Multifunctional Bacterial Cellulose/Covalent Organic Framework Composite Membranes with Antifouling and Antibacterial Properties for Dye Separation.

Decoupling synthesis and crystallization of covalent organic frameworks (COFs) for more crystalline layer targeting high efficiency dye separation

Interfacial polymerized and pore-variable covalent organic framework composite membrane for dye separation

Covalent organic frameworks (COFs) are crystalline and porous organic materials attractive for photocatalysis applications due to their structural versatility and tunable optical and electronic properties. The use of photocatalysts (PCs) for polymerizations enables the preparation of well-defined polymeric materials under mild reaction conditions. Herein, we report two porphyrin-based donor–acceptor COFs that are effective heterogeneous PCs for photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT). Using density functional theory (DFT) calculations, we designed porphyrin COFs with strong donor–acceptor characteristics and delocalized conduction bands. The COFs were effective PCs for PET-RAFT, successfully polymerizing a variety of monomers in both organic and aqueous media using visible light (λmax from 460 to 635 nm) to produce polymers with tunable molecular weights (MWs), low molecular weight dispersity, and good chain-end fidelity. The heterogeneous COF PCs could also be reused for PET-RAFT polymerization at least 5 times without losing photocatalytic performance. This work demonstrates porphyrin-based COFs that are effective catalysts for photo-RDRP and establishes design principles for the development of highly active COF PCs for a variety of applications.

The efficient preparation of two-dimensional large-sized monolayer covalent organic framework (COF) nanosheets for highly permeable membranes has posed a long-standing challenge in the COF field. While the self-exfoliation of charged COFs represents a promising method for nanosheet production, its efficiency requires further enhancement. In this study, we present a novel finding that the presence of hydroxyl groups on the monomer significantly influences the self-exfoliation efficiency of charged COFs. Through precise regulation of hydroxyl group numbers on the monomers, we successfully achieved the efficient fabrication of large monolayer cationic COF nanosheets with impressive solubilities in common organic solvents. By virtue of their positive charge, COF monolayer nanosheets rapidly interacted with negatively charged monolayer graphene oxide (GO) in solution, facilitating their assembly into interlaced composite membranes through electrostatic interactions. The composite membranes benefited from the strong Coulombic attraction between the COF and GO nanosheets, leading to enhanced membrane stability, while the shielding effect of GO on the COF pores contributed to improved size sieving efficiency. This innovative strategy enabled the composite membranes to achieve highly selective separation of ReO4- and MoO42-, with a remarkable 100% interception rate for MoO42-.

Sustainable synthesis of thin film composite covalent organic framework membranes using dual bio-derived solvents

A room-temperature solution phase reaction was developed to synthesize a covalent organic framework (COF) for the first time. The synthesized azodioxy-linked porphyrin-based COF (POR-COF) possesses a 2D chess board-like structure in the ab-plane and a 1D channel with an open-window size of around 1.9 nm along the c-axis in the modeled crystal structure. The electrical conductivity of POR-COF increases by more than 3 orders of magnitude through I2 doping. The photoconductivity of the I2-doped COF material was also studied firstly. POR-COF shows interesting doping-enhanced photo-current generation.

Introduction Nitrogen-doped carbon materials have been attracting great attention as one of the promising metal-free oxygen reduction reaction (ORR) catalysts due to the abundant resources, chemical stability, and high electronic conductivity, which could replace the high cost platinum-based materials limiting expansion of application fields of the fuel cells. Generally, nitrogen-doped carbons have been prepared by chemical vapor deposition with precursors containing nitrogen (pyridine or acetonitrile, etc.)[i], or by thermal/plasma treatment using graphitic carbons.[ii] The active site of nitrogen-doped carbons is yet controversial, though it has been suggested that incorporation of nitrogen atoms in the sp2 carbon network structures enhances ORR activity through active site formation by produced pyridinic N or graphitic N.1 Together with the nitrogen doped structures, the amount of the doped nitrogen atoms, surface area and degrees of graphitization can affect the ORR performance[iii] and control techniques of these factors are crucial to achieve the higher catalytic activity. Herein we fabricated the nitrogen-doped carbon from covalent organic frameworks (COFs) which have molecularly-ordered structures constructed by covalent linkage of organic building blocks. Due to the above unique structures and properties, COFs are promising for potential applications in gas storage, optoelectronic devices and catalysis.[iv] In this study, we focus on the structural features of COFs, which are versatile molecular design based on various combination of the building block molecules and the covalent bonding and highly porous structures. Thus we have been examining carbonization of COFs having hetero atoms such as N and B to create hetero atom doped carbon materials from the molecularly-ordered starting materials, COFs. Herein we synthesized two types of the nitrogen atom-containing COFs as the precursors. After carbonization, we found that the nitrogen-doped porous carbons were fabricated with high surface areas. The obtained materials would be useful to examine the effect of structural differences of the resulting nitrogen-doped structures on ORR activity to develop highly active carbon catalysts. Experiment Synthesis of COF1[v]Benzene-1,3,5-tricarboxylate (1, 24 mg) and phenylendiamine (2, 24 mg) were dissolved in dioxane (2.5 ml), respectively. After mixing the solutions, 3.0 M aqueous acetic acid (0.25 ml) was added. Two-day storage at 25 °C was found to generate a precipitate, which was collected by filtration, then washed with acetone. The obtained solid was dried overnight in vacuo at 80 °C to provide a yellow powder (COF1). Synthesis of ACOF-1 1 (24 mg) and hydrazine (3, 19 ml) were dissolved in dioxane (1.0 ml). Then 6.0 M tetrafluoroacetic acid (0.13 ml) was added. The solution was heated at 120 °C in a pressure resistant vessel yielding a precipitate, which was collected by filtration, then washed with acetone. The obtained solid was dried overnight in vacuo at 80 °C to provide a pale yellow powder (ACOF-1). Carbonization of COFs The obtained COF1 and ACOF-1 were heated at 800 °C for 3 h under N2 flow. Result and Discussion The XRD patterns of the obtained COFs show obvious diffraction peaks, which indicate crystalline structure formation. For porous structure investigation, N2 gas adsorption measurements were conducted. Based on the BET analysis, the surface area of COF1 and ACOF-1 were estimated to be 1528 m2/g and 1484 m2/g respectively. These results reveal that the prepared COFs have highly ordered structures with large surface areas. After carbonization of the both COFs, in Raman spectra, two peaks were observed at around 1300 cm-1 and 1590 cm-1, which are attributed to D band and G band of graphitic carbon structures. From deconvoluted XPS spectra of the N1s, three peaks were observed at 398, 400, and 402 eV ascribable to pyridinic, pyrrolic, and graphitic N. The results exhibit that the carbonized COFs have nitrogen-doped graphitic structures. The BET surface area of the carbonized COF1 and the carbonized ACOF-1 were calculated to be 538 m2/g and 1257 m2/g, respectively. Interestingly, the carbonized ACOF-1 showed a similar surface area to one before carbonization. This result indicates that COFs would be capable of producing porous carbon structures. The electrocatalytic properties of the carbonized ACOF-1 for ORR were investigated by cyclic voltammetry (CV) in 0.1M KOH saturated with N2 or O2 gas. Though no peak was observed in a N2 atmosphere condition, a significant reduction peak appeared at -0.198 V under an O2 atmosphere, which indicates ORR catalytic activity from the material. [i] M. Kawaguchi et al. Chem. Mater. 1996, 8, 1197. [ii] X. Wang et al. Science, 2009, 324, 768. [iii] C. H. Choi et al. ACS nano, 2 012, 6, 7084. [iv] A. P. Cote et al. Science, 2005, 310, 1166. [v] T. Shiraki et al. Chem. Lett. 2015, 44, 1488. Figure 1

Network interpenetration plays a crucial role in functionalizing porous framework materials. However, controlling the degree of interpenetration in covalent organic frameworks (COFs) to influence their pore sizes, shapes, and functionalities still remains a significant challenge. Here, we demonstrate a steric tuning strategy to control the degree of COF interpenetration and modulate their physicochemical properties. By imine condensations of 1,1'-bi-2-naphthol-derived tetraaldehydes bearing different alkyl substituents with the monomer tetra(p-aminophenyl)-methane, we synthesized and characterized a family of two-component and three-component chiral COFs with different interpenetrated dia networks. The alkyl groups are periodically appended on the pore walls, and their types/contents that can be synthetically tuned control the interpenetration degree of COFs by minimizing repulsive interactions between the alkyl groups. Specifically, the COF with -OH groups adopts an interpenetrated dia-c5 topology, those with -OMe/-OEt groups take an interpenetrated dia-c4 topology, whereas those with the bulky -OnPr/-OnBu groups exhibit a noninterpenetrated dia-c1 topology. The multivariate COFs with both -OH and -OnBu groups display either a noninterpenetrated or dia-c5 topology, depending on the proportion of -OnBu groups. The extent of interpenetration in COFs significantly affects their porosity, thermal stability, and chemical stability, resulting in varying selective performances in the adsorption and separation of dyes and asymmetric catalysis. This work highlights the potential of using steric hindrance to tune and control interpenetration, porosity, stability, and functionalities of COFs materials, broadening the range of their applications.

Aheteropore covalent organic framework (COF)-based composite membrane material was prepared and proved to have a satisfactory effect on the pretreatment of vegetable samples. Thecomposite membrane was fabricated by in situ growth of a dual-pore COF on the surface of polydopamine (PDA)-aminated non-woven (NW) fabric. Due to the difference in the strength of the interaction between the phytochromes/COF and the pesticides/COF, the removal of phytochromes and the recovery of pesticides can be achieved by adjusting the composition of the solution. Through a simple immersion or filtration operation, NW@PDA@COF composite membrane can quickly and almost completely remove interfering phytochromes in the samples. The recovery of pesticides was determinedby HPLC-MS/MS, and the recovery efficiencies were 72.3~101.7% and 67.3~106.7% for immersion and filtration modes of five different vegetable samples, respectively; theRSD is between 1.1 and 19% (n= 3). The limits of detection and quantification for the 13 pesticides investigatedwere 0.08μg·L-1 and 0.23μg·L-1, respectively. A wide linear range of 1~1000μg·L-1 was observed with R2 values from 0.9774 to 0.9998. The membrane can be repeatedly used for at least 10 times by using a facile elution treatment. Compared to other commonly used sample pretreatment materials, heteropore COF-based composite membrane is superior in terms of sorbent amount, treatment time, operation simplicity, and material reusability.

The treatment of wastewater containing organic dyes is an urgent environmental challenge, necessitating the development of advanced functional adsorbents. In this study, three covalent organic frameworks (COFs) with tailored pore sizes were synthesized from benzotrithiophene tricarboxaldehyde and different diamine linkers-benzidine, naphthalene-1,4-diamine, and p-phenylenediamine. These COFs were grown in situ onto UiO-66-NH2 to construct core-shell MOF@COF composites. The materials were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their adsorption performance toward Congo Red (CR), Rhodamine B (RB), and Malachite Green (MG) was systematically evaluated to clarify the influence of COF building units. The composites retained the chemical stability and hydrophobicity of the COF shell while overcoming the instability typical of pristine MOFs. Among them, UiO-66-NH2@BTT-BZ-COF1 exhibited the highest adsorption capacities-2228.6 mg g-1 for MG, 2037.2 mg g-1 for RB, and 1503.7 mg g-1 for CR-and could be reused for at least five cycles, demonstrating promising potential for dye removal applications.

Desalination behavior of composite membrane with petal shaped pore—formed by superimposition of covalent organic framework with large aperture difference

Stringing covalent organic framework particles for preparing highly loaded mixed-matrix membranes for efficient and precise dye separation

Crown ethers are a class of macrocyclic molecules with unique flexible structures but they are rarely integrated in covalent organic frameworks (COFs). To date, employing flexible organic units such as crown ethers to construct COFs with high crystallinity and surface area are still a challenge. In this work, two new COFs with different flexible crown ethers as backbone rather than side chains are synthesized and further employed for alkali metal ions separation. Both of COFs possess high surface areas, good crystallinity, and excellent chemical stability. Interestingly, these two new COFs with 18‐crown‐6 or 24‐crown‐8 units showed remarkable binding ability of K+ or Cs+ owing to the size‐fit effect. This work demonstrated that the unique structural features of crown ethers will lead to increase interest in fabricating COFs with crown ethers.

Covalent organic frameworks (COFs) have been recognised as an excellent candidate for gas-phase storage, separation and catalysis due to their high porosity and stability and has been explored as a versatile and robust molecular platform, but the use of interchangeable substituents to enhance porosity and stability while retaining a functional framework has yet to be deeply explored. Herein, we report the properties and synthesis of a fluorinated COF, showing improved porosity as well as modifiable linkers for modular functionality. This was accomplished via imine condensation between a non-fluorinated monomer (5,10,15,20-tetrakis (4-aminophenyl)porphyrin) and a fluorinated monomer (2,3,5,6-tetrafluoroterephthaldehyde) to produce the COF in good yield. This compound was then compared with related COFs in a two-way comparison to relate their properties, such as the non-fluorinated analogues of the porphyrin-based COF, as well as COFs incorporating tris(aminophenyl)benzene. Upon analysis with PXRD and UV–Vis spectroscopy, correlating UV–Vis absorbance with pore size and thus porosity, it was concluded that the incorporation of fluorine in the compound indeed resulted in higher porosity in the products, possibly owing to the formation of electron-deficient tetrafluorobenzene centres in the COF, inducing coordination with the electron-rich porphyrin and triphenylbenzene units.

Identifying facile strategies for hierarchically structuring crystalline porous materials is critical for realizing diffusion length scales suitable for broad applications. Here, we elucidate synthesis-structure-function relations governing how room temperature catalytic conditions can be exploited to tune covalent organic framework (COF) growth and thereby access unique hierarchical morphologies without the need to introduce secondary templates or structure directing molecules. Specifically, we demonstrate how scandium triflate, an efficient catalyst involved in the synthesis of imine-based COFs, can be exploited as an effective growth modifier capable of selectively titrating terminal amines on 2D COF layers to facilitate anisotropic crystal growth. We systematically map a compositional pseudo-phase space and uncover key mechanistic insights governing the catalyst-derived evolution of globular COFs with sub-micron diffusion length scales into unique rosette structures. Comprised of interconnected, high-aspect-ratio crystalline porous sheets of only several unit cells in thickness, the resulting COFs offer orders of magnitude reduction in diffusion length scales and several-fold increase in external surface area, enabling rapid uptake of bulky dyes. Generally, the resulting synthesis-structure-function relations hold promise for realizing unique control over COF mesostructure, morphology, and function.