Construction of Covalent Organic Framework Nanofiber Membranes for Efficient Adsorption of Antibiotics

A robust amphiphilic ionic covalent organic framework intercalated into functionalized graphene oxide hybrid membranes for ultrafast extraction uranium from wastewater

The efficient capture of uranium from wastewater is crucial for environmental remediation and the sustainable development of nuclear energy, yet it poses considerable challenges. In this study, amphiphilic ionic covalent organic framework intercalated into graphene oxide (GO) nanosheets functionalized with polyethyleneimine (PEI) were used to construct hybrid membranes with ultrafast uranium adsorption. These hybrid membranes achieved equilibrium in just 10 min and the adsorption capacity was as high as 358.8 mg g-1 at pH = 6. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) analyses revealed that the strong interaction between sulfonic acid groups and uranyl ions was the primary reason for the high adsorption capacity and selectivity. The extended transition state and natural orbitals for chemical valence (ETS-NOCV) analysis revealed that the interaction between the 7 s and 5f orbitals of uranyl and the 2p orbitals of S and O in the sulfonate was the primary reason for the strong interaction between the sulfonate and the uranyl ion. This research presents an effective method for the rapid extraction of uranium from wastewater.

Optimizing 3d electronic structure of LaCoO3 based on spin state tuning for enhancing photo-Fenton activity on tetracycline degradation

The water pollution caused by the abuse of antibiotics has significant harmful effects on the environment and human health. The photo-Fenton process is currently the most effective method for removing antibiotics from water, but it encounters challenges such as inadequate response to visible light, low yield and utilization of photogenerated electrons, and slow electron transport. In this study, spin state regulation was introduced into the photo-Fenton process, and the spin state of Co3+ was regulated through Ce displacement doping. The intermediate-spin state Ce-LaCoO3 could degrade 91.6 % of tetracycline within 120 min in the photo-Fenton system, which is 15.2 % higher than that of low-spin state LaCoO3. The improved degradation effect is attributed to the reasons that Ce-LaCoO3 in the intermediate-spin state have lower band gap, better charge transfer ability, and stronger adsorption capacity of H2O2, which can accelerate the redox cycle of Co2+/Co3+ and promote the generation of ·OH. This study presents a unique strategy for synthesizing efficient photo-Fenton materials to treat antibiotic wastewater effectively.

Ultrathin Free-Standing Porous Aromatic Framework Membranes for Efficient Anion Transport

Porous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid-solid interfacial polymerization. The rigid backbone and the stable C-C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH- conductivity of 356.6 mS ⋅ cm-1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH- conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH- conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.

Nanofibrous Porous Organic Polymers and Their Derivatives: From Synthesis to Applications

Engineering porous organic polymers (POPs) into 1D morphology holds significant promise for diverse applications due to their exceptional processability and increased surface contact for enhanced interactions with guest molecules. This article reviews the latest developments in nanofibrous POPs and their derivatives, encompassing porous organic polymer nanofibers, their composites, and POPs-derived carbon nanofibers. The review delves into the design and fabrication strategies, elucidates the formation mechanisms, explores their functional attributes, and highlights promising applications. The first section systematically outlines two primary fabrication approaches of nanofibrous POPs, i.e., direct bulk synthesis and electrospinning technology. Both routes are discussed and compared in terms of template utilization and post-treatments. Next, performance of nanofibrous POPs and their derivatives are reviewed for applications including water treatment, water/oil separation, gas adsorption, energy storage, heterogeneous catalysis, microwave absorption, and biomedical systems. Finally, highlighting existent challenges and offering future prospects of nanofibrous POPs and their derivatives are concluded.

Covalent Organic Framework-derived Composite Membranes for Water Treatment

Water treatment has experienced a surge in the adoption of membrane separation technology. Covalent organic frameworks (COFs), a class of metal-free and open-framework materials, have emerged as potential membrane materials owing to their interconnected periodic porosity, tunability, and chemical stability. However, the challenges associated with processing COF powders into self-standing membranes have spurred the emergence of COF composite membranes. This review article highlights the rationale behind developing COF composite membranes and their categories, including mixed matrix membranes (MMMs) and thin film composite (TFC) membranes. The common fabrication techniques of each category are presented. In addition, the influence of COF additives on the performance of the resultant composite membranes is systematically discussed, with a focus on the recent progress in applying COF composite membranes in the separation of different categories of water pollutants, including organic ions/molecules, toxic solvents, proteins, toxic heavy metals, and radionuclides.

Ambient Aqueous Synthesis of Imine-Linked Covalent Organic Frameworks (COFs) and Fabrication of Freestanding Cellulose Nanofiber@COF Nanopapers

Covalent organic frameworks (COFs) are usually synthesized under solvothermal conditions that require the use of toxic organic solvents, high reaction temperatures, and complicated procedures. Additionally, their insolubility and infusibility present substantial challenges in the processing of COFs. Herein, we report a facile, green approach for the synthesis of imine-linked COFs in an aqueous solution at room temperature. The key behind the synthesis is the regulation of the reaction rate. The preactivation of aldehyde monomers using acetic acid significantly enhances their reactivity in aqueous solutions. Meanwhile, the still somewhat lower imine formation rate and higher imine breaking rates in aqueous solution, in contrast to conventional solvothermal synthesis, allow for the modulation of the reaction equilibrium and the crystallization of the products. As a result, highly crystalline COFs with large surface areas can be formed in relatively high yields in a few minutes. In total, 16 COFs are successfully synthesized from monomers with different molecular sizes, geometries, pendant groups, and core structures, demonstrating the versatility of this approach. Notably, this method works well on the gram scale synthesis of COFs. Furthermore, the aqueous synthesis facilitates the interfacial growth of COF nanolayers on the surface of cellulose nanofibers (CNFs). The resulting CNF@COF hybrid nanofibers can be easily processed into freestanding nanopapers, demonstrating high efficiency in removing trace amounts of antibiotics from wastewater. This study provides a route to the green synthesis and processing of various COFs, paving the way for practical applications in diverse fields.

A porous polyacrylonitrile (PAN)/covalent organic framework (COF) fibrous membrane photocatalyst for highly efficient and ultra-stable hydrogen evolution

Photocatalytic water splitting has been regarded as one of the most promising technologies to generate hydrogen as an ideal energy carrier in the future. However, most of the experience for such process are derived from the researches based on the suspension powder photocatalysts under a stirring condition and a practical scaling application is urgently calling for the high-efficient panel reactors based on the membrane photocatalysts. Herein, we develop a new series of flexible and ultrastable membrane photocatalysts through a controllable growth of covalent organic framework (COF) photocatalysts on the polyacrylonitrile (PAN) electrospun fiber membrane. Multiple characterization techniques verify the successful anchoring of the COF-photocatalysts on the PAN fibers, forming a three-dimensional porous PAN/COF membrane photocatalyst with excellent light absorption ability, high specific surface area, and good hydrophily. As a result, the optimized PAN/COF membrane photocatalyst exhibits excellent hydrogen evolution rate up to 1.25 mmol g-1h-1 under visible-light irradiation without stirring, which is even higher than that of the corresponding suspension COF-powder photocatalyst with stirring. In particular, the PAN/COF membrane photocatalyst demonstrates a much more superior hydrogen evolution stability and also a much better recyclability. This study gives some experience for the practical scaling application of solar-driven water splitting.

A nanofiber with a p-π conjugated structure designed based on the Jahn-Teller effect for the removal of cupric tartrate from wastewater

Copper organic complexes with strong chemical stability and high solubility in water are difficult to eliminate with traditional adsorbents. In this work, a novel amidoxime nanofiber (AO-Nanofiber) with the p-π conjugated structure was fabricated through homogeneous chemical grafting coupled with electrospinning and applied to capture cupric tartrate (Cu-TA) from aqueous solutions. The adsorption capacity of Cu-TA by AO-Nanofiber was 198.4 mg/g at an equilibrium time of 40 min, and the adsorption performance remains basically unchanged after 10 times adsorption-desorption cycles. The capture mechanism of Cu-TA by AO-Nanofiber was jointly validated by experiments and characterization such as Fourier Transform Infrared Spectrometer (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Density functional theory (DFT) calculations. These results demonstrated that the lone pair of electrons of the N atom from the amino groups and the O atom from hydroxyl groups in the AO-Nanofiber is partially transferred to the 3d orbital of the Cu(II) ions in Cu-TA, leading to the Jahn-Teller distortion of the Cu-TA and the more stable structure of AO-Nanofiber@Cu-TA was generated.

Water/Vapor Assisted Fabrication of Large-Area Superprotonic Conductive Covalent Organic Framework Membranes

Fabrication of large-area ionic covalent organic framework membranes (iCOMs) remains a grand challenge. Herein, the authors report the liquid water and water vapor-assisted fabrication of large-area superprotonic conductive iCOMs. A mixed monomer solution containing 1,3,5-triformylphloroglucinol (TFP) in 1,4-dioxane and p-diaminobenzenesulfonic acid (DABA) in water is first polymerized to obtain a pristine membrane which subsequently underwent crystallization process in mixed vapors containing water vapor. During the polymerization stage, water played a role of a diluting agent, weakening the Coulombic repulsion between sulfonic acid groups. During the crystallization stage, water vapor played a role of a structure-directing agent to facilitate the formation of highly crystalline, large-area iCOMs. The resulting membranes achieved a proton conductivity value of 0.76 S cm-1 at 90 °C under 100% relative humidity, which is among the highest ever reported. Using liquid water and water vapor as versatile additives open a novel avenue to the fabrication of large-area membranes from covalent organic frameworks and other kinds of crystalline organic framework materials.