Multivariate covalent organic frameworks guided carboxyl functionalized magnetic adsorbent for enrichment of fluoroquinolones in milk prior to high performance liquid chromatographic analysis

Herein, we prepared a carboxyl functionalized magnetic covalent organic framework (Fe3O4@iCOF-COOH) by combining multivariate synthetic strategy with post-synthetic modification. It was used as an adsorbent for magnetic solid phase extraction (MSPE) of six fluoroquinolones (FQs), and showed good absorption performance at neutral pH. Carboxyl groups are found to be crucial for the adsorption of fluoroquinolones. The adsorption mechanism was primarily attributed to strong hydrogen bonding, π-π interaction as well as potential hydrophobic effect. The optimal extraction conditions are sample pH at 6.0, adsorbent dosage of 3 mg, eluent of 1.0 mL methanol solution containing 7.5% ammonia, and extraction/desorption time of 30 min. Under the optimized conditions, the Fe3O4@iCOF-COOH was used as an adsorbent for MSPE of FQs in milk, an analytical method was established by combining with high-performance liquid chromatography-ultraviolet detection (HPLC-UV). The limits of detection (LODs) and limit of quantification (LOQs) were 1.24-4.58 ng⋅mL-1 and 4.12-15.3 ng⋅mL-1, respectively. The recoveries of target FQs in spiked milk were 68.4-105%. This work provides a new way to prepare covalent organic framework based adsorbents for solid phase extraction, and can be readily extended to other type of adsorbents.

Ratiometric Detection of Ochratoxin A Using a Regenerable COF-Au-MB-Apt Signal Probe on a Thermal-Regulated Sensor Module

Ochratoxin A (OTA) frequently contaminates grains and consequently threatens human health. Herein, we develop a regenerable signal probe and apply it to a Au-based screen-printed electrode module (SPE) for OTA determination. The signal probe, containing a structural covalent organic framework, gold nanoparticles (AuNPs), indicative methylene blue (MB), and a highly selective aptamer, is synthesized with hydrothermal and self-assembly methods. The SPE is permanently functionalized with Prussian blue (PB), AuNPs, and semicomplementary ssDNA. The signal probe, absorbed onto this SPE via hybridization, is competitively expelled by OTA, providing a ratiometric readout of ΔIMB/IPB. Probe regeneration, to erase expired COF-Au-MB-Apt after each analysis, is established with the synergy of OTA-conducted Apt-ssDNA dissociation and on-chip thermal regulation. This advantage powerfully guarantees reduplicative analyses by avoiding irreversible Apt-OTA combination and accumulation on the sensing interface. Regenerations are performed in repetitive cycles (N = 7) with 98.5% reproduction efficiency, and IMB and IPB fluctuations are calculated as 1.45 and 1.12%. This method shows log-linear OTA response in a wide range from 0.2 pg/mL to 0.6 μg/mL, and the limit of detection is 0.12 pg/mL. During natural OTA determinations, recommended readouts match well with HPLC with less than 4.82% relative error.

Covalent organic frameworks-based smart materials for mitigation of pharmaceutical pollutants from aqueous solution

Covalent organic frameworks (COFs) are an emergent group of crystalline porous materials that have gained incredible interest in recent years. With foreseeable controllable functionalities and structural configurations, the constructions and catalytic properties of these organic polymeric materials can be controlled to fabricate targeted materials. The specified monomer linkers and pre-designed architecture of COFs facilitate the post-synthetic modifications for introducing novel functions and useful properties. By virtue of inherent porosity, robust framework, well-ordered geometry, functionality, higher stability, and amenability to functionalization, COFs and COFs-based composites are regarded as prospective nanomaterials for environmental clean-up and remediation. This report spotlights the state-of-the-art advances and progress in COFs-based materials to efficiently mitigate pharmaceutical-based environmental pollutants from aqueous solutions. Synthesis approaches, structure, functionalization, and sustainability aspects of COFs are discussed. Moreover, the adsorptive and photocatalytic potential of COFs and their derived nanocomposites for removal and degradation of pharmaceuticals are thoroughly vetted. In addition to deciphering adsorption mechanism/isotherms, the stability, regeneratability and reproducibility are also delineated. Lastly, the outcomes are summed up, and new directions are proposed to widen the promise of COF-based smart materials in diverse fields.

Sustainable solid form screening: mechanochemical control over nucleobase hydrogen-bonded organic framework polymorphism

The choice is yours! Liquid-assisted grinding can be used to control HOF polymorphism.

Bio-adhesive Nanoporous Module: Toward Autonomous Gating

Here we report a bio-adhesive porous organic module (^Glue COF) composed of hexagonally packed 1D nanopores based on a covalent organic framework. The nanopores are densely decorated with guanidinium ion (Gu⁺ ) pendants capable of forming salt bridges with oxyanionic species. ^Glue COF strongly adheres to biopolymers through multivalent salt-bridging interactions with their ubiquitous oxyanionic species. By taking advantage of its strong bio-adhesive nature, we succeeded in creating a gate that possibly opens the nanopores through a selective interaction with a reporter chemical and releases guest molecules. We chose calmodulin (CaM) as a gating component that can stably entrap a loaded guest, sulforhodamine B (SRB), within the nanopores (^CaM COF⊃SRB). CaM is known to change its conformation on binding with Ca²⁺ ions. We confirmed that mixing ^CaM COF⊃SRB with Ca²⁺ resulted in the release of SRB from the nanopores, whereas the use of weakly binding Mg²⁺ ions resulted in a much slower release of SRB.

Cationic covalent-organic framework for sulfur storage with high-performance in lithium-sulfur batteries

Covalent organic frameworks (COFs) with pre-designed structure and customized properties have been employed as sulfur storage materials for lithium-sulfur (Li-S) batteries. In this work, a cationic mesoporous COF (COF-NI) was synthesized by grafting a quaternary ammonium salt group onto the pore channel of COFs via a one-pot three components tandem reaction strategy. The post-functionalized COFs were utilized as the matrix framework to successfully construct the Li-S battery with high-speed capacity and long-term stability. The experimental results showed that, after loading active material sulfur, cationic COF-NI effectively suppressed the shuttle effect of the intermediate lithium polysulfide species in Li-S batteries, and exhibited better cycle stability than the as-obtained neutral COF (COF-Bu). For example, compared with COF-Bu based sulfur cathode (521 mA h g^-1), the cationic COF-NI based sulfur cathode maintained a discharge capacity of 758 mA h g^-1 after 100 cycles. These results clearly showed that appropriate pore environment of COFs can be prepared by rational design, which can reduce the shuttle effect of lithium polysulfide species and improve the performance of Li-S battery.

Intrinsic proton conduction in 2D sulfonated covalent organic frameworks through a post-synthetic strategy

A 2D sulfonated COF showed intrinsic proton conductivity up to 10−3 at 25 °C and 100% relative humidity and high conductivity up to 10−2 S cm−1 at 70 °C and 100% RH.

Construction of covalent organic framework with unique double-ring pore for size-matching adsorption of uranium

The separation and recovery of key nuclides such as uranium and plutonium from effluents related to nuclear industry is of great significance for alleviating the shortage of nuclear energy resources and protecting the environment and human health. However, the high temperature, strong acidity and radioactivity of the nuclear effluents pose a severe challenge to the separation materials used in such conditions. The diversity of structure, flexibility of design, and excellent physicochemical stability of covalent organic framework materials (COFs) provide the possibility for the directional design and preparation of adsorbents for use under harsh conditions. Herein, three COFs with similar structure, different pore sizes and connecting modules were synthesized. The ingenious structure predesign enables Dp-COF to have three carboxyl groups oriented toward the pore center and laid out in appropriate spatial positions, which builds hydrogen-bonding bridges between carboxycarbonyl and hydroxyl groups, and thus constructs for the first time a unique COF material with a double-ring pore. The inner pore size of the "double-ring" is slightly larger than the diameter of uranyl hydrate, which leads to a size-matching adsorption of uranium by Dp-COF, thus greatly reducing the effect of protonation. Even in the simulated spent fuel reprocessing liquid with pH = 1.0, the adsorption capacity of Dp-COF for uranium can reach 66.3 mg g^-1, and the adsorption capacity reaches 317.3 mg g^-1 at pH = 4.5, which is very rare among the reported COFs. More excitingly, the removal rate for uranium reaches up to an unprecedented 99.8% due to the size-matching effect, more than any analogous adsorbents. This study not only proposes new ideas for the design and regulation of the microscopic configuration of COF materials, but also provides an alternative approach for the preparation of efficient uranium adsorbents.

Covalent Organic Frameworks: Design, Synthesis, and Functions

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures. Unlike other polymers, a significant feature of COFs is that they are structurally predesignable, synthetically controllable, and functionally manageable. In principle, the topological design diagram offers geometric guidance for the structural tiling of extended porous polygons, and the polycondensation reactions provide synthetic ways to construct the predesigned primary and high-order structures. Progress over the past decade in the chemistry of these two aspects undoubtedly established the base of the COF field. By virtue of the availability of organic units and the diversity of topologies and linkages, COFs have emerged as a new field of organic materials that offer a powerful molecular platform for complex structural design and tailor-made functional development. Here we target a comprehensive review of the COF field, provide a historic overview of the chemistry of the COF field, survey the advances in the topology design and synthetic reactions, illustrate the structural features and diversities, scrutinize the development and potential of various functions through elucidating structure-function correlations based on interactions with photons, electrons, holes, spins, ions, and molecules, discuss the key fundamental and challenging issues that need to be addressed, and predict the future directions from chemistry, physics, and materials perspectives.

Postsynthetic functionalization of covalent organic frameworks

Covalent organic frameworks (COFs) have been at the forefront of porous-material research in recent years. With predictable structural compositions and controllable functionalities, the structures and properties of COFs could be controlled to achieve targeted materials. On the other hand, the predesigned structure of COFs allows fruitful postsynthetic modifications to introduce new properties and functions. In this review, the postsynthetic functionalizations of COFs are discussed and their impacts towards structural qualities and performances are comparatively elaborated on. The functionalization involves the formation of specific interactions (covalent or coordination/ionic bonds) and chemical reactions (oxidation/reduction reaction) with pendant groups, skeleton and reactive linkages of COFs. The chemical stability and performance of COFs including catalytic activity, storage, sorption and opto-electronic properties might be enhanced by specific postsynthetic functionalization. The generality of these strategies in terms of chemical reactions and the range of suitable COFs places them as a pivotal role for the development of COF-based smart materials.

Crystalline quantum dots of covalent organic frameworks for fast and sensitive detection of uranium

A crystalline quantum dot of a COF was prepared for the first time by original BRB method for fast uranium detection.

Pore surface engineering of covalent organic frameworks: structural diversity and applications

Connecting molecular building blocks by covalent bonds to form extended crystalline structures has caused a sharp upsurge in the field of porous materials, especially covalent organic frameworks (COFs), thereby translating the accuracy, precision, and versatility of covalent chemistry from discrete molecules to two-dimensional and three-dimensional crystalline structures. COFs are crystalline porous frameworks prepared by a bottom-up approach from predesigned symmetric units with well-defined structural properties such as a high surface area, distinct pores, cavities, channels, thermal and chemical stability, structural flexibility and functional design. Due to the tedious and sometimes impossible introduction of certain functionalities into COFs via de novo synthesis, pore surface engineering through judicious functionalization with a range of substituents under ambient or harsh conditions using the principle of coordination chemistry, chemical conversion, and building block exchange is of profound importance. In this review, we aim to summarize dynamic covalent chemistry and framework linkage in the context of design features, different methods and perspectives of pore surface engineering along with their versatile roles in a plethora of applications such as biomedical, gas storage and separation, catalysis, sensing, energy storage and environmental remediation.

Unprecedented green-emissive boranyl-hydrazone supramolecular assemblies and their in vitro diagnostic applications

This paper describes a novel symmetric N,N'-diethylsalicylaldehyde boranyl hydrazone (1) and its in situ-generated assemblies displaying opto-analytical capabilities for the diagnosis of nucleic acids under physiological conditions. The sensing capabilities of these unprecedented supramolecular assemblies were characterized using UV-Vis spectroscopy, fluorescence spectroscopy, 1D and 2D NMR spectroscopy, dynamic light scattering, and zeta potential measurements. Model compounds lacking boranyl units (2, 3) were prepared to correlate and evaluate the sensing mechanism. The rationally designed probe 1 displays unusual aggregation-induced emissive (AIE) properties, with an average particle size of 1096 nm exhibiting green emission upon excitation at 377 nm in pH-7.2 TRIZMA buffer. A selective switch on response toward organic PO₄^3- accompanied through specific nano-aggregations patterns and sizes, thereby causing a significant red-shift through AIE. Exploiting such switch on in green channel behavior has allowed the monitoring of DNase I activities and polymerase chain reactions.

Recyclable magnetic covalent organic framework for the extraction of marine biotoxins

A novel procedure for the preparation of magnetic covalent organic frameworks (COFs) is reported. In situ functionalization of Fe3O4 with dopamine rapidly afforded amino-functionalized magnetic nanoparticles, which after decoration with a COF building block and subsequent COF growth gave access to magnetic composite mTpBD-Me2. The optimized synthesis conditions yielded crystalline and superparamagnetic material with no loss in surface area as compared to bulk COF. The composite material was employed for the first time in magnetic solid-phase extraction of marine biotoxins from seawater with high efficiency, where calculated maximum adsorption capacities of 812 mg g-1 and 830 mg g-1 were found for okadaic acid (OA) and dinophysistoxin-1 (DTX-1), respectively, corresponding to an increase of ∼500-fold for OA and ∼300-fold for DTX-1 as compared to the commonly used non-magnetic macroporous resins. Nearly quantitative desorption efficiency of both biotoxins was obtained using 2-propanol as solvent, rendering the composite materials recyclable with merely minor losses in adsorption capacity after five consecutive cycles of adsorption/desorption. In addition, retention of crystallinity after the adsorption cycles highlights the stability of the composite in seawater. These results illustrate the great efficiency of the novel material in biotoxin adsorption and show great promise for its application in environmental monitoring programs.

Polyaminoazide mixtures for the synthesis of pH-responsive calixarene nanosponges

Two mixtures of polyaminoazides were synthesized by a nucleophilic displacement strategy providing no separation of the components. The mixtures were adequately characterized by means of combined HR-ESIMS, FTIR and NMR techniques and, despite their complexity, they were successfully used to accomplish the subsequent preparation of pH-sensitive calixarene hyper-reticulated nanosponge materials. The desired responsivity to pH variations of the nanosponges obtained was verified by means of absorption tests on a set of organic pollutant model molecules.

Post-synthetic modification of covalent organic frameworks

This review is aimed at providing an in-depth understanding of the potential of post-synthetic strategies for the modification of covalent organic frameworks.

Switching acidic and basic catalysis through supramolecular functionalization in a porous 3D covalent imine-based material

Non-covalent inclusion of small acid and base molecules in an imine structure based on COF-300 nanoparticles is presented.