Covalent organic frameworks (COFs) for environmental applications

Ultra-Low Density Covalent Organic Framework Sponges with Exceptional Compression and Functional Performance

The emergence of covalent organic frameworks (COFs) macroscopic objects with hierarchical porous structures addresses the limitations of traditional COF powders, which are challenging to process, thus bringing them closer to practical applications. However, the brittleness of the parent COF powder results in poor mechanical stability of these COF macroscopic objects, presenting a significant challenge that must be overcome for their continued development. In this work, we successfully obtained a continuous, hierarchically porous, and interconnected open-cell COF structure made up of hollow sponge walls of thickness 100-250 nm through a template-assisted framework process. This unique structure endows the COF sponge with a high surface area (1655 m2 g-1), ultralow density (2.2 mg cm-3), and exceptional mechanical stability. Even after 300 000 compressions at a 50% compression rate, its stress and height decreased by only 7.9% and 7.1%, respectively. These properties grant the COF sponge excellent solvent absorption capacity, catalytic performance, and reusability. Therefore, this work broadens the development pathway for COF macroscopic objects and is expected to further unlock the potential of COFs in practical applications.

Rational Design of Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

Photocatalytic production of hydrogen peroxide (H2O2) represents a significant approach to achieving sustainable energy generation through solar energy, addressing both energy shortages and environmental pollution. Among various photocatalytic materials, covalent organic frameworks (COFs) have gained widespread attention and in-depth research due to their unique advantages, including high porosity, predesignability, and atomic-level tunability. In recent years, significant progress has been made in the development, performance enhancement, and mechanistic understanding of COF-based photocatalysts. This review focuses on the latest advancements in photocatalytic H2O2 production using COFs, particularly emphasizing the rational design of COF structures to regulate catalytic performance and exploring the fundamental processes involved in photocatalysis. Based on current research achievements in this field, this paper also discusses existing challenges and future opportunities, aiming to provide a reference for the application of COFs in photocatalytic H2O2 production.

Efficient capture of 99TcO4-/ReO4- via node and linker bifunctional anion exchange covalent organic frameworks

In nuclear wastewater treatment, ion-scavenging materials designed to trap 99TcO4- is urgently needed. However, strong acid/base, high radiation and high salt concentration of nuclear wastewater usually result in inadequate stability and adsorption capacity of the adsorbent. Herein, we report a new class of bifunctional anion-exchange olefin-linked COF (BPDC-MTMP) prepared via Knoevenagel condensation reactions, the first example exploring the synergistic integration of positively charged fragments at both nodes and linkers. Surprisingly, BPDC-MTMP exhibits a record ReO4- (a non-radioactive surrogate of 99TcO4-) adsorption capacity up to 1593.21 mg g-1, its outstanding adsorption capacity can be attributed to the synergistic enhancement of the positively charged fragments of the nodes and linkers leading to a significant increase in the positive charge density and the number of anion exchange sites. BPDC-MTMP's hydrophobicity is enhanced by the highly conjugated bulky alkyl skeleton, the affinity toward ReO4- and chemical stability are therefore significantly improved, ReO4- can be selectively and reversibly extracted even under strong acid/base and high salt concentration solutions. This study illustrates that the node and linker bifunctional anion exchange COF is of great potential for ReO4-/99TcO4- trapping, which provides a new method to design high-performance adsorbents for the treatment of nuclear wastewater.

Porphyrin-based covalent organic frameworks with undulated layers for efficient photocatalytic CO2 reduction

Two-dimensional (2D) porphyrin (Por)-based covalent organic frameworks (COFs) provide an attractive and effective strategy for photocatalytic CO2 reduction, but the layered structure due to π-π stacking is challenging for the exposure of active sites and transfer of mass and photogenerated carriers. In this study, a series of 2D conjugated porphyrin-based COFs were prepared using porphyrin blocks with linking units having different degrees of twisting. According to the experimental and theoretical calculation results, owing to the large spatial steric hindrance between the two carbazole units connected by the N-N single bond, a greatly undulating layered structure was formed in NN-Por-COF, which enhanced mass transfer and exposed more catalytic sites. The introduction of carbazole also modulated the electronic structure of the porphyrin Co center, which lowered the reaction energy barrier. The optimization of the structural and electronic effects led to the excellent photocatalytic CO2 reduction performance of NN-Por-COF, with CO conversion rates as high as 22.38 and 3.02 mmol g-1 h-1 under pure and diluted (10%) CO2 atmosphere, respectively, which are superior to those of most of the reported porphyrin-based photocatalysts.

Noble-Metal-Free Electrocatalysts for Selective Hydrogen Peroxide Generation via Oxygen Reduction Reaction

Hydrogen peroxide (H2O2) is a versatile chemical widely used in various industries. The traditional anthraquinone method for H2O2 synthesis has environmental and safety concerns due to the use of organic solvents and hazardous by-products. The direct synthesis of H2O2 from H2 and O2 poses risks of flammability and explosion. Recently, the 2-electron oxygen reduction reaction (2e- ORR) method has emerged as a promising alternative, offering safety, environmental friendliness, and cost-effectiveness. This method utilizes gas diffusion electrodes to efficiently generate H2O2 without the need for additional dilution. In this review, we focus on the recent advancements in noble-metal-free materials for 2e- ORR electrocatalysis, which play a crucial role in the efficient production of H2O2. These materials, including transition metal compounds, macrocyclic complexes, carbon-based catalysts, framework materials, and MXenes catalysts, demonstrate significant advantages in enhancing H2O2 yield. The development of these non-precious metal catalysts can reduce costs and improve sustainability and promote the commercialization of related technologies. The review concludes with an outlook on the future trends of 2e- ORR electrocatalysts.

Simultaneous Achievement of Enhanced Nonlinear Optical Absorption and Nonlinear Refraction in Highly Crystalline 2D Covalent Organic Frameworks Ultrathin Films

Large enhancement of nonlinear absorption and nonlinear refraction are achieved simultaneously in highly ordered two dimensional (2D) covalent organic framework (COF) films prepared by solidliquid interface one-step method to overcome the weakness of COF powders in solubility. In the intrinsic nonlinear optical response obtained at 532 nm with 5 ns pulse, the nonlinear absorption coefficients (β) of two COF films are -4.87 × 10-5 and -1.29 × 10-5 m W-1, respectively. Simultaneously, the fitted closed-aperture curves also show large nonlinear refractive indexes (n2), -5.62 × 10-12 m2 W-1 and -0.76 × 10-12 m2 W-1. The 4f coherent imaging performed at the same condition with a single-shot pulse further verifies the outstanding nonlinear optical response without any damage probably experienced in the Z-scan technique. Moreover, the differences in framework electronic structure and photoexcited states between two COF films are compared to explain the difference in nonlinear optical response. All the results indicate that two COF crystalline films with intrinsic giant nonlinear optical response can be capable of modulating both amplitude and phase of light, providing huge potential in all-optical manipulating and switching at the nanoscale as outstanding nonlinear optical materials.

Covalent organic frameworks for metal ion separation: Nanoarchitectonics, mechanisms, applications, and future perspectives

Covalent organic frameworks (COFs) are a class of porous crystalline materials with high surface areas, tunable pore sizes, and customizable surface chemistry, making them ideal for selective metal ion separation. This review explores the nanoarchitectonics, mechanisms, and applications of COFs in metal ion separation. We highlight the diverse bonding types (e.g., imine, boronic ester) and topologies (2D and 3D) that enable precise separation for alkali, alkaline earth, transition, and precious metals. The influence of COFs' pore characteristics, such as surface area, pore size, and distribution, on their adsorption capacity and selectivity is discussed. Additionally, surface functionalization enhances ion adsorption through electrostatic, coordination, and polarity interactions. Despite significant progress, challenges remain, including optimizing functional design for complex metal systems, improving material stability, and developing cost-effective synthesis methods. COFs also show promise in energy material recovery, biomedical diagnostics, and environmental remediation. Combining COFs with other separation technologies can enhance performance, and integrating AI and robotics in COF design may address current limitations, enabling broader industrial and environmental applications.

Adsorption of heavy metals by biochar in aqueous solution: A review

Heavy metal pollution (e.g., Cd, Hg, Pb, Cu, Ni, Zn, As and Cr) has become a crucial issue worldwide. Among various remediation strategies, adsorption is widely recognized for its environmental sustainability, cost-effectiveness, and operational simplicity. In this context, biochar has gained significant attention due to its promising adsorption performance. To systematically support adsorption studies, this review compiled essential models for adsorption experiments, including commonly used adsorption kinetics models, isotherm models, and thermodynamic analysis methods. Moreover, we systematically analyzed key factors affecting heavy metal adsorption by biochar, such as its physicochemical properties, environmental pH, temperature, initial concentration, dosage, and the presence of coexisting ions, to identify the conditions that govern adsorption capacity. In addition, the adsorption performance of biochar toward eight significant heavy metals is reviewed in detail, with a focus on elucidating the underlying mechanisms, including complexation, ion exchange, cation-π bonding, electrostatic interactions, and precipitation. Finally, based on identified research gaps and critical challenges, we discuss emerging research tools, including machine learning and advanced surface modifications, to guide the targeted design of biochar materials for enhanced adsorption capacity.

Facile synthesis of high-swelling cyclodextrin polymer for sustainable water purification

Porous materials are widely used in the adsorption field to sequester pollutants to address the global sustainable water security and water scarcity concerns. However, there are still challenges that limit their industrial application, especially the required rational design and construction of porous structures. Here, we report a high-swelling cyclodextrin polymer (His-CDP) that is facilely synthesized without additional design and templates, to achieve high affinity, non-specific and rapid adsorption of pollutants. His-CDP rapidly swells in water with high swelling ratio (706 %), and swelling results in a significant increase in the specific surface area (from 38 m2∙g-1 of dry state to 562 m2∙g-1 of wet state) and abundant adsorption sites. The adsorption rates of His-CDP for methylene blue (MB), bisphenol A (BPA), and copper ion (Cu2+) are 0.304 g∙mg-1∙min-1, 0.370 g∙mg-1∙min-1, and 0.117 g∙mg-1∙min-1, respectively, which are 106-571 times, 5-15 times, and 36-58 times higher than those of activated carbons and low-swelling cyclodextrin polymer. The maximum adsorption capacities of His-CDP for MB, BPA, and Cu2+ are 1.06 mol∙g-1, 0.35 mol∙g-1, and 1.95 mol∙g-1, respectively. His-CDP has high stability, good reproducibility, cost-effective regeneration, and is expected to be produced on a large scale. As a demonstration application, we demonstrate that His-CDP outperforms activated carbons in rapid, high-capacity purification of tap water, treatment of industrial wastewater and remediation of polluted surface water. Our findings open the way for the application of high-swelling polymers in sustainable water purification.

Advanced Porous Aromatic Frameworks: A Comprehensive Overview of Emerging Functional Strategies and Potential Applications

Porous aromatic frameworks (PAFs) are a fundamental group of porous materials characterized by their distinct structural features and large surface areas. These materials are synthesized from aromatic building units linked by strong carbon-carbon bonds, which confer exceptional rigidity and long-term stability. PAFs functionalities may arise directly from the intrinsic chemistry of their building units or through the postmodification of aromatic motifs using well-defined chemical processes. Compared to other traditional porous materials such as zeolites and metallic-organic frameworks, PAFs demonstrate superior stability under severe chemical treatments due to their robust carbon-carbon bonding. Even in challenging environments, the chemical stability and ease of functionalization of PAFs demonstrate their flexibility and specificity. Research on PAFs has significantly expanded and accelerated over the past decade, necessitating a comprehensive overview of key advancements in this field. This review provides an in-depth analysis of the recent advances in the synthesis, functionalization, and dimensionality of PAFs, along with their distinctive properties and wide-ranging applications. This review explores the innovative methodologies in PAFs synthesis, the strategies for functionalizing their structures, and the manipulation of their dimensionality to tailor their properties for specific potential applications. Similarly, the key application areas, including batteries, absorption, sensors, CO2 capture, photo-/electrocatalytic usages, supercapacitors, separation, and biomedical are discussed in detail, highlighting the versatility and potential of PAFs in addressing modern scientific and industrial challenges.

The Feasibility of Using Electrostatic Interactions for Immobilizing Ru-bda Catalysts in Covalent Organic Framework: A Proof-of-Concept

Heterogenization of molecular catalysts effectively resolves the separation issues of homogeneous catalysts and expands their application scenarios. In recent years, more and more studies have been using non-covalent interactions to achieve the heterogenization of molecular catalysts. Herein, electrostatic attraction was used to immobilize molecular catalysts, Ru-bda small molecular catalysts in COF materials, where the charged Ru-bda catalysts were immobilized in the oppositely charged COF with a high [Ru] loading content of ~0.2 mmol [Ru] g-1 COF. The leakage experiment verified that the immobilization of Ru-bda catalysts in COF by electrostatic interactions is stable in 0.1 M HClO4 and less than 5 % of molecular Ru-bda catalysts were leached into the solution in 2 hours. The chemical water oxidation experiment was conducted as a model catalysis reaction to verify the feasibility of using electrostatic interactions for immobilizing Ru-bda catalysts in COFs. The prepared Ru(bda)@COFs demonstrate a high catalytic activity of 268 μmol L-1 s-1 O2 for chemical water oxidation, illustrating the electrostatic attractions between COF and small molecules that can be used to immobilize homogeneous catalysts in heterogeneous materials. However, the robustness of COF material itself under catalytic conditions should be considered in practical applications.

The COF Space: Materials Features, Gas Adsorption, and Separation Performances Assessed by Machine Learning

Covalent organic frameworks (COFs) are promising materials for gas adsorption; however, only a small number of COFs has been studied for a few types of gas separations to date. To unlock the full potential of the COF space, composed of 69 784 different types of materials, we studied the adsorption of five important gas molecules, CO2, CH4, H2, N2, and O2 in COFs at various pressures combining high-throughput molecular simulations and machine learning. Adsorbent performances of COFs were then explored for industrially critical separations, such as CO2/CH4, CO2/H2, CO2/N2, CH4/H2, CH4/N2, and O2/N2. The key structural and chemical properties of the most promising adsorbents were revealed. Our work offers the most extensive dataset produced for COFs in the literature composed of ∼4.3 million data points for all synthesized and hypothetical COFs' structural, chemical, and energetic features; gas adsorption properties; and selectivities to facilitate the materials discovery.

A Novel Gully-like Surface of Stainless-Steel Fiber Coated with COF-TPB-DMTP Nanoparticles for Solid-Phase Microextraction of Phthalic Acid Esters in Bottled Tea Beverages

A covalent organic framework TPB-DMTP was physically coated onto the gully-like surface of stainless-steel fiber. The fabricated TPB-DMTP-coated stainless-steel fiber was used to extract five phthalic acid esters (PAEs) prior to the GC-FID separation and determination in bottled tea beverages. The developed SPME-GC-FID method gave limits of detection (S/N = 3) from 0.04 µg·L-1 (DBP) to 0.44 µg·L-1 (BBP), with the enrichment factors from 268 (DEHP) to 2657 (DPP). The relative standard deviations (RSDs) of the built method for inter-day and fiber-to-fiber were 4.1-11.8% and 2.3-9.9%, respectively. The prepared TPB-DMTP-coated stainless-steel fibers could stand at least 180 cycles without a significant loss of extraction efficiency. The developed method was successfully applied for the determination of trace PAEs in different bottled tea beverages, with recoveries from 85.5% to 115%.

Integration of ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of tetracycline based on a novel Zn (II) functionalized magnetic covalent organic framework

BACKGROUND

Based on the low volatility and refractory nature of Tetracycline (TC), excessive use leads to its continuous accumulation in water environments, posing serious risks to the ecological environment and human health. Although a very limited number of nanomaterials capable of simultaneously detecting and removing TC have been fabricated, they generally exist issues associated with a single detection signal ("on" or "off") or low adsorption rates with low adsorption capacities. As a result, it is crucial to develop a reliable technique to achieve ratiometric detection as well as rapid and efficient removal of TC.

RESULTS

Herein, a novel Zn (II) Functionalized magnetic covalent organic framework (Fe3O4@COF@Zn) was created. As the role of a fluorescent probe, it had excellent characteristics of ratiometric (F529/F436), ultrafast response (1 min), and ultra-low detection limit (16 nM). As the role of an adsorbent, it demonstrated a high capacity of adsorption (414.94 mg/g) in the pH-neutral range, fast kinetics (10 min), desirable regeneration capability, and convenient magnetic separation. By theoretical and experimental analysis, the detection and adsorption mechanism for TC was systematically revealed. Moreover, as an attempt, Fe3O4@COF@Zn showed it potential for crop remediation by adsorbing TC-contaminated water.

SIGNIFICANCE

This work demonstrates the exceptional performance of Zn-functionalized fluorescent COF for ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of TC, thereby illustrating its significant potential for the rapid monitoring and treatment of TC contamination.

Defluorination of water solutions and glass industry wastewater using a magnetic pineapple hydrochar nanocomposite modified with a covalent organic framework

This study investigates the development and use of a novel magnetic composite, PAH/MnFe2O4/COF, synthesized from pineapple hydrochar (PAH) and modified with a covalent organic framework (COF) for Fluoride (Flu) elimination from water and industrial wastewater. Fluoride contamination poses serious health risks, making its removal essential. The composite was analyzed using scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and other methods, confirming its successful synthesis with a surface area of 102.960 m2/g and a saturation magnetization of 19.548 emu/g. The adsorption efficiency was modeled using a second-order polynomial, with a high R2 value of 0.9958, indicating excellent predictive accuracy. Optimal conditions for 99.54% Flu removal included a pH of 3.5, an adsorber mass of 1 g/L, a temperature of 50 °C, an adsorption time of 60 min, and a Flu concentration of 5 mg/L. The adsorption followed a pseudo-second-order model, indicating rapid chemical adsorption, while thermodynamic analysis revealed a spontaneous, endothermic process, supported by negative Gibbs free energy (ΔG°) values and an enthalpy (ΔH°) of 95.253 kJ/mol. The intraparticle diffusion model indicated multiple mechanisms were involved, including intraparticle diffusion and external surface adsorption. The composite showed a high adsorption capacity of 40.629 mg/g, outperforming the unmodified hydrochar. Additionally, the composite effectively reduced Flu ions, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), and total dissolved solids (TDS) levels in industrial wastewater. These findings demonstrate that the PAH/MnFe2O4/COF composite is an efficient and promising adsorber for addressing the defluorination of water, offering a potential solution to environmental and public health issues.

Design and engineering of microenvironments of supported catalysts toward more efficient chemical synthesis

Catalytic species such as molecular catalysts and metal catalysts are commonly attached to varieties of supports to simplify their separation and recovery and accommodate various reaction conditions. The physicochemical microenvironments surrounding catalytic species play an important role in catalytic performance, and the rational design and engineering of microenvironments can achieve more efficient chemical synthesis, leading to greener and more sustainable catalysis. In this review, we highlight recent works addressing the topic of the design and engineering of microenvironments of supported catalysts, including supported molecular catalysts and supported metal catalysts. Six types of materials, including oxide nano/microparticle, mesoporous silica nanoparticle (MSN), polymer nanomaterial, reticular material, zeolite, and carbon-based nanomaterial, are widely used as supports for the immobilization of catalytic species. We summarize and discuss the synthesis and modification of supports and the positive effects of microenvironments on catalytic properties such as metal-support interaction, molecular recognition, pseudo-solvent effect, regulating mass transfer, steric effect, etc. These design principles and engineering strategies allow access to a better understanding of structure-property relationships and advance the development of more efficient catalytic processes.

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.

Ozone-based advanced oxidation processes in water treatment: recent advances, challenges, and perspective

Water pollution, driven by a variety of enduring contaminants, poses considerable threats to ecosystems, human health, and biodiversity, highlighting the urgent need for innovative and sustainable treatment approaches. Ozone-based advanced oxidation processes (AOPs) have demonstrated significant efficacy in breaking down stubborn pollutants, such as organic micropollutants and pathogens, that are not easily addressed by traditional treatment techniques. This review offers an in-depth analysis of ozonation mechanisms, covering both the direct oxidation by ozone and the indirect reactions facilitated by hydroxyl radicals, emphasizing their effectiveness and adaptability across various wastewater matrices. Significant progress in the combination of ozonation with additional technologies, including UV irradiation, hydrogen peroxide (H₂O₂), catalytic systems, and biological treatments, is examined, highlighting their effectiveness in enhancing pollutant breakdown, increasing biodegradability, and reducing secondary pollution. Hybrid methods, including catalytic ozonation and ozone-biological treatment, show significant enhancements in process efficiency and cost-effectiveness, while effectively tackling challenges associated with energy use and byproduct generation. Despite the promising possibilities, obstacles remain, such as scalability issues, high operational costs, and the risk of generating potentially harmful transformation products. Cutting-edge approaches, including the creation of sophisticated catalysts, integration of processes, and refinement of reactor designs, are suggested to address these challenges and improve the real-world implementation of ozone-based advanced oxidation processes. This review highlights the significant potential of ozone-based advanced oxidation processes as sustainable approaches for wastewater treatment, providing an essential route to environmental conservation and safeguarding public health.

Photo(electro)catalytic Water Splitting for Hydrogen Production: Mechanism, Design, Optimization, and Economy

As an energy carrier characterized by its high energy density and eco-friendliness, hydrogen holds a pivotal position in energy transition. This paper elaborates on the scientific foundations and recent progress of photo- and electro-catalytic water splitting, including the corresponding mechanism, material design and optimization, and the economy of hydrogen production. It systematically reviews the research progress in photo(electro)catalytic materials, including oxides, sulfides, nitrides, noble metals, non-noble metal, and some novel photocatalysts and provides an in-depth analysis of strategies for optimizing these materials through material design, component adjustment, and surface modification. In particular, it is pointed out that nanostructure regulation, dimensional engineering, defect introduction, doping, alloying, and surface functionalization can remarkably improve the catalyst performance. The importance of adjusting reaction conditions, such as pH and the addition of sacrificial agents, to boost catalytic efficiency is also discussed, along with a comparison of the cost-effectiveness of different hydrogen production technologies. Despite the significant scientific advancements made in photo(electro)catalytic water splitting technology, this paper also highlights the challenges faced by this field, including the development of more efficient and stable photo(electro)catalysts, the improvement of system energy conversion efficiency, cost reduction, the promotion of technology industrialization, and addressing environmental issues.

Covalent organic frameworks for radioactive iodine capture: structure and functionality

The adsorption of radioactive iodine is a critical concern in nuclear safety and environmental protection due to its hazardous nature and long half-life. Covalent organic frameworks (COFs) have emerged as promising materials for capturing radioactive iodine owing to their tunable porosity, high surface area, and versatile functionalization capabilities. This review provides a comprehensive overview of the application of COFs in the adsorption of radioactive iodine. We begin by discussing the sources, properties, and hazards of radioactive iodine, as well as traditional capture techniques and their limitations. We then delve into the intrinsic structures of COFs, focusing on their porosity, conjugated frameworks, and hydrogen bonding, which are pivotal for effective iodine adsorption. The review further explores various functionalization strategies, including electron-rich COFs, flexible COFs, ionic COFs, COF nanosheets, and quasi-3D COFs, highlighting how these modifications enhance the adsorption performance. Finally, we conclude with an outlook on future research directions and potential applications, underscoring the significance of continued innovation in this field. This review aims to provide valuable insights for researchers and practitioners seeking to develop advanced materials for the efficient capture of radioactive iodine.

Single Na- and K-Ion-Conducting Sulfonated -NH-Linked Covalent Organic Frameworks

Highly ion-conductive solid electrolytes of nonlithium ions (sodium or potassium ions) are necessary for pursuing a more cost-effective and sustainable energy storage. Here, two classes of sulfonated -NH-linked covalent organic frameworks (COFs), specifically designed for sodium or potassium ion conduction (named i-COF-2 (Na or K) and i-COF-3 (Na or K)), were synthesized through a straightforward, one-step process using affordable starting materials. Remarkably, these COFs demonstrate high ionic conductivity at room temperature─3.17 × 10-4 and 1.02 × 10-4 S cm-1 for i-COF-2 (Na) and i-COF-2 (K) and 2.75 × 10-4 and 1.42 × 10-4 S cm-1 for i-COF-3 (Na) and i-COF-3 (K)─without the need for additional salt or solvent. This enhanced performance, including low activation energies of 0.21 eV for both i-COF-2 (Na) and i-COF-2 (K) and of 0.24 and 0.25 eV for i-COF-3 (Na) and i-COF-3 (K), is attributed to the strategic incorporation of sulfonate groups and the directional channels within the COF structure. The Na+ and K+ ion high conductivities, low cost, and intrinsic framework stability of i-COF-2 (Na or K) and i-COF-3 (Na or K) provide promising solid electrolyte candidates for the exploration of sustainable energy storage.

Aluminum Cluster Molecular Ring-Based Heterometallic Framework Materials for Iodine Capture

With the development of the nuclear industry, the risk of elements that are difficult to degrade in nuclear fission has been gradually increasing. Therefore, the efficient capture of iodine (I2) has attracted considerable attention in recent years. The aluminum cluster-based metal framework materials show great advantage in iodine adsorption due to the designable pore sizes, excellent physicochemical stability, and cheap raw materials. Herein, two cases of aluminum cluster-based heterometal framework materials, [Al10CuI2I2(CH3O)20(INA)10]n (1) and [Al3CuI0.5CuII0.25(INA)3(CH3O)6·Cl0.75]n (2), were assembled by isonicotinic acid (HINA), aluminum isopropoxide, and CuI. Their structures feature ringy Al10 and Al12 clusters as the secondary building units (SBUs) and Cu/CuI-pyridine as the linkers. Moreover, they can capture iodine from cyclohexane solution with high elimination rates and uptake amounts (93%, 0.772 g/g for 1; 98%, 0.810 g/g for 2). The better I2 adsorption performance for 2 may be ascribed to its larger pore volume than that of compound 1.

Assessing interactions between antibiotics and triazine porous organic polymeric sorbents by photophysics

This study purposes three triazine-based porous organic polymers (T-POPs 1-3) as advanced platforms for the early detection of antibiotic-polluted environments and effective water decontamination, in order to mitigate water pollution and antimicrobial resistance, which are two huge current problems damaging ecosystems and human health. T-POPs exhibited good performances as adsorbents for the removal of sulfamethazine (SMT) and tetracycline (TC) from water, with efficiencies up to 97% and 96%, and maximum adsorption capacities between (0.36-0.44) and (0.21-0.27) mmol g-1, respectively, which are similar or even higher (up to 40.3 times) than those reported for other materials. In addition, good reusability was achieved, particularly for T-POP2, despite being the polymer with the lowest surface area. A slightly higher selectivity of T-POPs for sulfonamides and the best performance of T-POP3 to remove six antibiotics from a micromolar solution were observed. T-POPs also acted as fluorescent chemosensors, since T-POP1 underwent linear Stern-Volmer fluorescence quenching in the presence of both SMT and TC, while the enhanced-fluorescent T-POP2 and T-POP3 experienced fluorescence extinction through a sphere of action mechanism in contact with TC, and bathochromic shift accompanied by a hyperchromic effect on the new fluorescent region with the increase in SMT concentration. Thus, T-POP2 and T-POP3 can both promote a selective on-site monitoring of each drug in contaminated water streams and an efficient water remediation, thanks to the synergy between hydrogen and van der Waals interactions. In summary, these triazine-based porous organic polymers are promising materials for the simultaneous monitoring and treatment of antibiotic-containing water and wastewaters.

Calcium-atom-modified boron phosphide (BP) biphenylene as an efficient hydrogen storage material

Porous nanosheets have attracted significant attention as viable options for energy storage materials because of their exceptionally large specific surface areas. A recent study (Int. J. Hydrogen Energy, 2024, 66, 33-39) has demonstrated that Li/Na-metalized inorganic BP-biphenylene (b-B3P3) and graphenylene (g-B6P6) analogues possess suitable functionalities for hydrogen (H2) storage. Herein, we evaluate the H2 storage performance of alkaline earth metal (AEM = Be, Mg, Ca)-decorated b-B3P3 and g-B6P6 structures based on first-principles density functional theory (DFT) calculations. Our investigations revealed that individual Be and Mg atoms are not stable on pure b-B3P3 and g-B6P6 sheets, and the formation of aggregates is favored due to their low binding energy to these surfaces. However, the binding energy improves for Ca-decorated b-B3P3 (b-B3P3(mCa)) and g-B6P6 (g-B6P6(nCa)) structures, forming stable and uniform mCa(nCa) (m and n stand for the numbers of Ca atom) coverages on both sides. Under maximum hydrogenation, the b-B3P3(8Ca) and g-B6P6(16Ca) structures exhibited the ability to adsorb up to 32H2 and 48H2 molecules with average adsorption energy (E a) values of -0.23 eV per H2 and -0.25 eV per H2, respectively. Gravimetric H2 uptakes of 7.28 wt% and 5.56 wt% were found for b-B3P3(8Ca)@32H2 and g-B6P6(16Ca)@48H2 systems, exceeding the target of 5.50 wt% set by the US Department of Energy (DOE) to be reached by 2025. Our findings indicate the importance of these b-B3P3 and g-B6P6 sheets for H2 storage technologies.

A Concise Review on Porous Adsorbents for Benzene and Other Volatile Organic Compounds

Emissions of volatile organic compounds (VOCs) such as benzene, toluene, xylene, styrene, hexane, tetrachloroethylene, acetone, acetaldehyde, formaldehyde, isopropanol, etc., increase dramatically with accelerated industrialization and economic growth. Most VOCs cause serious environmental pollution and threaten human health due to their toxic and carcinogenic nature. Adsorption on porous materials is considered one of the most promising technologies for VOC removal due to its cost-effectiveness, operational flexibility, and low energy consumption. This review aims to provide a comprehensive understanding of VOC adsorption on various porous adsorbents and indicate future research directions in this field. It is focused on (i) the molecular characterization of structures, polarity, and boiling points of VOCs, (ii) the adsorption mechanisms and adsorption interactions in the physical, chemical, and competitive adsorption of VOCs on adsorbents, and (iii) the favorable characteristics of materials for VOCs adsorption. Porous adsorbents that would play an important role in the removal of benzene and other VOCs are presented in detail, including carbon-based materials (activated carbons, active carbon fibers, ordered mesoporous carbons, and graphene-based materials), metal-organic frameworks, covalent organic frameworks, zeolites, and siliceous adsorbents. Finally, the challenges and prospects related to the removal of VOCs via adsorption are pointed out.

A comprehensive review of covalent organic frameworks (COFs) and their derivatives in environmental pollution control

Covalent organic frameworks (COFs) have gained considerable attention due to their design possibilities as the molecular organic building blocks that can stack in an atomically precise spatial arrangement. Since the inception of COFs in 2005, there has been a continuous expansion in the product range of COFs and their derivatives. This expansion has led to the evolution of three-dimensional structures and various synthetic routes, propelling the field towards large-scale preparation of COFs and their derivatives. This review will offer a holistic analysis and comparison of the spatial structure and synthesis techniques of COFs and their derivatives. The conventional methods of COF synthesis (i.e., ultrasonic chemical, microwave, and solvothermal) are discussed alongside the synthesis strategies of new COFs and their derivatives. Furthermore, the applications of COFs and their derived materials are demonstrated in air, water, and soil pollution management such as gas capture, catalytic conversion, adsorption, and pollutant removal. Finally, this review highlights the current challenges and prospects for large-scale preparation and application of new COFs and the derived materials. In line with the United Nations Sustainable Development Goals (SDGs) and the needs of digital-enabled technologies (AI and machine learning), this review will encompass the future technical trends for COFs in environmental pollution control.

Heavy-Metal Ions Removal and Iodine Capture by Terpyridine Covalent Organic Frameworks

Porous materials are excellent candidates for water remediation in environmental issues. However, it is still a key challenge to design efficient adsorbents for rapid water purification from various heavy metal ions-contaminated wastewater in one step. Here, two robust nitrogen-rich covalent organic frameworks (COFs) bearing terpyridine units on the pore walls by a "bottom-up" strategy are reported. Benefitting from the strong chelation interaction between the terpyridine units and various heavy metal ions, these two terpyridine COFs show excellent removal efficiency and capability for Pb2+, Hg2+, Cu2+, Ag+, Cd2+, Ni2+, and Cr3+ from water. These COFs are shown to remove such heavy metal ions with >90% of contents at one time after the aqueous metal ions mixture is passed through the COF filter. The nitrogen-rich features of the COFs also endow them with the capability of capturing iodine vapors, offering the terpyridine COFs the potential for environmental remediation applications.

Unraveling the Mechanism of Covalent Organic Frameworks-Based Functional Separators in High-Energy Batteries

Covalent organic frameworks (COFs) are promising porous materials due to their high specific surface area, adjustable structure, highly ordered nanochannels, and abundant functional groups, which brings about wide applications in the field of gas adsorption, hydrogen storage, optics, and so forth. In recent years, COFs have attracted considerable attention in electrochemical energy storage and conversion. Specifically, COF-based functional separators are ideal candidates for addressing the ionic transport-related issues in high-energy batteries, such as dendritic formation and shuttle effect. Therefore, it is necessary to make a comprehensive understanding of the mechanism of COFs in functional separators. In this review, the advantages, applications as well as synthesis of COFs are firstly presented. Then, the mechanism of COFs in functional separators for high-energy batteries is summarized in detail, including pore channels regulating ionic transport, functional groups regulating ionic transport, adsorption effect, and catalytic effect. Finally, the application prospect of COFs-based separators in high-energy batteries is proposed. This review may provide new insights into the design of functional separators for advanced electrochemical energy storage and conversion systems.

Dual-mode SERS/colorimetric sensing of nitrite in meat products based on multifunctional au NPs@COF composite

The presence of nitrite in food products has generated significant public concern. A simple and rapid dual-mode surface-enhanced Raman spectroscopy (SERS)/colorimetric detection of nitrite is proposed based on a diazo reaction and multifunctional gold nanoparticle-doped covalent organic framework (Au@COF) composite. Under acidic conditions, the reaction between toluidine blue and nitrite yielded a colorless diazo salt, simultaneously attenuating its characteristic absorption peak and Raman signal. The multifunctional Au@COF materials enhanced the Raman signal and ensured good reproducibility. Additionally, the reaction rates improved, and the sensitivity was enhanced due to the excellent adsorption capacity of the COF. The proposed method demonstrated high sensitivity and excellent recovery rates for nitrite detection in food samples. This approach shows potential for precisely detecting nitrite content in real-world food samples by integrating the simplicity of colorimetric analysis with the enhanced sensitivity of SERS.

The Functionalized N-Rich Covalent Organic Framework for Palladium Removal from Nuclear Wastewater

Efficiently adsorbing Pd(II) from acidic radioactive waste liquid is crucial for ensuring the safety of the radioactive waste vitrification process and significantly alleviating the scarcity of precious metals. However, the stability and selectivity of most current adsorbents are limited, hindering their practical application under acidic conditions. To address these limitations, a covalent organic framework (DHTP-TPB COF) was prepared with a high nitrogen content, leveraging the high affinity of its soft ligand N with palladium to achieve high selectivity. This work demonstrated that DHTP-TPB COF exhibits rapid adsorption kinetics, with equilibrium achieved within 10 min. The framework also boasts a high adsorption capacity of 142.8 mg/g and impressive reusability in 1.0 M nitric acid. Moreover, the DHTP-TPB COF displays excellent selectivity for Pd(II), even in the presence of 13 interfering ions. By combining FT-IR, XPS spectroscopy, and DFT theoretical calculations, the dense N sites in the framework have a strong affinity for Pd(II), resulting in exceptional adsorption performance that was confirmed. The findings of this study highlight the potential of COFs with robust linkers and customized functional groups to effectively and selectively capture Pd(II) under harsh environmental conditions of high-level liquid waste.

Magnetic hollow fibers of covalent organic frameworks (COF) for pollutant degradation and adsorptive removal

The shaping of covalent organic frameworks (COFs) from non-processible powder forms into applicable architectures with additional functionality remains a challenge. Using pre-electrospun polymer fibers as a sacrificial template, herein, we report a green synthesis of an architecture in the form of COF hollow fibers with an inner layer of peroxidase-like iron oxide nanoparticles as a catalytic material. When compared to peroxidase-like pristine iron oxide nanoparticles, these COF hollow fibers demonstrate higher catalytic breakdown of crystal violet due to their peroxidase-like activity via advanced oxidation process. Furthermore, as a potential adsorbent, hollow COF fibers exhibit significantly effective adsorption capacity and removal efficiency of organic solvent and oil from water. Because of their magnetic nature, COF hollow fibers can be easily recovered and have exhibited high recycling stability for both catalytic dye degradation and organic solvent removal from water.

Non-Noble Metal Anchored 2D Covalent Organic Framework for Ambient CO2 Fixation to High-Value Compounds

The catalytic functionalization of CO2 into high-value compounds comprises a promising approach to mitigate its atmospheric content and sustainable generation of fine chemicals. In this respect, covalent organic frameworks (COFs) offer great potential in carbon dioxide capture and utilization. Herein, we report application of a crystalline, nanoporous 2D COF (ET-BP-COF) obtained by condensation of 4,4',4'',4'''-(ethene-1,1,2,2-tetrayl) tetraaniline (ET-NH2) and 2,2'-bipyridyl-5,5'-dialdehyde (BP-CHO) building blocks for strategic utilization of CO2. The ET-BP-COF features a unique 2D kagome (kgm) topology composed of hexagonal and triangular 1D channels decorated with bipyridine sites, which were exploited for covalent anchoring of eco-friendly, alkynophilic Cu(I) by the post-synthetic method. The Cu(I) engrafted COF was applied as a recyclable catalyst for coupling CO2 with alkynes to generate two high-value compounds, α-alkylidene cyclic carbonates (α-ACCs) and 2-oxazolidinones. Notably, Cu(I)@ET-BP-COF demonstrated excellent catalytic performance for transforming propargylic amine and CO2 to 2-oxazolidinone, an essential building block for antibiotics. Besides, an efficient transformation of propargylic alcohols to generate α-ACCs, valuable commodity chemicals, has been achieved by utilizing carbon dioxide. Further, detailed theoretical simulations disclosed the insight mechanistic path of Cu(I) catalyzed coupling of CO2 and alkynes to produce 2-oxazolidinones and α-ACCs. Significantly, the Cu(I)@COF was reusable for multiple cycles without losing framework rigidity and catalytic performance. This study showcases the potential application of ET-BP-COF for stable anchoring of eco-friendly metals as catalytic sites for effective utilization of CO2 to produce two high-value products, 2-oxazolidinones and α-ACCs, under mild atmospheric conditions.

Photothermal Conversion Porous Organic Polymers: Design, Synthesis, and Applications

Solar energy is a primary form of renewable energy, and photothermal conversion is a direct conversion process with tunable conversion efficiency. Among various kinds of photothermal conversion materials, porous organic polymers (POP) are widely investigated owing to their controllable molecular design, tailored porous structures, good absorption of solar light, and low thermal conductivity. A variety of POP, such as conjugated microporous polymers (CMP), covalent organic frameworks (COF), hyper-crosslinked porous polymers (HCP), polymers of intrinsic microporosity (PIM), porous ionic polymers (PIP), are developed and applied in photothermal conversion applications of seawater desalination, latent energy storage, and biomedical fields. In this review, a comprehensive overview of the recent advances in POP for photothermal conversion is provided. The micro molecular structure characteristics and macro morphology of POP are designed for applications such as seawater desalination, latent heat energy storage, phototherapy and photodynamic therapy, and drug delivery. Besides, a probe into the underlying mechanism of structural design for constructing POP with excellent photothermal conversion performance is methodicalized. Finally, the remaining challenges and prospective opportunities for the future development of POP for solar energy-driven photothermal conversion applications are elucidated.

Covalent organic polyrotaxanes based on β-cyclodextrin for iodine capture

Herein, covalent organic polyrotaxanes (COPRs) were integrated with supermolecule self-assembly and dynamic imine bond formation to act as absorbents that captured radioactive iodine from water. The aromatic building blocks were initially complexed with β-cyclodextrin (β-CD) to form pseudorotaxanes, which were then condensed with aromatic tri-aldehyde via mechanical grinding and solvothermal synthesis in sequence. The threading of β-CD throughout the polymer skeleton effectively reduced the usage of expensive building blocks and significantly lowered the cost, while also remarkably enhancing the skeleton polarity, which is closely related to many special applications. Impressively, the threading of CD improved the water dispersibility of COPRs, which displayed an abnormally high iodine adsorption capacity. This novel synthetic strategy allows the incorporation of mechanically interlocked CDs into porous polymeric materials, which provides access to low-cost preparations of COPRs with a brand new structure for specific applications.

Covalent organic frameworks in tribology - A perspective

Two-dimensional covalent organic frameworks (2D COFs) are an emerging class of crystalline porous materials formed through covalent bonds between organic building blocks. COFs uniquely combine a large surface area, an excellent stability, numerous abundant active sites, and tunable functionalities, thus making them highly attractive for numerous applications. Especially, their abundant active sites and weak interlayer interaction make these materials promising candidates for tribological research. Recently, notable attention has been paid to COFs as lubricant additives due to their excellent tribological performance. Our review aims at critically summarizing the state-of-art developments of 2D COFs in tribology. We discuss their structural and functional design principles, as well as synthetic strategies with a special focus on tribology. The generation of COF thin films is also assessed in detail, which can alleviate their most challenging drawbacks for this application. Subsequently, we analyze the existing state-of-the-art regarding the usage of COFs as lubricant additives, self-lubrication composite coatings, and solid lubricants at the nanoscale. Finally, critical challenges and future trends of 2D COFs in tribology are outlined to initiate and boost new research activities in this exciting field.

Covalent-Organic Frameworks for Selective and Sensitive Detection of Antibiotics from Water

As the consumption of antibiotics rises, they have generated some negative impacts on organisms and the environment because they are often unable to be effectively degraded, and seeking effective detection methods is currently a challenge. Covalent-organic frameworks (COFs) are new types of crystalline porous crystals created based on the strong covalent interactions between blocked monomers, and COFs demonstrate great potential in the detection of antibiotics from aqueous solutions because of their large surface area, adjustable porosity, recyclability, and predictable structure. This review aims to present state-of-the-art insights into COFs (properties, classification, synthesis methods, and functionalization). The key mechanisms for the detection of antibiotics and the application performance of COFs in the detection of antibiotics from water are also discussed, followed by the challenges and opportunities for COFs in future research.

When covalent organic frameworks meet zeolites: Enhancing rhodamine B removal through the synergy in the emerging organic-inorganic nanoadsorbents

The development of new porous materials has attracted intense attention as adsorbents for removing pollutants from wastewater. However, pure inorganic and organic porous materials confront various problems in purifying the wastewater. In this work, we integrated a covalent organic framework (TpPa-1) with an inorganic zeolite (TS-1) for the first time via a solvothermal method to fabricate new-type nanoadsorbents. The covalent organic framework/zeolite (TpPa-1/TS-1) nanoadsorbents combined the merits of the zeolite and COF components and possessed efficient adsorptive removal of organic contaminants from solution. Structural morphology and chemical composition characterization by powder X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis demonstrated the successful preparation of TpPa-1/TS-1 composite nanoadsorbents. The resultant composite adsorbent TpPa-1/TS-1 removed rhodamine B at 1.7 and 2.6 times the efficiency of TpPa-1 and TS-1, respectively. Additional investigation revealed that the Freundlich adsorption isotherm and the pseudo-second-order kinetic model could be employed to represent the adsorption process more appropriately. Thermodynamic calculation analysis showed that the adsorption process proceeded spontaneously and exothermically. Besides, the effects of pH, absorbent mass and ionic strength on the adsorption performance were systematically investigated. The prepared composite adsorbent showed a slight decrease in removal efficiency after eight cycles of repeated use, and real water environment experiments also showed the high stability of the adsorbent. The enhanced performance can be attributed to electrostatic interaction, acid-base interaction, hydrogen bonding and π-π interactions.

A cobalt-modified covalent organic framework enables highly efficient degradation of 2,4-dichlorophenol in high concentrations through peroxymonosulfate activation

The development of covalent organic frameworks (COFs) which can rapidly degrade high concentrations of 2,4-dichlorophenol is of great significance for its practical application. In this work, we report a cobalt-doped two-dimensional (2D) COF (JLNU-307-Co) for the ultra-efficient degradation of high concentration 2,4-dichlorophenol (2,4-DCP) by activating peroxymonosulfate (PMS). The JLNU-307-Co/PMS system takes only 3 min to degrade 100% of 50 mg L-1 2,4-DCP and shows excellent catalytic stability in real water. The superoxide radical (O2˙-) and singlet oxygen (1O2) play a major role in the system through capture experiments and electron spin resonance (ESR) tests. Compared to most previously reported catalysts, JLNU-307-Co/PMS showed the highest efficiency to date in degrading 2,4-DCP. This work not only demonstrates the potential of COFs as a catalyst for water environmental treatment, but also provides unprecedented insights into the degradation of organic pollutants.

Designing External Pores of Aluminum Oxo Polyhedrons for Efficient Iodine Capture

Although metal-organic polyhedra (MOPs) expansion has been studied to date, it is still a rare occurrence for their porous intermolecular assembly for iodine capture. The major limitation is the lack of programmable and controllable methods for effectively constructing and utilizing the exterior cavities. Herein, the goal of programmable porous intermolecular assembly is realized in the first family of aluminum oxo polyhedrons (AlOPs) using ligands with directional H-bonding donor/acceptor pairs and auxiliary alcohols as structural regulation sites. The approach has the advantage of avoiding the use of expensive edge-directed ditopic and face-directed tritopic ligands in the general synthesis strategy of MOPs. Combining theoretical calculations and experiments, the intrinsic relationship is revealed between alcohol ligands and the growth mechanism of AlOPs. The maximum I2 uptake based on the mass gain during sorption corresponds to 2.35 g g-1, representing the highest reported I2 sorption by an MOP. In addition, it can be easily regenerated and maintained the iodine sorption capacity, revealing its further potential application. This method of constructing stable and programmable porous materials will provide a new way to solve problems such as radionuclide capture.

Iron-decorated covalent organic framework as efficient catalyst for activating peroxydisulfate to degrade 2,4-dichlorophenol: Performance and mechanism insight

Herein, a novel two-dimensional double-pore covalent organic framework (JLNU-305) was synthesized using N,N,N',N'-tetrakis(4-aminophenyl)-1,4-phenylenediamine (TAPD) and 2,2'-bipyridine-5,5'-dicarboxaldehyde (BPDA). The extended π-π conjugated structure and nitrogen-riched pyridine in JLNU-305 (JLNU = Jilin Normal University) provide abundant binding sites for Fe doping. The obtained JLNU-305-Fe exhibited high and recycled catalytic efficiency for peroxydisulfate (PDS) activation to completely degrade 10 mg/L 2,4-dichlorophenol (2,4-DCP) within 8 min. The JLNU-305-Fe/PDS system showed excellent catalytic activity and cyclic stability. The capture experiments and electron paramagnetic resonance (ESR) analysis indicated that the catalytic behavior of JLNU-305-Fe/PDS is contributed to the synergistic effect between free radicals and non-free radicals. It is the first time to activate PDS for covalent organic frameworks (COFs) being used to degrade 2,4-DCP, which has a great potential for development and practical application in related water environment remediation.

Metal-organic framework (MOF)/C-dots and covalent organic framework (COF)/C-dots hybrid nanocomposites: Fabrications and applications in sensing, medical, environmental, and energy sectors

Developing new hybrid materials is critical for addressing the current needs of the world in various fields, such as energy, sensing, health, hygiene, and others. C-dots are a member of the carbon nanomaterial family with numerous applications. Aggregation is one of the barriers to the performance of C-dots, which causes luminescence quenching, surface area decreases, etc. To improve the performance of C-dots, numerous matrices including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and polymers have been composited with C-dots. The porous crystalline structures, which are constituents of metal nodes and organic linkers (MOFs) or covalently attached organic units (COFs) provide privileged features such as high specific surface area, tunable structures, and pore diameters, modifiable surface, high thermal, mechanical, and chemical stabilities. Also, the MOFs and COFs protect the C-dots from the environment. Therefore, MOF/C-dots and COF/C-dots composites combine their features while retaining topological properties and improving performances. In this review, we first compare MOFs with COFs as matrices for C-dots. Then, the recent progress in developing hybrid MOFs/C-dots and COFs/C-dots composites has been discussed and their applications in various fields have been explained briefly.

Porphyrin-based covalent organic frameworks from design, synthesis to biological applications

Covalent organic frameworks (COFs) constitute a class of highly functional porous materials composed of lightweight elements interconnected by covalent bonds, characterized by structural order, high crystallinity, and large specific surface area. The integration of naturally occurring porphyrin molecules, renowned for their inherent rigidity and conjugate planarity, as building blocks in COFs has garnered significant attention. This strategic incorporation addresses the limitations associated with free-standing porphyrins, resulting in the creation of well-organized porous crystal structures with molecular-level directional arrangements. The unique optical, electrical, and biochemical properties inherent to porphyrin molecules endow these COFs with diversified applications, particularly in the realm of biology. This review comprehensively explores the synthesis and modulation strategies employed in the development of porphyrin-based COFs and delves into their multifaceted applications in biological contexts. A chronological depiction of the evolution from design to application is presented, accompanied by an analysis of the existing challenges. Furthermore, this review offers directional guidance for the structural design of porphyrin-based COFs and underscores their promising prospects in the field of biology.

Nitrogen-rich covalent organic framework as a practical coating for effective determinations of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are high-profile organic pollutants to be poisonous, carcinogenic, and mutagenic, and widely distributed at trace levels in the environment. In order to effectively enrich PAHs, two stable covalent organic frameworks (COFs, TAPT-OMe-PDA and TPB-DMTP) were prepared by combining 2,4,6-tri(4-aminophenyl)-1,3,5-triazine (TAPT) and 1,3,5-tri(4-aminophenyl) benzene (TAPB) with 2,5-dimethoxy-phenyl-1,4-diformaldehyde (OMe-PDA), respectively. Even though the surface area of TAPT-OMe-PDA was much lower than that of TPB-DMTP, it still demonstrated much better extraction efficiencies towards PAHs as the solid phase microextraction (SPME) coating. Therefore, the TAPT-OMe-PDA coated fiber was coupled with gas chromatography-mass spectrometry (GC-MS) to establish a practical and sensitive method, after the extraction parameters (extraction time, extraction temperature, desorption temperature, desorption time, salt concentration and pH) were optimized. This developed analytical method showed wide linear ranges, low limits of detection, good repeatability and reproducibility. Finally, five PAHs in three water samples were detected and quantified precisely (2.72-38.7 ng·L-1) with satisfactory recoveries (88.3%-118%).

Chiral-induced synthesis of chiral covalent organic frameworks core-shell microspheres for HPLC enantioseparation

Two chiral covalent organic frameworks (CCOFs) core-shell microspheres based on achiral organic precursors by chiral-induced synthesis strategy for HPLC enantioseparation are reported for the first time. Using n-hexane/isopropanol as mobile phase, various kinds of racemates were selected as analytes and separated on the CCOF-TpPa-1@SiO2 and CCOF-TpBD@SiO2-packed columns with a low column backpressure (3 ~ 9 bar). The fabricated two CCOFs@SiO2 chiral columns exhibited good separation performance towards various racemates with high column efficiency (e.g., 19,500 plates m-1 for (4-fluorophenyl)ethanol and 18,900 plates m-1 for 1-(4-chlorophenyl)ethanol) and good reproducibility. Some effects have been investigated such as the analyte mass and column temperature on the HPLC enantioseparation. Moreover, the chiral separation results of the CCOF-TpPa-1@SiO2 chiral column and the commercialized Chiralpak AD-H column show a good complementarity. This study demonstrates that the usage of chiral-induced synthesis strategy for preparing CCOFs core-shell microspheres as a novel stationary phase has a good application potential in HPLC.

Rapid and Accurate Screening of the COF Space for Natural Gas Purification: COFInformatics

In this work, we introduced COFInformatics, a computational approach merging molecular simulations and machine learning (ML) algorithms, to evaluate all synthesized and hypothetical covalent organic frameworks (COFs) for the CO2/CH4 mixture separation under four different adsorption-based processes: pressure swing adsorption (PSA), vacuum swing adsorption (VSA), temperature swing adsorption (TSA), and pressure-temperature swing adsorption (PTSA). We first extracted structural, chemical, energy-based, and graph-based molecular fingerprint features of every single COF structure in the very large COF space, consisting of nearly 70,000 materials, and then performed grand canonical Monte Carlo simulations to calculate the CO2/CH4 mixture adsorption properties of 7540 COFs. These features and simulation results were used to develop ML models that accurately and rapidly predict CO2/CH4 mixture adsorption and separation properties of all 68,614 COFs. The most efficient separation process and the best adsorbent candidates among the entire COF spectrum were identified and analyzed in detail to reveal the most important molecular features that lead to high-performance adsorbents. Our results showed that (i) many hypoCOFs outperform synthesized COFs by achieving higher CO2/CH4 selectivities; (ii) the top COF adsorbents consist of narrow pores and linkers comprising aromatic, triazine, and halogen groups; and (iii) PTSA is the most efficient process to use COF adsorbents for natural gas purification. We believe that COFInformatics promises to expedite the evaluation of COF adsorbents for CO2/CH4 separation, thereby circumventing the extensive, time- and resource-intensive molecular simulations.

Tailoring functional two-dimensional nanohybrids: A comprehensive approach for enhancing photocatalytic remediation

Photocatalysis is gaining prominence as a viable alternative to conventional biohazard treatment technologies. Two-dimensional (2D) nanomaterials have become crucial for fabricating novel photocatalysts due to their nanosheet architectures, large surface areas, and remarkable physicochemical properties. Furthermore, a variety of applications are possible with 2D nanomaterials, either in combination with other functional nanoparticles or by utilizing their inherent properties. Henceforth, the review commences its exploration into the synthesis of these materials, delving into their inherent properties and assessing their biocompatibility. Subsequently, an overview of mechanisms involved in the photocatalytic degradation of pollutants and the processes related to antimicrobial action is presented. As an integral part of our review, we conduct a systematic analysis of existing challenges and various types of 2D nanohybrid materials tailored for applications in the photocatalytic degradation of contaminants and the inactivation of pathogens through photocatalysis. This investigation will aid to contribute to the formulation of decision-making criteria and design principles for the next generation of 2D nanohybrid materials. Additionally, it is crucial to emphasize that further research is imperative for advancing our understanding of 2D nanohybrid materials.

Novel Covalent Bonds and Hydrogen Bonds Linked Porous Organic Frameworks as Chemosensor for Detecting 2,4,6-Trinitrophenol in Water and Soil Samples

A novel and unconventional structural porous organic framework combined through the synergistic effect of covalent bonds and hydrogen bonds was prepared with the combination of 4,4',4″,4‴-(pyrene-1,3,6,8-tetrayl)tetraaniline (Py) and 5-hydroxyisophthalaldehyde (HP). It was the second example of CHOF until now and had been designated as Py-HP CHOF. The suspension of Py-HP CHOF in various solvents, such as ethanol, CH3CN, and methanol, exhibited a remarkably selective and sensitive "on-off" fluorescence response toward 2,4,6-trinitrophenol (TNP) compared with other explosives, with exceptionally low detection limits. The X-ray diffraction (XRD) spectra confirmed that the framework of Py-HP CHOF collapsed after interaction with TNP and acid, further indicating the existence of hydrogen bonds in the framework of Py-HP CHOF. The fluorescence quenching can be ascribed to the photoinduced electron transfer and the absorption competition quenching, as supported by XRD, X-ray photoelectron spectroscopy results, UV-vis absorption spectra, and density functional theory calculations. Fluorescence channels can be utilized by Py-HP CHOF to function as chemosensor, enabling the identification and detection of TNP in water and soil, and Py-HP CHOF is also the second CHOF example of sensing TNP reported to date. The application of this technique exhibits considerable potential in the analysis and detection of environmental pollutants, thereby presenting substantial practical implications.

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.

POPs to COFs by post-modification: CO2 chemisorption and dissolution

Porous organic polymers (POPs) and covalent organic frameworks (COFs) are hierarchical nano materials with variable applications. To our knowledge, this is the first report of a post-modified, non-renewable, DMSO-soluble M-POP/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) upon atmospheric H2O/CO2 trapping after 48 h, forming a DBUH+·HCO3- adduct, as verified by solution carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy. The success of the post-modification resulting from aldehyde enriched POPs was proven spectroscopically. The accessible functional group was reacted with excess monoethanolamine (MEA) resulting in the formation of M-POP. Away from CO2 physisorption, only few examples have been reported on the chemisorption process. One such example is the ethylene diamine-functionalized E-COF, capable of capturing CO2via carbamation. This was evidenced by several qualitative measurements including colorimetry and conductivity, which showed an unprecedented water solubility for a 2D COF material. The crystallinity of COFs as a result of post-modification was proven by powder X-ray diffraction (PXRD).

A Luminescent Cd-MOF Used as a Chemosensor for High-Efficiency Sensing of Fe3+, Cr(IV), Trinitrophenol, and Colchicine

A Cd-MOF was constructed based on 3,5-bis(4-carboxyphenyl) pyridine under solvothermal conditions. Its structure and phase purity were verified by single-crystal X-ray diffraction. Thereafter, some studies on the morphology, structure, and luminescent properties of the compound were carried out. The compound exhibited a highly sensitive response to Fe3+, Cr(IV), trinitrophenol (TNP), and colchicine based on the fluorescence-quenching mechanism. The possible mechanism of luminescence quenching was discussed in detail.