A Hollow Microtubular Triazine‐ and Benzobisoxazole‐Based Covalent Organic Framework Presenting Sponge‐Like Shells That Functions as a High‐Performance Supercapacitor

In this paper we report the construction of a hollow microtubular triazine‐ and benzobisoxazole‐based covalent organic framework (COF) presenting a sponge‐like shell through a template‐free [3+2] condensation of the planar molecules 2,4,6‐tris(4‐formylphenyl)triazine (TPT‐3CHO) and 2,5‐diaminohydroquinone dihydrochloride (DAHQ‐2HCl). The synthesized COF exhibited extremely high crystallinity, a high surface area (ca. 1855 m² g^?1), and ultrahigh thermal stability. Interestingly, a time‐dependent study of the formation of the hollow microtubular COF having a sponge‐like shell revealed a transformation from initial ribbon‐like crystallites into a hollow tubular structure, and confirmed that the hollow nature of the synthesized COF was controlled by inside‐out Ostwald ripening, while the non‐interaction of the crystallites on the outer surface was responsible for the sponge‐like surface of the tubules. This COF exhibited significant supercapacitor performance: a high specific capacitance of 256 F g^?1 at a current density of 0.5 A g^?1, excellent cycling stability (98.8 % capacitance retention over 1850 cycles), and a high energy density of 43 Wh kg^?1. Such hollow structural COFs with sponge‐like shells appear to have great potential for use as high‐performance supercapacitors in energy storage applications.     

Radical Covalent Organic Frameworks: A General Strategy to Immobilize Open‐Accessible Polyradicals for High‐Performance Capacitive Energy Storage

Ordered π‐columns and open nanochannels found in covalent organic frameworks (COFs) could render them able to store electric energy. However, the synthetic difficulty in achieving redox‐active skeletons has thus far restricted their potential for energy storage. A general strategy is presented for converting a conventional COF into an outstanding platform for energy storage through post‐synthetic functionalization with organic radicals. The radical frameworks with openly accessible polyradicals immobilized on the pore walls undergo rapid and reversible redox reactions, leading to capacitive energy storage with high capacitance, high‐rate kinetics, and robust cycle stability. The results suggest that channel‐wall functional engineering with redox‐active species will be a facile and versatile strategy to explore COFs for energy storage.     

Direct Synthesis of a Covalent Triazine‐Based Framework from Aromatic Amides

There have been extensive efforts to synthesize crystalline covalent triazine‐based frameworks (CTFs) for practical applications and to realize their potential. The phosphorus pentoxide (P₂O₅)‐catalyzed direct condensation of aromatic amide instead of aromatic nitrile to form triazine rings. P₂O₅‐catalyzed condensation was applied on terephthalamide to construct a covalent triazine‐based framework (pCTF‐1). This approach yielded highly crystalline pCTF‐1 with high specific surface area (2034.1 m² g^?1). At low pressure, the pCTF‐1 showed high CO₂ (21.9 wt % at 273 K) and H₂ (1.75 wt % at 77 K) uptake capacities. The direct formation of a triazine‐based COF was also confirmed by model reactions, with the P₂O₅‐catalyzed condensation reaction of both benzamide and benzonitrile to form 1,3,5‐triphenyl‐2,4,6‐triazine in high yield.     

Direct Solar‐to‐Electrochemical Energy Storage in a Functionalized Covalent Organic Framework

A covalent organic framework integrating naphthalenediimide and triphenylamine units (NT‐COF) is presented. Two‐dimensional porous nanosheets are packed with a high specific surface area of 1276 m² g^?1. Photo/electrochemical measurements reveal the ultrahigh efficient intramolecular charge transfer from the TPA to the NDI and the highly reversible electrochemical reaction in NT‐COF. There is a synergetic effect in NT‐COF between the reversible electrochemical reaction and intramolecular charge transfer with enhanced solar energy efficiency and an accelerated electrochemical reaction. This synergetic mechanism provides the key basis for direct solar‐to‐electrochemical energy conversion/storage. With the NT‐COF as the cathode materials, a solar Li‐ion battery is realized with decreased charge voltage (by 0.5 V), increased discharge voltage (by 0.5 V), and extra 38.7 % battery efficiency.     

A Tetrathiafulvalene‐Based Electroactive Covalent Organic Framework

Two‐dimensional covalent organic frameworks (2D COFs) provide a unique platform for the molecular design of electronic and optoelectronic materials. Here, the synthesis and characterization of an electroactive COF containing the well‐known tetrathiafulvalene (TTF) unit is reported. The TTF‐COF crystallizes into 2D sheets with an eclipsed AA stacking motif, and shows high thermal stability and permanent porosity. The presence of TTF units endows the TTF‐COF with electron‐donating ability, which is characterized by cyclic voltammetry. In addition, the open frameworks of TTF‐COF are amenable to doping with electron acceptors (e.g., iodine), and the conductivity of TTF‐COF bulk samples can be improved by doping. Our results open up a reliable route for the preparation of well‐ordered conjugated TTF polymers, which hold great potential for applications in fields from molecular electronics to energy storage.     

A Molecular Pillar Approach To Grow Vertical Covalent Organic Framework Nanosheets on Graphene: Hybrid Materials for Energy Storage

Hybrid 2D–2D materials composed of perpendicularly oriented covalent organic frameworks (COFs) and graphene were prepared and tested for energy storage applications. Diboronic acid molecules covalently attached to graphene oxide (GO) were used as nucleation sites for directing vertical growth of COF‐1 nanosheets (v‐COF‐GO). The hybrid material has a forest of COF‐1 nanosheets with a thickness of 3 to 15 nm in edge‐on orientation relative to GO. The reaction performed without molecular pillars resulted in uncontrollable growth of thick COF‐1 platelets parallel to the surface of GO. The v‐COF‐GO was converted into a conductive carbon material preserving the nanostructure of precursor with ultrathin porous carbon nanosheets grafted to graphene in edge‐on orientation. It was demonstrated as a high‐performance electrode material for supercapacitors. The molecular pillar approach can be used for preparation of many other 2D‐2D materials with control of their relative orientation.     

Copper‐Free Sonogashira Coupling for High‐Surface‐Area Conjugated Microporous Poly(aryleneethynylene) Networks

A modified one‐pot Sonogashira cross‐coupling reaction based on a copper‐free methodology has been applied for the synthesis of conjugated microporous poly(aryleneethynylene) networks (CMPs) from readily available iodoarylenes and 1,3,5‐triethynylbenzene. The polymerization reactions were carried out by using equimolar amounts of halogen and terminal alkyne moieties with extremely small loadings of palladium catalyst as low as 0.65 mol %. For the first time, CMPs with rigorously controlled structures were obtained without any indications of side reactions, as proven by FTIR and solid‐state NMR spectroscopy, while showing Brunauer–Emmett–Teller (BET) surface areas higher than any poly(aryleneethynylene) network reported before, reaching up to 2552 m² g^?1.     

3D Microporous Base‐Functionalized Covalent Organic Frameworks for Size‐Selective Catalysis

The design and synthesis of 3D covalent organic frameworks (COFs) have been considered a challenge, and the demonstrated applications of 3D COFs have so far been limited to gas adsorption. Herein we describe the design and synthesis of two new 3D microporous base‐functionalized COFs, termed BF‐COF‐1 and BF‐COF‐2, by the use of a tetrahedral alkyl amine, 1,3,5,7‐tetraaminoadamantane (TAA), combined with 1,3,5‐triformylbenzene (TFB) or triformylphloroglucinol (TFP). As catalysts, both BF‐COFs showed remarkable conversion (96 % for BF‐COF‐1 and 98 % for BF‐COF‐2), high size selectivity, and good recyclability in base‐catalyzed Knoevenagel condensation reactions. This study suggests that porous functionalized 3D COFs could be a promising new class of shape‐selective catalysts.     

Chemically Stable Covalent Organic Framework (COF)‐Polybenzimidazole Hybrid Membranes: Enhanced Gas Separation through Pore Modulation

Highly flexible, TpPa‐1@PBI‐BuI and TpBD@PBI‐BuI hybrid membranes based on chemically stable covalent organic frameworks (COFs) could be obtained with the polymer. The loading obtained was substantially higher (50 %) than generally observed with MOFs. These hybrid membranes show an exciting enhancement in permeability (about sevenfold) with appreciable separation factors for CO₂/N₂ and CO₂/CH₄. Further, we found that with COF pore modulation, the gas permeability can be systematically enhanced.     

High‐Flux Membranes Based on the Covalent Organic Framework COF‐LZU1 for Selective Dye Separation by Nanofiltration

Covalent organic frameworks (COFs) are attractive candidates for advanced water‐treatment membranes owing to their high porosity and well‐organized channel structures. Herein, the continuous two‐dimensional imine‐linked COF‐LZU1 membrane with a thickness of only 400 nm was prepared on alumina tubes by in situ solvothermal synthesis. The membrane shows excellent water permeance (ca. 760 L m^?2 h^?1 MPa^?1) and favorable rejection rates exceeding 90 % for water‐soluble dyes larger than 1.2 nm. The water permeance through the COF‐LZU1 membrane is much higher than that of most membranes with similar rejection rates. Long‐time operation demonstrates the outstanding stability of the COF‐LZU1 membrane. As the membrane has no selectivity for hydrated salt ions (selectivity <12 %), it is also suitable for the purification of dye products from saline solutions. The excellent performance and the outstanding water stability render the COF‐LZU1 membrane an interesting system for water purification.     

Lithium‐Doped 3D Covalent Organic Frameworks: High‐Capacity Hydrogen Storage Materials

Quick on the uptake : A multiscale theoretical method predicts that the gravimetric adsorption capacities of H₂ in Li‐doped covalent organic frameworks based on the building blocks shown (Li violet, H white, B pink, C green, O red, Si yellow) can reach nearly 7 % at T=298 K and p=100 bar, suggesting that these Li‐doped materials are promising adsorbents for hydrogen storage.

     

Microporous Crystalline γ‐Al2O3 Replicated from Microporous Covalent Triazine Framework and Its Application as Support for Catalytic Hydrolysis of Ammonia Borane

Significant progress has been made on the synthesis and application of mesoporous γ‐alumina. To date, little attention has been paid to the synthesis of microporous crystalline alumina. Here, fabrication of microporous crystalline γ‐alumina using a microporous covalent triazine framework (CTF‐1) as a template is described. Microporous crystalline γ‐alumina with a micro‐meso binary pore system was replicated by infiltration of aluminum nitrate into the micropores of the CTF‐1 template through a NH₃/water‐vapor‐induced internal hydrolysis method, followed by thermal treatment, and subsequent removal of the CTF‐1 template with a 30 % H₂O₂ aqueous solution. The obtained crystalline γ‐alumina material exhibits a large surface area (349 m² g⁻¹) with micropore distribution centered at about 1.27 nm. Ru supported on microporous γ‐Al₂O₃ can be employed as catalyst for hydrolytic dehydrogenation of ammonia borane, and it exhibits high catalytic activity and good durability. This finding provides a new benchmark for preparing well‐defined crystalline microporous alumina materials by a template method, which can be applied in a wide range of fields.     

Two‐Dimensional Tetrathiafulvalene Covalent Organic Frameworks: Towards Latticed Conductive Organic Salts

The construction of a new class of covalent TTF lattice by integrating TTF units into two‐dimensional covalent organic frameworks (2D COFs) is reported. We explored a general strategy based on the C₂+C₂ topological diagram and applied to the synthesis of microporous and mesoporous TTF COFs. Structural resolutions revealed that both COFs consist of layered lattices with periodic TTF columns and tetragonal open nanochannels. The TTF columns offer predesigned pathways for high‐rate hole transport, predominate the HOMO and LUMO levels of the COFs, and are redox active to form organic salts that exhibit enhanced electric conductivity by several orders of magnitude. On the other hand, the linkers between the TTF units play a vital role in determining the carrier mobility and conductivity through the perturbation of 2D sheet conformation and interlayer distance. These results open a way towards designing a new type of TTF materials with stable and predesignable lattice structures for functional exploration.     

Synthetic Control and Multifunctional Properties of Fluorescent Covalent Triazine‐Based Frameworks

Conjugated microporous polymers (CMPs), with the virtue of high porosity and optoelectronic activity, are attracting increasing research interest and have been used in various environmental and energy areas. Efficient synthesis and the exploitation of new functionalities are the research hotspots in the CMPs research area. Covalent triazine frameworks (CTFs) synthesized by CF₃SO₃H catalyzed trimerization reactions show properties quite alike to CMPs and this method avoids the use of noble metal catalysts. In this study, a series of novel fluorescent covalent triazine‐based frameworks (F‐CTFs) is prepared using different tetra‐cyano compounds as the starting monomers. Both porosity and fluorescence properties of the F‐CTFs can be adjusted by the monomer structure. Gas adsorption measurement reveals that F‐CTF1 with the largest surface area of 896 m² g⁻¹ shows the highest CO₂ uptake of 3.29 mmol g⁻¹ at 273 K and 1.13 bar among the polymers. Taking advantages of their large surface areas and strong fluorescence, these F‐CTFs could be used as efficient chemical sensing agents for various nitroaromatic compounds as well.

     

Covalent Triazine‐Based Frameworks as Visible Light Photocatalysts for the Splitting of Water

Covalent triazine‐based frameworks (CTFs) with a graphene‐like layered morphology have been controllably synthesized by the trifluoromethanesulfonic acid‐catalyzed nitrile trimerization reactions at room temperature via selecting different monomers. Platinum nanoparticles are well dispersed in CTF‐T1, which is ascribed to the synergistic effects of the coordination of triazine moieties and the nanoscale confinement effect of CTFs. CTF‐T1 exhibits excellent photocatalytic activity and stability for H₂ evolution in the presence of platinum under visible light irradiation (λ ≥ 420 nm). The activity and stability of CTF‐T1 are comparable to those of g‐C₃N₄. Importantly, as a result of the tailorable electronic and spatial structures of CTFs that can be achieved through the judicial selection of monomers, CTFs not only show great potential as organic semiconductor for photocatalysis but also may provide a molecular‐level understanding of the inherent heterogeneous photocatalysis.