Targeted synthesis of a 2D ordered porous organic framework for drug release

Solving the COF trilemma: towards crystalline, stable and functional covalent organic frameworks

Strategies in covalent organic frameworks and adjacent fields are highlighted for designing stable, ordered and functional materials.

Ultrafine Rh nanoparticles confined by nitrogen-rich covalent organic frameworks for methanolysis of ammonia borane

An Rh/PC-COF was synthesized using a metal–nitrogen coordination reduction strategy and was applied as a highly efficient catalyst for methanolysis of ammonia borane.

Facile Fabrication of Redox-Responsive Covalent Organic Framework Nanocarriers for Efficiently Loading and Delivering Doxorubicin

Covalent organic frameworks (COFs) as drug delivery systems have shown great promise, but their pharmaceutical applications are often limited by complex building blocks, tedious preparations, irregular shape, and uncontrolled drug release within target cells. Herein, a facile strategy is developed to prepare PEGylated redox-responsive nanoscale COFs (denoted F68@SS-COFs) for efficiently loading and delivering doxorubicin (DOX) by use of FDA-approved Pluronic F68 and commercially available building blocks. The obtained F68@SS-COFs with controlled size, high stability, and good biocompatibility can not only achieve a very high DOX-loading content (about 21%) and very low premature leakage at physiological condition but can also rapidly respond to the tumor intracellular microenvironment and efficiently release DOX to kill tumor cells. Considering the readily available raw materials, simple preparation process, and desirable redox-responsiveness, the strategy provided here opens up a promising avenue to develop well-defined COFs-based nanomedicines for cancer therapy.

Enabling Covalent Organic Framework Nanofilms for Molecular Separation: Perforated Polymer-Assisted Transfer

Covalent organic frameworks (COFs) with ordered arrays of sub-2 nm regular pores are drawing increasing attention in membrane separation, and it remains highly desirable for effective and controllable strategies to fabricate COF-based membranes. Herein, we demonstrate a perforated polymer-assisted transfer strategy enabling COF nanofilms for molecular separation. Solvothermal synthesis is used for the confined growth of TpPa, a stable, imine-linked COF, on the smooth surfaces of silicon substrates. Continuous, crystalline COF nanofilms are obtained, and their thicknesses are tunable in the range from a few tens to several hundred nanometers depending on monomer concentrations and reaction time. A block copolymer layer is coated on the COF nanofilms, which is then perforated to produce interconnected mesopores by the mechanism of selective swelling-induced pore generation. The perforated polymer coating functions as a protective but permeable layer enabling the easy transfer of the COF nanofilm onto porous substrates. Thus, we obtain a new type of composite membranes with the microporous COF nanofilm as the selective layer, sandwiched between the macroporous substrate and the mesoporous protective layer. The composite membranes exhibit good separation performances with water permeance up to ∼51 L m^-2 h^-1 bar^-1 and high rejection rates to various dyes. This work demonstrates a new method to prepare COF-based membranes for molecular separation, and the invented perforated polymer-assisted transfer technology is expected to find applications in transferring other ultrathin materials to demanded substrates.

Triazine-Based Covalent Organic Framework: A Promising Sorbent for Efficient Elimination of the Hydrocarbon Backgrounds of Organic Sample for GC-MS and 1H NMR Analysis of Chemical Weapons Convention Related Compounds

The strict monitoring and precise measurements of chemical warfare agents (CWAs) in environmental and other complex samples with high accuracy have great practical significance from the forensic and Chemical Weapons Convention (CWC) verification point of view. Therefore, this study was aimed to develop an efficient extraction and enrichment method for identification and quantification of toxic agents, especially with high sensitivity and multidetection ability in complex samples. It is the first study on solid-phase extraction (SPE) of CWAs and their related compounds from hydrocarbon backgrounds using covalent triazine-based frameworks (CTFs). This nitrogen-rich CTF sorbent has shown an excellent SPE performance toward sample cleanup by selective elimination of hydrocarbon backgrounds and enrich the CWC related analytes in comparison with the conventional and other reported methods. The best enrichment of the analytes was found with the washing solvent (1 mL of n-hexane) and the extraction solvent (1 mL of dichloromethane). Under the optimized conditions, the SPE method had good linearity in the concentration range of 0.050-10.0 μg mL^-1 for organophosphorus esters, 0.040-20.0 μg mL^-1 for nerve agents, and 0.200-20.0 μg mL^-1 for mustards with correlation coefficients ( r²) between 0.9867 and 0.9998 for all analytes. Limits of detection ( S/ N = 3:1) in the SIM mode were found to be in the range of 0.015-0.050 μg mL^-1 for organophosphorus esters, 0.010-0.030 μg mL^-1 for nerve agents, and 0.050-0.100 μg mL^-1 for blister agents. Limits of quantification ( S/ N = 10:1) were found in the range of 0.050-0.200 μg mL^-1 for organophosphorus esters, 0.040-0.100 μg mL^-1 for nerve agents, and 0.180-0.350 μg mL^-1 for blister agents in the SIM mode. The recoveries of all analytes ranged from 87 to 100% with the relative standard deviations ranging from 1 to 8%. This method was also successfully applied for the sample preparation of ¹H NMR analysis of sulfur and nitrogen mustards in the presence of hydrocarbon backgrounds. Therefore, this SPE method provides the single sample preparation for both NMR and GC-MS analyses.

Determination of Six Macrolide Antibiotics in Chicken Sample by Liquid Chromatography-Tandem Mass Spectrometry Based on Solid Phase Extraction

In this paper, a simple and effective method for the determination of six macrolide antibiotics (MACs), including tylosin, tilmicosin, azithromycin, clarithromycin, roxithromycin, and kitasamycin, in the chicken sample using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed based on a self-built porous aromatic framework- (PAF-) based solid phase sorbent. The main parameters influencing the extraction efficiency, such as sorbent amounts, type of the eluent, pH of the sample, and the eluent volume, were evaluated. Under the optimized condition, the limits of detection were from 0.2 to 0.5 μg·kg^-1. The recoveries of the method ranged from 82.1% to 101.4% with the relative standard deviations less than 11.1%. All the results demonstrated that the established method is potential for the determination of macrolide antibiotics in food safety analysis and monitoring.

Cobalt, Nitrogen-Doped Porous Carbon Nanosheet-Assembled Flowers from Metal-Coordinated Covalent Organic Polymers for Efficient Oxygen Reduction

The breakthrough of nonprecious metal catalysts replacing platinum-based catalysts toward the oxygen reduction reaction (ORR) is extremely urgent for the development of high-efficiency energy conversation systems. Herein, a solution-processed condensation polymerization using cyanuric chloride and piperazine as the monomers was proposed for the synthesis of a nitrogen-rich covalent organic polymer (COP). High contents of precisely tailored pyridinic-N within the COP facilitate the formation of the Co/N coordination between Co ions and N species. As a result, the subsequent carbonization of the Co-coordinated COP led to the formation of the cobalt, nitrogen dual-doped porous carbon nanosheet-assembled flowers (Co/N-PCNF). The as-obtained Co/N-PCNF catalyst with a nearly 4-electron oxygen reduction pathway exhibits an excellent ORR catalytic activity with a half-wave potential of 0.835 V comparable to the commercial Pt/C catalysts (0.865 V). Most impressively, the Co/N-PCNF catalyst displays a long-term stability and a much better resistance to methanol than the Pt/C catalyst because of its high surface area, well-defined porous structure, and homogeneous distributions of active sites within the carbon matrix. Therefore, this work establishes an operating rule for tailored synthesis of COP-derived nonprecious metal catalysts offering high activity for the ORR in electrochemical energy conversations.

Efficient enrichment of triazole fungicides from fruit and vegetable samples by a spherical porous aromatic framework

A porous aromatic framework was synthesized and utilized as a novel SPME coating for efficient enrichment of triazole fungicides.

Recent progress in covalent organic framework thin films: fabrications, applications and perspectives

As a newly emerging class of porous materials, covalent organic frameworks (COFs) have attracted much attention due to their intriguing structural merits (e.g., total organic backbone, tunable porosity and predictable structure). However, the insoluble and unprocessable features of bulk COF powder limit their applications. To overcome these limitations, considerable efforts have been devoted to exploring the fabrication of COF thin films with controllable architectures, which open the door for their novel applications. In this critical review, we aim to provide the recent advances in the fabrication of COF thin films not only supported on substrates but also as free-standing nanosheets via both bottom-up and top-down strategies. The bottom-up strategy involves solvothermal synthesis, interfacial polymerization, room temperature vapor-assisted conversion, and synthesis under continuous flow conditions; whereas, the top-down strategy involves solvent-assisted exfoliation, self-exfoliation, mechanical delamination, and chemical exfoliation. In addition, the applications of COF thin films including energy storage, semiconductor devices, membrane-separation, sensors, and drug delivery are summarized. Finally, to accelerate further research, a personal perspective covering their synthetic strategies, mechanisms and applications is presented.

Ultrafine Ag Nanoparticles Encapsulated by Covalent Triazine Framework Nanosheets for CO2 Conversion

This paper describes the fabrication of covalent triazine framework nanosheet-encapsulated Ag nanoparticles (Ag⁰@CTFN) via a simple combination of the ultrasonic exfoliation and solution infiltration method. The as-prepared Ag⁰@CTFN displays an order layered-sheet structure with abundant micropores and mesopores, whereas ultrafine Ag nanoparticles are confined and stabilized in their interlayers through the interaction between N sites of triazine units and Ag nanoparticles. Considering that the Ag⁰@CTFN possesses the merits of high nitrogen, low density, and abundant basic sites, it was thus believed to have enough abilities to adsorb and activate CO₂ in the CO₂ conversion and catalysis. Importantly, the Ag⁰@CTFN, as a heterogeneous catalyst, showed highly catalytic activity in the carboxylation of various alkynes with CO₂ at ambient pressure and low temperature. This catalyst also exhibited good functional group tolerance and excellent stability without any significant loss of its activity after six recycles. This work not only achieves valuable and novel composite material but also provides the first application of covalent triazine framework nanosheets in chemical conversion of CO₂, opening a new field in preparing recyclable heterogeneous catalysts to accelerate the utilization of CO₂.

Recent Trends in Covalent and Metal Organic Frameworks for Biomedical Applications

Materials science has seen a great deal of advancement and development. The discovery of new types of materials sparked the study of their properties followed by applications ranging from separation, catalysis, optoelectronics, sensing, drug delivery and biomedicine, and many other uses in different fields of science. Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) are a relatively new type of materials with high surface areas and permanent porosity that show great promise for such applications. The current study aims at presenting the recent work achieved in COFs and MOFs for biomedical applications, and to examine some challenges and future directions which the field may take. The paper herein surveys their synthesis, and their use as Drug Delivery Systems (DDS), in non-drug delivery therapeutics and for biosensing and diagnostics.

Soluble Hyperbranched Porous Organic Polymers

Soluble porous organic polymers (SPOPs) are currently the subject of extensive investigation due to the enhanced processability compared to insoluble counterparts. Here, a new concept for the construction of SPOPs is presented, which combines the unique topological structure of hyperbranched polymers with rigid building blocks. By using this facile, one-step strategy, a class of novel SPOPs which possess surface areas up to 646 m² g^-1 have been synthesized. The extended π-conjugated backbone affords the polymers bright fluorescence under UV irradiation. Interestingly, after dissolution in a suitable solvent that was slowly evaporated, the polymers retain a large extent of porosity. The SPOPs are potential candidates for gas storage and separation, photovoltaic, and biological applications. In particular, due to the presence of an internal porous structure and open conformations, they show high drug loading efficiency (1.91 g of ibuprofen per gram), which is considerably higher than conventional porous organic polymers.

Porous Organic Polymer-Derived Carbon Composite as a Bimodal Catalyst for Oxygen Evolution Reaction and Nitrophenol Reduction

Ethylene diamine-based porous organic polymer (EPOP) was synthesized, carbonized at different temperatures, and characterized. The successful formation of the triazine polymer was confirmed by Fourier-transform infrared spectroscopy, ¹³C, and ¹⁵N cross-polarization magic angle spinning solid-state NMR. The two-dimensional layered architecture and graphitic nature of the samples resembled that of nitrogen-doped amorphous carbon, as confirmed by Raman, powder X-ray diffraction, and transmission electron microscopy measurements. The catalytic activity of these materials toward nitrophenol reduction and electrocatalytic activity toward oxygen evolution reaction (OER) were systematically evaluated in detail. Electrocatalytic activity toward oxygen evolution reaction was systematically evaluated by chronoamperometry and linear sweep voltammetry. Results clearly demonstrate that all of these catalysts exhibit good OER activity and excellent stability. Among all catalysts, EPOP-700 showed better OER activity, as reflected by its onset potential and current density, comparable with that of the metal-based OER catalysts and better than that of metal-free catalysts. Further, their catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol was tested with NaBH₄; although all of these catalysts showed good catalytic activity; EPOP-800 displayed better catalytic activity.

A nanoscale porous glucose-based polymer for gas adsorption and drug delivery

A glucose-based nanoporous organic polymer with the –OH group shows significant CO₂ uptake capacities and good drug release behaviour.

Folate decorated hollow spheres of microporous organic networks as drug delivery materials

Hollow and microporous organic networks post-modified with folic acids showed promising potential as DOX delivery materials.

Microextraction of polycyclic aromatic hydrocarbons by using a stainless steel fiber coated with nanoparticles made from a porous aromatic framework

A porous aromatic framework of type PAF-6 was synthesized and explored as a coating onto a steel wire for using in solid-phase microextraction of polycyclic aromatic hydrocarbons (PAHs), phthalate plasticizers, and n-alkanes. The extraction temperature, extraction time, salt concentration, agitation speed, desorption temperature, and desorption time were optimized. This method for SPME resulted in the enrichment factors ranging from 122 to 1090 for PAHs (naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene), from 122 to 271 for plasticizers (diisobutyl phthalate, dibutyl phthalate, benzyl butyl phthalate, dicyclohexyl phthalate), and from 9 to 113 for n-alkanes (n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-octadecane and n-eicosane). The good extraction of the PAHs is assumed to be due to their π-stacking interaction and hydrophobic effect. The PAF-6 coated fibers are durable and can be reused more than 100 times without significant loss of extraction performance. In combination with GC-MS detection, the method has limits of detection in the range from 0.8 to 4.2 ng L^-1 in case of PAHs. The relative standard deviations for five replicate determinations of the PAHs by using one fiber are in the range from 5.2 to 8.5%. When using different fibers, they range from 7.1 to 9.6%. The recoveries of PAHs from water samples at a spiking level of 20 ng L^-1 are in the range from 89.5 to 103.1%, with relative standard deviations ranging from 4.0 to 9.3%. Graphical abstract A porous aromatic framework of type PAF-6 was synthesized and used as a novel coating for the solid-phase microextraction of polycyclic aromatic hydrocarbons prior to their determination by gas chromatography with mass spectrometric detection.

Imparting Catalytic Activity to a Covalent Organic Framework Material by Nanoparticle Encapsulation

Integrating covalent organic frameworks (COFs) with other functional materials is a useful route to enhancing their performances and extending their applications. We report herein a simple encapsulation method for incorporating catalytically active Au nanoparticles with different sizes, shapes, and contents in a two-dimensional (2D) COF material constructed by condensing 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dimethoxyterephthaldehyde (DMTP). The encapsulation is assisted by the surface functionalization of Au nanoparticles with polyvinylpyrrolidone (PVP) and follows a mechanism based on the adsorption of nanoparticles onto surfaces of the initially formed polymeric precursor of COF. The incorporation of nanoparticles does not alter obviously the crystallinity, thermal stability, and pore structures of the framework matrices. The obtained COF composites with embedded but accessible Au nanoparticles possess large surface areas and highly open mesopores and display recyclable catalytic performance for reduction of 4-nitrophenol, which cannot be catalyzed by the pure COF material, with activities relevant to contents and geometric structures of the incorporated nanoparticles.

Fabrication of Palladium Nanoparticles on Porous Aromatic Frameworks as a Sensing Platform to Detect Vanillin

Here, we report the fabrication of palladium nanoparticles on porous aromatic frameworks (Pd/PAF-6) using a facile chemical approach, which was characterized by various spectro- and electrochemical techniques. The differential pulse voltammetry (DPV) response of Pd/PAF-6 toward the vanillin (VA) sensor shows a linear relationship over concentrations (10-820 pM) and a low detection limit (2 pM). Pd/PAF-6 also exhibited good anti-interference performance toward 2-fold excess of ascorbic acid, nitrophenol, glutathione, glucose, uric acid, dopamine, ascorbic acid, 4-nitrophenol, glutathione, glucose, uric acid, dopamine, and 100-fold excess of Na(+), Mg(2+), and K(+) during the detection of VA. The developed electrochemical sensor based on Pd/PAF-6 had good reproducibility, as well as high selectivity and stability. The established sensor revealed that Pd/PAF-6 could be used to detect VA in biscuit and ice cream samples with satisfactory results.

Recent Advances in Boron-Containing Conjugated Porous Polymers

Porous polymers, integrating the advantages of porous materials and conventional polymers, have been well developed and exhibited tremendous attention in the fields of material, chemistry and biology. Of these, boron-containing conjugated porous polymers, featuring tunable geometric structures, unique Lewis acid boron centers and very rich physical properties, such as high specific surface, chargeable scaffold, strong photoluminescence and intramolecular charge transfer, have emerged as one of the most promising functional materials for optoelectronics, catalysis and sensing, etc. Furthermore, upon thermal treatment, some of them can be effectively converted to boron-doped porous carbon materials with good electrochemical performance in energy storage and conversion, extensively enlarging the applicable scope of such kinds of polymers. In this review, the synthetic approaches, structure analyses and various applications of the boron-containing conjugated porous polymers reported very recently are summarized.

Porous Covalent Triazine Polymer as a Potential Nanocargo for Cancer Therapy and Imaging

A microporous covalent triazine polymer (CTP) network with a high surface area was synthesized via the Friedel-Crafts reaction and employed as a potential transport system for drug delivery and controlled release. The CTP was transformed to the nanoscale region by intense ultrasonication followed by filtration to yield nanoscale CTP (NCTP). This product showed excellent dispersibility in physiological solution while maintaining its chemical structure and porosity. An anticancer drug, doxorubicin (DOX), was loaded onto the NCTP through hydrophobic and π-π interactions, and its release was controlled at pH 4.8 and 7.4. The NCTP showed no toxicity toward cancer or normal cells, but the NCTP-DOX complex showed high efficacy against both types of cells in vitro. In-vitro cell imaging revealed that NCTP is a potential material for bioimaging. The potency of NCTP on cellular senescence was confirmed by the expression of senescence associated marker proteins p53 and p21. These results suggest that NCTP can be used as a new platform for drug delivery and imaging with potential applications in diagnosis and therapy.

Preparation and engineering of oriented 2D covalent organic framework thin films

Hybrid metal/COF stack multilayers and patterned COF films were fabricated via the flexible combination of solvothermal deposition and compatible film processing techniques.

Modifiable diyne-based covalent organic framework: a versatile platform for in situ multipurpose functionalization

A COF material (TCD) containing diynes as both building blocks and active sites was prepared by microwave irradiation and employed as a versatile platform for the preparation of diverse functional materials.

A bifunctional cationic porous organic polymer based on a Salen-(Al) metalloligand for the cycloaddition of carbon dioxide to produce cyclic carbonates

A Salen-(Al)-based bifunctional cationic porous organic polymer (Al-CPOP) exhibited high activity and good recyclability for chemical fixation of CO₂.

Nanoscale porous triazine-based frameworks with cyanate ester linkages for efficient drug delivery

An easy modulation of the pore size of cyanate ester resins allows amount of inserted drug and its release behavior that depend on pore size and host–drug interactions rather than the surface controllable.

Synthesis of copper nanoparticles supported on a microporous covalent triazine polymer: an efficient and reusable catalyst for O-arylation reaction

Cu NPs immobilized on a microporous covalent triazine polymer obtained by a cost-effective synthesis method were evaluated as a catalyst for Ullmann coupling of O-arylation.