Preparation and application of solid-phase microextraction fiber based on dual-functional MOF@COF composite material

Abstract

This invention provides the preparation and application of a solid-phase microextraction fiber based on a bifunctionalized MOF@COF composite. The method involves first preparing a bihydroxyl-functionalized UiO-66-(OH)2 (MOF) via a solvothermal method; then functionalizing the UiO-66-(OH)2 surface with amino groups; then preparing a core-shell UiO-66-(OH)2@COF-OCH3 composite; and finally, preparing a MOF@COF-coated solid-phase microextraction fiber via an adhesive bonding method. The prepared MOF@COF composite adsorbent material exhibits a high specific surface area, excellent water and thermal stability, and high porosity. Furthermore, the composite material, which contains bifunctional groups (hydroxyl and methoxy), a π-electron structure, and metal ions, exhibits specific enrichment of halogenated persistent organic pollutants, such as polybrominated diphenyl ethers, organochlorine pesticides, and hydroxylated polychlorinated biphenyls, and has promising application prospects in environmental analysis and monitoring.

Description

Technical Field

[0001] The present invention relates to a method for preparing a dual-functionalized MOF@COF framework composite coated fiber based on a dual-ligand-assisted strategy. Specifically, MOF is amino-functionalized using two polymer ligands, followed by in-situ growth of an imine COF on its surface. The resulting MOF@COF framework composite is then used to prepare solid-phase microextraction fibers. Furthermore, by pre-functionalizing either the MOF or COF, different application requirements can be met. This invention belongs to both the field of crystalline porous materials and the field of analytical chemistry. Background Art

[0002] Solid-phase microextraction (SPME), a novel sample pretreatment technique proposed in the early 1990s, integrates sampling, extraction, enrichment, and injection. Compared to traditional extraction techniques, SPME is solvent-free, miniaturized, rapid, portable, and easy to use. It can also be easily integrated with gas chromatography-mass spectrometry (GC-MS) for the analysis of volatile pollutants. It has been widely used for the preconcentration and extraction of target analytes from food, environmental, fragrance, and biological samples. Fiber-based SPME is currently the most widely used extraction method. By coating or polymerizing various coating materials on the surface of a fiber support, target compounds can be extracted and enriched using headspace or direct immersion methods, making it easy to use online and time-saving. The coating material is a key factor influencing the extraction efficiency of target compounds. Currently, commonly used commercial SPME fiber coating materials are primarily based on their polarity and properties, enriching target compounds according to the "like dissolves like" principle. While they have broad applicability, they often lack specific interactions with the target compounds, resulting in limited extraction efficiency, selectivity, and stability. Therefore, the preparation of novel coated fibers with high selectivity and stability is of great significance for the analysis of trace pollutants.

[0003] New crystalline porous materials are porous materials composed of organic molecular units connected by coordination bonds, covalent bonds, or supramolecular interactions. Based on their bonding mechanism, they can be categorized as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), and supramolecular organic frameworks (SOFs). Due to their designable long-range ordered structures, high surface area, accessible pores, and easily modifiable pores, crystalline porous materials have shown great potential in recent years for applications in adsorption separation, heterogeneous catalysis, and sensing. MOFs are porous polymers formed by coordination bonds between metal ions or metal oxide clusters and organic ligands, while COFs are crystalline porous polymers connected by covalent bonds. Both have become research hotspots in the materials field due to their large specific surface area, high porosity, and easily tunable structures. Current research focuses on their synthesis, properties, and applications. However, in terms of sample pretreatment, these two materials have some inherent defects. For example, MOF materials are unstable in aqueous solution or to heat, and their structure is prone to collapse. COF materials have good stability but no metal nodes, relatively simple functions, and insufficient specific enrichment capabilities, which to a certain extent limit the extraction application performance.

[0004] To improve the performance of single-framework materials, research has gradually shifted to the synthesis of composite materials. Compared to single materials, MOF-COF composites (MOF / COF) offer functional integration and synergistic effects, overcoming their inherent shortcomings while introducing new functional sites to form dual / multifunctional composites, exhibiting excellent stability and specificity. Currently, MOF / COF composites have been widely used in membrane separation due to their robust gas separation capabilities. They are also beginning to be used as adsorbents for extracting pharmaceutical residues and pollutants from complex matrices such as the environment and organisms, demonstrating excellent enrichment performance. Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants that are ubiquitous in the environment and organisms, with pollution on the rise, posing potential hazards to both the environment and human health. As emerging persistent organic pollutants, PBDEs have become a research hotspot in environmental science, necessitating the development of efficient trace analysis techniques. Currently, researchers have developed coatings or adsorbents based on COFs, MOFs, and carbon nanotubes for PBDE enrichment, but there have been no reports on the enrichment of PBDEs using MOF / COF composites. Summary of the Invention

[0005] The present invention provides a method for preparing a solid-phase microextraction fiber based on a bifunctional MOF@COF composite. This MOF@COF-coated fiber exhibits excellent specificity and stability and can be used to enrich halogenated persistent organic pollutants (POPs), such as polybrominated diphenyl ethers (PBDEs), organochlorine pesticides, and hydroxylated polychlorinated biphenyls (PCBs). Furthermore, it can be used in conjunction with GC-MS or LC-MS for highly sensitive detection of trace contaminants in environmental and food samples.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a dual-functional MOF@COF composite solid phase microextraction fiber, the specific process of which includes:

[0008] (1) Preparation of UiO-66-(OH)2

[0009] 29.7-49.5 mg of 2,5-dihydroxyterephthalic acid and 34.9-93.5 mg of MCl4 (M = Zr, Hf, Th) were added to 5-15 mL of N,N-dimethylformamide and dissolved under ultrasonication. 1.5-4.5 mL of glacial acetic acid was added as a catalyst. The mixed solution was transferred to a 25 mL polytetrafluoroethylene-lined autoclave and reacted at 100-140°C for 24 h. The resulting product was then washed six times with ethanol, centrifuged at 5000-8000 rpm for 5 min, and the precipitate was collected and dried in vacuo at 60-80°C overnight to obtain UiO-66-(OH)2.

[0010] (2) Surface amino functionalization of UiO-66-(OH)2

[0011] 75-125 mg of UiO-66-(OH)2 was placed in a round-bottom flask containing 25 mL of ethanol and ultrasonically dispersed evenly. 5 mL of an ethanol mixed solution containing 70-120 mg / mL polyethyleneimine and polyvinylpyrrolidone was slowly added dropwise under stirring. The mixture was magnetically stirred at room temperature for 12-24 h. The resulting solid product was then washed four times with ethanol, centrifuged at 5000-8000 rpm for 5 min, and the precipitate was collected and dried in vacuum at 60-80 °C overnight to obtain amino-functionalized UiO-66-(OH)2.

[0012] (3) Preparation of UiO-66-(OH)2@COF-OCH3 composite material

[0013] 5-35 mg of amino-functionalized UiO-66-(OH)2, 1.2-4.6 mg of 2,5-dimethoxyterephthalaldehyde, and 1.4-5.6 mg of 1,3,5-tris(4-aminophenyl)benzene were added to a round-bottom flask containing 4-8 mL of a mixed solvent of n-butanol / o-dichlorobenzene (v:v=1:1) and dissolved by ultrasonication. 80-120 μL of glacial acetic acid was then added and reacted at room temperature for 4-8 h. 300-600 μL of 12 M acetic acid solution was then added to the reaction solution, ultrasonically mixed, and reacted at 70-100 °C for 24 h. After the reaction, the product was washed three times with tetrahydrofuran and ethanol respectively. The precipitate was collected by centrifugation at 5000-8000 rpm for 5 min and then dried in vacuum at 60-80 °C for 12-24 h to obtain a powdered UiO-66-(OH)2@COF-OCH3 composite material.

[0014] (4) Preparation of solid phase microextraction fiber coating using UiO-66-(OH)2@COF-OCH3 composite material

[0015] The stainless steel fiber was ultrasonically cleaned with deionized water and ethanol, respectively. One end (2-4 cm) of the fiber was then immersed in aqua regia and etched for 6-10 minutes. After removal, the fiber was ultrasonically cleaned again with deionized water and ethanol. The cleaned etched end of the fiber was then vertically inserted into a silicone sealant, slowly rotated, and then rapidly pulled out. The fiber was then transferred to a centrifuge tube containing UiO-66-(OH)2@COF-OCH3 composite powder and slowly rotated for 2-3 revolutions to evenly coat the fiber surface. The composite-coated fiber was then cured in a 100°C oven for 3-5 hours to obtain a solid-phase microextraction fiber based on the MOF@COF composite. Before use in extraction, the fiber was conditioned in a gas chromatography inlet at 200-250°C for 2-4 hours to remove volatile impurities.

[0016] The present invention first uses a solvothermal reaction to prepare dihydroxy-functionalized UiO-66-(OH)2 (MOF), then uses polyethyleneimine and polyvinylpyrrolidone to amino-functionalize MOF through a dual-ligand-assisted strategy, thereby providing a basis for the effective heterogeneous nucleation of imine-linked COF on its surface; the amino-functionalized UiO-66-(OH)2 is then added to the precursor solution of COF-OCH3 to prepare a core-shell structured UiO-66-(OH)2@COF-OCH3 composite material; finally, the composite material is coated onto an etched stainless steel fiber by an adhesive method to prepare a dual-functionalized MOF@COF-coated solid-phase microextraction fiber.

[0017] The MOF@COF composite prepared in this invention has a core-shell structure. Therefore, to prevent homogeneous nucleation of the COF, which would prevent the core-shell structure from forming, the amount of COF monomer added must be strictly controlled during the composite preparation. While ensuring heterogeneous nucleation on the MOF surface, the COF shell thickness can be adjusted by varying the amount of COF monomer added, thereby improving the enrichment performance of the target compound.

[0018] The main advantages of the present invention are:

[0019] (1) The coated fiber prepared by the present invention has specific selectivity and has good selectivity for halogenated persistent organic pollutants such as polybrominated diphenyl ethers, organochlorine pesticides, and hydroxylated polychlorinated biphenyls. It can specifically enrich such target substances and improve the detection sensitivity of the combined method;

[0020] (2) The UiO-66-(OH)2@COF-OCH3 composite coating material prepared in this invention has a large specific surface area, good hydrophobicity, and a hierarchical porous structure. At the same time, it contains abundant bifunctional groups (hydroxyl and methoxy groups) and π-electron structures, which enable it to generate multiple interactions such as hydrogen bonds, halogen bonds, π-π interactions, and hydrophobic interactions with active sites such as bromine, oxygen atoms, and benzene rings contained in the target. The coated fiber was used for SPME extraction of trace PBDEs in actual water samples and coupled with GC-MS detection to achieve highly sensitive and selective rapid analysis of pollutants. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to further illustrate the above and other advantages and features of the present invention, the following is a detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings. The accompanying drawings only illustrate typical examples of the present invention.

[0022] Figure 1 Transmission electron microscopy image of UiO-66-(OH)2@COF-OCH3 composite material;

[0023] Figure 2 Scanning electron microscopy images of the etched stainless steel fiber and the UiO-66-(OH)2@COF-OCH3 coated fiber;

[0024] Figure 3 N2 adsorption-desorption isotherms of UiO-66-(OH)2@COF-OCH3 fiber coating;

[0025] Figure 4 Selected ion chromatograms of environmental water samples. Black line: blank lake water sample; red line: spiked lake water sample, spiked concentration: 10 ng L -1 ; Blue line: spiked lake water sample, spike concentration: 100 ng L -1The chromatographic peaks in the figure correspond to the PBDEs mixture (BDE-28, BDE-47, BDE-100, BDE-99, BDE-154, BDE-153). DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below by means of specific examples. The following examples are illustrative rather than restrictive, and the scope of protection of the present invention cannot be limited by the following examples.

[0027] Example 1

[0028] (1) Preparation of UiO-66-(OH)2: 34 mg of 2,5-dihydroxyterephthalic acid and 40 mg of ZrCl4 were added to 10 mL of N,N-dimethylformamide and ultrasonically dissolved, and 3 mL of glacial acetic acid was added as a catalyst; the mixed solution was transferred to a 25 mL polytetrafluoroethylene-lined autoclave and reacted at 120 °C for 24 h. The obtained product was then washed with ethanol six times, and the precipitate was collected by centrifugation at 8000 rpm for 5 min and vacuum dried at 60 °C overnight to obtain UiO-66-(OH)2.

[0029] (2) Surface amino functionalization treatment of UiO-66-(OH)2: 100 mg of UiO-66-(OH)2 was weighed and placed in a round-bottom flask containing 25 mL of ethanol and ultrasonicated for 1 h to disperse it evenly. 5 mL of a mixed solution of polyethyleneimine (100 mg / mL) and polyvinylpyrrolidone (100 mg / mL) in ethanol was slowly added dropwise under stirring. After the addition was completed, the mixture was stirred at room temperature for 12 h. The obtained amino-functionalized UiO-66-(OH)2 product was then washed four times with ethanol, and the precipitate was collected by centrifugation at 8000 rpm for 5 min and dried in vacuum at 60 °C for 12 h.

[0030] (3) Preparation of UiO-66-(OH)2@COF-OCH3 composite material: 20 mg of amino-functionalized UiO-66-(OH)2, 2.8 mg of 2,5-dimethoxyterephthalaldehyde, and 2.3 mg of 1,3,5-tris(4-aminophenyl)benzene were added sequentially into a 6 mL round-bottom flask containing a mixed solvent of n-butanol and o-dichlorobenzene (v:v=1:1) and dissolved by ultrasonication; 100 μL of glacial acetic acid was added to the mixed solution and reacted at room temperature for 4 h. Then, 400 μL of 12 M acetic acid solution was added to the reaction solution, ultrasonically mixed, and reacted at 80 °C for 24 h; after the reaction, the product was washed three times with tetrahydrofuran and ethanol respectively, the precipitate was collected by centrifugation at 8000 rpm for 5 min, and vacuum dried at 60 °C for 24 h to obtain a powdered UiO-66-(OH)2@COF-OCH3 composite material.

[0031] (4) Preparation of solid-phase microextraction fiber based on UiO-66-(OH)2@COF-OCH3 composite material: First, ultrasonically clean the stainless steel fiber with deionized water and ethanol respectively. Then, immerse one end of the stainless steel fiber (3 cm) in aqua regia and etch it for 10 min. After taking it out, ultrasonically clean it again with deionized water and ethanol. Then, insert the etched end of the stainless steel fiber vertically into the organic silicone sealant, rotate it slowly first and then pull it out quickly. Then, transfer it into a centrifuge tube containing UiO-66-(OH)2@COF-OCH3 composite material powder and rotate it slowly for 2 circles to ensure that the surface of the etched end of the fiber is evenly coated. The stainless steel fiber coated with the composite material is placed in a 100℃ oven for curing for 3 h to obtain the MOF@COF composite material solid-phase microextraction fiber. Before being used for extraction, the fiber needs to be aged at 250℃ in the gas chromatography inlet for 1 h to remove volatile impurities.

[0032] Figure 1 This is a transmission electron microscopy image of the UiO-66-(OH)2@COF-OCH3 fiber coating material; it can be seen from the figure that the prepared composite material has a core-shell structure and the thickness of the COF shell is 45.5 nm.

[0033] Figure 2 This is a scanning electron microscope image of UiO-66-(OH)2@COF-OCH3 stainless steel fiber and its coating; Figure 2 Figure a is a scanning electron microscope image of stainless steel fiber after aqua regia etching. Figure 2 Figure b is a scanning electron microscope image of the fiber after coating; comparing the two images, it can be clearly seen that the UiO-66-(OH)2@COF-OCH3 coating (34.5 μm) has been evenly coated on the surface of the stainless steel fiber.

[0034] Figure 3The N2 adsorption-desorption isotherm of the UiO-66-(OH)2@COF-OCH3 fiber coating is shown in the figure. It can be seen from the figure that it is a type IV isotherm, and the specific surface area of ​​the coating material is 972.67 m 2 / g. The large specific surface area can provide more adsorption sites for the fiber coating, thereby improving the enrichment capacity of the analyte.

[0035] Example 2

[0036] In order to verify the enrichment performance of the UiO-66-(OH)2@COF-OCH3 composite framework material coated fiber for polybrominated diphenyl ethers, the coated fiber prepared in Example 1 was used to perform solid phase microextraction of PBDEs, and GC-MS was combined with the detection of trace PBDEs in complex samples. The specific extraction and detection conditions were as follows:

[0037] The chromatographic conditions were as follows: capillary column (30 m × 0.25 mm id × 0.25 μm); carrier gas: high-purity He; flow rate: constant flow, 1.0 mL / min; injection mode: splitless injection; injection port temperature: 280 °C; heating program: initial temperature 110 °C, hold for 1 min, increase the temperature to 210 °C at a rate of 20 °C / min, hold for 1 min, then increase the temperature to 280 °C at a rate of 10 °C / min, hold for 10 min; mass spectrometry conditions: interface temperature: 250 °C; solvent delay: 6 min; ion source: EI source; ionization energy: 70 eV; ion source temperature: 230 °C; SPME extraction conditions were optimized using full scan mode (Scan), mass scan range (m / z): 50-750 amu; quantitative analysis was performed using selected ion monitoring mode (SIM)), and the optimal SPME extraction conditions (extraction temperature: 85 °C, extraction time: 45 min, desorption temperature: 280 ℃, desorption time of 7 min, extraction stirring rate of 1200 rpm, NaCl content of 0%), SPME-GC-MS was used to enrich and detect PBDEs in actual lake water samples. The detection method has a low detection limit (0.0026-0.034 ng L -1 ).

[0038] Figure 4 Selected ion chromatograms of lake water samples measured in SIM mode. The recoveries of the six PBDEs at two spike concentrations ranged from 79.0% to 117.4%, meeting the detection requirements of GC-MS.

[0039] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a solid-phase microextraction fiber based on a dual-functional MOF@COF composite material, characterized by: The following steps are involved: (1) Preparation of dihydroxy-functionalized UiO-66-(OH)2: 29.7-49.5 mg of 2,5-dihydroxyterephthalic acid and 34.9-93.5 mg of MCl4 (M = Zr, Hf, Th) were added to N,N-dimethylformamide for ultrasonic dissolution, and glacial acetic acid was added as a catalyst. The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave and reacted at 100-140 °C for 24 h. The obtained product was then washed with ethanol, collected by centrifugation, and vacuum dried overnight to obtain UiO-66-(OH)2; (2) Surface amino functionalization of UiO-66-(OH)2: UiO-66-(OH)2 was added to 25 mL of ethanol and dispersed evenly by ultrasonication. 5 mL of a mixed solution of polyethyleneimine and polyvinylpyrrolidone in ethanol was slowly added dropwise under stirring. The mixture was magnetically stirred at room temperature for 12-24 h. The resulting solid product was then washed with ethanol, collected by centrifugation, and vacuum dried overnight to obtain amino-functionalized UiO-66-(OH)2. (3) Preparation of UiO-66-(OH)2@COF-OCH3 composite material: 5-35 mg of amino-functionalized UiO-66-(OH)2, 1.2-4.6 mg of 2,5-dimethoxyterephthalaldehyde, and 1.4-5.6 mg of 1,3,5-tris(4-aminophenyl)benzene were added to a mixed solvent of n-butanol and o-dichlorobenzene and dissolved by ultrasonication. Glacial acetic acid was then added to the mixed solution and reacted at room temperature for 4-8 h. A certain amount of 12 M acetic acid solution was then added to the reaction solution, ultrasonically mixed, and reacted at 70-100 °C for 24 h. After the reaction, the product was washed three times with tetrahydrofuran and ethanol, collected by centrifugation, and then vacuum dried for 12-24 h to obtain a powdered UiO-66-(OH)2@COF-OCH3 composite material. (4) Preparation of UiO-66-(OH)2@COF-OCH3 composite solid phase microextraction fiber: First, ultrasonically clean the stainless steel fiber with deionized water and ethanol respectively, then immerse one end of the stainless steel fiber in aqua regia for etching, take it out and ultrasonically clean it again with deionized water and ethanol, then vertically insert the etched end of the stainless steel fiber into the organic silicone sealant, first slowly rotate it and then quickly pull it out and move it into a centrifuge tube containing UiO-66-(OH)2@COF-OCH3 composite material powder and slowly rotate it 2-3 times to make it evenly coated. The stainless steel fiber coated with the composite material is placed in a 100 °C oven for curing to obtain the MOF@COF composite material solid phase microextraction fiber.

2. The method for preparing a dual-functionalized MOF@COF composite solid phase microextraction fiber according to claim 1, characterized in that: The volume of N,N-dimethylformamide used in step (1) is 5-15 mL, and the volume of glacial acetic acid is 1.5-4.5 mL; the prepared MOF is any one of UiO-66(Zr)-(OH)2, UiO-66(Hf)-(OH)2, and UiO-66(Th)-(OH)2.

3. The method for preparing a dual-functionalized MOF@COF composite solid phase microextraction fiber according to claim 1, characterized in that: In step (2), the concentration of the ethanol dispersion of UiO-66-(OH)2 is 3-5 mg / mL; the concentrations of both ligands in the ethanol mixed solution of polyethyleneimine and polyvinylpyrrolidone are 70-120 mg / mL.

4. The method for preparing a dual-functionalized MOF@COF composite solid phase microextraction fiber according to claim 1, characterized in that: In step (3), the volume ratio of n-butanol to o-dichlorobenzene is 1:1, and the total volume is 4-8 mL.

5. The method for preparing a dual-functionalized MOF@COF composite solid phase microextraction fiber according to claim 1, characterized in that: In step (3), 80-120 μL of glacial acetic acid is added at room temperature. After the reaction is complete, 300-600 μL of 12 M acetic acid solution is added.

6. The method for preparing a dual-functionalized MOF@COF composite solid phase microextraction fiber according to claim 1, characterized in that: In step (4), the etching temperature of the stainless steel fiber is room temperature, and the etching time is 6-10 min; the fiber is cured in an oven at 100°C for 3-5 h.

7. The method for preparing a dual-functionalized MOF@COF composite solid phase microextraction fiber according to claim 1, characterized in that: In steps (1) to (3), the centrifugal speed is 5000-8000 rpm, the centrifugal time is 4-8 min, and the vacuum drying temperature is 60-80°C.

8. A solid phase microextraction fiber based on a dual-functional MOF@COF composite material obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the dual-functional MOF@COF composite solid phase microextraction fiber according to claim 8 in the enrichment of polybrominated diphenyl ethers, organochlorine pesticides, and hydroxylated polychlorinated biphenyl organic pollutants.

10. The use according to claim 8, characterized in that: The dual-functional MOF@COF composite solid phase microextraction fiber needs to be aged in a gas chromatography inlet before being used for extraction to remove volatile impurities; wherein, the aging temperature of the gas chromatography inlet fiber is 200-250 ° C, and the aging time is 2-4 h.

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