Heteroporous 3D covalent organic framework-based magnetic nanospheres for sensitive detection of bisphenol A

A BODIPY-Containing Covalent Organic Framework as a Highly Porous Photosensitizer for Environmental Remediation and Pollutants Adsorption

The direct incorporation of borondipyrromethene (BODIPY) subunits into the structural backbone of covalent organic frameworks (COFs) gives facile access to porous photosensitizers but is still a challenging task. Here, we introduce β-ketoenamine-linked BDP-TFP-COF, which crystallizes in AA-stacking mode with hcb topology. A comprehensive characterization reveals high crystallinity and enhanced stability in a variety of solvents, excellent mesoporosity (SABET=1042 m2 g-1), broad light absorption in the visible region, and red emission upon the exfoliation of few-layer COF nanosheets. The versatility of multifunctional BODIPY-COFs is highlighted in various applications. Pollutants Bisphenol A (BPA, qmax=426 mg g-1) and Methylene Blue (MB, qmax=96 mg g-1) have been efficiently removed from H2O. Fluorescence quenching or enhancement of exfoliated BDP-TFP-COF nanosheets have been utilized for dual-mode sensing of MB or NEt3, respectively. Ultimately, the photosensitizing effect of the BODIPY units is retained in the COF. Thus, BPD-TFP-COF was established as a metal-free triplet photosensitizer, which efficiently oxidized a mustard gas simulant under visible light irradiation.

Covalent organic frameworks with nitrogen-rich triazine units and suitable pore size for highly efficient adsorption and sensitive detection of bisphenols in water

Herein, using 1,3,5-triformylphloroglucinol (Tp) and 4,4',4″-(1,3,5-triazine-2,4,6-triyl) tris(1,1'-biphenyl) trianiline (Ttba) as ligands, nitrogen-rich triazine unit-based covalent organic frameworks (COFs) with a suitable pore size, named TpTtba-COFs, were synthesized, and they were employed as adsorbents for the extraction and detection of three bisphenols (BPs)-BP A (BPA), BP B (BPB), and BP S (BPS)-in water. Using 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (Tapt) and 1,3,5-tris(4-aminophenyl)benzene (Tapb) ligands as substitutes for Ttba, nitrogen-rich triazine unit-based COFs with a smaller pore size and nitrogen-poor triazine unit-based COFs, named TpTapt-COFs and TpTapb-COFs, respectively, were also prepared for comparison. The adsorption performances of the three COF adsorbents with regard to the three BPs were tested. Owing to nitrogen-rich triazine units and a pore size suitable for BP adsorption, the maximum adsorption capacities of TpTtba-COFs for BPA, BPB, and BPS were 1.13, 1.33, and 1.37 times those of TpTapt-COFs and 2.10, 2.27, and 1.92 times those of TpTapb-COFs, respectively. The adsorption behavior and possible adsorption mechanism of the BPs on the TpTtba-COFs were also investigated. In addition, a TpTtba-COF-based dispersive solid-phase extraction-high-performance liquid chromatography/ultraviolet method exhibited an excellent linear range (1-800 ng/mL) and satisfactory limit of detection values (0.20-0.32 ng/mL) for the three BPs. The spiked recoveries of the three BPs in river and lake water ranged within 81.9%-101.9% and 82.8%-100.8%, respectively. Overall, this study offers valuable insights into the rational design of adsorbents for adsorption and sensitive detection of BPs in environmental water.

Advances in covalent organic frameworks for sample preparation

Sample preparation is crucial in analytical chemistry, impacting result accuracy, sensitivity, and reliability. Solid-phase separation media, especially adsorbents, are vital for preparing of liquid and gas samples, commonly analyzed by most analytical instruments. With the advancements in materials science, covalent organic frameworks (COFs) constructed through strong covalent bonds, have been increasingly employed in sample preparation in recent years. COFs have outstanding selectivity and/or excellent adsorption capacity for a single target or can selectively adsorb multiple targets from complex matrix, due to their large specific surface area, adjustable pore size, easy modification, and stable chemical properties. In this review, we summarize the classification of COFs, such as pristine COFs, COF composite particles, and COFs-based substrates. We aim to provide a comprehensive understanding of the different classifications of COFs in sample preparation within the last three years. The challenges and development trends of COFs in sample preparation are also presented.

Magnetic adsorbents for removal of bisphenol A: Design strategies of materials and adsorption mechanisms

Bisphenol A (BPA) is a representative endocrine-disrupting chemical widely utilized in the plastic industry, and its leakage into the environment poses various health risks. There is an urgent need for effective removal technologies, and magnetic adsorption shows promise due to its high efficiency and ease of recovering adsorbents. This review provides a comprehensive and critical summary of recent advances in magnetic adsorbents for the removal of BPA. It covers intrinsic magnetic materials and composite magnetic adsorbents which include magnetic organic adsorbents (covalent organic frameworks, β-cyclodextrin-based adsorbents, and molecularly imprinted polymers), magnetic carbonaceous adsorbents (graphene, activated carbon, biochar, and carbon nanotubes), magnetic inorganic adsorbents and magnetic metal-organic frameworks. After comparing and discussing the different magnetic adsorbents, the adsorption mechanisms are summarized, and the advantages and disadvantages are compared and discussed. Strategies for designing magnetic matrices with appropriate morphology and adsorption materials with optimal porous structures are proposed. The challenges associated with maintaining adsorption performance while integrating a magnetic matrix are also discussed. The research direction for future work is also prospected. This review aims to guide the development of magnetic adsorbents for the removal of BPA and other emerging pollutants.

Covalent Organic Framework-Involved Sensors for Efficient Enrichment and Monitoring of Food Hazards: A Systematic Review

The food safety issues caused by environmental pollution have posed great risks to human health that cannot be ignored. Hence, the precise monitoring of hazard factors in food has emerged as a critical concern for the food safety sector. As a novel porous material, covalent organic frameworks (COFs) have garnered significant attention due to their large specific surface area, excellent thermal and chemical stability, modifiability, and abundant recognition sites. This makes it a potential solution for food safety issues. In this research, the synthesis and regulation strategies of COFs were reviewed. The roles of COFs in enriching and detecting food hazards were discussed comprehensively and extensively. Taking representative hazard factors in food as the research object, the expression forms and participation approaches of COFs were explored, along with the effectiveness of corresponding detection methods. Finally, the development directions of COFs in the future as well as the problems existing in practical applications were discussed, which was beneficial to promote the application of COFs in food safety and beyond.

Magnetic covalent organic frameworks as sorbents in the chromatographic analysis of environmental organic pollutants

Covalent organic frameworks (COFs) are featured with large specific surface areas, good thermal stability, and abundant pores. These properties are exactly what the sorbents used for extraction or adsorption of interest substances are desired with. While, the low density and hydrophobicity of COFs often makes them difficult to be dispersed evenly and recovered from the aqueous solution. Magnetic covalent organic frameworks (MCOFs) inherit magnetic property of the magnetic particles and porous structure of COFs. They have improved dispersity in aqueous solution and phase separation can be rapidly achieved via external magnetic fields. This review summarized the synthesis strategies for MCOFs, and their application in trace environmental organic pollutants analysis by chromatography techniques. The selection of COFs types and modification with active groups for a certain adsorption purpose is discussed, along with the exploration of adsorption mechanisms, which is beneficial for the design and synthesis of MCOFs.

Bisphenol A contamination in Hilsa shad and assessment of potential health hazard: A pioneering investigation in the national river Ganga, India

The anadromous Hilsa, often known as the "Queen of Fishes" (Tenualosa ilisha), is the most valuable fishery in the Ganga-Hooghly delta estuary. Although BPA exposure has been shown to be harmful to aquatic organisms, no research has looked at the effects of BPA on the commercially valuable Hilsa shad of river Ganga. To close this information vacuum, we examined BPA levels in Hilsa fish from the Ganga estuary. Liver, muscle, kidney, and gonads were all positive for BPA among the Hilsa fish of all ages. Liver BPA levels were highest in adult males (272.16 ± 0.38 ng/g-dw), and lowest in juveniles (5.46 ± 0.06 ng/g-dw). BPA concentrations in the Hilsa shad muscle were highest in reproductively mature females (196.23 ± 0.41 ng/g-dw). The study also discovered a correlation between fish development and BPA exposure, with higher levels of BPA being identified in adult Hilsa species. This is the first study to look at the impact of BPA pollution on aquatic ecosystems and fisheries, and it showed that Hilsa shad is contaminated with BPA and poses health hazards to human beings. The results, which demonstrate BPA contamination, are useful for protecting Hilsa in the river Ganga.

Monolithic 3D structural-substrate SERS sensing platform for ultrasensitive and highly-specific analysis of trace bisphenol A

Constructing advanced substrates with excellent features is promising for sensitive surface-enhanced Raman spectroscopy (SERS) detection. Here a novel capillary monolithic 3D structural-substrate SERS platform with Au@cDNA@Ag@Cyanine 3-aptamer nanoparticles (Au@cDNA@Ag@Cy3-Apt NPs) was fabricated for rapid, highly specific profiling of ultra-trace Bisphenol A (BPA). The proposed SERS platform combined both in-capillary SERS and aptamer-affinity recognition strategies, in which the superior SERS properties of Au-Ag NPs, aptamer selectivity, and the advantages of capillary monolith were integrated. A 3D hierarchically porous network was constructed in the monolithic column, which was endowed with rich hotspots for SERS, rapid sample permeation, and better analysis efficiency than most plane-shaped SERS modes. By varying the amount of Ag+ precursor, the Ag-shell thickness on SERS was finely tuned to guarantee Cy3 label in proximity to the plasmonic surface. Based on the biorecognition of aptamer, the selective identification of BPA occurred and exhibited a significant change in SERS intensity without obvious interference. As a result, the monolithic SERS platform featured facile operation, excellent specificity, and rapid analysis (10 min, much less than the solution-based or planar substrate SERS modes). Ultra-high sensitivity and robust reproducibility for BPA analysis was achieved with a low limit of detection (LOD) at 9.12 × 10-4 ng/L. The feasibility of this SERS platform for monitoring BPA in water and milk samples was also validated. This work lights a new access to capillary monolithic SERS-sensing platform for ultrasensitive and specific analysis of BPA.

Magnetic Covalent Organic Framework Composites for Wastewater Remediation

Covalent organic frameworks (COFs) with high specific surface area, tailored structure, easy functionalization, and excellent chemical stability have been extensively exploited as fantastic materials in various fields. However, in most cases, COFs prepared in powder form suffer from the disadvantages of tedious operation, strong tendency to agglomerate, and poor recyclability, greatly limiting their practical application in environmental remediation. To tackle these issues, the fabrication of magnetic COFs (MCOFs) has attracted tremendous attention. In this review, several reliable strategies for the fabrication of MCOFs are summarized. In addition, the recent application of MCOFs as outstanding adsorbents for the removal of contaminants including toxic metal ions, dyes, pharmaceuticals and personal care products, and other organic pollutants is discussed. Moreover, in-depth discussions regarding the structural parameters affecting the practical potential of MCOFs are highlighted in detail. Finally, the current challenges and future prospects of MCOFs in this field are provided with the expectation to boost their practical application.

Adsorption and catalytic degradation of bisphenol A and p-chlorophenol by magnetic carbon nanotubes

Phenolic compounds are common industrial pollutants that seriously endangers water ecology and human health. Therefore, the development of efficient and recyclable adsorbents is of importance for wastewater treatment. In this research, HCNTs/Fe3O4 composites were constructed using co-precipitation way by loading magnetic Fe3O4 particles onto hydroxylated multi-walled carbon nanotubes (MWCNTs), showing excellent adsorption capacity for Bisphenol A (BPA) and p-chlorophenol (p-CP), and excellent catalytic ability of activating potassium persulphate (KPS) for degradation of BPA and p-CP. The adsorption capacity and catalytic degradation potential were evaluated for the removal of BPA and p-CP from solutions. The results showed that the adsorption took only 1 h to reach equilibrium and HCNTs/Fe3O4 had maximum adsorption capacities of 113 mg g-1 for BPA and 41.6 mg g-1 for p-CP at 303 K, respectively. The adsorption of BPA fitted well using the Langmuir, Temkin and Freundlich models while the adsorption of p-CP fitted well using the Freundlich and Temkin models. BPA adsorption on HCNTs/Fe3O4 was dominated by π-π stacking and hydrogen bonding forces. The adsorption included both the mono-molecular layer adsorption on the adsorbent surface and the multi-molecular layer adsorption on the non-uniform surface. The adsorption of p-CP on HCNTs/Fe3O4 was a multi-molecular layer adsorption on a dissimilar surface. The adsorption was controlled by forces such as π-π stacking, hydrogen bonding, partition effect and molecular sieve effect. Moreover, KPS was added to the adsorption system to initiate a heterogeneous Fenton-like catalytic degradation. Over a wide pH range (4-10), 90% of the aqueous BPA solution and 88% of the p-CP solution were degraded in 3 and 2 h, respectively. After three adsorption-regeneration or degradation cycles, the removal of BPA and p-CP remained up to 88% and 66%, indicating that HCNTs/Fe3O4 composite is cost-effective, stable and highly efficient to remove BPA and p-CP from solution.

Composite materials based on covalent organic frameworks for multiple advanced applications

Covalent organic frameworks (COFs) stand for a class of emerging crystalline porous organic materials, which are ingeniously constructed with organic units through strong covalent bonds. Their excellent design capabilities, and uniform and tunable pore structure make them potential materials for various applications. With the continuous development of synthesis technique and nanoscience, COFs have been successfully combined with a variety of functional materials to form COFs-based composites with superior performance than individual components. This paper offers an overview of the development of different types of COFs-based composites reported so far, with particular focus on the applications of COFs-based composites. Moreover, the challenges and future development prospects of COFs-based composites are presented. We anticipate that the review will provide some inspiration for the further development of COFs-based composites.

Sensitive determination of bisphenols in environmental samples by magnetic porous carbon solid-phase extraction combined with capillary electrophoresis

Bisphenol compounds exist widely in the environment and pose potential hazards to the environment and human health, which has aroused widespread concern. Therefore, there is an urgent need for an efficient and sensitive analytical method to enrich and determine trace bisphenols in environmental samples. In this work, magnetic porous carbon (MPC) was synthesized by one-step pyrolysis combined with a solvothermal method for magnetic solid-phase extraction of bisphenols. The structural properties of MPC were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and saturation magnetization analysis. Its adsorption properties were evaluated by adsorption kinetics and adsorption isotherm studies. By optimizing the magnetic solid-phase extraction and capillary electrophoresis separation conditions, a capillary electrophoresis separation and detection method for four bisphenols was successfully constructed. The results showed that the detection limits of the proposed method for the four bisphenols were 0.71-1.65 ng/mL, the intra-day and inter-day precisions were 2.27-4.03% and 2.93-4.42%, respectively, and the recoveries were 87.68%-108.0%. In addition, the MPC could be easily recycled and utilized, and even if the magnetic solid-phase extraction was repeated 5 times, the extraction efficiency could still be kept above 75%.

Electrochemical sensor based on confined synthesis of gold nanoparticles @ covalent organic frameworks for the detection of bisphenol A

Covalent-organic frameworks (COFs), a kind of conjugate crystalline polymers, has great potential for high performance electrochemical sensors due to high porosity, controllable pores and structure, and large specific surface area, etc. Herein, we developed an electrochemical sensor based on confined synthesis of gold nanoparticles @ 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) connected COFs (Au NPs@TpBD-COFs) for electrochemical detection of bisphenol A (BPA). Firstly, Au NPs were grown on the surface and in the pores of COFs by confinement synthesis strategy, which aimed to improve the conductivity and catalytic activity of COFs. Then, this composite was used to constitute electrochemical sensor for the oxidation of BPA, resulting a good electrocatalytic activity in the phosphate buffer solution (pH 7.4). Due to high conductivity of Au NPs and TpBD-COFs recognize BPA via π-π stacking interactions and hydrogen bonds, the proposed sensor for the detection of BPA has the linear range of 5-1000 μM and the detection limit of 1 μM. Finally, the proposed sensor was used to measure the content of BPA in real water samples with a satisfactory recovery from 98.6 to 106.9%. Those good results confirmed that the proposed electrochemical sensors for monitoring of BPA in the application of COFs provided a significant guidance.

Recent advances and applications of magnetic covalent organic frameworks in food analysis

Recently, covalent organic frameworks (COFs) have been widely used to prepare magnetic adsorbents for food analysis due to their highly tunable porosity, large specific surface area, excellent chemical and thermal stability and large delocalised π-electron system. This review summarises the main types and preparation methods of magnetic COFs and their applications in food analysis for the detection of pesticide residues, veterinary drugs, endocrine-disrupting phenols and estrogens, plasticisers and other food contaminants. Furthermore, challenges and future outlook in the development of magnetic COFs for food analysis are discussed.

Magnetic covalent-organic frameworks-based extraction followed by UHPLC-MS/MS for determination and pharmacokinetic study of trace angoroside C in rat plasma after oral administration of Xuanbo Shuangsheng Granule

The composition of the traditional Chinese medicine compound preparation is complex, while the content of each active ingredient is extremely low, which brings difficulties to the plasma concentration detection. In this study, the magnetic covalent-organic frameworks were synthesized by a simple one-step Schiff base reaction and applied for the specific extraction of trace angoroside C in rat plasma prior to ultra-high-performance liquid chromatography-tandem mass spectrometry detection. The synthesized magnetic covalent-organic frameworks have high magnetic responsiveness (35.67 emu·g^-1 ), large surface area (110.9 m² ·g^-1 ), and strong stability. The as-prepared material can quickly extract angoroside C from plasma with high extraction efficiency, be easily separated with a magnet afterward, and can be reused for at least five times. The established method was systematically validated showing good linearity (0.1-5 ng·ml^-1 ), low limit of quantification (0.1 ng·ml^-1 ), good accuracy (93.18%-105.36%), and good precision (percentage relative standard deviation 3.60%-10.90%). Finally, the method was used to the pharmacokinetic study of trace angoroside C in rats after oral administration of Xuanbo Shuangsheng Granule.

Highly sensitive multiplex detection of foodborne pathogens using a SERS immunosensor combined with novel covalent organic frameworks based biologic interference-free Raman tags

Rapid and reliable multiplex detection of foodborne pathogens is in great demand for ensuring food safety and preventing foodborne diseases. In this study, we developed a highly sensitive SERS immunosensor for the simultaneous detection of multiple foodborne pathogens. Novel biologic interference-free Raman tags synthesized by using the covalent organic frameworks (COF) TBDP as nanocontainer to load biologic interference-free Raman reporters and specific antibodies for interested targets were used to convert and amplify signals of foodborne pathogens. In addition, lectin functionalized magnetic nanoparticles (MNPs@Con A) which could efficiently bind to the carbohydrate constituents on the surface of pathogens were prepared to capture and isolate multiple pathogens simultaneously. The recognition of the target foodborne pathogen impels the generation of sandwich-like composites of MNPs@Con A/pathogen/TBDP@Raman tags, and these composites could be quickly separated from the sample matrix with the assistance of an external magnet. Besides, a mass of Raman reporters was released by eluting the collected MNPs@Con A/pathogen/TBDP@Raman tags composites. Combined with a portable Raman system, characteristic Raman signals (2271 and 2113 cm^-1) of the occupied reporters located at the biologic interference-free region were observed and used for the simultaneous detection of two different foodborne pathogenic strains. And an equal limit of detection of 10¹ CFU/mL was achieved for each strain. This strategy provides new insight into the application of SERS in the detection of pathogenic bacteria.

Functional Nanoparticles with Magnetic 3D Covalent Organic Framework for the Specific Recognition and Separation of Bovine Serum Albumin

Glutathione functionalized magnetic 3D covalent organic frameworks combined with molecularly imprinted polymer (magnetic 3D COF–GSH MIPs) were developed for the selective recognition and separation of bovine serum albumin (BSA). Ultrasonication was used to prepare magnetic 3D COFs with high porosity (~1 nm) and a large surface area (373 m² g⁻¹). The magnetic 3D COF–GSH MIP nanoparticles had an imprinting factor of 4.79, absorption capacity of 429 mg g⁻¹, magnetic susceptibility of 32 emu g⁻¹, and five adsorption–desorption cycles of stability. The proposed method has the advantages of a shorter equilibrium absorption time (1.5 h), higher magnetic susceptibility (32 emu g⁻¹), and larger imprinting factor (4.79) compared with those reported from other studies. The magnetic 3D COF–GSH MIPs used with BSA had selectivity factors of 3.68, 2.76, and 3.30 for lysozyme, ovalbumin, and cytochrome C, respectively. The successful recognition and separation of BSA in a real sample analysis verified the capability of the magnetic 3D COF–GSH MIP nanoparticles.