Novel Melamine/o-Phthalaldehyde Covalent Organic Frameworks Nanosheets: Enhancement Flame Retardant and Mechanical Performances of Thermoplastic Polyurethanes

A Fluorescence-SERS Dual-Mode Nanoprobe for Imaging of HSP90 mRNA and Peroxynitrite in Living Cells

The dysregulation of heat shock protein 90 mRNA (HSP90 mRNA) and reactive oxygen species (ROS) is implicated in stress response and various diseases. Visualizing HSP90 mRNA and ROS dynamics is important to studying their interactions and related physiopathological mechanisms. However, effective methods for detecting both remain lacking. Herein, a covalent organic framework-based (COF-based) dual-mode nanoprobe is designed to monitor HSP90 mRNA and ONOO- (ROS model). The nanoprobe is prepared by in situ assembly of a COF shell as the aptamer carrier on the gold nanorods (AuNRs), followed by conjugation of the ONOO--responsive molecule, 4-mercaptophenylboronic acid (4-MPBA), to the AuNRs and modification of the HSP90 mRNA aptamer (HSP90MB) onto the COF shell. The prepared nanoprobe enables sensitive and selective fluorescence (FL) and surface-enhanced Raman spectroscopy (SERS) detection of HSP90 mRNA and ONOO-, respectively. The dual-channel detection highlights the advantages of facilitating spectral analysis and eliminating mutual interference. In addition, the proposed strategy visualizes a positive interaction between HSP90 mRNA and ONOO- in living cells, revealing their cellular response mechanism under stress conditions and related diseases.

Study on the Catalytic Performance of Nickel(II) Complexes with Distinct Triazine Support Structures in Ethylene Oligomerization via Different Experiment Designs

Covalent organic frameworks hold great promise for heterogeneous catalysis because of their porous structure for gas adsorption and tunable functionality. Two triazine support materials (MAmPA-COF and MAoPA-COF) were prepared by using melamine as the linked monomer and meta-phthalaldehyde (MPA) or ortho-phthalaldehyde (OPA) as the sub-construction monomer. Two nickel(II) complexes (Ni@MAmPA-COF and Ni@MAoPA-COF) based on the synthesized COFs were prepared to use for ethylene oligomerization. The nickel(II) complexes had good catalytic activities in ethylene oligomerization. Moreover, the substituent position of the aldehyde group in the sub-construction monomer had a certain influence on the specific surface area, morphology and catalytic activity. The morphology of Ni@MAmPA-COF was spherical, while Ni@MAoPA-COF exhibited layered stacking shapes and had a large specific surface area. Ni@MAoPA-COF has a higher catalytic activity and higher selectivity for low-carbon olefins in ethylene oligomerization due to its larger specific surface area and smaller pore width. Ni@MAoPA-COF has good recyclability and still had excellent catalytic activity after three cycles. Based on the gray correlation analysis and single factor experiment, the reaction pressure was the most important factor affecting the activity of Ni@MAoPA-COF in ethylene oligomerization, and the molar ratio of Al/Ni was the main important factor affecting the selectivity.

Ultrathin zwitterionic COF membranes from colloidal 2D-COF towards precise molecular sieving

Membrane technology is an important component of resource recovery. Covalent organic frameworks (COFs) with inherent long-range ordered structure and permanent porosity are ideal materials for fabricating advanced membrane. Zwitterionic COFs have unique features beyond single ionic COFs containing anions or cations. Here, a zwitterionic colloidal 2D-COF (TpPa-Py) is synthesized via a single-phase method. ultrathin zwitterionic COF membranes are fabricated via a facile blade-coating method. Experimental and molecular dynamics simulation results showed that due to the unique amphiphilic nature of the TpPa-Py, the TpPa1-Py1 membrane exhibits high level permeance and rejection of both positively and negatively charged dyes. Moreover, the TpPa1-Py1 membrane exhibits excellent dye/dye and dye/salt separation performance. The selectivity factors were 89 for the separation of acid blue and rhodamine B, and 47.8 for the separation of methyl blue and NaCl. This work provides a promising solution for the development of high-performance membranes tailored for resource recovery of dye wastewater, addressing a critical need in water treatment.

A perspective on recent advances in polysaccharide/covalent organic framework composite materials with applications potential in water remediation

Researching the potential of various composite materials to remove water pollutants is an important issue for scientists, and polysaccharides are considered desirable materials in this field. Despite the unique advantages, combining these natural materials with a secondary component, especially porous compounds, could improve the performance of the desired system. Recently, highly porous constructs, such as covalent organic frameworks (COFs), was introduced for the composition of polysaccharides. Also, this combinations can solve the aggregation concern of COFs in water treatment areas. Therefore, the composition of the polysaccharides and COF materials effectively has demonstrated their ability to remove contaminants. The hydrogels, films, aerogels, and membranes are some formulations for these kind systems. When polysaccharides are combined with other substances like COF and Fe3O4 the resulting system displays new properties that expand its applicability while having the properties of both components. A survey of the published reports shows that up to now some comprehensive research explored the potential of polysaccharide/COF composite materials for water treatment. Considering these, the current mini review paper highlights the conducted studies on evaluated polysaccharide/COF composite materials, with a focus on the chitosan (CS), cellulose, alginate, and κ-carrageenan for water treatment containing various pollutants such as dyes, metals, pharmaceuticals and other chemical compounds.

A novel photoreduction deposition induced AuNPs/COFs composite for SERS detection of macrolide antibiotics

As we all know, SERS (Surface-enhanced Raman spectroscopy) is widely used in sensing, analysis and detection. The covalent organic frameworks (COFs) have performed well as a material for supporting metal nanoparticles and facilitating analyte adsorption in SERS, which may greatly enhance the detection sensitivity and reproducibility. The synthesis of traditional metal/COFs composites involved chemical reduction methods, however, the resulting metallic NPs exhibited reduced capacity to enhance SERS due to their small particle sizes (usually <20 nm). This paper presented a novel photoreduction method for the facile growth of AuNPs (diameters: 75 nm) on COFs matrix under light control, which represents the first report of such synthesis on COF. Subsequently, the photoreduction deposition induced AuNPs/COFs composites, which served as highly sensitive and reproducible SERS-active substrates for capturing the spectral information of four types of macrolide antibiotics. The detection limits for the four macrolide antibiotics were determined to be 3.30 × 10-11, 3.43 × 10-10, 1.10 × 10-10 and 5.78 × 10-11 M, respectively, exhibiting excellent linear relationships within the concentration range of 10-10 to 10-3 M. Therefore, our proposed SERS method opens up a new idea for the development of SERS substrates and environmental safety monitoring, and it has great potential for ensuring food safety in the future.

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.

Thickness-Driven Synthesis and Applications of Covalent Organic Framework Nanosheets

Covalent organic frameworks (COFs) are two-dimensional, crystalline porous framework materials with numerous scopes for tunability, such as porosity, functionality, stability and aspect ratio (thickness to length ratio). The manipulation of π-stacking in COFs results in truly 2D materials, namely covalent organic nanosheets (CONs), adds advantages in many applications. In this Minireview, we have discussed both top-down (COFs→CONs) and bottom-up (molecules→CONs) approaches with precise information on thickness and lateral growth. We have showcased the research progress on CONs in a few selected applications, such as batteries, catalysis, sensing and biomedical applications. This Minireview specifically highlights the reports where the authors compare the performance of CONs with COFs by demonstrating the impact of the thickness and lateral growth of the nanosheets. We have also provided the possible scope of exploration of CONs research in terms of inter-dimensional conversion, such as graphene to carbon nanotube and future technologies.

Mechanical reinforcement from two-dimensional nanofillers: model, bulk and hybrid polymer nanocomposites

Thanks to their intrinsic properties, multifunctionality and unique geometrical features, two-dimensional nanomaterials have been used widely as reinforcements in polymer nanocomposites. The effective mechanical reinforcement of polymers is, however, a multifaceted problem as it depends not only on the intrinsic properties of the fillers and the matrix, but also upon a number of other important parameters. These parameters include the processing method, the interfacial properties, the aspect ratio, defects, orientation, agglomeration and volume fraction of the fillers. In this review, we summarize recent advances in the mechanical reinforcement of polymer nanocomposites from two-dimensional nanofillers with an emphasis on the mechanisms of reinforcement. Model, bulk and hybrid polymer nanocomposites are reviewed comprehensively. The use of Raman and photoluminescence spectroscopies is examined in light of the distinctive information they can yield upon stress transfer at interfaces. It is shown that the very diverse family of 2D nanofillers includes a number of materials that can attribute distrinctive features to a polymeric matrix, and we focus on the mechanical properties of both graphene and some of the most important 2D materials beyond graphene, including boron nitride, molybdenum disulphide, other transition metal dichalcogenides, MXenes and black phosphorous. In the first part of the review we evaluate the mechanical properties of 2D nanoplatelets in "model" nanocomposites. Next we examine how the performance of these materials can be optimised in bulk nanocomposites. Finally, combinations of these 2D nanofillers with other 2D nanomaterials or with nanofillers of other dimensions are assessed thoroughly, as such combinations can lead to additive or even synergistic mechanical effects. Existing unsolved problems and future perspectives are discussed.

Core-Shell Gold Nanoparticles@Pd-Loaded Covalent Organic Framework for In Situ Surface-Enhanced Raman Spectroscopy Monitoring of Catalytic Reactions

A core-shell nanostructure of gold nanoparticles@covalent organic framework (COF) loaded with palladium nanoparticles (AuNPs@COF-PdNPs) was designed for the rapid monitoring of catalytic reactions with surface-enhanced Raman spectroscopy (SERS). The nanostructure was prepared by coating the COF layer on AuNPs and then in situ synthesizing PdNPs within the COF shell. With the respective SERS activity and catalytic performance of the AuNP core and COF-PdNPs shell, the nanostructure can be directly used in the SERS study of the catalytic reaction processes. It was shown that the confinement effect of COF resulted in the high dispersity of PdNPs and outstanding catalytic activity of AuNPs@COF-PdNPs, thus improving the reaction rate constant of the AuNPs@COF-PdNPs-catalyzed hydrogenation reduction by 10 times higher than that obtained with Au/Pd NPs. In addition, the COF layer can serve as a protective shell to make AuNPs@COF-PdNPs possess excellent reusability. Moreover, the loading of PdNPs within the COF layer was found to be in favor of avoiding intermediate products to achieve a high total conversion rate. AuNPs@COF-PdNPs also showed great catalytic activities toward the Suzuki-Miyaura coupling reaction. Taken together, the proposed core-shell nanostructure has great potential in monitoring and exploring catalytic processes and interfacial reactions.

Two-Dimensional Conjugated Polymers: a New Choice For Organic Thin-Film Transistors

Organic thin-film transistors (OTFTs) as a vital component among transistors have shown great potential in smart sensing, flexible displays, and bionics due to their flexibility, biocompatibility and customizable chemical structures. Even though linear conjugated polymer semiconductors are common for constructing channel materials of OTFTs, advanced materials with high charge carrier mobility, tunable band structure, robust stability, and clear structure-property relationship are indispensable for propelling the evolution of OTFTs. Two-dimensional conjugated polymers (2DCPs), featured with conjugated lattice, tailorable skeletons, and functional porous structures, match aforementioned criteria closely. In this review, we firstly introduce the synthesis of 2DCP thin films, focusing on their characteristics compatible with the channels of OTFTs. Subsequently, the physics and operating mechanisms of OTFTs and the applications of 2DCPs in OTFTs are summarized in detail. Finally, the outlook and perspective in the field of OTFTs using 2DCPs are provided as well.

In Situ-Generated Heat-Resistant Hydrogen-Bonded Organic Framework for Remarkably Improving Both Flame Retardancy and Mechanical Properties of Epoxy Composites

In this study, the heat-resistant hydrogen-bonded organic framework (HOF) material HOF-FJU-1 was synthesized via in situ generation and then used as flame retardants (FRs) to improve the flame retardancy of epoxy resin (EP). HOF-FJU-1 can maintain high crystallinity at 450 °C and thus function as a flame retardant in EP. The study found that HOF-FJU-1 facilitates the improvement of char formation in EP, thus inhibiting heat transfer and smoke release during combustion. For EP/HOF-FJU-1 composites, the in situ-generated HOF-FJU-1 can remarkably improve both the mechanical properties and the flame retardancy of EP. Furthermore, the in situ-generated HOF-FJU-1 has better fire safety than the ex situ-generated HOF-FJU-1 at the same filling content. Thermal degradation products and flame retardation mechanisms in the gas and condensed phases were further investigated. This work demonstrates that the in situ-generated HOF-FJU-1 is promising to be an excellent flame-retardant candidate.

Facile Ball Milling Preparation of Flame-Retardant Polymer Materials: An Overview

To meet the growing needs of public safety and sustainable development, it is highly desirable to develop flame-retardant polymer materials using a facile and low-cost method. Although conventional solution chemical synthesis has proven to be an efficient way of developing flame retardants, it often requires organic solvents and a complicated separation process. In this review, we summarize the progress made in utilizing simple ball milling (an important type of mechanochemical approach) to fabricate flame retardants and flame-retardant polymer composites. To elaborate, we first present a basic introduction to ball milling, and its crushing, exfoliating, modifying, and reacting actions, as used in the development of high-performance flame retardants. Then, we report the mixing action of ball milling, as used in the preparation of flame-retardant polymer composites, especially in the formation of multifunctional segregated structures. Hopefully, this review will provide a reference for the study of developing flame-retardant polymer materials in a facile and feasible way.

Impact of a Novel Phosphoramide Flame Retardant on the Fire Behavior and Transparency of Thermoplastic Polyurethane Elastomers

In many application fields of thermoplastic polyurethane (TPU), excellent flame retardancy and transparency are required. However, higher flame retardancy is often at the expense of transparency. It is difficult to achieve high flame retardancy while maintaining the transparency of TPU. In this work, a kind of TPU composite with good flame retardancy and light transmittance was obtained by adding a new synthetic flame retardant named DCPCD, which was synthesized by the reaction of diethylenetriamine and diphenyl phosphorochloridate. Experimental results showed that 6.0 wt % DCPCD endowed TPU with a limiting oxygen index value of 27.3%, passing the UL 94 V-0 rating in the vertical burning test. The cone calorimeter test results showed that the peak heat release rate (PHRR) of the TPU composite was dramatically reduced from 1292 kW/m² (pure TPU) to 514 kW/m² by adding only 1 wt % DCPCD. With the increase of DCPCD contents, the PHRR and total heat release gradually decreased, and the char residue gradually increased. More importantly, the addition of DCPCD has little effect on the transparency and haze of TPU composites. In addition, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy were carried out to investigate the morphology and composition of the char residue for TPU/DCPCD composites and explore the flame retardant mechanism of DCPCD in TPU.

Triazine-Based Porous Organic Polymers: Synthesis and Application in Dye Adsorption and Catalysis

The scientific community has been developing promising materials to increase the sustainability and efficiency of production processes and pollutant environmental remediation strategies. Porous organic polymers (POPs) are of special interest, as they are insoluble custom-built materials at the molecular level, endowed with low densities and high stability, surface areas, and porosity. This paper describes the synthesis, characterization, and performance of three triazine-based POPs (T-POPs) in dye adsorption and Henry reaction catalysis. T-POPs were prepared by a polycondensation reaction between melamine and a dialdehyde (terephthalaldehyde (T-POP1) or isophthalaldehyde derivatives with a hydroxyl group (T-POP2) or both a hydroxyl and a carboxyl group (T-POP3)). The crosslinked and mesoporous polyaminal structures, with surface areas between 139.2 and 287.4 m² g^-1, positive charge, and high thermal stability, proved to be excellent methyl orange adsorbents, removing the anionic dye with an efficiency >99% in just 15-20 min. The POPs were also effective for methylene blue cationic dye removal from water, reaching efficiencies up to ca. 99.4%, possibly due to favorable interactions via deprotonation of T-POP3 carboxyl groups. The modification of the most basic polymers, T-POP1 and T-POP2, with copper(II) allowed the best efficiencies in Henry reactions catalysis, leading to excellent conversions (97%) and selectivities (99.9%).

AuNPs-COFs Core-Shell Reversible SERS Nanosensor for Monitoring Intracellular Redox Dynamics

The redox homeostasis in living cells is greatly crucial for maintaining the redox biological function, whereas accurate and dynamic detection of intracellular redox states still remains challenging. Herein, a reversible surface-enhanced Raman scattering (SERS) nanosensor based on covalent organic frameworks (COFs) was prepared to dynamically monitor the redox processes in living cells. The nanosensor was fabricated by modifying the redox-responsive Raman reporter molecule, 2-Mercaptobenzoquione (2-MBQ), on the surface of gold nanoparticles (AuNPs), followed by the in situ coating of COFs shell. 2-MBQ molecules can repeatedly and quickly undergo reduction and oxidation when successively treated with ascorbic acid (AA) and hypochlorite (ClO^-) (as models of reductive and oxidative species, respectively), which resulted in the reciprocating changes of SERS spectra at 900 cm^-1. The construction of the COFs shell provided the nanosensor with great stability and anti-interference capability, thus reliably visualizing the dynamics of intracellular redox species like AA and ClO^- by SERS nanosensor. Taken together, the proposed SERS strategy opens up the prospects to investigate the signal transduction pathways and pathological processes related with redox dynamics.

Imine-Linked Covalent Organic Framework with a Naphthalene Moiety as a Sensitive Phosphate Ion Sensing

Due to the excellent ion-sensing potential of covalent organic frameworks (COFs), the new imine-linked conjugated COF (IC-COF) is synthesized through a water-based synthesis reaction between 1,5-diaminonaphthalene and 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine to create a luminescence sensor. It is noteworthy that the green synthesized IC-COF shows excellent selectivity to phosphate ions (PO₄^3-) with a detection limit of 0.61 μM. The recyclability performance of IC-COF is high, indicating that it can be reused without a significant reduction in performance (5.2% decline after 5 cycles). Theoretical calculations using the density functional theory are performed on the IC-COF-PO₄^3- and IC-COF-Cu⁺ complexes to explore the sensing mechanism. The fluorescence quenching in the presence of PO₄^3- ions is attributed to the difference between PO₄^3- binding sites to the IC-COF compared to Cu⁺, which leads to the considerable change in the IC-COF absorption spectrum from 400 to 600 nm.

A novel flame retardant consisting of functionalized Salen-Ni based polyphosphazene microspheres

A functionalized cross-linked polyphosphazenes microsphere (Salen-PZN-Ni@DHPP-PTS) was prepared by wrapping Salen-Ni basis polyphosphazenes (Salen-PZN-Ni) with a kind of hybrid flame retardant (DHPP-PTS) to improve the flame retardancy and smoke suppression properties of epoxy (EP) composites. Thermogravimetric analysis showed that the addition of Salen-PZN-Ni@DHPP-PTS greatly improved the thermal stability of the EP composites. The addition of 5 wt% Salen-PZN-Ni@DHPP-PTS remarkably improved the fire safety of EP, which was illustrated by the results of the cone calorimeter. For example, the peak heat release rate and total heat release rate of the EP composites were reduced by 44.2% and 33.1%, respectively. The limiting oxygen index value of 5% Salen-PZN-Ni@DHPP-PTS/EP composite reached 29.8% and UL-94 achieved V-1 rating. In addition, the introduction of Salen-PZN-Ni@DHPP-PTS effectively suppressed the production of toxic CO and other volatiles. Meantime, the synergistic effect between Salen-PZN-Ni and DHPP-PTS was found. The potential flame retardant mechanism of Salen-PZN-Ni@DHPP-PTS is regarded as the synergistic catalytic carbonization effect and the extremely thermally stable components forming. Enhanced fire safety of EP composites by synergistic interaction of various components (nickel and DHPP-PTS) with polyphosphazenes microspheres.

2D Covalent Organic Frameworks: From Synthetic Strategies to Advanced Optical-Electrical-Magnetic Functionalities

Covalent organic frameworks (COFs), an emerging class of organic crystalline polymers with highly oriented structures and permanent porosity, can adopt 2D or 3D architectures depending on the different topological diagrams of the monomers. Notably, 2D COFs have particularly gained much attention due to the extraordinary merits of their extended in-plane π-conjugation and topologically ordered columnar π-arrays. These properties together with high crystallinity, large surface area, and tunable porosity distinguish 2D COFs as an ideal candidate for the fabrication of functional materials. Herein, this review surveys the recent research advances in 2D COFs with special emphasis on the preparation of 2D COF powders, single crystals, and thin films, as well as their advanced optical, electrical, and magnetic functionalities. Some challenging issues and potential research outlook for 2D COFs are also provided for promoting their development in terms of structure, synthesis, and functionalities.

Porous organic polymers for high-performance supercapacitors

With the aim of addressing the global warming issue and fossil energy shortage, eco-friendly and sustainable renewable energy technologies are urgently needed. In comparison to energy conversion, studies on energy storage fall behind and remain largely to be explored. By storing energy from electrochemical processes at the electrode surface, supercapacitors (SCs) bridge the performance gap between electrostatic double-layer capacitors and batteries. Organic electrode materials have drawn extensive attention because of their special power density, good round trip efficiency and excellent cycle stability. Porous organic polymers (POPs) have drawn extensive attention as attractive electrode materials in SCs. In this review, we present and discuss recent advancements and design principles of POPs as efficient electrode materials for SCs from the perspectives of synthetic strategies and the structure-performance relationships of POPs. Finally, we put forward the outlook and prospects of POPs for SCs.

Mixed matrix of MOF@COF hybrids for enrichment and determination of phenoxy carboxylic acids in water and vegetables

A novel mixed matrix of MOF@COF hybrid was firstly formed by coating of hexahedral cage structure MOF with lightweight porous COF, and applied in dispersive solid-phase extraction of the phenoxy carboxylic acids (PCAs) from water and vegetable samples. Combined with liquid chromatography-tandem mass spectrometry, an excellent method with low limits of detection (0.69-1.79 ng·L^-1/0.002-0.006 ng·g^-1), good reproducibility (1.32%-7.02%/1.81%-6.71%), and excellent linearities (10-1000 ng·L^-1, R ≥ 0.9955/0.04-50 ng·g^-1, R ≥ 0.9966) was established. The adsorption mechanisms deduced that the π-π interaction, hydrophobic effects, hydrogen bond, and halogen bond may promote the excellent adsorption of the PCAs. Finally, the applicability of the method was verified by spiking four kinds of water and vegetable samples with PCAs, and satisfying recoveries were obtained (between 83.3% and 104.9%).

Two-Dimensional Polymers and Polymerizations

Synthetic chemists have developed robust methods to synthesize discrete molecules, linear and branched polymers, and disordered cross-linked networks. However, two-dimensional polymers (2DPs) prepared from designed monomers have been long missing from these capabilities, both as objects of chemical synthesis and in nature. Recently, new polymerization strategies and characterization methods have enabled the unambiguous realization of covalently linked macromolecular sheets. Here we review 2DPs and 2D polymerization methods. Three predominant 2D polymerization strategies have emerged to date, which produce 2DPs either as monolayers or multilayer assemblies. We discuss the fundamental understanding and scope of each of these approaches, including: the bond-forming reactions used, the synthetic diversity of 2DPs prepared, their multilayer stacking behaviors, nanoscale and mesoscale structures, and macroscale morphologies. Additionally, we describe the analytical tools currently available to characterize 2DPs in their various isolated forms. Finally, we review emergent 2DP properties and the potential applications of planar macromolecules. Throughout, we highlight achievements in 2D polymerization and identify opportunities for continued study.

Solution-processed perylene diimide-ethylene diamine cathodes for aqueous zinc ion batteries

Organic electroactive compounds can be applied as alternative cathodes in rechargeable zinc ion batteries (ZIBs) instead of using inorganic cathode materials with low stability or high toxicity. However, many reported organic ZIB cathodes have some limitations, which are their tedious synthesis processes and low yields. In this work, perylene diimide-ethylenediamine/carbon black (PDI-EDA/CB) composites are prepared with a high yield of over 88% under mild conditions via a solution-based processing method. As the organic cathodes in aqueous ZIBs, the PDI-EDA/CB composites have a high specific capacity of 118.0 mA h g^-1 at 0.05 A g^-1; this capacity can be maintained as 95.0 mA h g^-1 even at a high current density of 5.00 A g^-1. Also, PDI-EDA/CB has good cycling stability by reserving 70.5% of its initial capacity after 1500 charge-discharge cycles at 1.00 A g^-1, outperforming many recently reported ZIB cathodes. As disclosed by the structural and electrochemical characterization of PDI-EDA/CB, its excellent electrochemical performance is due to the zinc ion storage mechanism of PDI-EDA and the solution-based fabrication method.

Strategies and applications of covalent organic frameworks as promising nanoplatforms in cancer therapy

Cancer nanomedicine is the best option to face the limits of conventional chemotherapy and phototherapy methods, and thus the intensive quest for new nanomaterials to improve therapeutic efficacy and safety is still underway. Owing to their low density, well-defined structures, large surface area, finely tunable pore size, and metal ion free features, covalent organic frameworks (COFs) have been extensively studied in many research fields. The recent great interest in nanoscale COFs to improve the properties of bulk COFs has led to broadening of their applicability in the biomedical field, such as nanocarriers with an outstanding loading capacity and efficient delivery of therapeutic agents, smart theranostic nanoplatforms with excellent stability, high ROS generation, light-to-heat conversion capabilities, and different response and diagnostic characteristics. The COFs and related nanoplatforms with a wide variety of designability and functionalization have opened up a new avenue for exciting opportunities in cancer therapy. Herein we review the state-of-the-art technical and scientific developments in this emerging field, focusing on the overall progress addressed so far in building versatile COF-based nanoplatforms to enhance chemotherapy, photodynamic/photothermal therapy, and combination. Future perspectives for achieving the synergistic effect of cancer elimination and clinical translation are further discussed to motivate future contributions and explore new possibilities.

Barrier function of graphene for suppressing the smoke toxicity of polymer/black phosphorous nanocomposites with mechanism change

Recently, black phosphorous (BP) nanosheets as an emerging nanomaterial have presented significant fire safety improvement in polymer nanocomposites. However, as elemental phosphorus, fire safety improvement effect of BP nanosheets on polymer composites builds on the conversion of gaseous pyrolysis products into smoke particles, which inevitably promotes the formation and release of smoke particles. From the perspective of overall fire safety improvement, it is vital to simultaneously suppress the heat release and smoke production of polymer/BP composites. Herein, melamine-mediated graphene/black phosphorous nanohybrids (GNS/MA/BP) were fabricated through electrostatic-driving self-assembly process and introduced into polyether thermoplastic polyurethane (TPU). During combustion, the barrier function provided by thermally stable layered structure of graphene (GNS) enables more pyrolysis products of BP nanosheets to be kept within condensed phase and react with polymer matrix. Compared to pure TPU, the incorporated hierarchical nanostructure (GNS/MA/BP-2) decreases PHRR, THR, and total CO₂ release of TPU composite by 54.7%, 23.5%, and 32.5%, respectively. Beside, in contrast to TPU-BP composite, the release rate of toxic smoke and CO gas of TPU-GNS/MA/BP-2 composite are reduced by 46.7% and 49.4%. With barrier function of graphene, the heat and smoke release behavior of polymer/BP nanocomposites is effectively suppressed.

Nanoscale covalent organic frameworks as theranostic platforms for oncotherapy: synthesis, functionalization, and applications

Cancer nanomedicine is one of the most promising domains that has emerged in the continuing search for cancer diagnosis and treatment. The rapid development of nanomaterials and nanotechnology provide a vast array of materials for use in cancer nanomedicine. Among the various nanomaterials, covalent organic frameworks (COFs) are becoming an attractive class of upstarts owing to their high crystallinity, structural regularity, inherent porosity, extensive functionality, design flexibility, and good biocompatibility. In this comprehensive review, recent developments and key achievements of COFs are provided, including their structural design, synthesis methods, nanocrystallization, and functionalization strategies. Subsequently, a systematic overview of the potential oncotherapy applications achieved till date in the fast-growing field of COFs is provided with the aim to inspire further contributions and developments to this nascent but promising field. Finally, development opportunities, critical challenges, and some personal perspectives for COF-based cancer therapeutics are presented.

Exfoliation of 2D Materials for Energy and Environmental Applications

The fascinating properties of single-layer graphene isolated by mechanical exfoliation have inspired extensive research efforts toward two-dimensional (2D) materials. Layered compounds serve as precursors for atomically thin 2D materials (briefly, 2D nanomaterials) owing to their strong intraplane chemical bonding but weak interplane van der Waals interactions. There are newly emerging 2D materials beyond graphene, and it is becoming increasingly important to develop cost-effective, scalable methods for producing 2D nanomaterials with controlled microstructures and properties. The variety of developed synthetic techniques can be categorized into two classes: bottom-up and top-down approaches. Of top-down approaches, the exfoliation of bulk 2D materials into single or few layers is the most common. This review highlights chemical and physical exfoliation methods that allow for the production of 2D nanomaterials in large quantities. In addition, remarkable examples of utilizing exfoliated 2D nanomaterials in energy and environmental applications are introduced.

Improving the flame retardancy of waterborne polyurethanes based on the synergistic effect of P-N flame retardants and a Schiff base

A novel reactive intumescent fire retardant hexa-[4-[(2-hydroxy-ethylimino)-methyl]-phenoxyl]-cyclotriphosphazene (HEPCP), containing both cyclotriphosphazene and Schiff base structures, is successfully prepared. The chemical structures of HEPCP and flame-retardant waterborne polyurethane (WPU) (FR-WPU) were characterized via³¹P, ¹H NMR and FT-IR. Thermogravimetric (TG) analysis showed that HEPCP exhibited excellent thermal stability and produced rich char residue under high temperature compared with the control sample. The Schiff base and cyclotriphosphazene had a synergistic effect on the WPU. Limiting oxygen index (LOI) values of up to 26.7% were recorded; the dripping behavior was simultaneously improved and achieved a V-1 rating in the UL-94 test by incorporating 0.5 wt% phosphorus. In contrast to the pure WPU, the peak heat release rate (pHRR) of the FR-WPU/HEPCP5 decreased by 43.8%. The char residues increased from 0.63% to 6.96%, and scanning electron microscopy (SEM) showed a relatively continuous and membranous substance, with few holes. The results of TGA-FIR, Py-GC/MS and SEM indicated that HEPCP displayed a fire-retardant mechanism in the condensed-phase. In addition, the thermomechanical behaviors and the mechanical properties indicated that both mechanical properties and T_gh increased.

A novel reactive intumescent fire retardant hexa-[4-[(2-hydroxy-ethylimino)-methyl]-phenoxyl]-cyclotriphosphazene (HEPCP), containing both cyclotriphosphazene and Schiff base structures, is successfully prepared.

A nanoporous covalent organic framework for the green-reduction of CO2 under visible light in water

Herein, we designed a sheet-like nanoporous covalent organic framework (TFP-DM COF) based nanomaterial, which was formed via an easy solvothermal synthetic method.

Bulk COFs and COF nanosheets for electrochemical energy storage and conversion

The current advances, structure-property relationship and future perspectives in covalent organic frameworks (COFs) and their nanosheets for electrochemical energy storage (EES) and conversion (EEC) are summarized.

Interface decoration of exfoliated MXene ultra-thin nanosheets for fire and smoke suppressions of thermoplastic polyurethane elastomer

Thermoplastic polyurethane (TPU) has broad applications as lightweight materials due to its multiple advantages and unique properties. Nevertheless, toxicity emission under fire conditions remains a major concern, particularly in building fire scenarios. To circumvent the problem, it is imperative that an effective flame retardant is sought to suppress the flame and release of combustion/smoke products whilst maintaining the favorable material properties of TPU. In the current work, a simple method is proposed for the preparation and utilization of cetyltrimethyl ammonium bromide (CTAB) and tetrabutyl phosphine chloride (TBPC) modified Ti₃C₂ (MXene) ultra-thin nanosheets. During the cone calorimeter tests, significant reduction in peak heat release rate (51.2% and 52.2%), peak smoke production rate (57.1% and 57.4%), peak CO production (39.4% and 41.6%) and peak CO₂ production (49.7% and 51.7%) were recorded by the mere introduction of 2 wt.% CTAB-Ti₃C₂ and TBPC-Ti₃C₂ to TPU. These superior fire safety properties resulting from the significant reduction of the fire, smoke and toxicity hazards are attributed to the excellent dispersion, catalytic and barrier effect of Ti₃C₂ ultra-thin nanosheets in TPU. Future applications of exfoliated MXene nanosheets as flame retardant appear to be very promising.

Recent progress in covalent organic framework thin films: fabrications, applications and perspectives

As a newly emerging class of porous materials, covalent organic frameworks (COFs) have attracted much attention due to their intriguing structural merits (e.g., total organic backbone, tunable porosity and predictable structure). However, the insoluble and unprocessable features of bulk COF powder limit their applications. To overcome these limitations, considerable efforts have been devoted to exploring the fabrication of COF thin films with controllable architectures, which open the door for their novel applications. In this critical review, we aim to provide the recent advances in the fabrication of COF thin films not only supported on substrates but also as free-standing nanosheets via both bottom-up and top-down strategies. The bottom-up strategy involves solvothermal synthesis, interfacial polymerization, room temperature vapor-assisted conversion, and synthesis under continuous flow conditions; whereas, the top-down strategy involves solvent-assisted exfoliation, self-exfoliation, mechanical delamination, and chemical exfoliation. In addition, the applications of COF thin films including energy storage, semiconductor devices, membrane-separation, sensors, and drug delivery are summarized. Finally, to accelerate further research, a personal perspective covering their synthetic strategies, mechanisms and applications is presented.

Enhanced optomechanical properties of mechanochemiluminescent poly(methyl acrylate) composites with granulated fluorescent conjugated microporous polymer fillers

With the combination of mechanochemiluminescence from 1,2-dioxetane coupled polymers and conjugated microporous polymer nanosheets, a new kind of filling-type mechanolumninescent polymer composite was developed.

With the combination of mechanochemiluminescence from 1,2-dioxetane coupled polymers and granulated conjugated microporous polymer (CMP) nanosheets, a new kind of filling-type mechanolumninescent polymer composite was developed. Herein, polymeric 1,2-dioxetane performed as an autoluminescent probe of chain scission. Besides benefiting from their excellent optical properties and good interfacial compatibility with poly(methyl acrylate) (PMA) media, two stable and fluorescent CMP nanosheets were prepared and dispersed in crosslinked PMA, which can serve as effective energy acceptors and reinforcing nano-fillers. These polymer nanocomposites present both reinforced mechanical strength and mechanochemiluminescence, and offer exciting opportunities to study the failure process of polymer nanocomposites with unprecedented temporal and spatial resolution.