reversible formation of carbon-carbon double bonds remains limited. In this study, a new class of 2D vinylene-linked COFs were synthesized using dimethyldiketopyrrolopyrrole (DM-DPP) as the key monomer. The strong electron deficiency of diketopyrrolopyrrole (DPP) makes its methyl substituents readily activated upon the cocatalysis of L-proline and 4-dimethylaminopyridine in aqueous solution to conduct dynamic condensation with tritopic aromatic aldehydes. The resulting COFs crystallized in an eclipsed AA stacking arrangement and featured abundant, regular nanochannels. Their robust vinyl DPP-linking mode enhanced donor-π-acceptor conjugation and promoted π-stacked alignment along the vertical direction. Consequently, the synthesized COFs exhibited band gaps as narrow as 1.02 eV and demonstrated excellent light-harvesting capability across the visible to near-infrared I (NIR-I) regions. Furthermore, the COFs could be converted into free-standing thin pellets through simple pressure casting, and show excellent photothermal response and cycling stability under different light sources.

A Self-Adjuvanting Large Pore 2D Covalent Organic Framework as a Vaccine Platform

Vaccines are one of the greatest human achievements in public health, as they help prevent the spread of diseases, reduce illness and death rates, saving thousands of lives with few side effects. Traditional vaccine development is centered around using live attenuated or inactivated pathogens, which is expensive and has resulted in vaccine-associated illnesses. Advancements have led to the development of safer subunit vaccines, which contain recombinant proteins isolated from pathogens. Their short half-life and small size make most subunit vaccines less immunogenic. Here, we introduce a large pore 2D covalent organic framework (COF), PyCOFamide, as a promising solution for an effective subunit platform. Our study demonstrates that simple adsorption of a model antigen, ovalbumin (OVA), onto PyCOFamide (OVA@COF) significantly enhances humoral and cell-mediated immune response compared to free OVA. OVA@COF exhibited heightened immune cell activation and acts as an antigen reservoir, facilitating antigen-presenting cell trafficking to the draining lymph nodes, amplifying the humoral immune response. Additionally, the breakdown of the COF releases monomers that adjuvant the activation of immune cells vital to creating strong immunity. This platform offers a potential avenue for safer, more effective subunit vaccines.

Four-State Electrochromism in Tris(4-aminophenyl)amine- terephthalaldehyde-based Covalent Organic Framework

Covalent organic frameworks (COFs) are of massive interest due to their potential application spanning diverse fields such as gas storage and separation, catalysis, drug delivery systems, sensing, and organic electronics. In view of their application-oriented quest, the field of electrochromism marked a significant stride with the reporting of the first electrochromic COF in 2019 [J. Am. Chem. Soc. 2019, 141, 19831-19838]. Since then, new and novel COF structures with electrochromic features (denoted as ecCOFs) have been searched continuously. Yet, only a handful of ecCOFs have been constructed to date. A closer look at these reports suggests that multielectrochromism (showing at least three redox color states) in a COF assembly has only been achieved once, manifested through three-state electrochromism [Angew. Chem. 2021, 133, 12606-1261]. Herein, we report four-state electrochromism in tris(4-aminophenyl)amine-terephthalaldehyde (TAPA-PDA)-based COF constructed through the metal-catalyst free Schiff base approach. The four-state (orange, pear, green, and cyan) electrochromism demonstrated by the TAPA-PDA ecCOF opens several futuristic avenues for ecCOF's end use in flip-flop logic gates, intelligent windows, decorative displays, and energy-saving devices.

Solvothermal Template-Induced Hierarchical Porosity in Covalent Organic Frameworks: A Pathway to Enhanced Diffusivity

The rapid advancement of covalent organic frameworks (COFs) in recent years has firmly established them as a new class of molecularly precise and highly tuneable porous materials. However, compared to other porous materials, such as zeolites and metal-organic frameworks, the successful integration of hierarchical porosity into COFs remains largely unexplored. The challenge lies in identifying appropriate synthetic methods to introduce secondary pores without compromising the intrinsic structural porosity of COFs. In this study, a template-induced synthetic methodology is realized to facilitate the construction of hierarchically porous COFs (hCOFs). This novel approach utilizes commercially available zinc oxide nanoparticles as a hard template, enabling to increase the total pore volume of a series of β-ketoenamine-linked COFs as well as an imine-based COF while preserving their surface areas. In addition to transmission electron microscopy and gas adsorption analyses, small-angle X-ray scattering and pulsed field gradient nuclear magnetic resonance techniques are employed to investigate the hierarchical porosity and diffusivity of guest molecules within hCOFs. This study demonstrates that the hierarchically porous nature of hCOFs significantly reduces diffusion limitations, thus leading to simultaneous enhancements in adsorption capacity, diffusivity, and catalytic performance.

Hierarchical-Porous Hollow Nitrogen-Doped Carbon-Supported Pt Alloy Catalysts with a Controllable Triheterointerface for Methanol Electrooxidation

Carbon-supported Pt-based catalysts are the most effective catalysts for direct methanol fuel cells (DMFCs). However, challenges such as high Pt loading, cost, and susceptibility to CO poisoning severely hinder the development of DMFCs. In this paper, CoFe2O4@polymer@ZIF-67 is prepared successfully through sequential solution polymerization and in situ growth with modified CoFe2O4 as the core. Subsequently, a hierarchical-porous hollow nitrogen-doped carbon-confined controllable triheterointerface catalyst, PtCoFe-CoFeOx@N-HHCS, was successfully prepared via a strategy involving high-temperature-induced phase migration and in situ chemical replacement. Under the optimal conditions, the mass activity of PtCoFe-CoFeOx@N-HHCS reached 1054 mA mgPt-1, which is 4.1 and 2.1 times higher than those of commercial Pt/C and commercial PtRu/C, respectively. The peak potential of the CO electrooxidation of the PtCoFe-CoFeOx@N-HHCS shifts negatively by 70 mV compared with commercial Pt/C. The high methanol oxidation performance is attributed to the highly dispersed triheterointerface, hierarchical-porous hollow structure, and nitrogen-doped ultrathin carbon layer. The highly dispersed triheterointerface of PtCoFe-CoFeOx@N-HHCS promotes the release of Pt and enhances the electron transfer rate through interfacial interaction, significantly improving the catalyst activity. The confinement effect of the nitrogen-doped ultrathin carbon layer prevents Pt dissolution and enhances the stability of the catalyst. The hierarchical-porous hollow structure provides rapid mass transfer channels for the methanol oxidation reaction, enhancing the reaction rate. The synergistic effect of multiple approaches endows PtCoFe-CoFeOx@N-HHCS with good methanol oxidation performance. This work provides important prospects for preparing highly active, stable, and low-loading Pt catalysts.

Thiol-Ene Click Chemistry: A General Strategy for Tuning the Properties of Vinylene-Linked Covalent Organic Frameworks

Vinylene-linked Covalent Organic Frameworks (V-2D-COFs) are a class of promising porous organic materials that feature fully π-conjugated structures, high crystallinity, ultrahigh chemical stability, and extraordinary optoelectronic properties. However, the types of reactions and the availability of monomers for synthesizing sp2-c linked COFs are considerably limited by the irreversibility of the C═C bond, and the complete π-conjugated structure restricts their in-depth research in hydrophilicity, membrane materials, and proton conductivity. Postsynthetic modification (PSM), which can avoid these problems by incorporating functional moieties into the predetermined framework, provides an alternative way to construct diverse V-2D-COFs. Herein, we report a general strategy to introduce C-C, C-S-C, and functional groups into sp2-c-COFs via the thiol-ene click reaction. To demonstrate the universality of this approach, we synthesized two sp2-c COFs (COF-CN and COF-1), and subsequently introduced six different types of thiol compounds at their skeletal C═C sites. The quantitative yield was confirmed by X-ray Photoelectron Spectroscopy (XPS) and cross-polarization magic angle spinning 13C NMR spectroscopy. This thiol-ene click modification of vinylene-linked COFs at skeletal C═C sites allows for flexible structural design, providing these COFs with new linkages (C-C and C-S-C) that are otherwise difficult to produce directly. Thus, it facilitates precise modulation of their properties, such as photophysical properties, hydrophilicity, and proton conductivity, promising a diverse range of compelling applications for the future.

Catalytic Edges in One-Dimensional Covalent Organic Frameworks for the Oxygen Reduction Reaction

Metal-free covalent organic frameworks (COFs) are employed in oxygen reduction reactions (ORR) because of their diverse structural units and controllable catalytic sites, and the edge sites have high catalytic activity than the basal sites. However, it is still challenge to modulate the edge sites in COFs, because the extended frameworks in two- or three-dimensional topologies resulted in limited edge parts. In this study, we have demonstrated the edge site modulation engineering based on one dimensional (1D) COFs to catalyze the ORR, which featured distinct edge groups-carbonyl, diaminopyrazine, phenylimidazole, and benzaldehyde imidazole units. The synthesized COFs have same ordered frameworks, similar pore structure, but had different electronic states of the carbons along the edge sites, which results in tailored catalytic properties. Notably, the COF functionalized with a phenylimidazole edge group exhibited superior catalytic performance compared to the other synthesized COFs. And the theoretical calculation further revealed the different edge sites had tunable binding ability of the intermediates OOH*, which contributed modulated activity. Our findings introduce a novel way for designing COFs optimized for ORR applications through molecular level control of edge sites.

Bonding of Polyethylenimine in Covalent Organic Frameworks for CO2 Capture from Air

We have developed a polyethylenimine-functionalized covalent organic framework (COF) for capturing CO2 from the air. It was synthesized by the crystallization of an imine-linked COF, termed imine-COF-709, followed by linkage oxidation and polyamine installation through aromatic nucleophilic substitution. The chemistry of linkage oxidation and amine installation was fully characterized through Fourier transform infrared spectroscopy, elemental analysis, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. Sorption isotherms and dynamic breakthrough were applied to study the sorption behavior of the resulting sorbent (COF-709). The COF exhibited a CO2 capacity of 0.48 mmol g-1 under dry conditions and 1.24 mmol g-1 under 75% relative humidity, both from simulated air containing 400 ppm of CO2 at 25 °C. The CO2 capacity and adsorption rate of COF-709 showed a strong relationship with the relative humidity in the environment, in accordance with the CO2 adsorption mechanism revealed by ssNMR. The chemical stability of C-S bonds utilized to covalently install the polyamine in COF pores prevented its amine loss and hydrolysis, giving COF-709 an excellent cycling stability, which was confirmed by applying 10 adsorption-desorption cycles under simulated direct air capture conditions, showing no uptake loss.

Development of Amino-Functionalized Silica by Co-condensation and Alkylation for Direct Air Capture

CO2 chemisorption using amine-based sorbents is one of the most effective techniques for carbon capture and storage. Solid CO2 sorbents with amines immobilized on their surface have been attracting attention due to the easy collection of sorbents and reusability. In this study, we developed a solid CO2 adsorbent by co-condensation of a silanizing reagent having a chloroalkyl group and tetraethyl ethoxysilane, followed by alkylation of the chloroalkyl group with diamine. The fabricated amine-immobilized silica with a high density of amino groups on its surface achieved the chemical adsorption of 400 ppm of CO2 with 4.3 wtCO2 % loading, CO2 release upon heating at 80 °C, and reusability for adsorption and desorption cycles with high amine utilization efficiency (0.20 molCO2 /mol-N). This surface modification method is applicable to various amines bearing more than two amino functional groups, enabling the development of solid CO2 sorbents for the selective capture of low-concentration CO2 directly from the air.

Three-Dimensional Mesoporous Covalent Organic Framework for Photocatalytic Oxidative Dehydrogenation to Quinoline

Developing precious metal-free catalysts for organic reactions under mild conditions is urgent. Herein, we report a three-dimensional covalent organic framework (3D-COF) with high crystallinity and permanent pores, termed 3D-TABPA-COF, for the oxidation of tetrahydroquinoline to quinoline. The 3D-TABPA-COF assembled based on N4,N4-bis(4'-amino-[1,1'-biphenyl]-4-yl)-[1,1'-biphenyl]-4,4'-diamine (TABPA) is the catalytic active center for the conversion of tetrahydroquinoline. The triphenylamine in the structure is an effective photosensitizer, which not only enhances the light absorption capacity but also facilitates the rapid transfer of photogenerated electrons and ensures effective carrier separation. The obtained 3D-TABPA-COF has a high specific surface area (2745.06 m2 g-1) and mesopores of 3.57 nm. This is attributed to the fact that the bor topology is not easy to interpenetrate. It can oxidize tetrahydroquinoline to obtain quinoline efficiently under visible light irradiation. In addition, we also performed various photochemical characterizations combined with density functional theory calculations to elucidate the reaction mechanism from tetrahydroquinoline to quinoline. This work provides a feasible strategy for constructing 3D-COF to achieve efficient photocatalytic organic reactions.

Photons, Excitons, and Electrons in Covalent Organic Frameworks

Covalent organic frameworks (COFs) are created by the condensation of molecular building blocks and nodes to form two-dimensional (2D) or three-dimensional (3D) crystalline frameworks. The diversity of molecular building blocks with different properties and functionalities and the large number of possible framework topologies open a vast space of possible well-defined porous architectures. Besides more classical applications of porous materials such as molecular absorption, separation, and catalytic conversions, interest in the optoelectronic properties of COFs has recently increased considerably. The electronic properties of both the molecular building blocks and their linkage chemistry can be controlled to tune photon absorption and emission, to create excitons and charge carriers, and to use these charge carriers in different applications such as photocatalysis, luminescence, chemical sensing, and photovoltaics. In this Perspective, we will discuss the relationship between the structural features of COFs and their optoelectronic properties, starting with the building blocks and their chemical connectivity, layer stacking in 2D COFs, control over defects and morphology including thin film synthesis, exploring the theoretical modeling of structural, electronic, and dynamic features of COFs, and discussing recent intriguing applications with a focus on photocatalysis and photoelectrochemistry. We conclude with some remarks about present challenges and future prospects of this powerful architectural paradigm.

Microbial community assemblage altered by coprecipitation of artificial humic substances and ferrihydrite: Implications for carbon fixation pathway transformation

The suppression of soil carbon mineralization has been demonstrated to be effectively facilitated by carbon‑iron interactions, yet the specific mechanisms by which artificial humic substances (A-HS) coupled with ferrihydrite influence this process remain insufficiently explored. This study is to investigate how the A-HS, specifically artificial fulvic acid (A-FA) and artificial humic acid (A-HA), coupled with ferrihydrite, affect carbon mineralization under anaerobic system that simulates paddy flooding conditions. The object is to investigate trends in carbon emissions and to delineate microbial community structure and functional pathways. The findings indicate that A-HA and A-FA substantially reduce CO2 and CH4 emissions, with A-FA having a particularly pronounced effect on carbon fixation, halving CO2 concentrations. The low concentration of Fe(II) observed suggest that A-FA and A-HA impede the dissimilatory iron reduction (DIR) process. Detailed 16S rDNA sequencing and gene prediction analyses reveal changes in microbial community structures and functions, highlighting Methanobacterium as the dominant hydrogenotrophic methanogens. The reductive citric acid cycle, predominantly utilized by Clostridium carboxidivorans, was identified as the principal carbon fixation pathway. This work provides a novel insight into the microbial mechanisms of carbon sequestration and highlights the potential of A-HS in improving soil fertility and contributing to climate change mitigation through enhancing soil carbon storage.

Seawater alkalization via an energy-efficient electrochemical process for CO2 capture

Electrochemical pH-swing strategies offer a promising avenue for cost-effective and energy-efficient carbon dioxide (CO2) capture, surpassing the traditional thermally activated processes and humidity-sensitive techniques. The concept of elevating seawater's alkalinity for scalable CO2 capture without introducing additional chemical as reactant is particularly intriguing due to its minimal environmental impact. However, current commercial plants like chlor-alkali process or water electrolysis demand high thermodynamic voltages of 2.2 V and 1.23 V, respectively, for the production of sodium hydroxide (NaOH) from seawater. These high voltages are attributed to the asymmetric electrochemical reactions, where two completely different reactions take place at the anode and cathode. Here, we developed a symmetric electrochemical system for seawater alkalization based on a highly reversible and identical reaction taking place at the anode and cathode. We utilize hydrogen evolution reaction at the cathode, where the generated hydrogen is looped to the anode for hydrogen oxidation reaction. Theoretical calculations indicate an impressively low energy requirement ranging from 0.07 to 0.53 kWh/kg NaOH for established pH differences of 1.7 to 13.4. Experimentally, we achieved the alkalization with an energy consumption of 0.63 kWh/kg NaOH, which is only 38% of the theoretical energy requirements of the chlor-alkali process (1.64 kWh/kg NaOH). Further tests demonstrated the system's potential of enduring high current densities (~20 mA/cm2) and operating stability over an extended period (>110 h), showing its potential for future applications. Notably, the CO2 adsorption tests performed with alkalized seawater exhibited remarkably improved CO2 capture dictated by the production of hydroxide compared to the pristine seawater.

Carbon dioxide capture from open air using covalent organic frameworks

Capture of CO2 from the air offers a promising approach to addressing climate change and achieving carbon neutrality goals1,2. However, the development of a durable material with high capacity, fast kinetics and low regeneration temperature for CO2 capture, especially from the intricate and dynamic atmosphere, is still lacking. Here a porous, crystalline covalent organic framework (COF) with olefin linkages has been synthesized, structurally characterized and post-synthetically modified by the covalent attachment of amine initiators for producing polyamines within the pores. This COF (termed COF-999) can capture CO2 from open air. COF-999 has a capacity of 0.96 mmol g-1 under dry conditions and 2.05 mmol g-1 under 50% relative humidity, both from 400 ppm CO2. This COF was tested for more than 100 adsorption-desorption cycles in the open air of Berkeley, California, and found to fully retain its performance. COF-999 is an exceptional material for the capture of CO2 from open air as evidenced by its cycling stability, facile uptake of CO2 (reaches half capacity in 18.8 min) and low regeneration temperature (60 °C).

Molecularly Woven Cationic Covalent Organic Frameworks for Highly Selective Electrocatalytic Conversion of CO2 to CO

Coupling carbon capture with electrocatalytic carbon dioxide reduction (CO2R) to yield high-value chemicals presents an appealing avenue for combating climate change, yet achieving highly selective electrocatalysts remains a significant challenge. Herein, two molecularly woven covalent organic frameworks (COFs) are designed, namely CuCOF and CuCOF+, with copper(I)-bisphenanthroline complexes as building blocks. The metal-organic helical structure unit made the CuCOF and CuCOF+ present woven patterns, and their ordered pore structures and cationic properties enhanced their CO2 adsorption and good conductivity, which is confirmed by gas adsorption and electrochemical analysis. In the electrocatalytic CO2R measurements, CuCOF+ decorated with extra ethyl groups exhibit a main CO product with selectivity of 57.81%, outperforming the CuCOF with 42.92% CO at the same applied potential of 0.8 VRHE. After loading Pd nanoparticles, CuCOF-Pd and CuCOF+-Pd performed increased CO selectivity up to 84.97% and 95.45%, respectively. Combining the DFT theoretical calculations and experimental measurements, it is assumed that the molecularly woven cationic COF provides a catalytic microenvironment for CO2R and ensures efficient charge transfer from the electrode to the catalytic center, thereby achieving high electrocatalytic activity and selectivity. The present work significantly advances the practice of cationic COFs in real-time CO2 capture and highly selective conversion to value-added chemicals.

Cascade CO2 Insertion in Carbanion Ionic Liquids Driven by Structure Rearrangement

The CO2 chemisorption in state-of-the-art sorbents based on oxide/hydroxide/amine moieties is driven by strong chemical bonding formation in the carbonate/bicarbonate/carbamate products, which in turn leads to high energy input in sorbent regeneration. In addition, the CO2 uptake capacity was limited by the active sites' utilization efficiency, with each active site incorporating one CO2 molecule or less. In this work, a new concept and generation of sorbent was developed to achieve cascade insertion of multiple CO2 molecules by leveraging structure rearrangement as the driving force, leading to in situ generation of extra CO2-binding sites and significantly reduced energy input for CO2 release. The designed ionic liquids (ILs) containing carbanions with conjugated and asymmetric structure, deprotonated (methylsulfonyl)acetonitrile ([MSA]) anion, allowed the cascade insertion of two CO2 molecules via consecutive C-C and O-C bond formations. The proton transfer and structure rearrangement of the carboxylic acid intermediates played critical roles in stabilizing the first integrated CO2 and generating extra electron-rich oxygen sites for the insertion of the second CO2. The structure variation and reaction pathway were confirmed by operando spectroscopy, magnetic resonance spectroscopy (NMR), mass spectroscopy, and computational chemistry. The energy input in sorbent regeneration could be further reduced by harnessing the phase-changing behavior of the carbanion salts in ether solutions upon reacting with CO2, avoiding the energy consumption in heating the solvent. The fundamental insights obtained herein provide a promising approach to greatly improve the CO2 sorption performance via sophisticated molecular-scale structural engineering of the sorbents.

Structural Reassignment of Covalent Organic Framework-Supported Palladium Species: Heterogenized Palladacycles as Efficient Catalysts for Sustainable C-H Activation

Recent decades have witnessed remarkable progress in ligand-promoted C-H activation with palladium catalysts. While a number of transformations have been achieved with a fairly broad substrate scope, the general requirements for high palladium loadings and enormous challenges in catalyst recycling severely limit the practical applications of C-H activation methodologies in organic synthesis. Herein, we incorporate N,C-ligand-chelated palladacycles into rigid, porous, and crystalline covalent organic frameworks for the C-H arylation of indole and pyrrole derivatives. These heterogeneous palladium catalysts exhibit superior stability and recyclability compared to their homogeneous counterparts. We not only produce several highly reactive palladacycles embedded on new framework supports to facilitate C-H activation/C-C bond-forming reactions but also reassign heterogenized palladium species on frameworks containing a benzaldehyde-derived imine moiety as imine-based palladacycles via comprehensive characterization. Our findings provide guidance for the rational design of framework-supported metallacycles in the development of heterogeneous transition-metal catalysis.

Metal-Organic Framework-Induced Rh Monocoodination on Diphosphine Ligand Enables Catalytic Hydroformylation of Aliphatic Olefins at Room Temperature and Pressure

Persistent challenges in hydroformylation of olefins include controlling regioselectivity, particularly for short aliphatic olefins and conducting reactions under ambient conditions. We report here the synthesis of monophosphine-Rh complexes on a typical chelated diphosphine ligand mediated by a Zr-MOF through isolating a pair of phosphorus atoms. We demonstrate that single-crystal X-ray diffraction can elucidate the structural transformation of the Rh catalyst during olefin hydroformylation, providing valuable information on active site reconstruction during catalysis. The Rh-MOF catalyst demonstrates excellent catalytic and recyclable performance in the hydroformylation of short aliphatic olefins with linear to branched ratios of up to 99 : 1. Due to the framework's capacity to adsorb and concentrate gases, the catalytic reactions occur under room temperature and pressure, eliminating the need for the high temperature and pressures typically required in homogeneous systems. This study show that Zr-MOF can be a unique platform for synthesizing unusual catalytic species that cannot exist in solutions for meaningful chemical transformations and elucidate valuable structural information pertaining to metal-based catalysis.

Unveiling the Role of Hydrophobicity on Multilayer Carbon Nanosheets Enriched in sp2-Carbon for Toluene Adsorption under Humid Conditions

Carbon materials are regarded as a promising adsorbent for the adsorption of volatile organic compounds (VOCs). However, their adsorption behaviors are usually compromised at ambient conditions, attributed to the competitive VOCs adsorption with water vapor. In this study, we demonstrated that the selectivity for toluene than water of carbon can be effectively enhanced by introducing more sp2-carbon with two-dimensional nanosheets stacked. The multilayer carbon nanosheets enriched with sp2-carbon (CNS-MCA) exhibit a 151° H2O-contact angle, indicating hydrophobicity. Dynamic adsorption behaviors revealed that CNS-MCA retain 71% of their toluene adsorption capacity (91 mg/g) even at 60% relative humidity. Density functional theory (DFT) calculations, static adsorption studies, in situ Raman spectroscopy, and time-resolved in situ nuclear magnetic resonance (NMR) spectroscopy collectively indicate that toluene exhibits enhanced adsorption and selectivity due to π-π* interactions between its aromatic rings and the sp2-carbon. Conversely, water adsorption is attenuated, attributed to the reduced availability of surface-exposed hydrogen bonds associated with sp2-carbon and the inherent hydrophobic nature of multilayer graphene. This study extends a novel solution for the enhancement of VOCs adsorption under humid conditions.

Ionic Pairs-Engineered Fluorinated Covalent Organic Frameworks Toward Direct Air Capture of CO2

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO2 (400 ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO2 insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400 ppm) CO2 from gas mixtures via O─C bond formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using 13C-labeled CO2 sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40 kJ mol-1 between CO2 and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO2 release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO2 insertion. The as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO2 in crystalline scaffolds.

Construction of Benzoxazine-linked One-Dimensional Covalent Organic Frameworks Using the Mannich Reaction

Covalent polymerization of organic molecules into crystalline one-dimensional (1D) polymers is effective for achieving desired thermal, optical, and electrical properties, yet it remains a persistent synthetic challenge for their inherent tendency to adopt amorphous or semicrystalline phases. Here we report a strategy to synthesize crystalline 1D covalent organic frameworks (COFs) composing quasi-conjugated chains with benzoxazine linkages via the one-pot Mannich reaction. Through [4+2] and [2+2] type Mannich condensation reactions, we fabricated stoichiometric and sub-stoichiometric 1D covalent polymeric chains, respectively, using doubly and singly linked benzoxazine rings. The validity of their crystal structures has been directly visualized through state-of-the-art cryogenic low-dose electron microscopy techniques. Post-synthetic functionalizations of them with a chiral MacMillan catalyst produce crystalline organic photocatalysts that demonstrated excellent catalytic and recyclable performance in light-driven asymmetric alkylation of aldehydes, affording up to 94 % enantiomeric excess.

Efficient Capture and Release of the Rare-Earth Element Neodymium in Aqueous Solution by Recyclable Covalent Organic Frameworks

Rare-earth elements (REEs) are present in a broad range of critical materials. The development of solid adsorbents for REE capture could enable the cost-effective recycling of REE-containing magnets and electronics. In this context, covalent organic frameworks (COFs) are promising candidates for REE adsorption due to their exceptionally high surface area. Despite having attractive physical properties, COFs are heavily underutilized for REE capture applications due to their limited lifecycle in aqueous acidic environments, as well as synthetic challenges associated with the incorporation of ligands suitable for REE capture. Here, we show how the Ugi multicomponent reaction can be leveraged to postsynthetically modify imine-based COFs for the introduction of a diglycolic acid (DGA) moiety, an efficient scaffold for REE capture. The adsorption capacity of the DGA-functionalized COF was found to be more than 40 times higher than that of the pristine imine COF precursor and more than four times higher than that of the next-best reported DGA-functionalized solid support. This rationally designed COF has appealing characteristics of high adsorption capacity, fast and efficient capture and release of the REE ions, and reliable recyclability, making it one of the most promising adsorbents for solid-liquid REE ion extractions reported to date.

Isoreticular Covalent Organic Pillars: Engineered Nanotubular Hosts for Tailored Molecular Recognition

In the realm of nanoscale materials design, achieving precise control over the dimensions of nanotubular architectures poses a substantial challenge. In our ongoing pursuit, we have successfully engineered a novel class of single-molecule nanotubes─isoreticular covalent organic pillars (iCOPs)─by stacking formylated macrocycles through multiple dynamic covalent imine bonds, guided by principles of reticular chemistry. Our strategic selection of rigid diamine linkers has facilitated the synthesis of a diverse array of iCOPs, each retaining a homologous structure yet offering distinct cavity shapes influenced by the linker choice. Notably, three of these iCOP variants feature continuous one-dimensional channels, exhibiting length-dependent host-guest interactions with α,ω-dibromoalkanes, and each presenting a distinct critical guest alkyl chain length threshold for efficient guest encapsulation. This newfound capability not only provides a platform for tailoring nanotubular structures with precision, but also opens new avenues for innovative applications in molecular recognition and the purification of complex mixtures.

Adsorption, Orientation, and Speciation of Amino Acids at Air-Aqueous Interfaces for the Direct Air Capture of CO2

Amino acids make up a promising family of molecules capable of direct air capture (DAC) of CO2 from the atmosphere. Under alkaline conditions, CO2 reacts with the anionic form of an amino acid to produce carbamates and deactivated zwitterionic amino acids. The presence of the various species of amino acids and reactive intermediates can have a significant effect on DAC chemistry, the role of which is poorly understood. In this study, all-atom molecular dynamics (MD) based computational simulations and vibrational sum frequency generation (vSFG) spectroscopy studies were conducted to understand the role of competitive interactions at the air-aqueous interface in the context of DAC. We find that the presence of potassium bicarbonate ions, in combination with the anionic and zwitterionic forms of amino acids, induces concentration and charge gradients at the interface, generating a layered molecular arrangement that changes under pre- and post-DAC conditions. In parallel, an enhancement in the surface activity of both anionic and zwitterionic forms of amino acids is observed, which is attributed to enhanced interfacial stability and favorable intermolecular interactions between the adsorbed amino acids in their anionic and zwitterionic forms. The collective influence of these competitive interactions, along with the resulting interfacial heterogeneity, may in turn affect subsequent capture reactions and associated rates. These effects underscore the need to consider dynamic changes in interfacial chemical makeup to enhance DAC efficiency and to develop successful negative emission and storage technologies.

Programming Tetrathiafulvalene-Based Covalent Organic Frameworks for Promoted Photoinduced Molecular Oxygen Activation

Despite the pivotal role of molecular oxygen (O2) activation in artificial photosynthesis, the activation efficiency is often restricted by sluggish exciton dissociation and charge transfer kinetics within polymer photocatalysts. Herein, we propose two tetrathiafulvalene (TTF)-based imine-linked covalent organic frameworks (COFs) with tailored donor-acceptor (D-A) structures, TTF-PDI-COF and TTF-TFPP-COF, to promote O2 activation. Because of enhanced electron push-pull interactions that facilitated charge separation and transfer behavior, TTF-PDI-COF exhibited superior photocatalytic activity in electron-induced O2 activation reactions over TTF-TFPP-COF under visible light irradiation, including the photosynthesis of (E)-3-amino-2-thiocyano-α,β-unsaturated compounds and H2O2. These findings highlight the significant potential of the rational design of COFs with D-A configurations as suitable candidates for advanced photocatalytic applications.

Carbon Dioxide Capture by Emerging Innovative Polymers: Status and Perspectives

A significant amount of research has been conducted in carbon dioxide (CO2) capture, particularly over the past decade, and continues to evolve. This review presents the most recent advancements in synthetic methodologies and CO2 capture capabilities of diverse polymer-based substances, which includes the amine-based polymers, porous organic polymers, and polymeric membranes, covering publications in the last 5 years (2019-2024). It aims to assist researchers with new insights and approaches to develop innovative polymer-based materials with improved capturing CO2 capacity, efficiency, sustainability, and cost-effective, thereby addressing the current obstacles in carbon capture and storage to sooner meeting the net-zero CO2 emission target.

Probing Self-Diffusion of Guest Molecules in a Covalent Organic Framework: Simulation and Experiment

Covalent organic frameworks (COFs) are a class of porous materials whose sorption properties have so far been studied primarily by physisorption. Quantifying the self-diffusion of guest molecules inside their nanometer-sized pores allows for a better understanding of confinement effects or transport limitations and is thus essential for various applications ranging from molecular separation to catalysis. Using a combination of pulsed field gradient nuclear magnetic resonance measurements and molecular dynamics simulations, we have studied the self-diffusion of acetonitrile and chloroform in the 1D pore channels of two imine-linked COFs (PI-3-COF) with different levels of crystallinity and porosity. The higher crystallinity and porosity sample exhibited anisotropic diffusion for MeCN parallel to the pore direction, with a diffusion coefficient of Dpar = 6.1(3) × 10-10 m2 s-1 at 300 K, indicating 1D transport and a 7.4-fold reduction in self-diffusion compared to the bulk liquid. This finding aligns with molecular dynamics simulations predicting 5.4-fold reduction, assuming an offset-stacked COF layer arrangement. In the low-porosity sample, more frequent diffusion barriers result in isotropic, yet significantly reduced diffusivities (DB = 1.4(1) × 10-11 m2 s-1). Diffusion coefficients for chloroform at 300 K in the pores of the high- (Dpar = 1.1(2) × 10-10 m2 s-1) and low-porosity (DB = 4.5(1) × 10-12 m2 s-1) samples reproduce these trends. Our multimodal study thus highlights the significant influence of real structure effects such as stacking faults and grain boundaries on the long-range diffusivity of molecular guest species while suggesting efficient intracrystalline transport at short diffusion times.

An Azulene-Based Crystalline Porous Covalent Organic Framework for Efficient Photothermal Conversion

The designed synthesis of a crystalline azulene-based covalent organic framework (COF-Azu-TP) is presented and its photothermal property is investigated. Azulene, a distinctive 5-7 fused ring non-benzenoid aromatic compound with a large intramolecular dipole moment and unique photophysical characteristics, is introduced as the key feature in COF-Azu-TP. The incorporation of azulene moiety imparts COF-Azu-TP with broad-spectrum light absorption capability and interlayer dipole interactions, which makes COF-Azu-TP a highly efficient photothermal conversion material. Its polyurethane (PU) composite exhibits a solar-to-vapor conversion efficiency (97.2%) and displays a water evaporation rate (1.43 kg m-2 h-1) under one sun irradiation, even at a very low dosage of COF-Azu-TP (2.2 wt%). Furthermore, COF-Azu-TP is utilized as a filler in a polylactic acid (PLA)/polycaprolactone (PCL) composited shape memory material, enabling rapid shape recovery under laser stimulation. A comparison study with a naphthalene-based COF isomer further emphasizes the crucial role of azulene in enhancing photothermal conversion efficiency. This study demonstrates the significance of incorporating specific building blocks into COFs for the development of functional porous materials with enhanced properties, paving the way for future applications in diverse fields.

Radiation-Assisted Assembly of a Highly Dispersed Nanomolybdenum-Functionalized Covalent Organic Framework

Two-dimensional covalent organic frameworks (2D COFs), featuring a large surface area and 1D pore structure, serve as promising scaffolds for anchoring functional guest compounds, which can significantly enhance their performance and thus expand their potential applications. Postsynthetic strategy for COFs functionalization is versatile but challenging because of their tedious procedure with high time and energy consumption, generation of excess reaction waste, and damage to COF crystallinity. We report in this work a general strategy for the synthesis of inorganic nanocompound-functionalized COF composites in a one-pot way. Specifically, a high-crystallinity nanoscale molybdenum compound is successfully introduced into a COF skeleton with high dispersion in situ during the crystallization process of the COF induced by gamma ray radiation under ambient conditions. The obtained COF@Mo composites exhibit remarkable sorption performance for methylene blue and many other organic dyes in aqueous solution with the advantages of ultrarapid uptake dynamics and high removal efficiency.

Techno-Economic Assessment of Electromicrobial Production of n-Butanol from Air-Captured CO2

Electromicrobial production (EMP), where electrochemically generated substrates (e.g., H2) are used as energy sources for microbial processes, has garnered significant interest as a method of producing fuels and other value-added chemicals from CO2. Combining these processes with direct air capture (DAC) has the potential to enable a truly circular carbon economy. Here, we analyze the economics of a hypothetical system that combines adsorbent-based DAC with EMP to produce n-butanol, a potential replacement for fossil fuels. First-principles-based modeling is used to predict the performance of the DAC and bioprocess components. A process model is then developed to map material and energy flows, and a techno-economic assessment is performed to determine the minimum fuel selling price. Beyond assessing a specific set of conditions, this analytical framework provides a tool to reveal potential pathways toward the economic viability of this process. We show that an EMP system utilizing an engineered knallgas bacterium can achieve butanol production costs of <$6/gal ($1.58/L) if a set of optimistic assumptions can be realized.

Structural Regulation of Covalent Organic Frameworks for Catalysis

ConspectusChemical reactions can be promoted at lower temperatures and pressures, thereby reducing the energy input, by introducing suitable catalysts. Despite its significance, the quest for efficient and stable catalysts remains a significant challenge. In this context, addressing the efficiency of catalysts stands out as a paramount concern. However, the challenges posed by the vague structure and limited tailorability of traditional catalysts would make it highly desirable to fabricate optimized catalysts based on the understanding of structure-activity relationships. Covalent organic frameworks (COFs), a subclass of fully designed crystalline materials formed by the polymerization of organic building blocks through covalent bonds have garnered widespread attention in catalysis. The precise and customizable structures of COFs, coupled with attributes such as high surface area and facile functional modification, make COFs attractive molecular platforms for catalytic applications. These inherent advantages position COFs as ideal catalysts, facilitating the elucidation of structure-performance relationships and thereby further improving the catalysis. Nevertheless, there is a lack of systematic emphasis on and summary of structural regulation at the atomic/molecular level for COF catalysis. Consequently, there is a growing need to summarize this research field and provide deep insights into COF-based catalysis to promote its further development.In this Account, we will summarize recent advances in structural regulation achieved in COF-based catalysts, placing an emphasis on the molecular design of the structures for enhanced catalysis. Considering the unique components and structural advantages of COFs, we present the fundamental principles for the rational design of structural regulation in COF-based catalysis. This Account starts by presenting an overview of catalysis and explaining why COFs are promising catalysts. Then, we introduce the molecular design principle for COF catalysis. Next, we present the following three aspects of the specific strategies for structural regulation of COF-based catalysts: (1) By designing different functional groups and integrating metal species into the organic unit, the activity and/or selectivity can be finely modulated. (2) Regulating the linkage facilitates charge transfer and/or modulates the electronic structure of catalytic metal sites, and accordingly, the intrinsic activity/selectivity can be further improved. (3) By means of pore wall/space engineering, the microenvironment surrounding catalytic metal sites can be modulated to optimize performance. Finally, the current challenges and future developments in the structural regulation of COF-based catalysts are discussed in detail. This Account provides insight into the structural regulation of COF-based catalysts at the atomic/molecular level toward improving their performance, which would provide significant inspiration for the design and structural regulation of other heterogeneous catalysts.

Solvent Effects on Metal-free Covalent Organic Frameworks in Oxygen Reduction Reaction

Binding water molecules to polar sites in covalent organic frameworks (COFs) is inevitable, but the corresponding solvent effects in electrocatalytic process have been largely overlooked. Herein, we investigate the solvent effects on COFs for catalyzing the oxygen reduction reaction (ORR). Our designed COFs incorporated different kinds of nitrogen atoms (imine N, pyridine N, and phenazine N), enabling tunable interactions with water molecules. These interactions play a crucial role in modulating electronic states and altering the catalytic centers within the COFs. Among the synthesized COFs, the one with pyridine N atoms exhibits the highest activity, with characterized by a half-wave potential of 0.78 V and a mass activity of 0.32 A mg-1, which surpass those from other metal-free COFs. Theoretical calculations further reveal that the enhanced activity can be attributed to the stronger binding ability of *OOH intermediates to the carbon atoms adjacent to the pyridine N sites. This work sheds light on the significance of considering solvent effects on COFs in electrocatalytic systems, providing valuable insights into their design and optimization for improved performance.

12 Connecting Sites Linked Three-dimensional Covalent Organic Frameworks with Intrinsic Non-interpenetrated shp Topology for Photocatalytic H2O2 Synthesis

Developing high connectivity (>8) three-dimensional (3D) covalent organic frameworks (COFs) towards new topologies and functions remains a great challenge owing to the difficulty in getting high connectivity organic building blocks. This however represents the most important step towards promoting the diversity of COFs due to the still limited dynamic covalent bonds available for constructing COFs at this stage. Herein, highly connected phthalocyanine-based (Pc-based) 3D COFs MPc-THHI-COFs (M=H2, Ni) were afforded from the reaction between 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine M(TAPc) (M=H2, Ni) and 5,5',5'',5''',5'''',5'''''-(triphenylene-2,3,6,7,10,11-hexayl)hexa(isophthalohydrazide) (THHI) with 12 connecting sites. Powder X-ray diffraction analysis together with theoretical simulations and transmission electron microscopy reveals their crystalline nature with an unprecedented non-interpenetrated shp topology. Experimental and theoretical investigations disclose the broadened visible light absorption range and narrow optical band gap of MPc-THHI-COFs. This in combination with their 3D nanochannels endows them with efficient photocatalysis performance for H2O2 generation from O2 and H2O via 2e- oxygen reduction reaction and 2e- water oxidation reaction under visible-light irradiation (λ >400 nm). This work provides valuable result for the development of high connectivity functional COFs towards diverse application potentials.

Sustainable remediation of pesticide pollutants using covalent organic framework - A review on material properties, synthesis methods and application

Covalent organic frameworks (COF) have emerged as a potential class of materials for a variety of applications in a wide number of sectors including power storage, environmental services, and biological applications due to their ordered and controllable porosity, large surface area, customizable structure, remarkable stability, and diverse electrical characteristics. COF have received a lot of attention in recent years in the field of environmental remediation, It also find its way to eliminate the emerging pollutant from the environment notably pesticide from polluted water. This review more concentrated on the application of COF in pesticide removal by modifying COF structure, COF synthesis and material properties. To increase the adsorption ability and selectivity of the material towards certain pesticides removal, the synthesis of COF involves organic linkers with various functional groups such as amine, carboxylic acid groups etc. The COF have a high degree of stability and endurance make them suitable for intermittent usage in water treatment applications. This review manifests the novel progress where modified COFs employed in a prominent manner to remove pesticides from polluted water. Some examples of COF application in the eradication of pesticides are triformyl phenylene framework functionalized with amine groups has capacity to remove up to 50 mg/l of Organophosphorus - chlorpyrifos. COF modified to improve their photocatalytic capacity to breakdown the pesticide under visible light irradiation. COF tetraphenyl ethylene linked with carboxylic acid group shows efficient photocatalytic degradation of 90% of organochlorine insecticide endosulfan when subjected to visible light. Atrazine and imidacloprid are reduced from 100 ppm to 1 ppm in aqueous solutions by COF based on high adsorption capacity. In addition, the strategies, technique, synthesis and functional group modification design of COF are discussed.