Solvent-Responsive Reversible and Controllable Conversion between a Polyimine Membrane and an Organic Molecule Cage

Fabrication of monodisperse micron-sized and aldehyde-functionalized microspheres coating with covalent organic framework for efficient and rapid removal of copper ions from wastewater

Covalent organic frameworks (COFs) possess an excellent ability for absorbing heavy metals, but their uneven particle size, difficult separation, and poor dispersion limit their wide application in the treatment of heavy metal pollution. In this paper, a monodisperse poly(4-allyloxybenzaldehyde-co-divinylbenzene) microsphere (denoted as PAD) was prepared with 4-allyloxybenzaldehyde as a functional monomer and divinylbenzene (DVB) as a crosslinker by one-step seed swelling polymerization. Subsequently, oxalyldihydrazide (ODH) and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) were chosen as the precursors for coating the COF layer onto the surface of PAD through a one-pot method. The resulting monodisperse particles (diameter = 6.3 μm) with a core-shell structure were assigned as PAD@COF and possessed excellent dispersibility in water along with a high specific surface area of 163.8 m2 g-1. In isothermal and dynamic adsorption experiments, the maximum adsorption capacity of Cu2+ reached 270.9 mg g-1, with the adsorption amount reaching 93 mg g-1 after only 10 min. The Langmuir isothermal adsorption model and pseudo-second-order kinetic model were consistent with the adsorption process, indicating that the adsorption of Cu2+ on PAD@COF occurred as a monolayer and that the adsorption process was controlled by chemical processes.

In Situ Transformation of an Amorphous Supramolecular Coating to a Hydrogen-Bonded Organic Framework Membrane to Trigger Selective Gas Permeation

We introduce a "solution-processing-transformation" strategy, deploying solvent vapor as scaffolds, to fabricate high-quality hydrogen-bonded organic framework (HOF) membranes. This strategy can overcome the mismatch in processing conditions and crystal growth thermodynamics faced during the facile solution processing of the membrane. The procedure includes the vapor-trigged in situ transformation of dense amorphous supramolecules to crystalline HOF-16, with HOF-11 as the transient state. The mechanism involves a vapor-activated dissolution-precipitation equilibrium shifting and hydrogen bonding-guided molecule rearrangement, elucidated through combined experimental and theoretical analysis. Upon removal of the molecular scaffolds, the resulting HOF-16 membranes showcase significant improvement in hydrogen separation performance over their amorphous counterparts and previously reported HOF membranes. The method's broad applicability is evidenced by successfully extending it to other substrates and HOF structures. This study provides a fundamental understanding of guest-induced ordered supramolecular assembly and paves the way for the advanced manufacture of high-performance HOF membranes for gas separation processes.

Soft-Rigid Construction of Mechanically Robust, Thermally Stable, and Self-Healing Polyimine Networks with Strongly Recyclable Adhesion

Reversible and recyclable thermosets have garnered increasing attention for their smart functionality and sustainability. However, they still face challenges in balancing comprehensive performance and dynamic features. Herein, silicon (Si)─oxygen (O) and imidazole units covalent bonds are coupled to generate a new class of bio-polyimines (Bio-Si-PABZs), to endow them with high performance and excellent reprocessing capability and acid-degradability. By tailoring the molar content of diamines, this Bio-Si-PABZs displayed both a markedly high glass transition temperature (162 °C) and a high char yield at 800 °C in an oxygen atmosphere (73.1%). These Bio-Si-PABZs with their favorable properties outperformed various previously reported polyimines and competed effectively with commercial fossil-based polycarbonate. Moreover, the scratch (≈10 µm) on the surface of samples can be self-healing within only 2 min, and an effective "Bird Nest"-to-"Torch" recycling can also be achieved through free amines solution. Most importantly, a bio-based siloxane adhesive derived from the intermediate Bio-Si-PABZ-1 by acidic degradation demonstrated broad and robust adhesion in various substrates, with values reaching up to ≈3.5 MPa. For the first time, this study lays the scientific groundwork for designing robust and recyclable polyimine thermosets with Si─O and imidazole units, as well as converting plastic wastes into thermal-reversibility and renewable adhesives.

Helical Polyallenes: From Controlled Synthesis to Distinct Properties

Polyallenes with appropriate pendants can form stable helices and exhibit significant optical activity. These helical polyallenes contain reactive double bonds that allow for further functionalization, making them a class of chiral functional materials with broad application prospects. This review article delves into the intricacies of synthesizing well-defined helical polyallenes through controlled synthetic methodologies, including helix-sense selective living polymerization, regioselective and asymmetric living polymerization, and one-pot block copolymerization of allenes with aryl monomers. The systemically outlined characteristics of the resulting helical polyallenes and related copolymers are summarized include their unique chiroptical properties, stimuli-responsiveness, helix-induced chiral self-assembly, and circularly polarized luminescence (CPL). Additionally, current challenges and future perspectives in the research of controlled synthesis, functionalities, and applications of helical polyallenes are discussed in detail.

Development of Fluorenyl-Based Copolyimines with Adjustable Mechanical Properties, Recyclability and Friction Resistance

Dynamic polyimines are a class of fascinating dynamic polymers with recyclability and reparability owing to their reversible Schiff-base reactions. However, balancing the dynamic properties and mechanical strength of dynamic polyimines presents a major challenge due to the dissociative and associative nature of the imine bonds. Herein, we introduced bulky fluorene groups and polyether amine into the skeleton of polyimine networks to achieve a tradeoff in comprehensive properties. The resulting dynamic polyimines with fluorene groups (Cardo-DPIs) were successfully synthesized by combining the rigid diamine 9,9-bis(4-aminophenyl)fluorene and the flexible polyether amine, demonstrating a high tensile strength of 64.7 MPa. Additionally, Cardo-DPIs films with more content of rigid fluorene groups exhibited higher water resistance, glass transition temperature and wear-resisting ability. Moreover, the Cardo-DPIs films not only efficiently underwent thermal reshaping, but also exhibited excellent self-healing capabilities and chemical degradation in acidic solutions. Furthermore, the resulting films can achieve fully closed-loop recovery by free amine solution for 2 h at room temperature. This study broadens the scope of dynamic polyimine materials and promotes the balanced development of their functional and mechanical properties.

Commercializable Naphthalene Diimide Anolytes for Neutral Aqueous Organic Redox Flow Batteries

Neutral aqueous organic redox flow batteries (AORFBs) hold the potential to facilitate the transition of renewable energy sources from auxiliary to primary energy, the commercial production of anolyte materials still suffers from insufficient performance of high-concentration and the high cost of the preparation problem. To overcome these challenges, this study provides a hydrothermal synthesis methodology and introduces the charged functional groups into hydrophobic naphthalene diimide cores, and prepares a series of high-performance naphthalene diimide anolytes. Under the synergistic effect of π-π stacking and H-bonding networks, the naphthalene diimide exhibits excellent structural stability and the highest water solubility (1.85 M for dex-NDI) reported to date. By employing the hydrothermal method, low-cost naphthalene diimides are successfully synthesized on a hundred-gram scale of $0.16 g-1 ($2.43 Ah-1), which is also the lowest price reported to date. The constructed full battery achieves a high electron concentration of 2.4 M, a high capacity of 54.4 Ah L-1, and a power density of 318 mW cm-2 with no significant capacity decay observed during long-duration cycling. These findings provide crucial support for the commercialization of AORFBs and pave the way for revolutionary developments in neutral AORFBs.

Bio-based ionic liquid filter with enhanced electrostatic attraction for outside filtration and inside collection of viral aerosols

Hazardous biological pathogens in the air pose a significant public environmental health concern as infected individuals emit virus-laden aerosols (VLAs) during routine respiratory activities. Mask-wearing is a key preventive measure, but conventional filtration methods face challenges, particularly in high humidity conditions, where electrostatic charge decline increases the risk of infection. This study introduces a bio-based air filter comprising glycine ionic liquids (GILs) and malleable polymer composite (GILP) with high polarity and functional group density, which are wrapped around a melamine-formaldehyde (MF) resin skeleton, forming a conductive, porous GIL functionized ionic network air filter (GILP@MF). When subjected to low voltage, the GILP@MF composite efficiently captures VLAs including nanoscale virus particles through the enhanced electrostatic attraction, especially in facing high humidity bioaerosols exhaled by human body. The filtration/collection efficiency and quality factor can reach 98.3% and 0.264 Pa-1 at 0.1 m s-1, respectively. This innovative filter provides effective VLA protection and offers potential for non-invasive respiratory virus sampling, advancing medical diagnosis efforts.

Smart touchless human-machine interaction based on crystalline porous cages

The rise of touchless technology, driven by the recent pandemic, has transformed human-machine interaction (HMI). Projections indicate a substantial growth in the touchless technology market, nearly tripling from $13.6 billion in 2021 to an estimated $37.6 billion by 2026. In response to the pandemic-driven shift towards touchless technology, here we show an organic cage-based humidity sensor with remarkable humidity responsiveness, forming the basis for advanced touchless platforms in potential future HMI systems. This cage sensor boasts an ultrafast response/recovery time (1 s/3 s) and exceptional stability (over 800 cycles) across relative humidity (RH) changes from 11% to 95%. The crystal structure's 3D pore network and luxuriant water-absorbing functional groups both inside and outside of the cage contribute synergistically to superior humidity sensing. Demonstrating versatility, we showcase this cage in smart touchless control screens and touchless password managers, presenting cost-effective and easily processable applications of molecularly porous materials in touchless HMI.

Probing the Solubility of Imine-Based Covalent Adaptable Networks

Covalent adaptable networks (CANs) are polymer materials that are covalently cross-linked via dynamic covalent bonds. The cross-linked polymer network is generally expected to be insoluble, as is seen for traditional thermosets. However, in recent years, it has become apparent that-under certain conditions-both dissociative and associative CANs can be dissolved in a good solvent. For some applications (e.g., those that require long-term (chemical) stability), the solubility of CANs can be problematic. However, many forget that (selective) solubility of CANs can also be applied advantageously, for example, in recycling or modification of the materials. In this work, we provide results and insights related to the tunable solubility of imine-based CANs. We observed that selected CANs could be fully dissolved in a good solvent without observing dissociation of imines. Only in an acidic environment (partial) dissociation of imines was observed, which could be reverted to the associated state by addition of a base. By adjusting the network composition, we were able to either facilitate or hamper solubility as well as control the size of the dissolved particles. DLS showed that the size of dissolved polymer particles decreased at lower concentrations. Similarly, decreasing cross-linking density resulted in smaller particles. Last, we showed that we could use the solubility of the CANs as a means for chemical recycling and postpolymerization modification. The combination of our studies with existing literature provides a better understanding of the solubility of CANs and their applications as recyclable thermosets.

Recent applications of organic cages in sensing and separation processes in solution

Organic cages are three-dimensional polycyclic compounds of great interest in the scientific community due to their unique features, which generally include simple synthesis based on the dynamic covalent chemistry strategies, structural tunability and high selectivity. In this feature article, we present the advances over the last ten years in the application of organic cages as chemosensors or components in chemosensing devices for the determination of analytes (pollutants, analytes of biological interest) in complex aqueous media including wine, fruit juice, urine. Details on the recent applications of organic cages as selective (back-)extractants or masking agents for potential applications in relevant separation processes, such as the plutonium and uranium recovery by extraction, are also provided. Over the last ten years, organic cages with permanent porosity in the liquid and solid states have been highly appreciated as porous materials able to discriminate molecules of different sizes. These features, combined with good solvent processability and film-forming tendency, have proved useful in the fabrication of membranes for gas separation, solvent nanofiltration and water remediation processes. An overview of the recent applications of organic cages in membrane separation technologies is given.