Covalent organic framework material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of heavy metal detection and removal, in particular to a covalent organic framework material as well as a preparation method and application thereof. According to the specific technical scheme, 4, 4 ', 4' ', 4 '''-(pyrene-1, 3, 6, 8-tetrayl) tetraphenylamine (TFPPy) is used as an electron donor, 3, 3 '-dihydroxy-[1, 1'-biphenyl]-4, 4 '-dicarboxaldehyde (OH) and benzo [C] [1, 2, 5] thiadiazole-4, 7-dicarboxaldehyde (BTD) are used as electron acceptors, and the D-A type three-component covalent organic framework material (recorded as BTD-OH-COF) is synthesized through a solvothermal method. The covalent organic framework material is used as a quick response fluorescent sensor for detecting Cr (VI) ions with high sensitivity, the linear response range is 0.2-300 mu M, and the detection limit is 19 nM. Meanwhile, the covalent organic framework material can also be used as an efficient Cr (VI) light reducing agent, and still has very high removal efficiency on Cr (VI) under an acidic condition.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal detection and removal, and particularly relates to a covalent organic framework material, a preparation method thereof, and an application thereof. Background Art

[0002] As one of the important trace nutrients in the human body, chromium (Cr) is an important blood sugar regulator and also a component of protein degrading enzymes, playing an important role in the carbohydrate and lipid metabolism and protein synthesis of the human body. Chromium mainly exists in two valence states: trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)). The toxicity of chromium is related to the valence state in which it exists. Cr(VI) is 100 times more toxic than Cr(III), is easily absorbed by the human body and accumulates in the body, seriously endangering human health. The pollution sources of chromium mainly include wastewater discharged from the processing of chromium-containing ores, metal surface treatment, leather tanning, printing and dyeing, etc.

[0003] Currently, the conventional detection methods for Cr(VI) all rely on large instruments that are not convenient to carry and can only be carried out in the laboratory, such as inductively coupled plasma mass spectrometry and atomic absorption spectrometry, etc. The detection and purification steps are separated from each other. Therefore, the costs of detection and purification are high and it cannot be commercially applied. Due to the advantages of high sensitivity, good selectivity, and good portability of fluorescence detection, it is considered a promising detection method for Cr(VI), but it can only complete one detection link and cannot achieve the synchronous removal of Cr(VI).

[0004] Currently, the common removal methods for Cr(VI) include chemical reduction, physical adsorption, electroreduction, membrane filtration, etc. These methods require long-term adsorption, complex operations and equipment, and do not have the ability of self-detection, and must be combined with some complex Cr(VI) sampling and detection instruments. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a covalent organic framework material, a preparation method thereof, and an application thereof, which can simultaneously detect and remove hexavalent chromium, can support the synchronous progress of the detection and purification steps of Cr(VI) in wastewater, without the need for complex instruments and equipment and processes, has a fast speed, high efficiency, good effect, and low cost for the detection and purification treatment of Cr(VI) in wastewater, the process is simple, can simultaneously meet various requirements of the industry for the detection and purification treatment of chromium-containing wastewater, and is easy to be popularized and applied on a large scale.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] The present invention discloses a covalent organic framework material, and the structure is as follows:

[0008]

[0009] Correspondingly, a preparation method of a covalent organic framework material is to mix 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde, benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde, an organic solvent and a catalyst, and under a vacuum state, heat and react, and prepare through a Schiff base condensation reaction to obtain the covalent organic framework material.

[0010] Preferably, the molar ratio of 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde, and benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde is 1:0.5 - 1:1 - 1.5.

[0011] Preferably, the temperature of the heating reaction is 100 - 150 °C, and the time of the heating reaction is 24 - 72 h.

[0012] Preferably, the catalyst is an acetic acid solution, and the concentration of the acetic acid solution is 1 - 12 mol / L.

[0013] Preferably, the organic solvent is one or more of o-dichlorobenzene and n-butanol.

[0014] Correspondingly, a fluorescence sensor includes the covalent organic framework material described above.

[0015] Correspondingly, a photocatalytic reduction material includes the covalent organic framework material described above.

[0016] Correspondingly, an application of the covalent organic framework material, the fluorescence sensor, or the photocatalytic reduction material described above in treating wastewater containing hexavalent chromium ions.

[0017] Preferably, the application of the covalent organic framework material, the fluorescence sensor, or the photocatalytic reduction material in simultaneously detecting and removing hexavalent chromium ions has a linear response range of 0.2 - 300 μM, and the detection limit is 19 nM.

[0018] The present invention has the following beneficial effects:

[0019] 1. The present invention explores the great potential of covalent organic framework materials as both sensitive Cr(VI) fluorescence sensors and efficient photocatalytic reduction materials, and broadens the applications of COFs in fluorescence sensing, metal ion removal, and environmental analysis.

[0020] 2. The present invention uses 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraphenylamine (TFPPy) as an electron donor, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde (OH) and benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde (BTD) as electron acceptors, and synthesizes a D-A type three-component covalent organic framework material (denoted as BTD-OH-COF) by a solvothermal method. This covalent organic framework material is used as a rapid-response fluorescent sensor for highly sensitive detection of Cr(VI) ions, with a linear response range of 0.2 - 300 μM and a detection limit of 19 nM. At the same time, this covalent organic framework material can also be used as an efficient photoreductant for Cr(VI). Under acidic conditions, it still has a high removal efficiency for Cr(VI). The photoreduction efficiency of this covalent organic framework material for Cr(VI) exceeds 99%, and no co-catalyst is required. The D-A type three-component covalent organic framework material disclosed in the present invention broadens the applications of covalent organic frameworks (COF) in fluorescence sensing, metal ion removal, and environmental analysis.

[0021] 3. The covalent organic framework material provided by the present invention has good crystallinity, a large specific surface area, excellent fluorescence properties, and uniformly distributed adsorption sites. The linear response range is 0.2 - 300 μM, and the detection limit is 19 nM. At the same time, the covalent organic framework material has a uniform and dense pore structure, and the reduction and degradation rate of hexavalent chromium at room temperature exceeds 99%. Description of the Drawings

[0022] Figure 1 XRD and Fourier transform infrared spectra of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1;

[0023] Figure 2 Scanning electron microscope and transmission electron microscope images of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1;

[0024] Figure 3 Specific surface area and adsorption / desorption isotherms of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1;

[0025] Figure 4 Selectivity effect diagrams of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 for different metal ions in aqueous solution;

[0026] Figure 5Linear relationship diagram of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 for the detection of Cr(VI); among them, (a) is the fluorescence spectrum diagram of adding Cr(VI) solutions with different concentrations to the dispersion liquid; (b) is the standard curve for the detection of Cr(VI).

[0027] Figure 6 Interference effects of other possible co-existing ions and organic substances in the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 on Cr(VI).

[0028] Figure 7 Relationship diagram between the Cr(VI) removal efficiency of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 and the solution pH.

[0029] Figure 8 Relationship diagram between different dosages of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 and the Cr(VI) removal efficiency.

[0030] Figure 9 Relationship diagram between the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 and the Cr(VI) removal efficiency at different concentrations.

[0031] Figure 10 Removal efficiency diagram of Cr(VI) after the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 is reused 4 times. Detailed implementation manners

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0033] If not specifically specified, the technical means used in the implementation examples are conventional means well known to those skilled in the art.

[0034] The present invention discloses a covalent organic framework material, the structure is as follows:

[0035]

[0036] The present invention efficiently synthesizes a multifunctional covalent organic framework material in one step from amines and aldehydes as raw materials. Its prominent feature is the combination of an adsorption group, a photocatalytic enrichment group, and a fluorescent group, synergistically enhancing the adsorption-photocatalytic function, achieving a bifunctional COF (covalent organic framework) material capable of simultaneously detecting and removing hexavalent chromium, and showing good crystallinity, high porosity, and excellent stability.

[0037] The synthesis route is as follows:

[0038]

[0039] The specific preparation process is as follows: 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline (TFPPy), 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde (OH), benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde (BTD), an organic solvent, and a catalyst are mixed in a Pyrex tube. Under a vacuum state, a heating reaction is carried out. After the reaction is completed, the obtained red solid is washed 2 - 5 times with methanol, tetrahydrofuran, and acetone respectively, and Soxhlet extracted in tetrahydrofuran for 3 - 8 h. It is taken out and vacuum dried at 60 - 80 °C for 24 h to obtain a D-A type three-component covalent organic framework material (denoted as BTD-OH-COF). The molar ratio of 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde, and benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde is 1:0.5 - 1:0.5 - 1. The catalyst is an acetic acid solution, and the concentration of the acetic acid solution is 1 - 12 mol / L, further preferably 6 - 12 mol / L. The organic solvent is one or more of o-dichlorobenzene and n-butanol.

[0040] Furthermore, the temperature of the heating reaction is 100 - 150 °C, and the time of the heating reaction is 24 - 72 h.

[0041] Illustrate the amounts of the catalyst and organic solvents as follows: Based on 0.025 mmol of 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, add organic solvents o-dichlorobenzene and n-butanol with a volume ratio of o-dichlorobenzene to n-butanol being 1:1. Ultrasonic for 10 - 20 min, then add acetic acid solution with a concentration of 6 - 12 mol / L. If using a 10 mL tube, the volumes of o-dichlorobenzene and n-butanol added can be 1 - 3 mL respectively, and the added volume range of acetic acid solution is 0.2 - 0.6 mL. Under the condition of a 77K liquid nitrogen bath, perform freeze - pump - thaw cycle three times for vacuum degassing, then flame - seal the Pyrex tube. Heat the obtained mixture to 110 - 120 °C and react for 24 - 72 h. After the reaction is completed, filter the mixture after the reaction ends. Wash the obtained red solid with methanol, tetrahydrofuran, and acetone 2 - 5 times each, and perform Soxhlet extraction by soaking in tetrahydrofuran for 3 - 8 h. Take out and vacuum - dry at 60 - 100 °C for 24 h to obtain the covalent organic framework material, which is in the form of a red powder.

[0042] The covalent organic framework material prepared by the present invention can be applied to treat wastewater containing hexavalent chromium ions and can detect and remove hexavalent chromium ions simultaneously.

[0043] The covalent organic framework material prepared by the present invention can be used as a rapid - response fluorescence sensor for highly sensitive detection of Cr(VI) ions, with a linear response range of 0.2 - 300 μM and a detection limit of 19 nM.

[0044] The covalent organic framework material prepared by the present invention can also be used as a photocatalytic reduction material. Under acidic conditions, it still has a high removal efficiency for Cr(VI). The efficiency of photocatalytic reduction of Cr(VI) by this covalent organic framework material exceeds 99%, and no co - catalyst is required.

[0045] The present invention will be further elaborated below in combination with specific examples.

[0046] Example 1

[0047] Synthesis steps of D - A type three - component covalent organic framework material (ETD - OH - COF):

[0048] Put 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, 3,3'-dihydroxy - [1,1'-biphenyl]-4,4'-dicarbaldehyde, and benzo[c][1,2,5]thiadiazole - 4,7 - dicarbaldehyde into a 5 mL Pyrex tube. The molar ratio of 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, 3,3'-dihydroxy - [1,1'-biphenyl]-4,4'-dicarbaldehyde, and benzo[c][1,2,5]thiadiazole - 4,7 - dicarbaldehyde is 1:1:1.

[0049] Based on 0.025 mmol of 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, 1 mL of n-butanol and 1 mL of o-dichlorobenzene were added, and ultrasonic treatment was carried out for 20 minutes. Then, 0.2 mL of 6 M acetic acid solution was added. Under the condition of a 77K liquid nitrogen bath, freeze / pump / thaw cycles were performed three times to evacuate and degas. Then, the Pyrex tube was flame-sealed, and the obtained mixture was heated to 120 °C and reacted for 72 h. After the reaction, the reaction mixture was filtered. The obtained red solid was washed 3 times with methanol, tetrahydrofuran, and acetone respectively, and subjected to Soxhlet extraction by soaking in tetrahydrofuran for 3 - 8 h, and vacuum-dried at 60 °C for 24 h to obtain the D-A type three-component covalent organic framework material (BTD-OH-COF).

[0050] Product effect test

[0051] 1. Characterization of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1

[0052] Figure 1 XRD and Fourier transform infrared spectra of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1. From Figure 1 a, it can be seen that obvious diffraction peaks of the material are at 3.2°, 4.7°, 6.4°, and 9.5°. The results show that the BTD-OH-COF material has good crystal forms. Figure 1 From b, it can be known that "TFPPy" represents 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraphenylamine, "OH" represents 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde, "BTD" represents benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde, and "BTD-OH-COF" represents the covalent organic framework material prepared in Example 1. The C=O characteristic peaks of OH and BTD monomers at 1700 cm -1 disappear, and the stretching vibration signal of -NH2 (3340 cm -1 ) in the TFPPy monomer also disappears, indicating that a Schiff base reaction occurs between OH, BTD, and TFPPy. The stretching vibration of C=N is found at 1610 cm -1 , confirming the formation of imine bonds and indicating the successful preparation of COF.

[0053] Figure 2 SEM( Figure 2 a) and TEM( Figure 2 b) characterizations of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1. From Figure 2 a, it can be seen that the material morphology is coral-like. FromFigure 2 As can be seen from b, the material has obvious lattice fringes, indicating good crystal form.

[0054] Figure 3 It is the nitrogen adsorption-desorption isotherm of the D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1. The results are as Figure 3 shown. The adsorption-desorption isotherm belongs to type IV. The specific surface area of BTD-OH-COF is 755 m 2 / g. The catalyst has a large specific surface area, thus obtaining more catalytic reaction active sites.

[0055] 2. Fluorescent detection of hexavalent chromium in water by D-A type three-component covalent organic framework material (BTD-OH-COF)

[0056] The D-A type three-component covalent organic framework material (BTD-OH-COF) prepared in Example 1 was dispersed in MDF, and ultrasonic treatment was carried out for 30 min to prepare a 10 μg / mL BTD-OH-COF suspension. Record the fluorescence intensity F0 of the fluorescent substance before contacting the sample solution to be detected. The solution of the sample to be detected containing Cr(VI) was added to the suspension. After contacting and reacting for no less than 3 s, record the fluorescence intensity F generated by the fluorescent substance after the reaction. Calculate the value of the linear equation F0 / F - 1, and then compare it with the standard curve to obtain the concentration value of Cr(VI) in the sample solution to be detected containing Cr(VI). All tests were carried out at an excitation wavelength of λex = 415 nm, and the corresponding emission wavelength was at λem = 483 nm to measure the fluorescence intensity.

[0057] Figure 4 It is the fluorescence selectivity performance of BTD-OH-COF. Some heavy metal ions were selected for testing. As Figure 4 can be seen, when adding Ag + , Ni 2+ , Pb 2+ , Hg 2+ , Mn 2+ , Zn 2+ , Cu 2+ , Cd 2+ , Sn 2+ , Co 2+ , Cr 3+ , As 3+ , Al 3+ there is no obvious fluorescence change, while for Cr 6+The response value of F0 / F-1 caused is the largest. The specific steps are as follows: Take a certain mass of the above different metal ions and prepare sample solutions with a concentration of 1.0 mmol / L for standby. Take 2.5 mL of the prepared green COFs material dispersion and place it in the sample cell of a fluorescence spectrophotometer for scanning. When the concentration of the cuvette is 50 μmol / L, perform a secondary scan. The generated fluorescence signal is detected by a detector and the change in fluorescence intensity before and after the addition of the COFs material is recorded.

[0058] Figure 5 It is the linear response of BTD-OH-COF to Cr(VI). The specific steps are as follows: Place the COFs material dispersion in the sample cell of a fluorescence spectrophotometer for scanning, and record the fluorescence spectrum intensity F0; After the COFs material is fully contacted with different concentrations of chromium(VI) standard solutions, then place it in the sample cell of a fluorescence spectrophotometer for scanning, and record the fluorescence spectrum intensity F. The linear equation of the fluorescence quenching degree F0 / F-1 of the COFs material with different concentrations of chromium(VI) is obtained through data processing. Thus, the fluorescence spectra of the COFs material after reacting with different concentrations of chromium(VI) dispersions are obtained. Prepare chromium(VI) standard solutions with concentrations of 0.2, 1.0, 5.0, 10.0, 20.0, 30.0, 40.0, 50.0, 75.0, 100.0, 150.0, 200.0, 300.0 μmol / L for standby. As Figure 5 It can be seen that there are two good linear relationships between the material and the chromium(VI) concentration C. When the chromium(VI) concentration is 0.2 - 50.0 μmol / L, the linear regression equation is F0 / F-1 = 0.008 - 0.001C, and the linear correlation coefficient R 2 = 0.9919. When the chromium(VI) concentration is 50.0 - 300.0 μmol / L, the linear regression equation is F0 / F-1 = 0.023 - 1.442C, and the linear correlation coefficient R 2 = 0.9998, and the detection limit (S / N = 3) is 19 nM.

[0059] Figure 6 It is the anti-interference performance of BTD-OH-COF to Cr(VI). Select the inorganic ions and organic substances that may coexist in the sample for testing, including Cl - 、CO3 2- 、SO4 2- 、K + 、Mg 2+ 、Ca +, starch, glucose, D-fructose, L-lysine, L-threonine, L-leucine, L-arginine. When interferents were added to solutions containing 50.0 μmol / L of chromium(VI) respectively, the change rate of the fluorescence signal of BTD-OH-COF was less than 10%, indicating that these potentially co-existing inorganic ions and organic substances in the water environment had little interference on the detection of chromium(VI).

[0060] 3. Photocatalytic removal of hexavalent chromium in water by D-A type three-component covalent organic framework material (denoted as BTD-OH-COF) fluorescence

[0061] At room temperature, 5 mg of the covalent organic framework material prepared in Example 1 was dispersed into 50 mL of a Ct(VI) solution with pH = 3 and a concentration of 15 mg / L. To achieve adsorption-desorption equilibrium, the suspension was magnetically stirred in the dark for 60 min and then irradiated with visible light, with a 300 W xenon lamp (λ > 420 nm) as the light source. A blank check was set up to verify that the direct photolysis of Cr(VI) by visible light was negligible. At given time intervals, 1 mL of the reaction suspension was taken with a syringe, and the catalyst was filtered through a 0.22 μm aqueous filter membrane to remove residual particles. In a colorimetric tube, 1 mL of the reaction suspension solution after photocatalytic reduction, 0.5 mL of sulfuric acid, 0.5 mL of phosphoric acid solution, and 2 mL of the color reagent solution prepared freshly were mixed, and then made up to 25 mL. Stir for about 1 min and let stand for about 15 min, and the concentration of Cr(VI) was measured at the maximum absorption wavelength of 540 nm on a UV-vis spectrophotometer according to the diphenylcarbazide colorimetric method. To ensure the accuracy of the results, each sample was tested three times and the average value was taken.

[0062] First, the effect on the photocatalytic performance was investigated when treating Cr(VI) solutions with different pH values. It can be intuitively seen from Figure 7 that when pH = 3, BTD-OH-COF had the best photocatalytic effect in the solution, followed by pH = 5, 7, and 9 (pH = 3: 92.7%, pH = 5: 65.7%, pH = 7: 31.4%, pH = 9: 22.7%). Thus, it was concluded that the composite photocatalyst had better photocatalytic performance under acidic conditions than under alkaline conditions. The photoreduction performance decreased with the increase of the pH value, which could be considered from the existence form of Cr(VI) and the surface potential of the catalyst. This was because Cr(VI) existed in different ionic forms in acidic and alkaline environments. Under alkaline conditions, it was CrO4 2- , and an oxidation-reduction reaction occurred with photogenerated electrons to form Cr(OH)3 precipitate; while under acidic conditions, Cr(VI) existed in the form of Cr2O7 2- , and an oxidation-reduction reaction occurred to form Cr 3+It can be seen that in the alkaline condition, Cr(OH)3 is easily generated in the reaction system, which further blocks the active sites on the surface of the photocatalyst. Therefore, the acidic condition is more conducive to the reduction of Cr(VI).

[0063] Figure 8 It is the influence of different dosages of BTD-OH-COF on the photocatalytic performance. With the increase of the catalyst content, the ability of BTD-OH-COF to reduce Cr(VI) within 2 h gradually increases (2.5 mg: 84.2%, 5 mg: 99.1%, 7.5 mg: 99.7%, 10 mg: 99.8%). This is due to the increase of active sites, which improves the reduction efficiency.

[0064] Figure 9 It is the influence of Cr(VI) solutions with different concentrations on the photocatalytic performance. With the increase of the amount of chromium ions in the solution (10 mg / L: 99.7%, 15 mg / L: 99.8%, 20 mg / L: 92.2%, 25 mg / L: 89.7%), the adsorption sites on the surface of BTD-OH-COF reach saturation, and the content of the reaction material decreases. This situation leads to the competition between chromium ions for the adsorption sites, resulting in a decrease in the possibility of each chromium ion being adsorbed by BTD-OH-COF, thus reducing the reduction efficiency.

[0065] Figure 10 It is the stable reusability of the BTD-OH-COF material. BTD-OH-COF performs excellently in 4 cyclic experiments, and the reduction rate can reach more than 95%. And there is no obvious change in the BTD-OH-COF composite material. Therefore, it can be considered that BTD-OH-COF has good cyclic stability and can be reused for the photocatalytic reduction of Cr(VI), showing good practical application prospects.

[0066] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A covalent organic framework material, characterized in that: The structure is as follows:

2. A method for preparing the covalent organic framework material according to claim 1, characterized in that: 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde, benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde, an organic solvent and a catalyst are mixed and heated under vacuum to obtain a covalent organic framework material.

3. The preparation method according to claim 2, characterized in that: The molar ratio of 4,4',4”,4”'-(pyrene-1,3,6,8-tetrayl)tetraaniline, 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde, and benzo[c][1,2,5]thiadiazole-4,7-dicarbaldehyde is 1:0.5 - 1:1 - 1.

5.

4. The preparation method according to claim 2, characterized in that: The temperature of the heating reaction is 100 - 150 °C, and the time of the heating reaction is 24 - 72 h.

5. The preparation method according to claim 2, characterized in that: The catalyst is an acetic acid solution, and the concentration of the acetic acid solution is 1 - 12 mol / L.

6. The preparation method according to claim 2, characterized in that: The organic solvent is one or more of o-dichlorobenzene and n-butanol.

7. A fluorescence sensor, characterized in that: It includes the covalent organic framework material described in claim 1.

8. A photocatalytic reduction material, characterized in that: It includes the covalent organic framework material described in claim 1.

9. Use of the covalent organic framework material described in claim 1, the fluorescence sensor described in claim 7, or the photocatalytic reduction material described in claim 8 in treating wastewater containing hexavalent chromium ions.

10. The application according to claim 9, wherein: Use of the covalent organic framework material, the fluorescence sensor, or the photocatalytic reduction material in simultaneously detecting and removing hexavalent chromium ions, with a linear response range of 0.2 - 300 μM and a detection limit of 19 nM.

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