Porphyrin-based COF and aerogel based on double-bridged monomers, preparation methods and applications

Abstract

The present invention discloses a porphyrin-based COF and aerogel based on a double-bridged monomer, as well as a preparation method and application, belonging to the field of advanced functional materials. The present invention utilizes two bridging monomers, 2,4,6-triformylphloroglucinol (Tp) and 2,6-pyridinedicarboxaldehyde (PDA), to prepare Tp-PDA-COF based on porphyrin-based COFs. The electron-withdrawing group in Tp optimizes the orbital energy levels of the metal ligands, promoting electron transfer and the formation of coordination bonds. PDA enables the COF to exist in a tetragonal topology, thereby reducing steric hindrance and exposing coordination sites, improving the selectivity and sensitivity for metal ions and enabling rapid and sensitive visual fluorescence detection. Furthermore, Tp-PDA-COF aerogel is prepared in combination with polyvinyl alcohol to address the problem of fluorescence quenching of porphyrin-based COFs in the solid state, thereby achieving the goal of developing COFs materials with both sensitive detection and efficient adsorption.

Description

Technical Field

[0001] The present invention belongs to the field of advanced functional materials, and specifically relates to a porphyrin-based COF and aerogel based on a double-bridged monomer, a preparation method and applications, especially applications in the fields of heavy metal fluorescence sensing and cooperative adsorption. Background Art

[0002] Heavy metal pollution has become a major global issue, posing a serious threat to human health and global food production. The development of materials with synergistic dual functions of specific recognition and effective adsorption of heavy metals has far-reaching significance for environmental pollution control and resource recovery economy. It is estimated that the annual global discharge of heavy metal wastewater exceeds 5 billion tons, and the recycling market value of toxic metals such as lead and cadmium alone is US$12 billion per year. However, currently about 87% of research focuses on single-functional materials (such as adsorption only or detection only). This functional separation leads to serious bottlenecks in practical applications. Therefore, the design and development of a single material with dual functions of detection and adsorption is an inevitable choice to solve resource constraints, technical bottlenecks and complex application requirements.

[0003] Organic covalent frameworks (COFs) are two- or three-dimensional crystalline porous polymers composed of organic building blocks linked by covalent bonds. Their regular pores, high surface area, and excellent chemical and thermal stability have shown potential applications in a variety of fields, including adsorption, catalysis, and separation. In 2005, American chemist Omar Yaghi's team successfully synthesized crystalline materials with two-dimensional honeycomb structures (such as COF-1 and COF-5) via borate ester condensation reactions, a breakthrough that filled the gap in purely organic porous materials. Subsequent years of development, breakthroughs in single-crystal X-ray diffraction techniques enabled the precise derivation of COF structures, laying the foundation for the targeted design of pore size and surface functional groups. Compared to other nanomaterials, COFs are based on organic molecules, which are widely available and diverse, resulting in a diverse building block structure that facilitates the manipulation of the structure and function of target materials. This characteristic gives COFs the potential to be multifunctional materials. In particular, COF materials constructed with organic fluorescent molecules as monomers, through flexible monomer selection and corresponding functional modification, not only possess the excellent adsorption and fluorescence visualization properties of COF, but also have more outstanding selectivity and anti-interference capabilities.

[0004] Porphyrins are large heterocyclic compounds with bright red fluorescence and are commonly used as building blocks for COFs (carbon-organic frameworks). COFs constructed using red-fluorescent porphyrin derivatives as monomers not only possess a larger backbone structure but also possess more potential coordination sites, significantly enhancing the application of COF materials in fluorescence sensing. In particular, the unique porous structure of porphyrin-based COFs offers excellent adsorption properties for heavy metals. Porphyrin monomers can further bind and stabilize metal ions, enabling visual detection of heavy metal ions. However, porphyrins are highly conjugated systems that can coordinate with different metal ions. This makes specific recognition of target heavy metal ions difficult. Therefore, designing COFs with specific recognition for target heavy metal ions by modulating the structure and function of COFs through monomer construction is extremely challenging. Furthermore, the compositional heterogeneity and inherent rigidity of COFs also expose several drawbacks in practical applications. Porphyrin-based COFs typically exist as insoluble powders with weak mechanical strength and poor processability. Due to the π-π stacking effect, porphyrin-based COFs can experience fluorescence quenching in the solid state. The above shortcomings limit the application of porphyrin-based COFs in the fields of analysis and detection.

[0005] Therefore, in order to achieve the dual goals of fluorescence sensing and coordinated adsorption of heavy metal ions, it is still necessary to construct and prepare new nanomaterials to solve the fluorescence quenching problem of solid-state COF. It is well known that excessive heavy metal content in the environment will pollute water, soil and food. Especially in the soil, acidic soil makes it easier for plants to absorb trace metal elements, posing a threat to human safety from food sources. In the case of serious heavy metal pollution, copper pollution has always been an inevitable problem. Excessive Cu 2+ It will seriously affect the health of the body and even lead to a series of diseases such as Wilson disease, Alzheimer's disease and Menkes disease. Therefore, sensitive detection and efficient enrichment of heavy metal Cu in the environment are necessary. 2+ Human contact can be minimized. Summary of the Invention

[0006] The present invention provides a porphyrin-based COF and aerogel based on a double-bridged monomer, a preparation method, and an application. The present invention utilizes two bridging monomers, 2,4,6-triformylphloroglucinol (Tp) and 2,6-pyridinedicarboxaldehyde (PDA), to construct a porphyrin-based COF (Tp-PDA-COF) with specific recognition ability for heavy metal ions, thereby overcoming the limitation of porphyrin-based COF in specific recognition of heavy metals. The Tp-PDA-COF aerogel is further prepared in combination with polyvinyl alcohol to solve the problem of fluorescence quenching of porphyrin-based COF in a solid state, thereby achieving the purpose of developing a COF material with the dual functions of sensitive detection and efficient adsorption.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] The present invention first prepares a porphyrin-based COF material with a tetragonal topological structure based on a double-bridged monomer, namely Tp-PDA-COF. The tetragonal topological structure formed in Tp-PDA-COF is formed by the two monomers Tp and PDA in a 1:1 molar ratio. Tp, which has a strong electron-withdrawing ability, can adjust the electron cloud density of the porphyrin ring, enhance the lone pair electron supply capacity of the N atom, and improve the coordination affinity. At the same time, the electron-withdrawing group in Tp optimizes the orbital energy level of the metal ligand, promotes electron transfer and the formation of coordination bonds. The addition of PDA enables COF to exist in a tetragonal topological structure, thereby reducing steric hindrance and fully exposing the coordination site. This structure improves the affinity to Cu 2+ The selectivity and sensitivity of Tp-PDA-COF enable rapid and sensitive visual fluorescence detection. Tp, with its strong electron-withdrawing ability, modulates the electron cloud density of the porphyrin ring and optimizes the metal-ligand orbital, thereby enhancing its coordination and specific recognition capabilities. PDA also stabilizes the COF's tetragonal topology, reducing steric hindrance, fully exposing coordination sites, and making it easier to control the COF interlayer stacking state, providing powerful conditions for the preparation of fluorescent COF aerogels. Pyrrolidone is then further combined with polyvinyl alcohol to produce the final porphyrin-based COF aerogel (Tp-PDA-COF aerogel).

[0009] The present invention provides a method for preparing a porphyrin-based COF based on a double-bridged monomer, comprising the following steps:

[0010] In a pressure tube, the porphyrin and two bridging monomers (2,6-pyridinedicarboxaldehyde and 2,4,6-triformylphloroglucinol) were dispersed in a mixed solvent consisting of o-dichlorobenzene, n-butanol, and acetic acid. The tube was degassed through three freeze-vacuum-thaw cycles, then sealed and heated at 100-150°C for 2-4 days. The precipitate was collected and purified by washing with tetrahydrofuran. Finally, the product was dried under vacuum at 30-50°C overnight to yield a purple-black solid powder, a porphyrin-based COF based on the dual-bridging monomer, labeled Tp-PDA-COF. Preferably, the porphyrin is tetraaminophenylporphyrin (TAPP), which has a symmetrical rigid structure and active amino groups and is an ideal monomer for constructing high-performance COFs. The molar ratio of 2,6-pyridinedicarboxaldehyde and 2,4,6-triformylphloroglucinol is 1:1, wherein the volume ratio of o-dichlorobenzene, n-butanol, and 6M acetic acid in the mixed solvent is (1-10): (1-10): (1-2); more preferably, it is 6: 6: 1.

[0011] The present invention also provides a method for preparing a porphyrin-based COF aerogel based on a double-bridged monomer, comprising the following steps: first, preparing Tp-PDA-COF according to the above content; stirring a polyvinyl alcohol aqueous solution at 80-100°C for 2-4 hours to obtain a polyvinyl alcohol hydrogel, adding Tp-PDA-COF to the solution and continuously stirring to obtain a uniform solution, and then placing the solution in a freeze dryer for 1-3 days after three freeze-thaw cycles to obtain the desired aerogel.

[0012] Using TAPP as the main monomer, a double-bridged porphyrin-based covalent organic framework (Tp-PDA-COF) with a tetragonal topology was prepared by adding two bridging monomers, 2,4,6-triformylphloroglucinol (Tp) and 2,6-pyridinedicarboxaldehyde (PDA) at a molar ratio of 1:1. This framework has the ability to selectively detect fluorescent light and effectively capture heavy metal ions. The addition of bridging monomers Tp and PDA promotes electron transfer and the formation of coordination bonds, enhances the coordination ability of the porphyrin ring, fully exposes the coordination sites, reduces steric hindrance, and makes the interlayer stacking state of COFs easier to adjust. The establishment of the Tp-PDA-COF structure enables the porphyrin monomers in the framework to exhibit strong fluorescence to heavy metal Cu ions. 2+ Furthermore, TP-PDA-COF aerogel was constructed by combining with polyvinyl alcohol polymer. 2+ The selective coordination and synergistic adsorption of the gel structure further improve the adsorption effect. At the same time, the presence of polyvinyl alcohol polymer increases the interlayer spacing of Tp-PDA-COF, blocks the π-π stacking effect, and solves the fluorescence quenching problem of Tp-PDA-COF in the solid state. Therefore, the designed Tp-PDA-COF can realize fluorescence sensing and synergistic adsorption of Cu 2+ The COF aerogel material provided by the present invention realizes the dual goal of heavy metal Cu 2+ The present invention further studies its response mechanism and provides valuable guidance for further research in the field of heavy metal adsorption and detection in the environment.

[0013] The present invention also provides the application of the porphyrin-based COF aerogel based on the double-bridged monomer described above, wherein the porphyrin-based COF aerogel can perform fluorescence sensing and cooperative adsorption of heavy metal ions in water, especially for Cu 2+ The Tp-PDA-COF aerogel prepared by the present invention has good sensitive detection and adsorption selectivity. Under 350-450 nm excitation, the overall fluorescence color of Tp-PDA-COF is red. 2+ concentration, the blue fluorescence of COF at 450-470 nm remains unchanged, while the red fluorescence at 600-700 nm is gradually quenched, showing a series of fluorescence changes from red to blue, thereby achieving the2+ Visual detection.

[0014] Preferably, the application of the Tp-PDA-COF is to prepare a mixture containing various Cu 2+ The prepared Tp-PDA-COF was dissolved in N,N-dimethylformamide (DMF) and the fluorescence intensity was detected under 350-450 nm ultraviolet light to establish the fluorescence intensity ratio I 691 / I 464 With Cu 2+ The concentration (0-50μM) standard curve and linear equation; the fluorescence intensity ratio I of the sample 691 / I 464 Detection, according to the standard curve and linear equation, the Cu content in the sample is obtained 2+ concentration, thereby achieving Cu 2+ Quantitative detection.

[0015] Preferably, Tp-PDA-COF aerogel is prepared based on the designed Tp-PDA-COF combined with polyvinyl alcohol polymer. The polyvinyl alcohol polymer is used to enlarge the interlayer spacing of Tp-PDA-COF, blocking the π-π stacking effect, so that it can better retain the fluorescence characteristics. The overall fluorescence color of the Tp-PDA-COF aerogel is red, and the fluorescence of the aerogel increases with the increase of Cu. 2+ concentration, the red fluorescence on the aerogel is gradually quenched, showing a series of fluorescence changes from red to dark blue, thus realizing the Cu 2+ The change of aerogel fluorescence further illustrates the effect of the prepared Tp-PDA-COF aerogel on Cu 2+ synergistic adsorption.

[0016] Preferably, the prepared Tp-PDA-COF aerogel is placed in 20-50 mL of heavy metal solution (40-60 μM) to achieve the Tp-PDA-COF aerogel to Cu 2+ Evaluation of adsorption capacity (pH, temperature, time, heavy metal concentration, etc.).

[0017] It should be noted that the Tp-PDA-COF method for detecting Cu 2+ The principle is based on the charge transfer mechanism, specifically, in combination with Cu 2+ Previously, the electrons of Tp-PDA-COF were transferred within the porphyrin ring under excitation, achieving local excitation (LE) and fluorescence generation. 2+ After binding, some electrons of Tp-PDA-COF-Cu are transferred from the porphyrin ring to the adjacent benzene ring in the excited state, resulting in fluorescence quenching. The entire fluorescence signal response can be completed within 3 minutes. By establishing a fluorescence intensity relationship with Cu 2+The relationship between the concentration of Cu 2+ Quantitative detection of .

[0018] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0019] 1. The present invention constructs a covalent organic framework material (Tp-PDA-COF) by adding two bridging monomers, Tp and PDA, to achieve the 2+ The ultra-high sensitive detection solves the limitations of some COF materials in the specific recognition of heavy metals.

[0020] 2. Tp-PDA-COF of the present invention for Cu 2+ The detection principle is explained in detail through simulation calculations.

[0021] 3. Tp-PDA-COF of the present invention for Cu 2+ The detection limit was 40.76 nM, which was much lower than that of Cu in soil. 2+ The allowed limit.

[0022] 4. The present invention prepares Tp-PDA-COF aerogel based on the designed Tp-PDA-COF combined with polyvinyl alcohol to solve the problem of fluorescence quenching of COFs in the solid state.

[0023] 5. In addition, Tp-PDA-COF aerogel 2+ Under the synergistic adsorption effect of the selective coordination and gel structure of Cu 2+ It has an ultra-high adsorption capacity (1954 mg / g).

[0024] 6. The Tp-PDA-COF aerogel prepared in the present invention is a material with dual functions of sensitive detection and efficient adsorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention.

[0026] Figure 1 Schematic diagram of the synthesis of Tp-PDA-COF in Example 1 of the present invention.

[0027] Figure 2 TEM images of Tp-PDA-COF prepared in Example 1 at different magnifications.

[0028] Figure 3 XRD pattern and fine structure diagram of Tp-PDA-COF prepared in Example 1.

[0029] Figure 4 FTIR spectrum and solid-state 13C NMR spectrum of the material prepared in Example 1 of the present invention.

[0030] Figure 5 This is the XPS spectrum of Tp-PDA-COF prepared in Example 1 of the present invention.

[0031] Figure 6 These are the N2 adsorption test results of the Tp-PDA-COF prepared in Example 1 of the present invention.

[0032] Figure 7 Thermogravimetric analysis results of Tp-PDA-COF prepared in Example 1 of the present invention.

[0033] Figure 8 These are the excitation and emission spectrum analysis results of Tp-PDA-COF prepared in Example 1 of the present invention.

[0034] Figure 9 These are the quantum yield and fluorescence lifetime analysis results of Tp-PDA-COF prepared in Example 1 of the present invention.

[0035] Figure 10 These are the experimental results of the selectivity of Tp-PDA-COF prepared in Example 1 of the present invention to different metals (50 μM).

[0036] Figure 11 Figure A shows the addition of different concentrations of Cu 2+ The effect on the fluorescence spectrum of Tp-PDA-COF, the inset is the corresponding photo taken under 365nm ultraviolet light; Figure B is the fluorescence intensity ratio of Tp-PDA-COF (I 464 / I 691 ) and Cu 2+ The linear relationship between the concentrations.

[0037] Figure 12 The Tp-PDA-COF prepared in Example 1 of the present invention is added with Cu 2+ Stability test results for the first 2 hours and the last 2 hours.

[0038] Figure 13 The fluorescence of Tp-PDA-COF prepared in Example 1 was affected by different conditions.

[0039] Figure 14 The Tp-PDA-COF prepared in Example 1 of the present invention is Cu 2+ Fluorescence reaction kinetics.

[0040] Figure 15 Tp-PDA-COF and Cu prepared in Example 1 of the present invention 2+Three mode coordination schemes.

[0041] Figure 16 Tp-PDA-COF and Cu prepared in Example 1 of the present invention 2+ Mechanism of fluorescence quenching.

[0042] Figure 17 The synthesis process of Tp-PDA-COF aerogel and its effect on Cu 2+ Schematic diagram of fluorescence sensing and cooperative adsorption.

[0043] Figure 18 Characterization spectra of the Tp-PDA-COF aerogel prepared in Example 2 of the present invention under different conditions.

[0044] Figure 19 The Tp-PDA-COF aerogel prepared in Example 2 of the present invention was subjected to Cu 2+ XRD patterns and XPS spectra after adsorption.

[0045] Figure 20 Figure A shows the effect of Tp-PDA-COF aerogel on Cu at different pH values. 2+ Figure B shows the effective adsorption of Cu by Tp PDA COF aerogel at different temperatures. 2+ effective adsorption.

[0046] Figure 21 Figure A in the middle is the Cu on Tp-PDA-COF aerogel 2+ Figure B is the adsorption kinetics curve of the pseudo-second-order model; Figure C is the adsorption kinetics curve of the Weber-Morris model.

[0047] Figure 22 Figure A is the Tp-PDA-COF aerogel on Cu 2+ Figure A is the adsorption isotherm of the Langmuir model. Figure B is the adsorption isotherm curve that conforms to the Langmuir model.

[0048] Figure 23 Figure A is the Tp-PDA-COF aerogel on Cu 2+ Figure B shows the adsorption selectivity of Tp-PDA-COF aerogel for different metal ions. DETAILED DESCRIPTION

[0049] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the following embodiments will help those skilled in the art to further understand the embodiments of the present invention, but do not limit the embodiments of the present invention in any form. It should be pointed out that for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the embodiments of the present invention. These all fall within the scope of protection of the embodiments of the present invention.

[0050] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0051] Example 1:

[0052] A preparation method of porphyrin-based COF based on double-bridged monomers, the synthesis diagram of which is shown in FIG. Figure 1 As shown, the following steps are included:

[0053] 1. In a pressure tube, 101.5 mg (0.15 mmol) of tetraaminophenylporphyrin (TAPP) and 0.1 mmol of ligand (the ligand includes 2,6-pyridinedicarboxaldehyde and 2,4,6-triformylphloroglucinol, where the molar ratio of 2,6-pyridinedicarboxaldehyde to 2,4,6-triformylphloroglucinol is 1:1) are dispersed in a mixed solvent consisting of 6 ml of o-dichlorobenzene, 6 ml of n-butanol, and 1 ml of 6M acetic acid.

[0054] 2. Degas the pressure tube by three freeze-vacuum-thaw cycles, seal it, and heat it at 120°C for 3 days.

[0055] 3. The precipitate was collected and purified by washing with tetrahydrofuran. Finally, the product was dried at 40°C under vacuum overnight to obtain a purple-black solid powder, i.e., the target product, which was labeled as Tp-PDA-COF.

[0056] Example 2

[0057] A method for preparing a porphyrin-based COF aerogel based on a double-bridged monomer comprises the following steps:

[0058] A polyvinyl alcohol aqueous solution was stirred at 90°C for 3 hours to obtain a 10% polyvinyl alcohol hydrogel solution. 30 mg of the Tp-PDA-COF powder prepared in Example 1 was added to the solution and stirred continuously to obtain a uniform solution. A blank aerogel, without Tp-PDA-COF, served as a control. After three freeze-thaw cycles and subsequent placement in a freeze dryer for 2 days, the desired COF aerogel was obtained, designated as the Tp-PDA-COF aerogel.

[0059] Structural Analysis of Tp-PDA-COF and Its Aerogel

[0060] Using TAPP as the main monomer, a double-bridged porphyrin-based covalent organic framework (Tp-PDA-COF) with a tetragonal topology was prepared by adding 2,4,6-triformylphloroglucinol (Tp) and 2,6-pyridinedicarboxaldehyde (PDA) bridging monomers at a molar ratio of 1:1. This framework has the ability to selectively detect fluorescent and effectively capture heavy metal ions. The addition of bridging monomers Tp and PDA promotes electron transfer and the formation of coordination bonds, enhances the coordination ability of the porphyrin ring, fully exposes the coordination sites, reduces steric hindrance, and makes the interlayer stacking state of COF easier to adjust. The establishment of the Tp-PDA-COF structure enables the porphyrin monomers in the framework to exhibit strong fluorescence to heavy metal Cu ions. 2+ Furthermore, TP-PDA-COF aerogel was constructed by combining with polyvinyl alcohol polymer. 2+ The selective coordination and synergistic adsorption of the gel structure further improve the adsorption effect. At the same time, the presence of polyvinyl alcohol polymer increases the interlayer spacing of Tp-PDA-COF, blocks the π-π stacking effect, and solves the fluorescence quenching problem of Tp-PDA-COF in the solid state. Therefore, the designed Tp-PDA-COF can realize fluorescence sensing and synergistic adsorption of Cu 2+ dual goals.

[0061] Tp-PDA-COF on Cu 2+ Visualized fluorescence detection

[0062] Formulated with various Cu 2+ The prepared Tp-PDA-COF was dissolved in N,N-dimethylformamide (DMF) and the fluorescence intensity was detected under 433 nm ultraviolet light. Under 433 nm excitation, the overall fluorescence color of the Tp-PDA-COF was red. 2+ With the concentration of COF, the blue fluorescence at 464 nm remains unchanged, while the red fluorescence at 691 nm is gradually quenched, showing a series of fluorescence changes from red to blue. The fluorescence intensity ratio I is established based on this. 464 / I 691 With Cu 2+ The concentration (0-50μM) standard curve and linear equation; the fluorescence intensity ratio I of the sample 464 / I 691 Detection, according to the standard curve and linear equation, the Cu content in the sample is obtained 2+ concentration, thereby achieving Cu 2+ Quantitative detection.

[0063] Tp-PDA-COF aerogel for Cu2+ Fluorescence sensing and cooperative adsorption

[0064] Tp-PDA-COF aerogel was prepared based on the designed Tp-PDA-COF combined with polyvinyl alcohol polymer. The polyvinyl alcohol polymer was used to enlarge the interlayer spacing of Tp-PDA-COF, blocking the π-π stacking effect, so that it better retained the fluorescence properties. The overall fluorescence color of the Tp-PDA-COF aerogel was red. 2+ concentration, the red fluorescence on the aerogel is gradually quenched, showing a series of fluorescence changes from red to dark blue, thus realizing the Cu 2+ The change of aerogel fluorescence further illustrates the effect of the prepared Tp-PDA-COF aerogel on Cu 2+ synergistic adsorption.

[0065] The various materials prepared in the examples of the present invention were characterized, as described in detail below:

[0066] Figure 2 TEM images of Tp-PDA-COF prepared in Example 1 at different magnifications, where Figure A is a TEM image of Tp-PDA-COF at 100 nm, and Figure B is a TEM image of Tp-PDA-COF at 20 nm. The figures show that lattice fringe arrangement with a plane spacing of 2.62 nm can be observed, exhibiting tetragonal crystal fringe diffraction.

[0067] Figure 3Figure 1 shows the XRD pattern and fine structure of Tp-PDA-COF prepared in Example 1. Figure A shows the XRD pattern of Tp-PDA-COF, and Figure B shows the fine structure and pore size of Tp-PDA-COF obtained through MS modeling. In Figure A, the crystal structure of Tp-PDA-COF was elucidated by powder X-ray diffraction (PXRD) measurements, geometry optimization of the structural model using Materials Studio, Pawley refinement, and XRD fitting of the experimental data. The calculated peak positions and intensities of the PXRD mode of Tp-PDA-COF are consistent with the experimental results. The lattice parameters were determined to be a = 25.27 Å, b = 25.00 Å, c = 4.32 Å, and α = β = γ = 90°. Good agreement factors (Rwp = 3.30% and Rp = 2.27%) were achieved between the experimental PXRD data and the refined Pawley model. Finally, the PXRD pattern shows several diffraction lines, including a unique peak centered at 2θ = 4.11°, which is attributed to the (110) diffraction plane of the Tp-PDA-COF network, followed by a broader signal spanning the 6-10° 2θ range, mainly attributed to the (020), (220) and (310) planes. In addition, a relatively sharp and strong peak was observed at 2θ = 19.29°, corresponding to the (111) reflection. This broad diffraction peak was recorded as a conjugate superposition of two-dimensional layers. Figure B shows the pore size after refinement, with different colors representing different atoms in the figure as follows: N is blue, O is red, C is gray, and H is white. It can be seen that the pore size of Tp-PDA-COF is 26Å, which matches the lattice fringe arrangement with a plane spacing of 2.62 nm observed by transmission electron microscopy. This fully demonstrates the rationality of the designed Tp-PDA-COF structure.

[0068] Figure 4 FTIR spectra and solid-state 13C NMR spectra of the material prepared in Example 1 of the present invention. Figure A shows the FTIR spectra of TAPP, PDA, and Tp-PDA-COF; Figure B shows the solid-state 13C NMR spectrum of Tp-PDA-COF. The figures demonstrate the formation of an imine bond (C=N bond) in the structure, fully demonstrating the synthesis of Tp-PDA-COF.

[0069] Figure 5This is the XPS spectrum of Tp-PDA-COF prepared in Example 1 of the present invention. Figure A shows the overall XPS spectrum of Tp-PDA-COF; Figure B shows the refined spectrum and peak fitting at the C 1s peak in Figure A; Figure C shows the refined spectrum and peak fitting at the N 1s peak in Figure A; and Figure D shows the refined spectrum and peak fitting at the O 1s peak in Figure A. The figure shows that the binding energy of 399.99 eV is attributed to the formation of CC=NC in Tp-PDA-COF, while the binding energy of 397.88 eV is attributed to the binding energy of RC=NR on the porphyrin ring, where R represents a carbon atom on the porphyrin ring. C=O / OH was observed at 531.20 eV on the O 1s peak. This is consistent with the IR and 13C results, further confirming the successful synthesis of Tp-PDA-COF.

[0070] Figure 6 These are the N adsorption test results for Tp-PDA-COF prepared in Example 1. Based on the nitrogen adsorption isotherm at 77 K, the Brunauer-Emmett-Teller (BET) specific surface area of ​​Tp-PDA-COF was calculated to be approximately 1251.81 m² / g.

[0071] Figure 7 Thermogravimetric analysis results of Tp-PDA-COF prepared in Example 1 of the present invention; Thermogravimetric analysis (TGA) results show that Tp-PDA-COF is stable below 300°C.

[0072] Figure 8 The excitation and emission spectra of Tp-PDA-COF prepared in Example 1 of the present invention are shown in the figure. The optimal excitation wavelength for Tp-PDA-COF is 433 nm. Under 433 nm excitation, Tp-PDA-COF exhibits strong red fluorescence (691 nm) and weak blue fluorescence (464 nm).

[0073] Figure 9 Quantum yield and fluorescence lifetime analysis results for Tp-PDA-COF prepared in Example 1 of the present invention; Figure A shows the quantum yield analysis of Tp-PDA-COF; Figure B shows the fluorescence lifetime analysis of Tp-PDA-COF. Calculated fluorescence quantum yield of Tp-PDA-COF is 15.23%, and fluorescence lifetime is 9.178 ns.

[0074] Figure 10 This is the selectivity experiment of Tp-PDA-COF prepared in Example 1 for different metals (metal concentration is 50μM). 2+The selectivity and quenching efficiency of Tp-PDA-COF clearly indicate that the designed chemical structure of Tp-PDA-COF is beneficial to the quenching of Cu 2+ It has good sensitivity and excellent selectivity.

[0075] Figure 11 Figure A shows the addition of different concentrations of Cu 2+ The effect on the fluorescence spectrum of Tp-PDA-COF, the inset is the corresponding photo taken under 365nm ultraviolet light; Figure B is the fluorescence intensity ratio of Tp-PDA-COF (I 691 / I 464 ) and Cu 2+ The linear relationship between the concentrations. As can be seen in Figure A, as Cu 2+ With the gradual increase in concentration, the emission peak of Tp-PDA-COF at 691nm continues to decrease, while the blue fluorescence at 464nm remains unchanged, causing the fluorescence of Tp-PDA-COF to change from red to light blue. Figure B shows the fluorescence intensity ratio of Tp-PDA-COF (I 691 / I 464 ) and Cu 2+ The concentration showed a good linear relationship (R 2 =0.9964). By calculating 3δ / slope, Tp-PDA-COF has a good affinity for Cu 2+ The limit of detection (LOD) was as low as 40.76 nM.

[0076] Figure 12 The Tp-PDA-COF prepared in Example 1 of the present invention is added with Cu 2+ Stability test for the first 2 hours and the last 2 hours, where: Figure A is Tp-PDA-COF after adding 50µm Cu 2+ Stability test within the first 2 hours; Figure B is Tp-PDA-COF after adding 50µm Cu 2+ The stability test within the last 2 hours shows that Tp-PDA-COF has good detection stability.

[0077] Figure 13 Figure 1 shows the effects of different conditions on the fluorescence of Tp-PDA-COF prepared in Example 1. Figure A shows the effect of pH on Tp-PDA-COF fluorescence, and Figure B shows the effect of temperature on Tp-PDA-COF fluorescence. Figure A shows that when the ambient pH is less than 6, Tp-PDA-COF's inherent acid and alkali resistance makes its detection performance very stable. When the pH exceeds 6, the presence of Cu(OH)2 in the solution interferes with the detection results. Therefore, combined with subsequent adsorption experiments, pH 6 is the optimal choice. Figure B demonstrates that Tp-PDA-COF is minimally affected by ambient temperature during the detection process.

[0078] Figure 14 The Tp-PDA-COF prepared in Example 1 of the present invention is Cu 2+ Fluorescence reaction kinetics. As can be seen from the figure, when 25µM and 50µM Cu 2+ After that, Tp-PDA COF 2+ The responses were completed quickly within 3 minutes.

[0079] Figure 15 TP-PDA-COF and Cu prepared in Example 1 of the present invention 2+ Three different coordination schemes, according to the metal coordination principle, are shown in Figure A, Mode 1 (Cu coordinated in the porphyrin ring) 2+ ), Mode 2 in Figure B (Cu coordinated with Tp monomer 2+ ) and mode 3 in Figure C (Cu coordinated with PDA monomer 2+ ). Different colors in the figure represent different atoms, as follows: N is blue, O is red, C is gray, H is white, and Cu is green. The structure was optimized using the computational simulation package (VASP) and the PAW method. 2+ The three coordination configurations were structurally optimized and the reaction free energy ΔG was calculated. The results are shown in Table 1 below:

[0080] Table 1

[0081]

[0082] ΔG=ΔE+ΔZPE-TΔS

[0083] where E is the calculated total energy, ZPE is the zero-point energy, T is the temperature, and S is the entropy.

[0084] It can be seen that mode 1 (Cu coordinated in the porphyrin ring) 2+ ) has a reaction free energy ΔG of 0.207 eV, and mode 2 (Cu coordinated with Tp monomer) 2+ ) has an interaction free energy ΔG of 0.491 eV, and mode 3 (Cu coordinated with PDA monomer) 2+ ) The free energy ΔG is 2.317. Among the three modes, the reaction free energy of mode 1 is the smallest, indicating that the reaction is most likely to occur in mode 1 and the corresponding structure is the most stable.

[0085] Figure 16 TP-PDA-COF and Cu prepared in Example 1 of the present invention 2+ Mechanism of fluorescence quenching. The blue and orange isosurfaces represent the hole and electron distributions, respectively. 2+The material formed after the combination is marked as TP-PDA-COF-Cu. The electron hole density map of the previously optimized corresponding structure was analyzed using Multiwfn software. It can be seen intuitively from the electron hole density map of Tp-PDA-COF and Tp-PDA-COF-Cu that after the combination of Cu 2+ Previously, the electrons of Tp-PDA-COF were transferred within the porphyrin ring under excitation (orange → blue), achieving local excitation (LE) and fluorescence generation. 2+ After binding, some electrons in the excited state of Tp-PDA-COF-Cu transfer from the porphyrin ring (blue) to the adjacent benzene ring (orange), resulting in fluorescence quenching. This is because the orbitals of the electrons before and after the transition do not overlap spatially, and the electron-hole separation is relatively complete, resulting in a decrease in oscillator strength during the transition. This phenomenon, known as the transition barrier, achieves fluorescence quenching by charge transfer excitation (CT).

[0086] The oscillator strengths of TP-PDA-COF and TP-PDA-COF-Cu were calculated, and the results are shown in Table 2:

[0087] Table 2

[0088]

[0089] Table 2 Further verification of Cu 2+ The fluorescence quenching effect and mechanism of Tp-PDA-COF were studied by using electronic DFT of ORCA quantum chemical calculation software to calculate the oscillator strength of the excited states of Tp-PDA-COF and Tp-PDA-COF-Cu. The corresponding structures were optimized based on the r2SCAN-3c algorithm. For Tp-PDA-COF, the ground state of the structure is the singlet state S0. In the first excited state S1 of the singlet state, the excitation energy is 2.1310 eV, and the calculated oscillator strength f=0.09597 (oscillator strength = experimental transition probability / ideal harmonic transition probability), which can produce fluorescence. Generally speaking, the smaller the oscillator strength, the higher the transition barrier. For Tp-PDA-COF-Cu, the ground state of the structure is the double excited state D0. In the first excited state D1 of the double excited state, the excitation energy is 2.2450 eV, and the calculated oscillator strength f is 0.01502. This substance does not produce fluorescence in the excited state. This also confirms our experimental phenomenon, that is, the addition of Cu 2+ It will quench the fluorescence of Tp-PDA-COF solution.

[0090] Figure 17 The synthesis process of Tp-PDA-COF aerogel and its effect on Cu 2+Schematic diagram of fluorescence sensing and cooperative adsorption. It can be seen from the figure that based on the π→π stacking effect, Tp-PDA-COF exhibits fluorescence quenching in the solid state (such as Figure 17 However, the presence of polyvinyl alcohol polymer in the Tp-PDA-COF aerogel enables the Tp-PDA-COF aerogel to maintain its fluorescence properties ( Figure 17 Figure II). When Cu 2+ When , the fluorescence of Tp-PDA-COF aerogel is quenched, as shown in Figure 17 As shown in Figure III, this shows that Tp-PDA-COF aerogel can absorb Cu in the solution. 2+ , complete Cu 2+ Detection.

[0091] Figure 18 The characterization graphs of Tp-PDA-COF aerogel prepared in Example 2 of the present invention under different conditions; Figure A shows the characterization graphs of Tp-PDA-COF aerogel under Cu 2+ SEM images before and after adsorption; Figure B is Cu 2+ EDS spectra of Tp-PDA-COF aerogel before and after adsorption; Figure C shows Tp-PDA-COF aerogel adsorbing Cu 2+ The mapping spectra after adsorption are respectively the mapping spectra of C, N, O, and Cu. By comparing the Tp-PDA-COF aerogel before adsorption and the Tp-PDA-COF aerogel after adsorption of Cu 2+ The SEM spectrum of Tp-PDA-COF aerogel after adsorption (Figure A) shows that the Tp-PDA-COF aerogel after adsorption has a relatively uniform and regular pore structure. Through the analysis of EDS data before and after adsorption (Figure B), the Cu element is evenly distributed at different positions on the surface of Tp-PDA-COF aerogel, which fully demonstrates that Cu 2+ was successfully captured by Tp-PDA-COF aerogel. Combined with mapping image analysis (Figure C), Cu 2+ The emergence of once again proves that Tp-PDA-COF aerogel can adsorb Cu well 2+ .

[0092] Figure 19 The Tp-PDA-COF aerogel prepared in Example 2 of the present invention was subjected to Cu 2+ XRD pattern and XPS spectrum after adsorption; Figure A is Cu 2+ XRD patterns of Tp-PDA-COF aerogel after adsorption; Figures B to F are Cu 2+ XPS spectrum of Tp-PDA-COF aerogel after adsorption. The appearance of Cu characteristic peaks in the XPS graph indicates that Cu 2+ Entered the interior of Tp-PDA-COF aerogel.

[0093] The prepared Tp-PDA-COF aerogel was placed in 30 mL of heavy metal solution with a heavy metal ion concentration of 50 μM to evaluate the adsorption capacity of Tp-PDA-COF aerogel for different heavy metals (pH, temperature, time, heavy metal concentration, etc.). The results are shown in Figure 2. Figure 20-23 As shown. pH value is an important parameter for the adsorption of heavy metal ions during the adsorption process, which affects the surface charge of the adsorbent and metal ions, such as Figure 20 As shown in Figure A, the heavy metal is Cu 2+ It can be seen that with the increase of pH value, Tp-PDA-COF aerogel has a 2+ The adsorption capacity of Cu2+ gradually increases. When pH=6, the adsorption capacity reaches a maximum of 1942 mg / g. When pH>6.0, some Cu2+ 2+ The adsorption capacity of Tp-PDA-COF aerogel decreases as it exists in the form of Cu(OH)2. In addition, the effect of temperature on adsorption is studied by thermodynamic experiments. 2+ The adsorption capacity of Figure 20 Figure B in the middle) This may be because the increase in temperature intensifies the movement between molecules, thus obtaining stronger fluidity. However, when the temperature is increased from room temperature 25℃ to 40℃, the adsorption capacity only increases by about 10%, which is not compatible with the detection environment and cost. Therefore, in subsequent experiments, Cu 2+ The optimal pH value for adsorption was designed to be 6.0 and the adsorption temperature was 25°C. In order to study the effect of adsorption time on the adsorption behavior of Tp-PDA-COF aerogel, we conducted adsorption kinetics experiments. Figure 21 As shown in Figure A, Tp-PDA-COF aerogel has a strong affinity for Cu 2+ The absorption rate of Cu is highest in the first 30 minutes, and the growth rate slows down in the next 30-180 minutes. 2+ The adsorption amount of α-β ... Figure 21 (B), we found that the adsorption kinetics of Tp-PDA-COF aerogel can be matched with the pseudo-second-order model, which well explains the Cu 2+ The adsorption on Tp-PDA-COF aerogel is mainly dominated by chemical adsorption. In addition, we divide the adsorption process into two parts by fitting the WM model ( Figure 21 Figure C). Within 0-180 min, the lone pair electrons provided by the four nitrogen atoms on the porphyrin ring interact with the Cu 2+ Coordination, Cu 2+ The Tp-PDA-COF aerogel was adsorbed in the COF framework until the adsorption equilibrium was reached after 180 min.

[0094] In addition, in order to further understand the adsorption process, the adsorption of 0-50 mM (0-3200 mg / L) Cu 2+ Adsorption isotherm experiments were conducted in the concentration range of Figure 22 As shown in Figure A, when Cu 2+ When the concentration is lower than 3200 mg / L, Tp-PDA-COF aerogel has a strong 2+ However, due to the limited number of active sites of Tp-PDA-COF, the absorption of Cu 2+ The absorption of Cu2+ remained almost unchanged at concentrations above 3200 mg / L. Surprisingly, Tp-PDA-COF aerogel could adsorb up to 1954 mg / g of Cu2+. 2+ , which is superior to most MOF or COF materials reported previously; Figure 22 Figure B is the adsorption isotherm curve that conforms to the Langmuir model, R 2 =0.990, Langmuir model fitting results show that the single layer adsorbed on Tp-PDA-COF aerogel Cu 2+ In order to further explore whether Tp-PDA-COF aerogel still maintains the adsorption of Cu 2+ The selectivity of Cu was evaluated in practice for the detection and adsorption of Cu 2+ To investigate the possibility of the aerogels to be 10 Tp-PDA-COF, a series of 3200 mg / L metal ion solutions (Ca 2+ , Pb 2+ 、Hg 2+ Mg 2+ 、Cd 2+ 、Zn 2+ 、Mn 2+ 、Fe 3+ 、Al 3+ and Cu 2+ ) to conduct adsorption experiments. Figure 23 As can be seen in Figure A, Tp-PDA-COF aerogel has a strong affinity for Ca 2+ , Pb 2+ 、Hg 2+ Mg 2+ 、Cd 2+ 、Zn 2+ 、Mn 2+ 、Fe 3+ 、Al 3+ and Cu 2+The adsorption capacities of Tp-PDA-COF aerogel on Cu 2+ The absorption rate is very high, which may be due to the 2+ Furthermore, by calculating the distribution coefficient (Kd) for each metal ion, the results are as follows Figure 23 As shown in Figure B, Tp-PDA-COF aerogel has a strong affinity for Cu 2+ The Kd value can reach 1085.20 mL / g. These results fully confirm that Tp-PDA-COF aerogel has excellent selectivity and adsorption performance, which can achieve Cu 2+ Adsorption detection.

[0095] The above describes in detail the preferred embodiments of the present invention, and describes the basic principles, main features and advantages of the present invention. However, those skilled in the art should understand that the embodiments of the present invention are not limited to the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Within the scope of knowledge possessed by ordinary technicians in this field, various changes can be made without departing from the purpose of the embodiments of the present invention. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from this are still within the scope of protection of the embodiments of the present invention.

Claims

1. A method for preparing a porphyrin-based COF based on a double-bridged monomer, characterized in that: The following steps are involved: Porphyrin, 2,6-pyridinedicarboxaldehyde and 2,4,6-triformylphloroglucinol are uniformly mixed in a solvent to obtain a mixture, the mixture is placed in a sealed environment for heating reaction, and after the reaction is completed, the product is purified to obtain a purple-black solid powder, which is the target product; The porphyrin is tetraaminophenylporphyrin.

2. The method for preparing a porphyrin-based COF based on a double-bridged monomer according to claim 1, wherein: The molar ratio of the 2,6-pyridinedicarboxaldehyde to the 2,4,6-triformylphloroglucinol is 1:

1.

3. The method for preparing a porphyrin-based COF based on a double-bridged monomer according to claim 1, wherein: The heating reaction temperature is 100-150°C and the time is 2-4 days.

4. The method for preparing a porphyrin-based COF based on a double-bridged monomer according to claim 1, wherein: The solvent is a mixed solvent consisting of o-dichlorobenzene, n-butanol and acetic acid.

5. The method for preparing a porphyrin-based COF based on a double-bridged monomer according to claim 4, wherein: The volume ratio of o-dichlorobenzene, n-butanol and acetic acid is (1-10): (1-10): (1-2).

6. A porphyrin-based COF based on a double-bridged monomer, characterized in that The invention discloses a novel novel polyol for preparing the polyol for use in a pharmaceutical composition comprising the steps of claim 1 , wherein the polyol for use in the pharmaceutical composition is prepared by the preparation method described in any one of claims 1 to 5 .

7. A method for preparing a porphyrin-based COF aerogel based on a double-bridged monomer, characterized in that: The following steps are involved: A porphyrin-based COF based on a double-bridged monomer is prepared according to the preparation method according to any one of claims 1 to 5; The porphyrin-based COF based on the double-bridged monomer is dispersed in a polyvinyl alcohol hydrogel, and the target product is obtained by freeze-drying.

8. A porphyrin-based COF aerogel based on a double-bridged monomer, characterized in that: The preparation method is as claimed in claim 7.

9. The use of the porphyrin-based COF aerogel based on a double-bridged monomer according to claim 8, characterized in that: The porphyrin-based COF aerogel is capable of performing fluorescent sensing and cooperative adsorption of heavy metal ions in water.

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