Synthesis of stable COF-300 nanofiltration membrane via in-situ growth with ultrahigh flux for selective dye separation

Imine-Linked 3D Covalent Organic Framework Membrane Featuring Highly Charged Sub-1 nm Channels for Exceptional Lithium-Ion Sieving

Coupling ion exclusion and interaction screening within sub-nanoconfinement channels in novel porous material membranes hold great potential to realize highly efficient ion sieving, particularly for high-performance lithium-ion extraction. Diverse kinds of advanced membranes have been previously reported to realize this goal but with moderate performance and complex operations gained. Herein, these issues are circumvented by preparing the consecutive and intact imine-linked three-dimensional covalent organic framework (i.e., COF-300) membranes via a simple solvothermal approach and employing the intrinsically interconnected sub-1 nm one-dimensional channels for exceptional lithium-ion sieving. The synthesized membranes with highly charged angstrom scale channels of ≈0.78 nm achieve an excellent Li+ permeance (0.123 mol m-2 h-1) with an ultrahigh Li+/Mg2+ of 36 in the binary system. The experimental measurement and theoretical calculation reveal that a channel size right exactly between Li+ and Mg2+ enables restricted Mg2+ penetration. Meanwhile, the ion affinity interaction screening with imine groups further strengthens the fast Li+ permeability but severely suppresses the Mg2+ passage. In particular, the synthesized three-dimensional covalent organic framwork membranes also have a remarkable separation performance during a long-term operation test without sacrificing trade-off, demonstrating chemistry stability and mechanical integrity under the high-salinity aqueous environment.

Introducing the SNW-1 Covalent Organic Framework to the Polyamide Layer of the TFC-RO Membrane with Enhanced Permeability and Desalination Performance

This study investigates the synthesis and characterization of Schiff base network-1 (SNW-1) covalent organic framework (COF) nanomaterials and their application in the fabrication of thin-film nanocomposite (TFN) membranes. The embedding of SNW-1 COF in reverse osmosis (RO) membranes with a polysulfone (PSf) substrate was done using the interfacial polymerization method. The result of the study demonstrated that the porous and hydrophilic structure of the COF increased the hydrophilic properties of the produced RO membranes. When the COF was embedded with a concentration of 0.02 wt %, the hydrophilicity of the RO membrane was higher than that of the other membranes, with a contact angle value of 45.2°. Pure water flux, saline solution flux, and humic acid (HA)/sodium chloride (NaCl) foulant solution flux were measured to determine the membrane performance, and it was found that as the COF ratio increased, the fluxes increased up to a certain concentration rate. The RO membrane with a SNW-1 concentration of 0.005 wt % had the highest values of pure water flux and saline solution flux with high salt rejection (34.2 and 32.2 LMH, 97.1%, respectively) and was the most resistant membrane against fouling. This study presents the potential of the SNW-1 COF with precise design capabilities and controlled unique properties as an additive for desalination applications.

Temperature-dependent structural dynamics in covalent organic frameworks observed by cryogenic infrared spectroscopy

Understanding the structural dynamics of covalent organic frameworks (COFs) in response to external temperature change is necessary for these materials' application at cryogenic temperatures. Herein, we report reversible structural dynamics observed in covalent organic frameworks as the temperature varies from 298 K to 30 K. A series of frameworks (COF-300, COF-300-amine, and COF-V) was studied in situ using a cryogenic infrared spectroscopy system. We observed peak shifts in the Fourier-transform infrared (FTIR) spectrum of COFs as temperature cooled to 30 K, and these peak shifts were reversed as temperature returned to 298 K. Comparison of these materials showed different degrees of temperature-dependent change, through the quantitative degree of the peak shift and a qualitative description of which peaks shifted. A general IR peak shift towards a higher frequency as temperature decreased was observed, with COF-300 exhibiting quantitatively larger blue shifts in key vibrational modes as compared with the other frameworks. The nature of the conformational changes giving rise to the IR shifts was studied using quantum-chemistry calculations on model systems. The results of the calculations indicate that key peak shifts arise from a pedal motion experienced by the frameworks during cooling. This understanding of temperature-dependent framework dynamics will enhance the development, selection, and application of covalent organic frameworks at extreme temperatures.

MgO-loaded tubular ceramic membrane with spatial nanoconfinement for enhanced catalytic ozonation in refractory wastewater treatment

Heterogeneous catalytic ozonation (HCO) enables the destruction of organic pollutants in wastewater via oxidation by powerful hydroxyl radicals (·OH). However, the availability of short-lived ·OH in aqueous bulk is low in practical treatment scenarios due to mass transfer limitations and quenching of water constituents. Herein, we overcome these challenges by loading MgO catalysts inside the pores of a tubular ceramic membrane (denoted as CCM) to confine ·OH within the nanopores and achieve efficient pollutant removal. When the pore size of the membrane was reduced from 1000 to 50 nm, the removal of ibuprofen (IBU) by CCM was increased from 49.6 % to 90.2 % due to the enhancement of ·OH enrichment in the nanospace. In addition, the CCM exhibited high catalytic activity in the presence of co-existing ions and over a wide pH range, as well as good self-cleaning ability in treating secondary wastewater. The experimental results revealed that ·OH were the dominant reactive oxygen species (ROS) in pollutant degradation, while surface hydroxyl groups were active sites for the generation of ·OH via ozone decomposition. This work provides a promising strategy to enhance the utilization of ·OH in HCO for the efficient degradation of organic pollutants in wastewater under spatial confinement.

Bonding states of gold/silver plasmonic nanostructures and sulfur-containing active biological ingredients in biomedical applications: a review

As one of the most instrumental components in the architecture of advanced nanomedicines, plasmonic nanostructures (mainly gold and silver nanomaterials) have been paid a lot of attention. This type of nanomaterial can absorb light photons with a specific wavelength and generate heat or excited electrons through surface resonance, which is a unique physical property. In innovative biomaterials, a significant number of theranostic (therapeutic and diagnostic) materials are produced through the conjugation of thiol-containing ingredients with gold and silver nanoparticles (Au and Ag NPs). Hence, it is essential to investigate Au/Ag-S interfaces precisely and determine the exact bonding states in the active nanobiomaterials. This study intends to provide useful insights into the interactions between Au/Ag NPs and thiol groups that exist in the structure of biomaterials. In this regard, the modeling of Au/Ag-S bonding in active biological ingredients is precisely reviewed. Then, the physiological stability of Au/Ag-based plasmonic nanobioconjugates in real physiological environments (pharmacokinetics) is discussed. Recent experimental validation and achievements of plasmonic theranostics and radiolabelled nanomaterials based on Au/Ag-S conjugation are also profoundly reviewed. This study will also help researchers working on biosensors in which plasmonic devices deal with the thiol-containing biomaterials (e.g., antibodies) inside blood serum and living cells.

Hierarchically Porous Covalent Organic Frameworks: Synthesis Methods and Applications

Covalent organic frameworks (COFs) with high porosity have garnered considerable interest for various applications owing to their robust and customizable structure. However, conventional COFs are hindered by their narrow pore size, which poses limitations for applications such as heterogeneous catalysis and guest delivery that typically involve large molecules. The development of hierarchically porous COF (HP-COF), featuring a multi-scale aperture distribution, offers a promising solution by significantly enhancing the diffusion capacity and mass transfer for larger molecules. This review focuses on the recent advances in the synthesis strategies of HP-COF materials, including topological structure design, in-situ templating, monolithic COF synthesis, defect engineering, and crystalline self-transformation. The specific operational principles and affecting factors in the synthesis process are summarized and discussed, along with the applications of HP-COFs in heterogeneous catalysis, toxic component treatment, optoelectronics, and the biomedical field. Overall, this review builds a bridge to understand HP-COFs and provides guidance for further development of them on synthesis strategies and applications.

Covalent Organic Framework Membranes and Water Treatment

Covalent organic frameworks (COFs) are an emerging class of highly porous crystalline organic polymers comprised entirely of organic linkers connected by strong covalent bonds. Due to their excellent physicochemical properties (e.g., ordered structure, porosity, and stability), COFs are considered ideal materials for developing state-of-the-art separation membranes. In fact, significant advances have been made in the last six years regarding the fabrication and functionalization of COF membranes. In particular, COFs have been utilized to obtain thin-film, composite, and mixed matrix membranes that could achieve effective rejection (mostly above 80%) of organic dyes and model organic foulants (e.g., humic acid). COF-based membranes, especially those prepared by embedding into polyamide thin-films, obtained adequate rejection of salts in desalination applications. However, the claims of ordered structure and separation mechanisms remain unclear and debatable. In this perspective, we analyze critically the design and exploitation of COFs for membrane fabrication and their performance in water treatment applications. In addition, technological challenges associated with COF properties, fabrication methods, and treatment efficacy are highlighted to redirect future research efforts in realizing highly selective separation membranes for scale-up and industrial applications.

Membranes based on Covalent Organic Frameworks through Green and Scalable Interfacial Polymerization using Ionic Liquids for Antibiotic Desalination

Covalent organic framework (COF) membranes featuring uniform topological structures and devisable functions, show huge potential in water purification and molecular separation. Nevertheless, the inability of uniform COF membranes to be produced on an industrial scale and their nonenvironmentally friendly fabrication method are the bottleneck preventing their industrial applications. Herein, we report a new green and industrially adaptable scraping-assisted interfacial polymerization (SAIP) technique to fabricate scalable and uniform TpPa COF membranes. The process used non-toxic and low-volatility ionic liquids (ILs) as organic phase instead of conventional organic solvents for interfacial synthesis of TpPa COF layer on a support membrane, which can simultaneously achieve the purposes of (i) improving the greenness of membrane-forming process and (ii) fabricating a robust membrane that can function beyond the conventional membranes. This approach yields a large-area, continuous COF membrane (19×25 cm2 ) with a thickness of 78 nm within a brief period of 2 minutes. The resulting membrane exhibited an unprecedented combination of high permeance (48.09 L m-2 h-1 bar-1 ) and antibiotic desalination efficiency (e.g., NaCl/adriamycin separation factor of 41.8), which is superior to the commercial benchmarking membranes.

Applications of covalent organic frameworks for the elimination of dyes from wastewater: A state-of-the-arts review

Covalent organic frameworks (COFs) are class of porous coordination polymers made up of organic building blocks joined together by covalent bonding through thermodynamic and controlled reversible polymerization reactions. This review discussed versatile applications of COFs for remediation of wastewater containing dyes, emphasizing the advantages of both pristine and modified materials in adsorption, membrane separation, and advanced oxidations processes. The excellent performance of COFs towards adsorption and membrane filtration has been centered to their higher crystallinity and porosity, exhibiting exceptionally high surface area, pore size and pore volumes. Thus, they provide more active sites for trapping the dye molecules. On one hand, the photocatalytic performance of the COFs was attributed to their semiconducting properties, and when coupled with other functional semiconducting materials, they achieve good mechanical and thermal stabilities, positive light response, and narrow band gap, a typical characteristic of excellent photocatalysts. As such, COFs and their composites have demonstrated excellent potentialities for the elimination of the dyes.

Locating Hydrogen Positions for COF-300 by Cryo-3D Electron Diffraction

Covalent organic frameworks (COFs) have wide-ranging applications, and their host-guest interactions play an essential role in the achievement of COF functions. To investigate these host-guest interactions, it is necessary to locate all atoms, especially hydrogen atoms. However, it is difficult to determine the hydrogen atomic positions in COFs because of the complexities in synthesizing high-quality large single crystals. Three-dimensional electron diffraction (3D ED) has unique advantages for the structural determination of nanocrystals and identification of light atoms. In this study, it was demonstrated for the first time that the hydrogen atoms of a COF, not only on the framework but also on the guest molecule, can be located by 3D ED using continuous precession electron diffraction tomography (cPEDT) under cryogenic conditions. The host-guest interactions were clarified with the location of the hydrogen atoms. These findings provide novel insights into the investigation of COFs.

Room-Temperature Preparation of Covalent Organic Framework Membrane for Nanofiltration

The uniquely tunable nature of covalent organic frameworks (COFs), whose pore size and stability can be controlled by choosing diverse organic building blocks and linkage types, makes COFs potential candidates for the membrane separation. Therefore, the preparation of membranes with effective separation efficiency based on COFs has aroused great interest among researchers. Although solvothermal approach has been the most popular method for the preparation of COF membranes, fabricating COF membranes at room temperature (RT) will provide a simple and captivating strategy for separation membranes. Herein, a P-COF membrane on porous alumina substrate at RT, showing 99.7% rejection of rhodamine B and excellent water permeance up to 52 L m^-2 h^-1 bar^-1 , which can effectively purify wastewater is successfully obtained. P-COF is directly grown on alumina to form the composite membrane, which enhances the mechanical strength of COF membrane and avoids the risk of damaging the membrane structure during the transfer process of self-standing membrane. Moreover, P-COF membrane is grown at RT, which is more energy efficient than the conventional solvothermal method. Thus, it is of great significance to obtain COF membranes with excellent nanofiltration performance in a simple and mild condition to alleviate environmental and energy concerns.

Enhancing bioelectrochemical performance of two-dimensional material attached by covalent/metal organic frameworks as cathode catalyst for microbial fuel cells

In this study, covalent/metal organic framework and two-dimensional material (COF-300/ZIF-8@Ti₃AlC₂) were composited by a three-step distributed feed method for cathode catalyst in microbial fuel cells (MFCs). The growth of irregular cube-like COF-300/ZIF-8 on the Ti₃AlC₂ substrate was observed. Al, Zn, Ti, N, C and O elements were observed uniformly and more active sites were offered through it. The external output voltage of COF-300/ZIF-8@Ti₃AlC₂-MFC was 576 mV and this could be almost unchanged for 9 days. The external output power density was 587.01 mW/m², and that was 1.25 times of COF-300@Ti₃AlC₂-MFC (469.30 mW/m²) and 1.67 times of COF-300/ZIF-8-MFC (352.09 mW/m²). Ti₃AlC₂ enhanced the electrical conductivity of the composite by its rich surface functional groups and much more surface active sites. COF-300/ZIF-8 mixture improved the instability and disorder of the monomer. This study would supply technical support for the expanded request of composite materials in microbial electrochemistry.

A Review of Advancing Two-Dimensional Material Membranes for Ultrafast and Highly Selective Liquid Separation

Membrane-based nanotechnology possesses high separation efficiency, low economic and energy consumption, continuous operation modes and environmental benefits, and has been utilized in various separation fields. Two-dimensional nanomaterials (2DNMs) with unique atomic thickness have rapidly emerged as ideal building blocks to develop high-performance separation membranes. By rationally tailoring and precisely controlling the nanochannels and/or nanoporous apertures of 2DNMs, 2DNM-based membranes are capable of exhibiting unprecedentedly high permeation and selectivity properties. In this review, the latest breakthroughs in using 2DNM-based membranes as nanosheets and laminar membranes are summarized, including their fabrication, structure design, transport behavior, separation mechanisms, and applications in liquid separations. Examples of advanced 2D material (graphene family, 2D TMDs, MXenes, metal-organic frameworks, and covalent organic framework nanosheets) membrane designs with remarkably perm-selective properties are highlighted. Additionally, the development of strategies used to functionalize membranes with 2DNMs are discussed. Finally, current technical challenges and emerging research directions of advancing 2DNM membranes for liquid separation are shared.

Solvent‐Influenced Fragmentations in Free‐Standing Three‐Dimensional Covalent Organic Framework Membranes for Hydrophobicity Switching

The ordered open organic frameworks membranes are attractive candidates for flow‐assisted molecular separations. The physicochemical properties of such membranes mostly depend on their selectively chosen functional building blocks. In this work, we have introduced a novel concept of functional switchability of three‐dimensional covalent organic framework (3D‐COF) membranes through a simple solvent‐influenced fragmentation method. This room‐temperature interfacial synthesis provides free‐standing 3D‐COF membranes with distinct physicochemical properties from the same building monomers. Notably, the change of solvent from chloroform to ethyl acetate switches the membrane property from hydrophilic (water contact angle 60°) to hydrophobic (water contact angle 142°) nature. The hydrophobic 3D‐COF membrane selectively passes oil molecules from an oil–water emulsion with a gravitational flux of 1536 L m⁻² h⁻¹.

Adsorption behavior and mechanism of sulfonamides on controllably synthesized covalent organic frameworks

In this work, four kinds of covalent organic framework (COF) materials (TpPa-1, TpBD, TpDT, and TFBBD) with different pore sizes or functional groups were synthesized by an ultrasonic method for the adsorption of five sulfonamides. Optimization experiments regarding the adsorption time, vortex speed, and pH were carried out to improve adsorption efficiency. In addition, kinetic and thermodynamic experiments were conducted to explore the adsorption mechanism of the sulfonamides on the different COFs. The adsorption processes of the five sulfonamides on the four COFs fit the pseudo-second-order kinetic model and Langmuir adsorption isotherm model. Additionally, pore filling, hydrogen bond interactions, and electrostatic attraction were found to be the main adsorption mechanisms.

Efficient extraction of trace organochlorine pesticides from environmental samples by a polyacrylonitrile electrospun nanofiber membrane modified with covalent organic framework

Detecting and analyzing of the trace organochlorine pesticides (OCPs) in the real water has become a big challenge. In this work, a novel functional electrospun nanofiber membrane (PAN@COFs) was synthesized through the in situ growth of covalent organic frameworks (COFs) on a polyacrylonitrile electrospun nanofiber membranes under room temperature and used in the solid-phase micro-extraction (SPME) to enrich trace organochlorine pesticides (OCPs) in water. The resulted PAN@COFs composite consisted of numerous nanofibers coated ample porous COFs spheres (~ 500 nm) and owned stable crystal structure, abundant functional groups, good stability. In addition, the enrichment experiments clearly revealed that PAN@COFs exhibited rather outstanding performance on adsorbing the trace OCPs (as low as 10 ng L^-1) with the enrichment of 482-2686 times. Besides, PAN@COFs displayed good reusability and could be reused 100 times. Notably, in the real water samples (sea water and river water), the high enrichment factors and recovery rates strongly confirmed the feasibility of PAN@COFs for detecting the trace OCPs. Furthermore, due to the synergy of π-π stacking interaction and hydrophobic interaction between the OCPs molecules and PAN@COFs, the OCPs could be efficiently adsorbed on PAN@COFs, even under the extremely low driving force.

The adsorption mechanism of CF4 on the surface of activated carbon made from peat and modified by Cu

In order to find a way to deal with CF₄ with good removal effect and easy to promote. In this study, peat was used as raw material, and copper-loaded activated carbon (Cu/AC) was successfully prepared through nitric acid oxidation and copper chloride impregnation. Compared with commercial activated carbon and widely used metal organic frameworks (MOFs), it shows a fast adsorption rate and larger adsorption capacity for CF₄. The static experiment was used to study the influence of Cu/AC on the adsorption of CF₄ in the adsorbent dosage, reaction time, temperature, and initial concentration. SEM, FTIR, XPS, XRF, and BET were used to study the changes of physical and chemical properties before and after the adsorption. It was found that the oxygen-containing group was consumed during this process. Unsaturated sites on Cu can accelerate the adsorption of CF₄, and the adsorption process is reversible. For the first time, the kinetic model, adsorption isotherm, and thermodynamic model are used to analyze the adsorption mechanism of CF₄ on the Cu/AC surface from different angles. The results show that the adsorption of CF₄ on the Cu/AC surface is a process of exothermic entropy reduction. The static adsorption process conforms to the pseudo-first-order, the pseudo-second-order, and the Freundlish adsorption model. Through 5 adsorption and desorption processes, it is found that Cu/AC has excellent recycling and recyclability performance.

Controllable Synthesis of Hollow Microtubular Covalent Organic Frameworks as an Enzyme-Immobilized Platform for Enhancing Catalytic Activity

Despite great achievement that has been made in the synthesis of covalent organic frameworks (COFs), precise construction of COFs with well-defined nano/microstructures poses a rigorous challenge. Herein, we introduce a simple template-free strategy for controllable synthesis of hollow microtubular COFs. The obtained COFs show a spontaneous morphology transformation from a microfiber to a hollow microtubular structure when the concentrations of catalytic acid are regulated elaborately. Furthermore, the as-prepared COFs exhibit high crystallinity, well-defined hollow tubular morphology, and high surface areas (∼2600 m2/g). Taking the advantages of the unique morphological structure, the hollow microtubular COFs can serve as an ideal host material for enzymes. The resultant biocomposites show high catalytic performance and can be successfully applied to rapid and high-efficiency proteolysis of proteins. This work blazes a trail for controllable synthesis of the hollow microtubular COFs through a template-free process and expands the application of COFs as a promising platform for enzyme immobilization.

A Perspective on the Application of Covalent Organic Frameworks for Detection and Water Treatment

Global population growth and water resource scarcity are significant social problems currently being studied by many researchers focusing on finding new materials for water treatment. The aim is to obtain quality water suitable for drinking and industrial consumption. In this sense, an emergent class of crystalline porous materials known as Covalent-Organic Frameworks (COFs) offers a wide range of possibilities since their structures can be designed on demand for specific applications. Indeed, in the last decade, many efforts have been made for their use in water treatment. This perspective article aims to overview the state-of-the-art COFs collecting the most recent results in the field for water detection of pollutants and water treatment. After the introduction, where we overview the classical design strategies on COF design and synthesis for obtaining chemically stable COFs, we summarize the different experimental methodologies used for COFs processing in the form of supported and free-standing membranes and colloids. Finally, we describe the use of COFs in processes involving the detection of pollutants in water and wastewater treatment, such as the capture of organic compounds, heavy metals, and dyes, the degradation of organic pollutants, as well as in desalination processes. Finally, we provide a perspective on the field and the potential technological use of these novel materials.