Charged nanochannels endow COF membrane with weakly concentration-dependent methanol permeability

Efficient construction of high-quality sulfonated porous aromatic frameworks by optimizing the swelling state of porous structures

Conventional post-modification methods usually face the fundamental challenge of balancing the high content of functional groups and large surface area for porous organic polymers (POPs). The reason, presumably, stems from ineffective and insufficient swelling of the porous structure of POP materials, which is detrimental to mass transfer and modification of functional groups, especially with large-sized ones. It is important to note that significant differences exist in the porous structures of POP materials in a solvent-free state after thermal activation and solvent swelling state. Herein, we propose that the improvement of the swelling state of the porous structure of POP materials is more conducive to obtaining high-quality sulfonated POP materials, and employ a one-pot modification strategy for preparing sulfonated porous aromatic frameworks (PAFs) to prove the proposal. These results show that the specific surface area of the resulting polymer is 580 m2 g-1 with a sulfur content of up to 13.2 wt%, which is superior to most sulfonated porous materials and the control sample. More importantly, we have also shown that the same conclusion is reached by performing similar treatments on hyper-crosslinked polymers (HCPs) and conjugated microporous polymers (CMPs), proving that our hypothesis is effective and feasible when compared to the conventional post-sulfonation method. The excellent hydrophilicity, rich content of sulfonic acid groups, high specific surface area and hierarchical pore structure make the resulting polymer an ideal adsorbent for micro-pollutants in water. The maximum adsorption capacities for Rhodamine B (RhB), Methylene Blue (MB), Tetracycline (TC) and Ciprofloxacin (CIP) are 1075 mg g-1, 1020 mg g-1, 826 mg g-1 and 1134 mg g-1, respectively. This study not only demonstrates the preparation of efficient sulfonated porous adsorbents for the efficient removal of cationic dyes and antibiotics but also illustrates an effective method for constructing high-quality functional POP materials by optimizing the swelling state of the porous structure.

Recent advances of pure/independent covalent organic framework membrane materials: preparation, properties and separation applications

Covalent organic frameworks (COF) are porous crystalline polymers connected by covalent bonds. Due to their inherent high specific surface area, tunable pore size, and good stability, they have attracted extensive attention from researchers. In recent years, COF membrane materials developed rapidly, and a large amount of research work has been presented on the preparation methods, properties, and applications of COF membranes. This review focuses on the research on independent/pure continuous COF membranes. First, based on the membrane formation mechanism, COF membrane preparation methods are categorized into two main groups: bottom-up and top-down. Four methods are presented, namely, solvothermal, interfacial polymerization, steam-assisted conversion, and layer by layer. Then, the aperture, hydrophilicity/hydrophobicity and surface charge properties of COF membranes are summarized and outlined. According to the application directions of gas separation, water treatment, organic solvent nanofiltration, pervaporation and energy, the latest research results of COF membranes are presented. Finally, the challenges and future directions of COF membranes are summarized and an outlook provided. It is hoped that this work will inspire and motivate researchers in related fields.

Squaraine-linked zwitterionic COF modified LLZTO nanoparticles for high performance polymer composite electrolytes in Li-S batteries

Lithium-sulfur (Li-S) batteries are severely restricted for practical application due to the polysulfide shuttle effect, Li dendrites and thermal runaway. The use of PEO-based polymer composite electrolytes (PCEs) as an alternative strategy suffers from limited lithium-ion conductivity with deficient long-range transfer route. Herein, Li6.4La3Zr1.4Ta0.6O12 (LLZTO) nanoparticles modified with an in situ-synthesized zwitterionic covalent organic framework layer (denoted as LLZTO@HUT4) were introduced into PEO-based PCEs. Zwitterionic HUT4 modified the lithiophobic LiOH/Li2CO3 layer on the surface of LLZTO nanoparticles, which could notably promote Li+ ion transport for superior electrochemical performance of PCEs. Additionally, the intermediate layer HUT4 located between LLZTO and PEO could further improve the mechanical properties of electrolytes due to the enhanced inorganic/organic interface compatibility and intermolecular interaction. As a result, the obtained LLZTO@HUT4-15%/PEO electrolyte exhibited a competent ionic conductivity of 0.73 mS cm-1 with a Li+ transference number of up to 0.74 at 60 °C. The assembled S@CNT|LLZTO@HUT4-15%/PEO|Li coin cell delivered a considerable initial discharge capacity of 1018 mA h g-1 at 0.2 C, with approximately 92.1% capacity retention after 100 cycles, elucidating an obviously suppressed shuttle effect.