Structural Evolution of 2D Microporous Covalent Triazine-Based Framework toward the Study of High-Performance Supercapacitors

Bipolar Supercapacitive Performance of N-Containing Carbon Materials Derived from Covalent Triazine-Based Framework

The search for new electrode materials for bipolar-supercapacitor performance is the intention of numerous research in the area of functional framework materials. Among various electrode materials, covalent triazine-based frameworks (CTFs) are in the spotlight drawing much attention as potential electrode material for energy storage owing to their tunable surface area, pore size distribution, and heteroatom content. Herein, we present the synthesis of nitrogen-functionalized CTFs marked as CTF-Py-600 and CTF-Py-700 with high nitrogen content (18 % and 14 %, respectively) for supercapacitor application by applying the 2,6-dicyanopyridine monomer via the polymerization reaction under ionothermal condition. The BET surface areas of these materials are in the range of 940-1999 m2 g-1. CTF-Py-700 demonstrates outstanding electrochemical performance in both potential windows. At the negative potential window, it exhibits a higher specific capacitance of 435 F g-1 (at 1 A g-1) compared to the positive potential window, where it shows a specific capacitance of 306 F g-1 (at 1 A g-1) owing to the synergistic existence of its large surface area (1999 m2 g-1) and high nitrogen content (14 %) with inherent microporosity. Remarkable cycling stability without noticeable degradation of specific capacitance after 15000 cycles was recorded for CTF-Py-700. This suggests that the nitrogen-functionalized CTFs are going to be a highly demanded electrode material for electrochemical energy storage applications.

Layered S-Bridged Covalent Triazine Frameworks via a Bifunctional Template-Catalytic Strategy Enabling High-Performance Zinc-Ion Hybrid Supercapacitors

Exploring covalent triazine frameworks (CTFs) with high capacitative activity is highly desirable and challenging. Herein, the S-rich CTFs cathode is pioneeringly introduced in Zn-ion hybrid supercapacitors (ZSC), achieving outstanding capacity and energy density, and satisfactory anti-freezing flexibility. Specifically, the S-bridged CTFs are synthesized by a bifunctional template-catalytic strategy, where ZnCl2 serves as both the catalyst/solvent and in situ template to construct triazine frameworks with interconnected pores and layered gaps. The resultant CTFs (CTFS-750) are employed as a reasonable pattern-like system to more deeply scrutinize the synergistic effect of S-bridged triazine and layered porous architecture for polymer-based cathodes in Zn-ion storage. The experimental results indicate that the adsorption barriers of Zn-ions on CTFS-750 are effectively weakened, and accessible Zn2+-absorption sites provided by the C─S─C and C═N bonds have been confirmed via DFT calculations. Consequently, the CTFS-750 cathode-assembled ZSC displays an ultra-high capacity of 211.6 mAh g-1 at 1.0 A g-1, an outstanding energy density of 202.7 Wh kg-1, and attractive cycling performance. Moreover, the resulting flexible ZSC device shows superior capacity, good adaptability, and satisfactory anti-freezing behavior. This approach sheds new light on constructing advanced polymer-based cathodes at the atom level and paves the way for fabricating high-performance ZSC and beyond.

Strategies for Enhancing the Photocatalytic and Electrocatalytic Efficiency of Covalent Triazine Frameworks for CO2 Reduction

Converting carbon dioxide (CO2) into fuel and high-value-added chemicals is considered a green and effective way to solve global energy and environmental problems. Covalent triazine frameworks (CTFs) are extensively utilized as an emerging catalyst for photo/electrocatalytic CO2 reduction reaction (CO2RR) recently recognized for their distinctive qualities, including excellent thermal and chemical stability, π-conjugated structure, rich nitrogen content, and a strong affinity for CO2, etc. Nevertheless, single-component CTFs have the problems of accelerated recombination of photoexcited electron-hole pairs and restricted conductivity, which limit their application for photo/electrocatalytic CO2RR. Therefore, emphasis will then summarize the strategies for enhancing the photocatalytic and electrocatalytic efficiency of CTFs for CO2RR in this paper, including atom doping, constructing a heterojunction structure, etc. This review first illustrates the synthesis strategies of CTFs and the advantages of CTFs in the field of photo/electrocatalytic CO2RR. Subsequently, the mechanism of CTF-based materials in photo/electrocatalytic CO2RR is described. Lastly, the challenges and future prospects of CTFs in photo/electrocatalytic CO2RR are addressed, which offers a fresh perspective for the future development of CTFs in photo/electrocatalytic CO2RR.

Breakthrough applications of porous organic materials for membrane-based CO2 separation: a review

Over the last decades, porous organic materials (POMs) have been extensively employed in various industrial approaches including gas separation, catalysis and energy production due to possessing indisputable advantages like great surface area, high permeability, controllable pore size, appropriate functionalization and excellent processability compared to traditional substances like zeolites, Alumina and polymers. This review presents the recent breakthroughs in the multifunctional POMs for potential use in the membrane-based CO2 separation. Some examples of highly-selective membranes using multifunctional POMs are described. Moreover, various classifications of POMs following with their advantages and disadvantages in CO2 separation processes are explained. Apart from reviewing the state-of-the-art POMs in CO2 separation, the challenges/limitations of POMs with tailored structures for reasonable application are discussed.

Towards the 4 V-class n-type organic lithium-ion positive electrode materials: the case of conjugated triflimides and cyanamides

Organic electrode materials have garnered a great deal of interest owing to their sustainability, cost-efficiency, and design flexibility metrics. Despite numerous endeavors to fine-tune their redox potential, the pool of organic positive electrode materials with a redox potential above 3 V versus Li+/Li0, and maintaining air stability in the Li-reservoir configuration remains limited. This study expands the chemical landscape of organic Li-ion positive electrode chemistries towards the 4 V-class through molecular design based on electron density depletion within the redox center via the mesomeric effect of electron-withdrawing groups (EWGs). This results in the development of novel families of conjugated triflimides and cyanamides as high-voltage electrode materials for organic lithium-ion batteries. These are found to exhibit ambient air stability and demonstrate reversible electrochemistry with redox potentials spanning the range of 3.1 V to 3.8 V (versus Li+/Li0), marking the highest reported values so far within the realm of n-type organic chemistries. Through comprehensive structural analysis and extensive electrochemical studies, we elucidate the relationship between the molecular structure and the ability to fine-tune the redox potential. These findings offer promising opportunities to customize the redox properties of organic electrodes, bridging the gap with their inorganic counterparts for application in sustainable and eco-friendly electrochemical energy storage devices.

Narrow-Pore Engineering of Vinylene-Linked Covalent Organic Frameworks with Weak Interaction-Triggered Multiple Responses

Vinylene-linked covalent organic frameworks (COFs) are emerging as promising crystalline materials, but their narrow pore engineering is severely impeded by the weak reversibility of the carbon-carbon double bond formation reaction, which has led to less exploration of their ultramicroporous structures and properties. Herein, we developed a single aromatic ring-based tetratopic monomer, tetramethylpyrazine, which undergoes a smooth Knoevenegal condensation at its four arylmethly carbon atoms with linear aromatic dialdehyde monomers upon the self-catalyzed activation of pyridine nitrogen-containing monomers in the presence of an organic anhydride. This has resulted in the formation of two vinylene-linked COFs, which both crystallized in orthorhombic lattices, and layered in AA stacking fashions along the vertical directions. They exhibit high surface areas and well-tailored ultramicropore sizes up to 0.5 nm. The unique cross-linking mode at two pairs of para-positions of each pyrazine unit through carbon-carbon double bonds afford them with π-extended conjugation over the in-plane backbones and substantial semiconducting characters. The resultant COFs can be well-dispersed in water to form stable sub-microparticles with negative charges (zeta potentials: ca. -30 mV), and exhibiting tunable aggregation behaviors through protonation/deprotonation. As a consequence, they exhibit pore-size-dependent colorimetric responses to various anions with different pKa values in high selectivity.

Superlithiation Performance of Pyridinium Polymerized Ionic Liquids with Fast Li+ Diffusion Kinetics as Anode Materials for Lithium-Ion Battery

Polymerized ionic liquids (PILs) with super ion diffusion kinetics have aroused considerable attention in rechargeable batteries, which are very promising to solve the problem of the slow ion diffusion kinetics in organic electrode materials. Theoretically, PILs incorporated redox groups are very suitable as anode materials to realize "superlithiation" performance, achieving high lithium storage capacity. In this study, redox pyridinium-based PILs (PILs-Py-400) have been synthesized through trimerization reactions by pyridinium ionic liquids with cyano groups under an appropriate temperature (400 °C). The positively charged skeleton, extended conjugated system, abundant micropores, and amorphous structure for PILs-Py-400 can boost the utilization efficiency of redox sites. A high capacity of 1643 mAh g-1 at 0.1 A g-1 (96.7% of the theoretical capacity) has been obtained, indicating intriguing 13 Li+ redox reactions in per repeating unit of one pyridinium ring, one triazine ring, and one methylene. Moreover, PILs-Py-400 exhibit excellent cycling stability with a capacity of around 1100 mAh g-1 at 1.0 A g-1 after 500 cycles, and the capacity retention is 92.2%.

An orientated mass transfer in Ni-Cu tandem nanofibers for highly selective reduction of CO2 to ethanol

Electrochemically reducing CO2 to ethanol is attractive but suffers from poor selectivity. Tandem catalysis that integrates the activation of CO2 to an intermediate using one active site and the subsequent formation of hydrocarbons on the other site offers a promising approach, where the control of the intermediate transfer between different catalytic sites is challenging. We propose an internally self-feeding mechanism that relies on the orientation of the mass transfer in a hierarchical structure and demonstrate it using a one-dimensional (1D) tandem core-shell catalyst. Specifically, the carbon-coated Ni-core (Ni/C) catalyzes the transformation of CO2-to-CO, after which the CO intermediates are guided to diffuse to the carbon-coated Cu-shell (Cu/C) and experience the selective reduction to ethanol, realizing the orientated key intermediate transfer. Results show that the Faradaic efficiency for ethanol was 18.2% at -1 V vs. RHE (VRHE) for up to 100 h. The following mechanism study supports the hypothesis that the CO2 reduction on Ni/C generates CO, which is further reduced to ethanol on Cu/C sites. Density functional theory calculations suggest a combined effect of the availability of CO intermediate in Ni/C core and the dimerization of key *CO intermediates, as well as the subsequent proton-electron transfer process on the Cu/C shell.

TM-Free and TM-Catalyzed Mechanosynthesis of Functional Polymers

Mechanochemically induced methods are commonly used for the depolymerization of polymers, including plastic and agricultural wastes. So far, these methods have rarely been used for polymer synthesis. Compared to conventional polymerization in solutions, mechanochemical polymerization offers numerous advantages such as less or no solvent consumption, the accessibility of novel structures, the inclusion of co-polymers and post-modified polymers, and, most importantly, the avoidance of problems posed by low monomer/oligomer solubility and fast precipitation during polymerization. Consequently, the development of new functional polymers and materials, including those based on mechanochemically synthesized polymers, has drawn much interest, particularly from the perspective of green chemistry. In this review, we tried to highlight the most representative examples of transition-metal (TM)-free and TM-catalyzed mechanosynthesis of some functional polymers, such as semiconductive polymers, porous polymeric materials, sensory materials, materials for photovoltaics, etc.

Nanoporous Hollow Carbon Spheres Derived from Fullerene Assembly as Electrode Materials for High-Performance Supercapacitors

The energy storage performances of supercapacitors are expected to be enhanced by the use of nanostructured hierarchically micro/mesoporous hollow carbon materials based on their ultra-high specific surface areas and rapid diffusion of electrolyte ions through the interconnected channels of their mesoporous structures. In this work, we report the electrochemical supercapacitance properties of hollow carbon spheres prepared by high-temperature carbonization of self-assembled fullerene-ethylenediamine hollow spheres (FE-HS). FE-HS, having an average external diameter of 290 nm, an internal diameter of 65 nm, and a wall thickness of 225 nm, were prepared by using the dynamic liquid-liquid interfacial precipitation (DLLIP) method at ambient conditions of temperature and pressure. High temperature carbonization (at 700, 900, and 1100 °C) of the FE-HS yielded nanoporous (micro/mesoporous) hollow carbon spheres with large surface areas (612 to 1616 m² g^-1) and large pore volumes (0.925 to 1.346 cm³ g^-1) dependent on the temperature applied. The sample obtained by carbonization of FE-HS at 900 °C (FE-HS_900) displayed optimum surface area and exhibited remarkable electrochemical electrical double-layer capacitance properties in aq. 1 M sulfuric acid due to its well-developed porosity, interconnected pore structure, and large surface area. For a three-electrode cell setup, a specific capacitance of 293 F g^-1 at a 1 A g^-1 current density, which is approximately 4 times greater than the specific capacitance of the starting material, FE-HS. The symmetric supercapacitor cell was assembled using FE-HS_900 and attained 164 F g^-1 at 1 A g^-1 with sustained 50% capacitance at 10 A g^-1 accompanied by 96% cycle life and 98% coulombic efficiency after 10,000 consecutive charge/discharge cycles. The results demonstrate the excellent potential of these fullerene assemblies in the fabrication of nanoporous carbon materials with the extensive surface areas required for high-performance energy storage supercapacitor applications.

Advances in the Synthesis of Covalent Triazine Frameworks

Covalent triazine frameworks (CTFs) are a class of organic polymer materials constructed by aromatic 1,3,5-triazine rings with planar π-conjugation properties. CTFs are highly stable and porous with N atoms in the frameworks, possessing semiconductive properties; thus they are widely used in gas adsorption and separation as well as catalysis. The properties of CTFs strongly depend on the type of monomers and the synthesis process. Synthesis methods including ionothermal polymerization, amino-aldehyde synthesis, trifluoromethanesulfonic acid catalyzed synthesis, and aldehyde-amidine condensation have been intensively studied in recent years. In this review, we discuss the recent advances and future developments of CTFs synthesis.

Organic Supercapacitors as the Next Generation Energy Storage Device: Emergence, Opportunity, and Challenges

Harnessing new materials for developing high-energy storage devices set off research in the field of organic supercapacitors. Various attractive properties like high energy density, lower device weight, excellent cycling stability, and impressive pseudocapacitive nature make organic supercapacitors suitable candidates for high-end storage device applications. This review highlights the overall progress and future of organic supercapacitors. Sustainable energy production and storage depend on low cost, large supercapacitor packs with high energy density. Organic supercapacitors with high pseudocapacitance, lightweight form factor, and higher device potential are alternatives to other energy storage devices. There are many recent ongoing research works that focus on organic electrolytes along with the material aspect of organic supercapacitors. This review summarizes the current research status and the chemistry behind the storage mechanism in organic supercapacitors to overcome the challenges and achieve superior performance for future opportunities.

Engineering Catalysis within a Saturated In(III)-Based MOF Possessing Dynamic Ligand-Metal Bonding

Metal-organic frameworks have developed into a formidable heterogeneous catalysis platform in recent years. It is well established that thermolysis of coordinated solvents from MOF nodes can render highly reactive, coordinatively unsaturated metal complexes which are stabilized via site isolation and serve as active sites in catalysis. Such approaches are limited to frameworks featuring solvated transition-metal complexes and must be stable toward the formation of "permanent" open metal sites. Herein, we exploit the hemilability of metal-carboxylate bonds to generate transient open metal sites in an In(III) MOF, pertinent to In-centered catalysis. The transient open metal sites catalyze the Strecker reaction over multiple cycles without loss of activity or crystallinity. We employ computational and spectroscopic methods to confirm the formation of open metal sites via transient dissociation of In(III)-carboxylate bonds. Furthermore, the amount of transient open metal sites within the material and thus the catalytic performance can be temperature-modulated.

Biomass Hierarchical Porous Carbonized Typha angustifolia Prepared by Green Pore-Making Technology for Energy Storage

The cost-effective biomass-derived carbon with high electrochemical performance is highly desirable for the sustainable development of advanced energy storage devices. In this manuscript, Typha angustifolia with a large output and loose porous characteristics was selected as the raw material of biomass. In the synthesis process, KHCO₃, which is more environmentally friendly, is used as a pore-forming agent, and the low-cost, easy-to-clean fluxing agent NaCl is used to assist the pore-forming process. Based on the analysis of thermogravimetric-infrared test results, the calcination procedure of porous carbon was designed reasonably, so that the functions of the pore-forming agent and fluxing agent could be fully exerted. Its high electrochemical performance is attributed to combined contributions from high surface area and hierarchical porous structures. The as-prepared carbon also showed an outstanding capacitance of 317.2 F/g at a current density of 1 A g^-1 and a high capacitance retention of over 97.83% after 5000 cycles at a current density of 4 A g^-1. This work provides an outstanding renewable candidate and a feasible route design strategy for the fabrication of high-performance electrodes.

Recent advances and applications of magnetic covalent organic frameworks in food analysis

Recently, covalent organic frameworks (COFs) have been widely used to prepare magnetic adsorbents for food analysis due to their highly tunable porosity, large specific surface area, excellent chemical and thermal stability and large delocalised π-electron system. This review summarises the main types and preparation methods of magnetic COFs and their applications in food analysis for the detection of pesticide residues, veterinary drugs, endocrine-disrupting phenols and estrogens, plasticisers and other food contaminants. Furthermore, challenges and future outlook in the development of magnetic COFs for food analysis are discussed.

A Sensitive Photoelectrochemical Sensor for Levodopa Detection Using Benzothiadiazole-Based Conjugated Microporous Polymer-Coated Graphene Heterostructures

Since the 1960s, levodopa (LDA) has been the standard drug for treating of Parkinson's disease. In this study, a novel benzothiadiazole-based conjugated microporous polymer-coated graphene heterostructure (CMP-rGO) was synthesized and used to construct a sensitive photoelectrochemical (PEC) sensor capable of detecting LDA. Under optimal experimental conditions, the intensity of the photocurrent produced by the sensor was linear from 0.005 to 40 μM, and the limit of detection of the sensor was 0.0027 μM. The sensor showed good repeatability, stability, and selectivity for LDA detection. Finally, the constructed sensor was used to detect LDA in levodopa tablets, human serum samples, and urine samples and satisfactory results were obtained. Therefore, the PEC sensor provides a novel platform for the detection of LDA in real samples and broadens the applications of conjugated microporous polymers in PEC sensing.

Catalytic Oxidation of Toluene over Fe-Rich Palygorskite Supported Manganese Oxide: Characterization and Performance

A series of Fe–rich palygorskite supported manganese oxide (X%Mn–Pal) catalysts were prepared by co-precipitation method and used as catalysts for toluene oxidation. The components and structure of the as-prepared catalysts were characterized by XRD, Raman, TEM, XPS, and in situ DRIFTS. The results showed that the 15%Mn–Pal catalyst exhibited the highest catalytic activity (T90 = 227 °C) and excellent cycling stability for the oxidation of toluene compared with other catalysts. The characterization results indicated that remarkable activity of the 15%Mn–Pal catalyst for toluene oxidation should be ascribed to the abundant surface oxygen vacancies. In situ DRIFTS results elucidated that benzoate was the main intermediate, which can be further oxidized into H2O and CO2. The objectives of this study are to (i) investigate the synergistic effect between Fe and Mn for toluene oxidation, (ii) develop an efficient catalyst for toluene abatement with high activity and low–cost, and (iii) promote the application of natural Fe–rich palygorskite in the control of VOCs.

Functionalized Triazines and Tetrazines: Synthesis and Applications

The molecules possessing triazine and tetrazine moieties belong to a special class of heterocyclic compounds. Both triazines and tetrazines are building blocks and have provided a new dimension to the design of biologically important organic molecules. Several of their derivatives with fine-tuned electronic properties have been identified as multifunctional, adaptable, switchable, remarkably antifungal, anticancer, antiviral, antitumor, cardiotonic, anti-HIV, analgesic, anti-protozoal, etc. The objective of this review is to comprehensively describe the recent developments in synthesis, coordination properties, and various applications of triazine and tetrazine molecules. The rich literature demonstrates various synthetic routes for a variety of triazines and tetrazines through microwave-assisted, solid-phase, metal-based, [4+2] cycloaddition, and multicomponent one-pot reactions. Synthetic approaches contain linear, angular, and fused triazine and tetrazine heterocycles through a combinatorial method. Notably, the triazines and tetrazines undergo a variety of organic transformations, including electrophilic addition, coupling, nucleophilic displacement, and intramolecular cyclization. The mechanistic aspects of these heterocycles are discussed in a detailed way. The bioorthogonal application of these polyazines with various strained alkenes and alkynes provides a new prospect for investigations in chemical biology. This review systematically encapsulates the recent developments and challenges in the synthesis and possible potential applications of various triazine and tetrazine systems.

A General Strategy for Kilogram-Scale Preparation of Highly Crystal-line Covalent Triazine Frameworks

Scalable and eco-friendly synthesis of crystalline porous covalent triazine frameworks (CTFs) is essential to realize their broad industrial applications but remains a great challenge, which requires the fundamental understanding of the two-dimensional polymerization mechanism. Herein, we report a universal polyphosphoric acid (H₆ P₄ O₁₃ )-catalyzed nitrile trimerization route to synthesize a series of highly crystalline CTFs with high specific surface areas. This new strategy enables the cost-effective large-scale fabrication of crystalline CTFs at kilogram level for the first time. Through density functional theory calculation and detailed controlled experiments, we reveal that the polyphosphate acid show much higher catalytic activity for trimerization reaction than its analogues such as P₂ O₅ and H₃ PO₄ . Furthermore, the crystalline CTFs with regular porosity and abundant triazine groups exhibit ultrahigh removal efficiency of micropollutants, indicating its great potential in environment remediation.

Covalent Triazine Frameworks and Porous Carbons: Perspective from an Azulene-Based Case

Covalent triazine frameworks (CTFs) are among the most valuable frameworks owing to many fantastic properties. However, molten salt-involved preparation of CTFs at 400-600 °C causes debate on whether CTFs represent organic frameworks or carbon. Herein, new CTFs based on the 1,3-dicyanoazulene monomer (CTF-Azs) are synthesized using molten ZnCl₂ at 400-600 °C. Chemical structure analysis reveals that the CTF-Az prepared at low temperature (400 °C) exhibits polymeric features, whereas those prepared at high temperatures (600 °C) exhibit typical carbon features. Even after being treated at even higher temperatures, the CTF-Azs retain their rich porosity, but the polymeric features vanish. Although structural de-conformation is a widely accepted outcome in polymer-to-carbon rearrangement processes, the study evaluates such processes in the context of CTF systems. A proof-of-concept study is performed, observing that the as-synthesized CTF-Azs exhibit promising performance as cathodes for Li- and K-ion batteries. Moreover, the as-prepared NPCs exhibit excellent catalytic oxygen reduction reaction (ORR) performance; hence, they can be used as air cathodes in Zn-air batteries. This study not only provides new building blocks for novel CTFs with controllable polymer/carbon features but also offers insights into the formation and structure transformation history of CTFs during thermal treatment.

Crystalline Covalent Triazine Frameworks with Fibrous Morphology via a Low-Temperature Polycondensation of Planar Monomer

The morphology regulation of covalent triazine frameworks (CTFs) is a great challenge, which may be due to the difficulty in controlling its morphology by traditional synthesis methods. Herein, a general approach to fabricate morphology controllable CTFs by a mild polycondensation reaction in mixed solvents without any templating agents is reported. As a proof of concept, a type of crystalline CTFs with distinctive fibrous morphology (MS-F-CTF-1) (MS: Mixed Solvent; F: Fibrous Morphology) is developed by adjusting the ratio of mixed solvents to control the solubility of monomers, so that the nucleation, crystal growth, and subsequent self-assembly are controlled, which facilitates the formation of fibrous morphology. The resultant crystalline MS-F-CTF-1 shows uniform fibrous morphology with a diameter of about 100 nm and a length of several micrometers. Notably, the fibrous morphology of CTFs can efficiently improve the photocatalytic hydrogen evolution performance, in which the hydrogen evolution rate can be boosted by about two times in comparison to block ones.

Graphitic Aza-Fused π-Conjugated Networks: Construction, Engineering, and Task-Specific Applications

2D π-conjugated networks linked by aza-fused units represent a pivotal category of graphitic materials with stacked nanosheet architectures. Extensive efforts have been directed at their fabrication and application since the discovery of covalent triazine frameworks (CTFs). Besides the triazine cores, tricycloquinazoline and hexaazatriphenylene linkages are further introduced to tailor the structures and properties. Diverse related materials have been developed rapidly, and a thorough outlook is necessitated to unveil the structure-property-application relationships across multiple subcategories, which is pivotal to guide the design and fabrication toward enhanced task-specific performance. Herein, the structure types and development of related materials including CTFs, covalent quinazoline networks, and hexaazatriphenylene networks, are introduced. Advanced synthetic strategies coupled with characterization techniques provide powerful tools to engineer the properties and tune the associated behaviors in corresponding applications. Case studies in the areas of gas adsorption, membrane-based separation, thermo-/electro-/photocatalysis, and energy storage are then addressed, focusing on the correlation between structure/property engineering and optimization of the corresponding performance, particularly the preferred features and strategies in each specific field. In the last section, the underlying challenges and opportunities in construction and application of this emerging and promising material category are discussed.

Triazine 2D Nanosheets as a New Class of Nanomaterials: Crystallinity, Properties and Applications

Based on the recent (2015–2021) literature data, the authors analyze the mutual dependence of crystallinity/amorphism and specific surface area and porosity in covalent triazine frameworks (CTFs), taking into account thermodynamic and kinetic control in the synthesis of these 2D nanosheets. CTFs have now become a promising new class of high-performance porous organic materials. They can be recycled and reused easily, and thus have great potential as sustainable materials. For 2D CTFs, numerous examples are given to support the known rule that the structure and properties of any material with a given composition depend on the conditions of its synthesis. The review may be useful for elder students, postgraduate students, engineers and research fellows dealing with chemical synthesis and modern nanotechnologies based on 2D covalent triazine frameworks.

Ultrastable Covalent Triazine Organic Framework Based on Anthracene Moiety as Platform for High-Performance Carbon Dioxide Adsorption and Supercapacitors

Conductive and porous nitrogen-rich materials have great potential as supercapacitor electrode materials. The exceptional efficiency of such compounds, however, is dependent on their larger surface area and the level of nitrogen doping. To address these issues, we synthesized a porous covalent triazine framework (An-CTFs) based on 9,10-dicyanoanthracene (An-CN) units through an ionothermal reaction in the presence of different molar ratios of molten zinc chloride (ZnCl₂) at 400 and 500 °C, yielding An-CTF-10-400, An-CTF-20-400, An-CTF-10-500, and An-CTF-20-500 microporous materials. According to N₂ adsorption–desorption analyses (BET), these An-CTFs produced exceptionally high specific surface areas ranging from 406–751 m²·g⁻¹. Furthermore, An-CTF-10-500 had a capacitance of 589 F·g⁻¹, remarkable cycle stability up to 5000 cycles, up to 95% capacity retention, and strong CO₂ adsorption capacity up to 5.65 mmol·g⁻¹ at 273 K. As a result, our An-CTFs are a good alternative for both electrochemical energy storage and CO₂ uptake.

Bio-inspired hierarchical nanoporous carbon derived from water spinach for high-performance supercapacitor electrode materials

Due to various properties, green carbon nanomaterials with high specific surface area and environmentally friendly features have aroused extensive interest in energy storage device applications. Here, we report a facile, one-step carbonization of water spinach to synthesize porous carbon that exhibits a high specific surface area of ∼1559 m2 g-1, high specific capacitance (∼1191 F g-1 at 1 A g-1), a low intercept (0.9 Ω), outstanding rate capability and superior cycling stability (94.3% capacitance retention after 10 000 cycles). Moreover, the assembled symmetric cell delivers a high energy density of ∼85 W h kg-1 at 1200 W kg-1 and ultra-high stability (loss of 6.8% after 10 000 cycles). An energy density of 49 W h kg-1 could also be achieved even with a power density of up to 24 kW kg-1, which indicates that this material could be a promising candidate for future applications in aqueous-based supercapacitors.

A Facile and Highly Efficient Approach to Obtain a Fluorescent Chromogenic Porous Organic Polymer for Lymphatic Targeting Imaging

Porous organic polymers have an open architecture, excellent stability, and tunable structural components, revealing great application potential in the field of fluorescence imaging, but this part of the research is still in its infancy. In this study, we aimed to tailor the physical and chemical characteristics of indocyanine green using sulfonic acid groups and conjugated fragments, and prepared amino-grafted porous polymers. The resulting material had excellent solvent and thermal stability, and possessed a relatively large pore structure with a size of 3.4 nm. Based on the synergistic effect of electrostatic bonding and π–π interactions, the fluorescent chromogenic agent, indocyanine green, was tightly incorporated into the pore cavity of POP solids through a one-step immersion method. Accordingly, the fluorescent chromogenic POP demonstrated excellent imaging capabilities in biological experiments. This preparation of fluorescent chromogenic porous organic polymer illustrates a promising application of POP-based solids in both fluorescence imaging and biomedicine applications.

Template-free construction of hollow mesoporous carbon spheres from a covalent triazine framework for enhanced oxygen electroreduction

The construction of hollow mesoporous carbon nanospheres (HMCS) avoiding the use of traditional soft/hard templates is highly desired for nanoscience yet challenging. Herein, we report a simple and straightforward template-free strategy for preparing nitrogen, sulfur dual-doped HMCSs (N/S-HMCSs) as oxygen reduction reaction (ORR) electrocatalysts. The unique hollow spherical and mesoporous structure was in-situ formed via a thermally initiated hollowing pathway from an elaborately engineered covalent triazine framework. Regulation of pyrolysis temperatures contributed to precisely tailoring of the shell thickness of HMCSs. The resulting N/S-HMCS₉₀₀ (pyrolyzed at 900 °C) possessed high N and S contents, large specific surface areas, rich and uniform mesopores distribution. Consequently, as a metal-free ORR electrocatalyst, N/S-HMCS₉₀₀ exhibits a high half-wave potential, excellent methanol tolerance and great long-term durability. Additionally, density functional theory calculations demonstrate that N, S-dual dopant can create extra active sites with higher catalytic activity than the isolated N-dopant. This strategy provides new insights into the construction of hollow and mesoporous multi-heteroatom-doped carbon materials with tunable nanoarchitecture for various electrochemical applications.

Rational design of covalent triazine frameworks based on pore size and heteroatomic toward high performance supercapacitors

A series of covalent triazine frameworks (CTFs) are prepared via ionothermal synthesis for supercapacitors. Due to the feature of adjustable pore structure and rich nitrogen, CTFs with regular structure can be used as a group of model compounds to further investigate the influence of pore size and heteroatom on supercapacitors. By comparing the performance of CTFs with different pore structures and nitrogen contents, the experimental results show that BPY-CTF with high specific surface area of 2278 m² g^-1, mesopores structure, and suitable nitrogen content displays a specific capacitance of 393.6 F g^-1 at 0.5 A g^-1. According to the results and analysis, the existence of mesopores largely enhance the contact area between the electrode material and electrolyte, and then boost the charge transfer. On the other hand, N-doping has a prominent effect on improving the Faradaic pseudo-capacitance and conductivity for CTF electrode materials. This work will inspire further research on the development of highly efficient electrode materials for energy storage devices.

Recycling decoration wastes toward a high-performance porous carbon membrane electrode for supercapacitive energy storage devices

A porous carbon membrane (DWCM) is facilely fabricated by direct carbonization of decoration waste using KOH as an activator and employed as a self-supported electrode for an aqueous supercapacitor (SC) with a superior capacitive performance.

Two-dimensionalcovalent triazine frameworks as superior nanocarriers for the delivery of thioguanine anti-cancer drugs: a periodic DFT study

This work aims to introduce a superior nanocarrier for thioguanine (TG) anti-cancer drug delivery, drug release, and cancer therapy through computational chemistry.

Balance of N-Doping Engineering and Carbon Chemistry to Expose Edge Graphitic N Sites for Enhanced Oxygen Reduction Electrocatalysis

Nitrogen-doped nanocarbon materials (NCMs) have been developed as promising metal-free oxygen reduction reaction (ORR) electrocatalysts. However, insufficient attention on the balance of N-doping engineering and carbon chemistry significantly suppressed the revelation of the real active configurations as well as the ORR mechanism for NCMs. Herein, 1,4-phenylenediurea (BDU) with multifunctional blocks was designed for the synthesis of NCMs, realizing synchronous manipulation of N-doping engineering and carbon chemistry. The good balance between N-doping engineering (especially graphitic edge N configurations) and carbon chemistry (including the specific surface area, porosity distribution, and graphitization degree) at a pyrolysis temperature of 1000 °C resulted in the best ORR performance for obtaining N-doped carbon nanorod (NCR) materials. A general descriptor χ was then proposed for evaluating the balance states between N-doping engineering and carbon chemistry. The prediction of the ORR performance of NCMs from their physical properties as well as searching for the optimal active configuration from the relationships between ORR performance and different configurations can be realized from such a practical descriptor, which can also be extended to other nanocarbon-based metal-free electrocatalytic reactions for deeply understanding their electrocatalytic mechanisms.

Sono-Cavitation and Nebulization-Based Synthesis of Conjugated Microporous Polymers for Energy Storage Applications

Conjugated microporous polymers (CMPs) are promising energy storage materials owing to their rigid and cross-linked microporous structures. However, the fabrication of nano- and microstructured CMP films for practical applications is currently limited by processing challenges. Herein, we report that combined sono-cavitation and nebulization synthesis (SNS) is an effective method for the synthesis of CMP films from a monomer precursor solution. Using the SNS, the scalable fabrication of microporous and redox-active CMP films can be achieved via the oxidative C-C coupling polymerization of the monomer precursor. Intriguingly, the ultrasonic frequency used during SNS strongly affects the synthesis of the CMP films, resulting in an approximately 30% improvement in reaction yields and ca. 1.3-1.7-times enhanced surface areas (336-542 m²/g) at a high ultrasonic frequency of 180 kHz compared to those at 120 kHz. Furthermore, we prepare highly conductive, three-dimensional porous electrodes [CMP/carbon nanotube (CNT)] by a layer-by-layer sequential deposition of CMP films and CNTs via SNS. Finally, an asymmetric supercapacitor comprising the CMP/CNT cathode and carbon anode shows a high specific capacitance of 477 F/g at 1 A/g with a wide working potential window (0-1.4 V) and robust cycling stability, exhibiting 94.4% retention after 10,000 cycles.

Highly Perfluorinated Covalent Triazine Frameworks Derived from a Low-Temperature Ionothermal Approach Towards Enhanced CO2 Electroreduction

Perfluorinated covalent triazine frameworks (F-CTFs) have shown unique features and attractive performance in separation and catalysis. However, state-of-the-art F-CTFs synthesized via the ZnCl₂ -promoted procedure have quite low fluorine contents due to C-F bond cleavage induced by chloride (a Lewis base) and the harsh conditions deployed (400-700 °C). Fabricating F-CTFs with high fluorine contents (>30 wt %) remains challenging. Herein, we present a low-temperature ionothermal approach (275 °C) to prepare F-CTFs, which is achieved via polymerization of tetrafluoroterephthalonitrile (TFPN) over the Lewis superacids, e.g., zinc triflimide [Zn(NTf₂ )₂ ] without side reactions. With low catalyst loading (equimolar), F-CTFs are afforded with high fluorine content (31 wt %), surface area up to 367 m²  g^-1 , and micropores around 1.1 nm. The highly hydrophobic F-CTF-1 exhibits good capability to boost electroreduction of CO₂ to CO, with faradaic efficiency of 95.7 % at -0.8 V and high current density (-141 mA cm^-2 ) surpassing most of the metal-free electrocatalysts.

Immobilized covalent triazine frameworks films as effective photocatalysts for hydrogen evolution reaction

Covalent triazine frameworks have recently been demonstrated as promising materials for photocatalytic water splitting and are usually used in the form of suspended powder. From a practical point of view, immobilized CTFs materials are more suitable for large-scale water splitting, owing to their convenient separation and recycling potential. However, existing synthetic approaches mainly result in insoluble and unprocessable powders, which make their future device application a formidable challenge. Herein, we report an aliphatic amine-assisted interfacial polymerization method to obtain free-standing, semicrystalline CTFs film with excellent photoelectric performance. The lateral size of the film was up to 250 cm², and average thickness can be tuned from 30 to 500 nm. The semicrystalline structure was confirmed by high-resolution transmission electron microscope, powder X-ray diffraction, grazing-incidence wide-angle X-ray scattering, and small-angle X-ray scattering analysis. Intrigued by the good light absorption, crystalline structure, and large lateral size of the film, the film immobilized on a glass support exhibited good photocatalytic hydrogen evolution performance (5.4 mmol h^-1 m^-2) with the presence of co-catalysts i.e., Pt nanoparticles and was easy to recycle.

Rapid, Ordered Polymerization of Crystalline Semiconducting Covalent Triazine Frameworks

The rapid synthesis of crystalline covalent triazine frameworks (CTFs) and exploration of the polymerization mechanism are highly desired for the research of crystalline porous polymers, but have not yet been reported. Herein, we demonstrate a scalable microwave-assisted synthetic strategy to successfully prepare a series of highly crystalline and semiconducting CTFs within 20 minutes for the first time. By in situ imaging and time-dependent characterization, we proposed an ordered two-dimensional (2D) polymerization mechanism for crystalline CTFs, in which the monomers rapidly polymerize into periodic 2D molecular sheets within 10 s and then grow into more ordered framework structures. Photocatalytic study of CTF with different crystallinity revealed that large crystalline domain could significantly improve the photocatalytic performance. Single-layer and few-layer crystalline 2D triazine polymer nanosheets could be obtained through simple ball-milling exfoliation of the bulk layered CTFs and exhibit nearly fivefold improved photocatalytic hydrogen evolution rate up to 7971 μmol g^-1  h^-1 .

A Solvent-Polarity-Induced Interface Self-Assembly Strategy towards Mesoporous Triazine-Based Carbon Materials

Triazine-based materials with porous structure have recently received numerous attentions as a fascinating new class because of their superior potential for various applications. However, it is still a formidable challenge to obtain triazine-based materials with precise adjustable meso-scaled pore sizes and controllable pore structures by reported synthesis approaches. Herein, we develop a solvent polarity induced interface self-assembly strategy to construct mesoporous triazine-based carbon materials. In this method, we employ a mixed solvent system within a suitable range of polarity (0.223≤Lippert-Mataga parameter (Δf) ≤0.295) to induce valid self-assembly of skeleton precursor and surfactant. The as-prepared mesoporous triazine-based carbon materials possess uniform tunable pore sizes (8.2-14.0 nm), high surface areas and ultrahigh nitrogen content (up to 18 %). Owing to these intriguing advantages, the fabricated mesoporous triazine-based carbon materials as functionalized porous solid absorbents exhibit predominant CO₂ adsorption performance and exceptional selectivity for the capture of CO₂ over N₂ .