Carbon Dioxide Conversion Upgraded by Host-guest Cooperation between Nitrogen-Rich Covalent Organic Framework and Imidazolium-Based Ionic Polymer

Recent progress in the synthesis and applications of covalent organic framework-based composites

Covalent organic frameworks (COFs) have historically been of interest to researchers in different areas due to their distinctive characteristics, including well-ordered pores, large specific surface area, and structural tunability. In the past few years, as COF synthesis techniques developed, COF-based composites fabricated by integrating COFs and other functional materials including various kinds of metal or metal oxide nanoparticles, ionic liquids, metal-organic frameworks, silica, polymers, enzymes and carbon nanomaterials have emerged as a novel kind of porous hybrid material. Herein, we first provide a thorough summary of advanced strategies for preparing COF-based composites; then, the emerging applications of COF-based composites in diverse fields due to their synergistic effects are systematically highlighted, including analytical chemistry (sensing, extraction, membrane separation, and chromatographic separation) and catalysis. Finally, the current challenges associated with future perspectives of COF-based composites are also briefly discussed to inspire the advancement of more COF-based composites with excellent properties.

The high-efficiency coupling of a Ni2+ coordinated/uncoordinated pyridine N-COF self-supporting nanofilm as an asymmetric supercapacitor

A large-area COFTAPB-BPY film with a pore size of 3.9 nm was prepared on a gas-liquid interface by the virtue of the limiting and guiding functions of sodium dodecylbenzene sulfonate, followed by modification by Ni2+ ions with the reversible redox reaction of Ni(II/III), where Ni2+ was evidently anchored on the N in BPY. The obtained COFTAPB-BPY and Ni-COFTAPB-BPY nanofilms could avoid the inevitable aggregation and stacking of bulk COFTAPB-BPY, which facilitated a high specific capacitance of 0.26 mF cm-2 for the COFTAPB-BPY nanofilm and 0.38 mF cm-2 for the Ni-COFTAPB-BPY nanofilm at 0.001 mA cm-2. Considering the pseudocapacitance and double-layer capacitance traits of Ni-COFTAPB-BPY and COFTAPB-BPY nanofilms, the asymmetric Ni-COFTAPB-BPY//COFTAPB-BPY film supercapacitor was assembled with a symmetric COFTAPB-BPY//COFTAPB-BPY film device as a control. The asymmetric Ni-COFTAPB-BPY//COFTAPB-BPY film supercapacitor could enhance the energy density of 273.9 mW h cm-3 at 14.09 W cm-3 from 85.2 mW h cm-3 at 4.38 W cm-3 for the symmetric COFTAPB-BPY//COFTAPB-BPY film device. This work provides a new perspective on the application of self-supporting COF nanofilms as film asymmetric supercapacitors.

Composite materials based on covalent organic frameworks for multiple advanced applications

Covalent organic frameworks (COFs) stand for a class of emerging crystalline porous organic materials, which are ingeniously constructed with organic units through strong covalent bonds. Their excellent design capabilities, and uniform and tunable pore structure make them potential materials for various applications. With the continuous development of synthesis technique and nanoscience, COFs have been successfully combined with a variety of functional materials to form COFs-based composites with superior performance than individual components. This paper offers an overview of the development of different types of COFs-based composites reported so far, with particular focus on the applications of COFs-based composites. Moreover, the challenges and future development prospects of COFs-based composites are presented. We anticipate that the review will provide some inspiration for the further development of COFs-based composites.

Enabling Ultrahigh Surface Area of Covalently-linked Organic Framework for Boosted CO2 Capture: An Air Liquid Interfacial Plasma as Post-furnishing Protocol

The cognitive intent of a highly ordered and robust adsorbent is extremely sensible and, in this context, Covalent Organic Framework (COF) materials have significantly burgeoned their scope in diverse applications. Herein, we present a simple time-competent hydrothermal procedure to construct a covalent framework with an ultrahigh surface area of 1428 m2/g that shows active adsorption of carbon dioxide (CO2) at variable temperature ranges. Moreover, we substantiate a facile scalably controlled post-synthetic air-liquid interfacial plasma (ALIP) induced protocol that explicitly amplifies the surface area of the pristine framework even to a higher value of 2051 m2/g. The post-synthetic plasma approach presented here led to the rapid enhancement of the surface area of the pristine COF by 43%, which concurrently advances the CO2 uptake up to 67%. Hence, the current study may open up a new frontier in the design as well as fine-tune the properties of the covalent framework that unfolds the advanced outlook in addressing the challenges of CO2 capture.

High-Surface-Area Metalloporphyrin-Based Porous Ionic Polymers by the Direct Condensation Strategy for Enhanced CO2 Capture and Catalytic Conversion into Cyclic Carbonates

Metalloporphyrin-based porous organic polymers (POPs) that behave as advanced biomimetic nanoreactors have drawn continuous attention for heterogeneous CO₂ catalysis in the past decades. Inspired by the double activation model of epoxides, the design and synthesis of metalloporphyrin-based porous ionic polymers (PIPs) are considered as one of the most promising approaches for converting CO₂ to cyclic carbonates under cocatalyst- and solvent-free conditions. To overcome the obstacle of poor reaction activity of ionic monomers or highly irregular stacking architecture, in this paper, we have proposed and demonstrated a modular bottom-up approach for constructing a series of high-surface-area metalloporphyrin-based PIPs in high yields by the direct condensation strategy, thus boosting the close contact of multiple active sites and achieving the enhanced CO₂ capture and catalytic conversion into cyclic carbonates with high turnover frequencies under mild conditions. These recyclable aluminum-porphyrin-based PIPs are featured with high surface areas, prominent CO₂ adsorptive capacities, rigid porphyrin skeletons, and flexible ionic pendants, as well as the matched amounts and spatial positions of metal centers and ionic sites, in which is demonstrated to be one of the quite competitive catalysts. Therefore, this strategy of introducing ionic components into the porphyrin frameworks as flexible side chains rather than main chains and adjusting the reactivity ratios of comonomers by structure-oriented methods, provides feasible guidance for the multifunctionalization of metalloporphyrin-based POPs, thereby increasing the accessibility of multiple active sites and improving their synergistic catalytic behavior.

Facile Construction of Carboxyl-Functionalized Ionic Polymer towards Synergistic Catalytic Cycloaddition of Carbon Dioxide into Cyclic Carbonates

The development of bifunctional ionic polymers as heterogeneous catalysts for effective, cocatalyst- and metal-free cycloaddition of carbon dioxide into cyclic carbonates has attracted increasing attention. However, facile fabrication of such polymers having high numbers of ionic active sites, suitable types of hydrogen bond donors (HBDs), and controlled spatial positions of dual active sites remains a challenging task. Herein, imidazolium-based ionic polymers with hydroxyl/carboxyl groups and high ionic density were facilely prepared by a one-pot quaternization reaction. Catalytic evaluation demonstrated that the presence of HBDs (hydroxyl or carboxyl) could enhance the catalytic activities of ionic polymers significantly toward the CO₂ cycloaddition reaction. Among the prepared catalysts, carboxyl-functionalized ionic polymer (PIMBr-COOH) displayed the highest catalytic activity (94% yield) in the benchmark cycloaddition reaction of CO₂ and epichlorohydrin, which was higher than hydroxyl-functionalized ionic polymer (PIMBr-OH, 76% yield), and far exceeded ionic polymer without HBDs groups (PIMBr, 54% yield). Furthermore, PIMBr-COOH demonstrated good recyclability and wide substrate tolerance. Under ambient CO₂ pressure, a number of epoxides were smoothly cycloadded into cyclic carbonates. Additionally, density functional theory (DFT) calculation verified the formation of strong hydrogen bonds between epoxide and the HBDs of ionic polymers. Furthermore, a possible mechanism was proposed based on the synergistic effect between carboxyl and Br⁻ functionalities. Thus, a facile, one-pot synthetic strategy for the construction of bifunctional ionic polymers was developed for CO₂ fixation.

Synergistic Catalysis of Ionic Liquid-Decorated Covalent Organic Frameworks with Polyoxometalates for CO2 Cycloaddition Reaction under Mild Conditions

The cycloaddition of carbon dioxide (CO₂) with epoxides to yield highly value-added cyclic carbonates is an effective way to chemically utilize and convert CO₂. Here, a heterogeneous catalyst of imidazole ionic liquid-decorated covalent organic framework with polyoxometalates (POM@ImTD-COF) was constructed by the covalent modification of ionic liquids to COFs and the electrostatic interaction between POMs and ionic liquids. The obtained POM@ImTD-COF shows high catalytic activity for CO₂ cycloaddition reaction under mild conditions (1 atm and 80 °C) in the presence of a co-catalyst, and the catalytic activity of POM@ImTD-COF has no obvious decrease during reusing five times. The excellent catalytic performance is mainly attributed to the synergistic effect of ionic liquids, POMs, and COFs. In the cycloaddition process, ionic liquids and the co-catalyst weaken the C-O bond of epoxides and promote the ring opening of epoxides. POMs as the Lewis acids facilitate the insertion of CO₂ to form reaction intermediates. The multiple activation effect of ionic liquids and POMs together with the CO₂ adsorption effect and well-dispersed active sites in COFs contribute to the remarkable catalytic performance.