Urchin-like fluorinated covalent organic frameworks decorated fabric for effective self-cleaning and versatile oil/water separation

Preparation of a Hydrophobic Fluorine-Containing Covalent Organic Framework and Its Interfacial Applications

Hydrophobic porous materials are of significant interest due to their potential for various large-scale industrial applications. In this study, we introduce the synthesis of a hydrophobic fluorine-containing covalent organic framework (F-COF), TAPB-TFA, using a low-temperature method, along with its applications in liquid marbles and oil/water separation. By a scandium(III) trifluoromethanesulfonate-catalyzed Schiff-base reaction, uniform spherical TAPB-TFA particles at the nanoscale are successfully synthesized. Results show that TAPB-TFA exhibits high crystallinity, excellent thermal and chemical stability, as well as superoleophilic/hydrophobic properties. The hydrophobic TAPB-TFA particles can be utilized to create various liquid marbles that exhibit excellent shape reconfigurability. Experiments confirm the outstanding performance of TAPB-TFA in separating oil/water mixtures and water-in-oil emulsions, achieving a separation efficiency of over 98.5%. The analysis concludes that the exceptional separation performance of TAPB-TFA is attributed to the synergistic effects of surface wetting-induced aggregation and size-sieving. TAPB-TFA demonstrates significant potential for applications in the environmental and energy sectors.

Room-temperature synthesis of fluorinated covalent organic framework coupled with liquid chromatography-mass spectrometry for determination of per- and polyfluoroalkyl substances in drinking water

The routine monitoring of per- and polyfluoroalkyl substances (PFASs) in drinking water has become an important task in the field of public health. In this study, a fluorinated covalent organic framework (COF) was synthesized at room temperature using tetra-(4-aminophenyl) methane (TAM) and 2,3,5, 6-tetrafluoro-terephthalal (TFTA) as building blocks and named as TAM-TFTA-COF. The adsorption characteristics of PFASs on the TAM-TFTA-COF were investigated through adsorption model-fitting and molecular calculation. The TAM-TFTA-COF was served as the solid phase extraction (SPE) cartridge packing for the enrichment of PFASs. Combined with liquid chromatography-tandem mass spectrometry, the proposed method showed good linearity in the range of 1.25-375 ng·L-1, low limits of detection (0.03-0.24 ng·L-1), and excellent intraday and interday precisions with RSD <10.3 %. Furthermore, this analytical method can be utilized for the determination of PFASs in tap water, spring water, and lake water with satisfactory accuracy.

Perfluoroalkyl Functionalized Superhydrophobic Covalent Organic Frameworks for Excellent Oil-Water Membrane Separation and Anhydrous Proton Conduction

Rapid economic development has led to oil pollution and energy shortage. Membrane separation has attracted much attention due to its simplicity and efficiency in oil-water-separation. The development of membrane materials with enhanced separation properties is essential to improve the separation-efficiency. Proton exchange membrane fuel cells (PEMFCs) are expected to replace conventional engines due to their high-power-conversion rates and other favorable properties. Anhydrous-proton-conducting materials are vital components of PEMFCs. However, developing stable proton-conducting materials that exhibit high conductivity at varying temperatures remains challenging. Herein, two covalent organic frameworks (COFs) with long-side-chains are synthesized, and their corresponding COF@SSN membranes. Both membranes can effectively separate oil-water mixtures and water-in-oil emulsions. The TFPT-AF membrane achieves a maximum oil-flux of 6.05 × 105 g h-1 m-2 with an oil-water separation efficiency of above 99%, which is almost unchanged after 20 consecutive uses. COF@H3PO4 doped with different ratios of H3PO4 is prepared, the results show that the perfluorocarbon-chain system has  excellent anhydrous proton conductivity , achieving an ultra-high proton-conductivity of 3.98 × 10-1 S cm-1 at 125 °C. This study lays the foundation for tailor-made-functionalization of COF through pre-engineering and surface-modification, highlighting the great potential of COFs for oil-water separation and anhydrous-proton-conductivity.

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.

Dipole moment regulation for enhancing internal electric field in covalent organic frameworks photocatalysts

Covalent organic frameworks (COFs) have recently emerged as a kind of promising photocatalytic platform in addressing the growing threat of trace pollutants in aquatic environments. Along this, we propose a strategy of constructing internal electric field (IEF) in COFs through the dipole moment regulation, which intrinsically facilitates the separation and transfer of photogenerated excitons. Two COFs of BTT-TZ-COF and BTT-TB-COF are developed by linking the electron-donor of benzotrithiophene (BTT) block and the electron-acceptor of triazine (TZ) or tribenzene (TB) block, respectively. DFT calculations demonstrate TZ block with larger dipole moment can achieve more efficient IEF due to the stronger electron-attractive force and hence narrower bandgap. Moreover, featuring the highly-order crystalline structure for accelerating photo-excitons transfer and rich porosity for facilitating the adsorption, BTT-TZ-COF exhibited an excellent universal performance of photocatalytic degradations of various dyes. Specifically, a superior photodegradation efficiency of 99% Rhodamine B (RhB) is achieved within 20 min under the simulated sunlight. Therefore, this convenient construction approach of enhanced IEF in COFs through rational regulation of the dipole moment can be a promising way to realize high photocatalytic activity.

Designing a superhydrophobic cotton fiber coating exploiting TiO2@g-C3N4 layered structure for augmented photocatalysis and efficient water-oil separation

This study introduces a novel approach to develop a multifunctional coating on cotton fabric, emphasizing the utilization of cotton fiber as a biological macromolecule, by integrating a TiO2@g-C3N4 layered structure to confer superhydrophobic properties and multiple functionalities. The engineered structure not only enhances fabric roughness but also incorporates non-fluoro hydrophobic agents, thereby imparting diverse capabilities such as photocatalysis, oil-water separation, and self-cleaning to the cotton substrate. Fabrication of the TiO2@g-C3N4 layered structure involved ultrasonic dispersion of TiO2 and g-C3N4, subsequently deposited onto cotton fabric. Sequential hydrophobic treatment with polydimethylsiloxane (PDMS) and isophorone diisocyanate (IPDI) achieved superhydrophobicity, exhibiting an exceptional water contact angle (WCA) of 157.9°. Comprehensive characterization via scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric validated the composite's structural and chemical properties. The introduced TiO2@g-C3N4 structure significantly enhanced fabric roughness, while PDMS treatment lowered surface energy and IPDI hydrolysis facilitated cross-linking, ensuring durability. The resultant TiO2@g-C3N4/PDMS cotton exhibited outstanding self-cleaning properties and demonstrated oil adsorption capacity, accommodating both heavy and light oils. Notably, this superhydrophobic cotton efficiently separated water-oil mixtures, achieving 96.8 % efficiency even after 10 cycles. Moreover, under simulated light, it displayed outstanding photocatalytic degradation (93.2 %) of methylene blue while maintaining a WCA of 150° post-degradation, highlighting sustained functionality. This innovation holds promise for sustainable applications, offering robust physical and chemical durability within the realm of biological macromolecules. The amalgamation of TiO2@g-C3N4 layered structure and PDMS treatment on cotton fabric underscores a sustainable approach to address water-oil separation challenges and enable efficient self-cleaning. This research demonstrates a significant step towards sustainable material applications and addresses pertinent real-world challenges in diverse technological domains.

Activated carbon fibers functionalized with superhydrophilic coated pDA/TiO2/SiO2 with photoluminescent self-cleaning properties for efficient oil-water separation

The adhesion of high-viscosity oil contamination poses limitations on three-dimensional (3D) materials' practical use in treating oilfield-produced water (OPW). In this study, we developed a hybrid pDA/TiO2/SiO2 coating (PTS) on the surface of hydrophilic activated carbon (ACF1) through a combination of dopamine (DA) polymerization, ethyl orthosilicate (TEOS) hydrolysis, and the condensation of TiO2 nanoparticles (NPs) with SiO2 NPs. This coating was designed for gravity-based oil-water separation. The inherent porosity and generous pore size of ACF1-PTS conferred it an ultra-high permeation flux (pure water flux of 3.72 × 105 L∙m-2∙h-1), allowing it to effectively separate simulated oil-water mixtures and oil-water emulsions while maintaining exceptional permeation flux and oil rejection efficiency. When compared to cleaning methods involving ethanol aqueous solutions and NaClO, ultraviolet (UV) illumination cleaning proved superior, enabling oil-contaminated ACF1-PTS to exhibit remarkable flux recovery efficiency and oil-removal capabilities during cyclic separation of actual OPW. Furthermore, the ACF1-PTS material demonstrated impressive stability and durability when exposed to acidic environments (acid, alkali, and salt), robust hydraulic washout conditions, and 25-cycle tests. This study offers valuable insights and research avenues for the development of highly efficient and environmentally friendly 3D oil-water separation materials for the actual treatment of OPW.

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.