Fabricating Industry-Compatible Olefin-Linked COF Resins for Oxoanion Pollutant Scavenging

Synthetic Leaves Based on Crystalline Olefin-Linked Covalent Organic Frameworks for Efficient CO2 Photoreduction with Water

We report, for the first time, a new synthetic strategy for the preparation of crystalline two-dimensional olefin-linked covalent organic frameworks (COFs) based on aldol condensation between benzodifurandione and aromatic aldehydes. Olefin-linked COFs can be facilely crystallized through either a pyridine-promoted solvothermal process or a benzoic anhydride-mediated organic flux synthesis. The resultant COF leaf with high in-plane π-conjugation exhibits efficient visible-light-driven photoreduction of carbon dioxide (CO2) with water (H2O) in the absence of any photosensitizer, sacrificial agents, or cocatalysts. The production rate of carbon monoxide (CO) reaches as high as 158.1 μmol g-1 h-1 with near 100% CO selectivity, which is accompanied by the oxidation of H2O to oxygen. Both theoretical and experimental results confirm that the key lies in achieving exceptional photoinduced charge separation and low exciton binding. We anticipate that our findings will facilitate new possibilities for the development of semiconducting COFs with structural diversity and functional variability.

Ultra-Strong Janus Covalent Organic Framework Membrane with Smart Response to Organic Vapor

Vapor-driven smart Janus materials have made significant advancements in intelligent monitoring, control, and interaction, etc. Nevertheless, the development of ultrafast response single-layer Janus membrane, along with a deep exploration of the smart response mechanisms, remains a long-term endeavor. Here, the successful synthesis of a high-crystallinity single-layer Covalent organic framework (COF) Janus membrane is reported by morphology control. This kind of membrane displays superior mechanical properties and specific surface area, along with excellent responsiveness to CH2Cl2 vapor. The analysis of the underlying mechanisms reveals that the vapor-induced breathing effect of the COF and the stress mismatch of the Janus structure play a crucial role in its smart deformation performance. It is believed that this COF Janus membrane holds promise for complex tasks in various fields.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Ultrafast and selective capture of 99TcO4-/ReO4- from wastewater by hyper-branched quaternary ammonium group-functionalized resin

99Tc primarily exists high mobility in the natural aqueous environment due to its extremely high solubility and non-complexing features, which can easily cause radioactive pollution. We herein report a general strategy for constructing a novel resin (SiPAN-PEI) with multiple positive charges nitrogen, exhibiting ultrafast adsorption kinetics (< 3 min), superior adsorption capacities (463.96 mg g-1), and excellent selectivity in the presence of excess competitive anions, which exceed those of most commercial resins. Moreover, based on impressive structure stability in extreme conditions, SiPAN-PEI can still maintain superior adsorption abilities after suffering irradiation, calcination, and immersion in strong acid. In addition, the separation performance kept excellently after five loading-washing-eluting cycles and the total adsorption ratio can still reach 97 %. Outstandingly, SiPAN-PEI can remove most of ReO4- from simulated nuclear wastewater through a sequential injection automatic separation system and can reduce the concentration of ReO4- to the maximum concentration standard set by the World Health Organization (WHO) in a short time. Leveraging density functional theory calculations and other characteristics clearly elucidated adsorption mechanism of anion-exchange between Cl- and TcO4-/ReO4-. In terms of superior adsorption property, SiPAN-PEI is demonstrated to be a pretty candidate for 99Tc elimination from wastewater.

Synthesis and performance of guanidinium-based cationic organic polymer for the efficient removal of TcO4-/ReO4. JOURNAL OF HAZARDOUS MATERIALS 2024;466:133602. [PMID: 38286051 DOI: 10.1016/j.jhazmat.2024.133602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Cationic organic polymers have found relatively extensive utility for TcO4-/ReO4- removal, but the harsh preparation conditions constrain their practical application. The bifunctional guanidinium-based cationic organic polymer (GBCOP) was successfully and facilely synthesized in benign conditions within 1 h. Batch experiments showed that GBCOP exhibited rapid removal kinetics (1 min, >98.0%) and a substantial removal capacity of 536.8 mg/g for ReO4-. Even in 1000-fold co-existing NO3- anions, the removal efficiency of GBCOP for ReO4- was 74.0%, indicating its good selectivity. Moreover, GBCOP had high removal efficiencies for ReO4- across a wide pH (3.0-10.0) range and presented remarkable stability under the conditions of strong acid and base. GBCOP could be reused four times while removing 80.8% ReO4- from simulated Hanford wastewater. SEM and XPS results revealed that the mechanism of ReO4- removal involved Cl- ion exchange within the channels of GBCOP. Theoretical calculation results supported that existing the strong electrostatic interaction between guanidinium and ReO4-. This dual-function GBCOP material is cost-effective and holds significant potential for large-scale preparation, making it a promising solution for TcO4- removal from nuclear wastewater.

Construction of Thiadiazole-Bridged sp2-Carbon-Conjugated Covalent Organic Frameworks with Diminished Excitation Binding Energy Toward Superior Photocatalysis

Sp2-carbon-conjugated covalent organic frameworks (sp2c-COFs) have emerged as promising platforms for phototo-chemical energy conversion due to their tailorable optoelectronic properties, in-plane π-conjugations, and robust structures. However, the development of sp2c-COFs in photocatalysis is still highly hindered by their limited linkage chemistry. Herein, we report a novel thiadiazole-bridged sp2c-COF (sp2c-COF-ST) synthesized by thiadiazole-mediated aldol-type polycondensation. The resultant sp2c-COF-ST demonstrates high chemical stability under strong acids and bases (12 M HCl or 12 M NaOH). The electro-deficient thiadiazole together with fully conjugated and planar skeleton endows sp2c-COF-ST with superior photoelectrochemical performance and charge-carrier separation and migration ability. As a result, when employed as a photocathode, sp2c-COF-ST exhibits a significant photocurrent up to ∼14.5 μA cm-2 at 0.3 V vs reversible hydrogen electrode (RHE) under visible-light irradiation (>420 nm), which is much higher than those analogous COFs with partial imine linkages (mix-COF-SNT ∼ 9.5 μA cm-2) and full imine linkages (imi-COF-SNNT ∼ 4.9 μA cm-2), emphasizing the importance of the structure-property relationships. Further temperature-dependent photoluminescence spectra and density functional theory calculations demonstrate that the sp2c-COF-ST has smaller exciton binding energy as well as effective mass in comparison to mix-COF-SNT and imi-COF-SNNT, which suggests that the sp2c-conjugated skeleton enhances the exciton dissociation and carrier migration under light irradiation. This work highlights the design and preparation of thiadiazole-bridged sp2c-COFs with promising photocatalytic performance.

Rapid and selective removal of aristolochic acid I in natural products by vinylene-linked iCOF resins

Rapid, efficient, and selective removal of toxicants such as aristolochic acid I (AAI) from complex natural product systems is of great significance for the safe use of herbal medicines or medicine-food plants. Addressing this challenge, we develop a high-performance separation approach based on ionic covalent organic frameworks (iCOFs) to separate and remove AAI. Two vinylene-linked iCOFs (NKCOF-46-Br- and NKCOF-55-Br-) with high crystallinity are fabricated in a green and scalable fashion via a melt polymerization synthesis method. The resulting materials exhibit a uniform morphology, high stability, fast equilibrium time, and superior affinity and selectivity for AAI. Compared to conventional separation media, NKCOF-46-Br- and NKCOF-55-Br- achieve the record high adsorption capacities of 246.0 mg g-1 and 178.4 mg g-1, respectively. Various investigations reveal that the positively charged framework and favorable pore microenvironment of iCOFs contribute to their high selectivity and adsorption efficiency. Moreover, the iCOFs exhibit excellent biocompatibility by in vivo toxicity assays. This study paves a new avenue for the rapid, selective and efficient removal of toxicants from complex natural systems.

Modulating Skeletons of Covalent Organic Framework for High-Efficiency Gold Recovery

Covalent organic frameworks (COFs) have attracted considerable attention as adsorbents for capturing and separating gold from electronic wastes. To enhance the binding capture efficiency, constructing hydrogen-bond nanotraps along the pore walls was one of the most widely adopted approaches. However, the development of absorbing skeletons was ignored due to the weak binding ability of the gold salts (Au). Herein, we demonstrated skeleton engineering to construct highly efficiently absorbs for Au capture. The strong electronic donating feature of diarylamine units enhanced the electronic density of binding sites (imine-linkage) and thus resulted in high capacities over 1750 mg g-1 for all three COFs. Moreover, the absorbing performance was further improved via the ionization of diarylamine units. The ionic COF achieved 90 % of the maximal adsorption capacity, 1.63 times of that from the charge-neutral COF within ten minutes, and showed remarkable uptakes of 1834 mg g-1 , exceptional selectivity (97.45 %) and cycling stability. The theoretical calculation revealed the binding sites altering from imine bonds to ionic amine sites after ionization of the frameworks, which enabled to bind the AuCl4 - via coulomb force and contributed to enhanced absorbing kinetics. This work inspires us to design molecular/ionic capture based on COFs.

A COF template-derived mesoporous CeO2-supported Au nanoparticles catalyst for the oxidative esterification of benzaldehydes and benzyl alcohols

The direct oxidative esterification of benzaldehydes and benzyl alcohols to high value-added aromatic esters under mild and green reaction conditions is significant in the fine chemical industry. The accurate design of catalysts with high catalytic performance is crucial for this process. Herein, 2,4,6-trimethylpyridine, benzoic anhydride, and terephthalaldehyde were used to prepare a covalent organic framework (COF) material, which was then used as a template to construct a mesoporous CeO2-supported Au nanoparticles catalyst. The obtained Au@CeO2 catalyst was thoroughly characterized, and it possessed a mesoporous structure with a high surface area. Meanwhile, the as-prepared Au@CeO2 exhibited excellent catalytic performance in the oxidative esterification of benzaldehydes and benzyl alcohols with methanol, affording the corresponding aromatic esters under mild and green reaction conditions. Furthermore, the Au@CeO2 catalyst could also be recycled. Therefore, this study provides a green and sustainable pathway for the synthesis of high-value-added esters through a direct oxidative esterification strategy.

Kilogram-Scale Fabrication of a Robust Olefin-Linked Covalent Organic Framework for Separating Ethylene from a Ternary C2 Hydrocarbon Mixture

One-step adsorptive purification of ethylene (C2H4) from a ternary mixture of acetylene (C2H2), C2H4, and ethane (C2H6) by a single material is of great importance but challenging in the petrochemical industry. Herein, a chemically robust olefin-linked covalent organic framework (COF), NKCOF-62, is designed and synthesized by a melt polymerization method employing tetramethylpyrazine and terephthalaldehyde as cheap monomers. This method avoids most of the disadvantages of classical solvothermal methods, which enable the cost-effective kilogram fabrication of olefin-linked COFs in one pot. Furthermore, NKCOF-62 shows remarkably selective adsorption of C2H2 and C2H6 over C2H4 thanks to its unique pore environments and suitable pore size. Breakthrough experiments demonstrate that polymer-grade C2H4 can be directly obtained from C2H2/C2H6/C2H4 (1/1/1) ternary mixtures through a single separation process. Notably, NKCOF-62 is the first demonstration of the potential to use COFs for C2H2/C2H6/C2H4 separation, which provides a blueprint for the design and construction of robust COFs for industrial gas separations.

Fabricating s-collidine-derived vinylene-linked covalent organic frameworks for photocatalysis

Research into vinyl-linked covalent organic frameworks (COFs) has grown significantly in recent years due to various attractive properties. Herein, we design and synthesize two highly crystalline and stable 2,4,6-collidine-derived vinylene-linked 2D COFs. Both COFs can act as efficient photocatalysts to facilitate visible-light-driven aerobic oxidation. The TM-TBT-COF was observed to exhibit superior activity and recyclability owing to its excellent semiconducting properties.

Post-synthetic modifications of covalent organic frameworks (COFs) for diverse applications

Covalent organic frameworks (COFs) are porous and crystalline organic polymers, which have found usage in various fields. These frameworks are tailorable through the introduction of diverse functionalities into the platform. Indeed, functionality plays a key role in their different applications. However, sometimes functional groups are not compatible with reaction conditions or can compete and interfere with other groups of monomers in the direct synthetic method. Also, pre-synthesis of bulky moieties in COFs can negatively affect crystal formation. To avoid these problems a post-synthetic modification (PSM) approach is a helpful tactic. Also, with the assistance of this strategy porous size can be tunable and stability can be improved without considerable effect on the crystallite. In addition, conductivity, hydrophobicity/ hydrophilicity, and chirality are among the features that can be reformed with this method. In this review, different types of PSM strategies based on recent articles have been divided into four categories: (i) post-functionalization, (ii) post-metalation, (iii) chemical locking, and (iv) host-guest post-modifications. Post-functionalization and chemical locking methods are based on covalent bond formation while in post-metalation and host-guest post-modifications, non-covalent bonds are formed. Also, the potential of these post-modified COFs in energy storage and conversion (lithium-sulfur batteries, hydrogen storage, proton-exchange membrane fuel cells, and water splitting), heterogeneous catalysts, food safety evaluation, gas separation, environmental domains (greenhouse gas capture, radioactive element uptake, and water remediation), and biological applications (drug delivery, biosensors, biomarker capture, chiral column chromatography, and solid-state smart nanochannels) have been discussed.

Thiadiazole-Derived Covalent Organic Framework Macroscopic Ultralight Aerogel

Shaping covalent organic frameworks (COFs) into macroscopic objects for practical application remains a huge challenge. Herein, a new thiadiazole-derived COF macroscopic ultralight aerogel (NNS-VCOF) was prepared through acid-catalyzed aldol condensation between 2,5-dimethyl-1,3,4-thiadiazole and a tritopic aromatic aldehyde derivative. NNS-VCOF aerogel shows extremely low density (ca. 0.020 g cm^-3), excellent mechanical properties (compression modulus of 16.65 kPa), thermal insulation properties (low thermal conductivity of 0.03270 W m^-1 K^-1 at 25 °C), and flame retardancy (quickly self-extinguishing after ignition) due to its three-dimensional sponge-like architecture and special nitrogen heterocyclic framework. To our delight, NNS-VCOF aerogel not only can be used as an outstanding macroscopic material but also shows efficient photocatalytic hydrogen evolution properties in a powder state because of the superhydrophilicity and appropriate optical properties.

Sulfonic-Pendent Vinylene-Linked Covalent Organic Frameworks Enabling Benchmark Potential in Advanced Energy

Both proton exchange membrane fuel cells and uranium-based nuclear techniques represent two green and advanced energies. However, both of them still face some intractable scientific and industrial problems. For the former, established proton-conduction materials always suffer one or another defect such as low proton conductivity, high activation energy, bad durability, or just small-scale product; while for the later, there still lacks available adsorbent to selectively recover of UO₂ ²⁺ from concentrated nitric acid (>1 M) during the spent fuel reprocessing due to the deactivation of the adsorption site or the decomposition of adsorbent under such rigorous conditions. It is found that the above two issues can be well solved by the construction of sulfonic-pendent vinylene-linked covalent organic frameworks (COFs), since these COFs contain abundant sulfonic units for both intrinsic proton conduction and UO₂ ²⁺ capture through strong coordination fixation and vinylene linkage that enhances the stability up to 12 M nitric acid (one of the best materials surviving in 12 M HNO₃ ).

Construction of Covalent Organic Frameworks via Multicomponent Reactions

Multicomponent reactions (MCRs) combine at least three reactants to afford the desired product in a highly atom-economic way and are therefore viewed as efficient one-pot combinatorial synthesis tools allowing one to significantly boost molecular complexity and diversity. Nowadays, MCRs are no longer confined to organic synthesis and have found applications in materials chemistry. In particular, MCRs can be used to prepare covalent organic frameworks (COFs), which are crystalline porous materials assembled from organic monomers and exhibit a broad range of properties and applications. This synthetic approach retains the advantages of small-molecule MCRs, not only strengthening the skeletal robustness of COFs, but also providing additional driving forces for their crystallization, and has been used to prepare a series of robust COFs with diverse applications. The present perspective article provides the general background for MCRs, discusses the types of MCRs employed for COF synthesis to date, and addresses the related critical challenges and future perspectives to inspire the MCR-based design of new robust COFs and promote further progress in this emerging field.