A two-dimensional covalent organic framework material based on fe doping and bipyridine ligand, preparation method and application thereof

Abstract

The application relates to a two-dimensional covalent organic framework material based on Fe doping and bipyridine ligands, a preparation method and application thereof, and belongs to the technical field of covalent organic framework materials. N,N,N',N'-tetra-(p-aminophenyl)-p-phenylenediamine (TAPD) and 2,2'-bipyridine-5,5'-diformyl (BPDA) are used as ligands to synthesize JLNU-305, and JLNU-305-Fe is obtained after reaction with ferrous sulfate heptahydrate, which has multiple active sites (Fe 2+ , Fe 3+ and pyridine N), and exhibits excellent catalytic performance in the activation of sodium persulfate (PDS) for the degradation of 2,4-dichlorophenol (2,4-DCP) under room temperature conditions. At room temperature, 10mg / L of 2,4-dichlorophenol can be removed at a removal rate of 100% by JLNU-305-Fe in only 8min, and the performance is far superior to that of inorganic or organic porous organic polymers, and the JLNU-305-Fe has good reusability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of covalent organic framework materials, and particularly relates to a two-dimensional covalent organic framework material based on Fe doping and bipyridine ligands, a preparation method and application thereof in degrading organic pollutants 2,4-dichlorophenol (2,4-DCP) under room temperature conditions by activating sodium persulfate (PDS). BACKGROUND

[0002] 2,4-dichlorophenol (2,4-DCP) with aromatic rings and chlorinated atoms is a typical persistent organic pollutant and a carcinogen, and is difficult to be degraded by traditional chemical oxidation or biological treatment technologies. There is an urgent need for new and advanced antibiotic wastewater treatment technologies to achieve efficient and reasonable treatment. Compared with other organic pollutant treatment technologies, advanced oxidation processes (AOPs) have the characteristics of strong oxidation capacity, high selectivity, environmental friendliness and wide application range, and show good activity in degrading various organic pollutants. Sodium persulfate (PDS) is an environmentally friendly, stable, non-toxic and easy-to-transport oxidant used in AOPs. PDS activated by transition metal-based heterogeneous catalysts has the advantages of simple synthesis, high efficiency, less secondary pollution and good recyclability. Therefore, it has become a research hotspot in the field of AOPs catalysis and can non-selectively degrade most of the refractory pollutants in wastewater, including aromatic compounds and part of heterocyclic compounds.

[0003] Covalent organic framework (COF) is a kind of porous crystalline material with clear structure and large porosity, which is connected by different ligands through strong covalent bonds. COF has a high specific surface area and rich heteroatoms, which provides more active sites for the loading of transition metals. The designed pore structure of COF can limit the growth of transition metals in the framework, avoid excessive aggregation of transition metals, and improve the dispersion degree, so that the composite material of transition metal-COF has higher catalytic performance. In addition, COF is formed by the periodic stacking of nanosheets, such as imine COF. This structure provides a highly conjugated π-electron system for COF, which improves the electron mass transfer efficiency in the oxidation process. Transition metals have the advantages of good stability, rich active sites and high dispersion, and the COF material combined with transition metals shows excellent catalytic performance in water purification process. SUMMARY

[0004] The application solves the problem of environmental pollution, synthesizes JLNU-305 by taking N,N,N',N'-tetrakis(p-aminophenyl)p-phenylenediamine (TAPD) and 2,2'-bipyridine-5,5'-diformyl (BPDA) as ligands, and then reacts with ferrous sulfate heptahydrate to obtain JLNU-305-Fe, which has multiple active sites (Fe 2+ , Fe 3+and pyridine N), showing excellent catalytic performance for 2,4-dichlorophenol (2,4-DCP) degradation.

[0005] As shown in Figure 1 The preparation method of the two-dimensional covalent organic framework material JLNU-305-Fe based on Fe doping and bipyridine ligand according to the present application is shown in the following steps:

[0006] (1) After mixing and grinding N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine (TAPD, 14.00-14.50 mg) and 2,2'-bipyridine-5,5'-diformyl (BPDA, 12.50-13.00 mg), the mixture is added to a high-temperature-resistant glass tube, and then 1,4-dioxane (1-1.2 mL) and 6 mol / L acetic acid (0.1-0.3 mL) mixed solvents are added;

[0007] (2) The glass tube of step (1) is frozen in liquid nitrogen, and the solution in the glass tube is kept in a non-flowing state. Vacuum is applied to make the pressure in the glass tube 0.10-0.20 mmHg, and then the mouth of the glass tube is sealed with a flame gun;

[0008] (3) The glass tube of step (2) is reacted at 100-130℃ for 3-7 days. After cooling to room temperature, the reaction product is taken out by opening the tube. The product is filtered and washed with acetone for 3-5 times. Then it is soaked in acetone for 3-5 hours. During the soaking period, the acetone is replaced for 3-5 times. Finally, the red-brown solid product JLNU-305 is obtained by vacuum drying;

[0009] (4) 50 mg of JLNU-305 obtained in step (3) and 100-110 mg of ferrous sulfate heptahydrate (Fe2SO4·7H2O) are soaked in a mixture of water and ethanol (volume ratio of water to ethanol is 1:1) for 24-26 hours, thereby obtaining JLNU-305-Fe, which is suitable for activating PDS to degrade 2,4-dichlorophenol.

[0010] The preparation method of the two-dimensional covalent organic framework material according to the above method is characterized in that: the two-dimensional covalent organic framework material JLNU-305 is prepared by using the strategy of bipyridine ligand. The synthesized metal-free COF is rich in active sites, which is convenient for modification or metal doping.

[0011] The two-dimensional covalent organic framework material JLNU-305-Fe based on Fe doping and bipyridine ligand is prepared by the above method.

[0012] The two-dimensional covalent organic framework material based on Fe doping and bipyridine ligand can be applied in the activation of sodium persulfate (PDS) to degrade organic pollutants 2,4-dichlorophenol (2,4-DCP) at room temperature.

[0013] The JLNU-305-Fe provided by the application shows excellent catalytic performance, Fe is introduced into the COF to form a Fe-COF composite material with a clear and stable structure, Fe has an electronic structure modulation effect on the COF framework, and generates a high-efficiency single-atom active site, so that the JLNU-305-Fe has excellent PDS activation performance. So far, there is no report on the synthesis of the material and its application in activating persulfate to degrade 2,4-dichlorophenol. At room temperature, the JLNU-305-Fe can remove 100% of 10 mg / L of 2,4-dichlorophenol in 8 min, and the performance is much better than that of inorganic or organic porous organic polymers.

[0014] Advantages

[0015] The application has the following innovations compared with the prior art:

[0016] 1. The covalent organic framework material JLNU-305 obtained by the application is synthesized by selecting a metal-ligand with catalytic function, and the synthesized metal-free COF is rich in active sites (pyridine N) and is convenient for modification or metal doping.

[0017] 2. The JLNU-305-Fe obtained by the application has excellent removal rate on 2,4-dichlorophenol in 8 min, and also has excellent degradation effect on high-concentration 2,4-dichlorophenol.

[0018] 3. The material obtained by the application is a new type of catalytic degradation catalyst, and after 4 cycles, the JLNU-305-Fe has basically consistent removal capacity on 2,4-dichlorophenol as the original catalyst, and has good reusability. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 : Synthesis schematic diagram of the bipyridine ligand covalent organic framework JLNU-305 and JLNU-305-Fe obtained in Example 1;

[0020] Figure 2 : PXRD spectrum of JLNU-305 (corresponding to figure a); experimental value of LNU-305 and AA stacking and AB stacking PXRD spectrum (corresponding to figure b); PXRD spectrum of JLNU-305 and JLNU-305-Fe (corresponding to figure c);

[0021] Figure 3 : FT-IR picture of the bipyridine ligand covalent organic framework JLNU-305 (corresponding to figure a) and JLNU-305-Fe (corresponding to figure b) obtained in Example 1;

[0022] Figure 4SEM images of the covalent organic framework JLNU-305 (corresponding to Figure a) and JLNU-305-Fe (corresponding to Figure b) obtained in Example 1;

[0023] Figure 5 Three-dimensional waterfall plot of JLNU-305-Fe degrading 2,4-DCP (corresponding to Figure a), removal rate curves of 2,4-DCP by different catalysts within 8 min (corresponding to Figure b); wherein the abscissa represents the reaction time, and the ordinate represents the pollutant concentration.

[0024] Figure 6 Removal rate curves of JLNU-305-Fe on different concentrations of 2,4-DCP (corresponding to Figure a); removal rate curves of 2,4-DCP by different radical quenchers (corresponding to Figure b); cycle stability curves of JLNU-305-Fe (corresponding to Figure c); removal rate curves of 2,4-DCP by different catalyst dosages (corresponding to Figure d); removal rate curves of 2,4-DCP by different PDS dosages (corresponding to Figure e); influence curves of different pH on the removal rate of 2,4-DCP (corresponding to Figure f). DETAILED DESCRIPTION

[0025] The application will be further described below in conjunction with the accompanying drawings and examples, but the scope of protection of the application is not limited to the following examples.

[0026] Example 1

[0027] N,N,N',N'-Tetrakis(p-aminophenyl)-p-phenylenediamine (TAPD, 14.18 mg, 0.03 mmol) and 2,2'-bipyridine-5,5'-diformyl (BPDA, 12.73 mg, 0.06 mmol) were mixed and ground for 30 min, then added to a high-temperature-resistant glass tube, followed by adding 1,4-dioxane (1.0 mL) and 6 mol / L acetic acid (0.1 mL) as mixed solvents. The glass tube was frozen in liquid nitrogen, the solution in the glass tube was kept in a non-flowing state, vacuum was drawn to make the pressure in the glass tube 0.15 mmHg, then the glass tube was sealed with a flame gun, and the length of the glass tube was reserved to about 13 cm. The glass tube was placed in an oven at 120℃ for 3 days to obtain a red-brown solid product. After cooling to room temperature, the product was filtered, washed with acetone three times, then soaked in acetone for 8 hours, and the acetone was replaced four times during the soaking period. Finally, vacuum drying was performed to obtain 22.90 mg of red-brown solid product JLNU-305. 50 mg of JLNU-305 and 100 mg of ferrous sulfate heptahydrate (Fe2SO4·7H2O) were soaked in a mixture of water and ethanol (volume ratio of water to ethanol was 1:1) for 24 h to obtain 56.98 mg of product, i.e. JLNU-305-Fe.

[0028] The material prepared by the above method was subjected to some structural characterization.

[0029] As shown in Figure 1 , it is shown that the obtained covalent organic framework material JLNU-305 is synthesized by selecting metal-free ligands N,N,N',N'-tetrakis(p-aminophenyl)paraphenylene diamine (TAPD) and 2,2'-bipyridine-5,5'-diformyl (BPDA) with catalytic function. The synthesized metal-free COF is a double-hole structure and rich in active sites, which is convenient for the doping of metal iron. Iron will be combined on bipyridine N to obtain JLNU-305-Fe.

[0030] As shown in Figure 2 (a), the crystal structure of JLNU-305 was determined by combining with the experimentally measured PXRD. The PXRD of JLNU-305 obtained by testing has a strong diffraction peak at 2.10°, proving that the material has a long-range ordered structure. The Pawley refinement result of the measured PXRD shows that the peaks of JLNU-305 at 2.10, 3.34, 4.02, 5.46, 6.22 and 7.30° positions correspond to the Bragg peaks of (100), (110), (200), (210), (300) and (310) planes, respectively. And the experimental value and the refinement result can be well matched Rwp=3.79%, Rp=2.93%. The experimental value and the data of the software-simulated AA packing are well matched (as shown in Figure 2 (b)). Based on the above results, the synthesized JLNU-305 is an AA-packed kgm topological framework structure. As shown in Figure 2 (c), it is a comparison of the PXRD patterns of JLNU-305 and JLNU-305-Fe. JLNU-305-Fe has a slightly decreased diffraction peak height at 2.10°, but the material structure after doping iron does not change.

[0031] As shown in Figure 3 (a) and 3(b), Fourier transform infrared (FT-IR) tests were performed on TAPD, BPDA, JLNU-305 and JLNU-305-Fe to characterize the changes of chemical bonds in the structure. From the infrared spectrum, it can be seen that the characteristic absorption peak intensity of C=O bond of BPDA at 1696 cm -1 -1 decreases at the same time, and the N-H stretching vibration peaks of TAPD at 3365, 3432 cm -1 -1 disappear after polycondensation. At the same time, the imine bond stretching vibration peak of JLNU-305 and JLNU-305-Fe at 1619 cm -1 -1 proves the existence of C=N bond in the structure. These results show that the material is successfully synthesized, and the structure of the material does not change after metal doping.

[0032] As Figure 4 (a) and (b) show the morphology size of JLNU-305 and JLNU-305-Fe characterized by scanning electron microscopy (SEM). From the SEM images, it can be seen that the morphology of JLNU-305 and JLNU-305-Fe materials is uniform dispersed cluster structure and the crystal morphology and crystal size are relatively uniform, with a small ball diameter of about 2.5 μm. The surface of JLNU-305-Fe is more rough than that of JLNU-305, which also indicates the successful doping of iron.

[0033] As Figure 5 (a) shows the three-dimensional waterfall plot of the degradation of 2,4-dichlorophenol. With the increase of degradation time, the peak of 2,4-dichlorophenol concentration becomes lower and lower until the peak height decreases to 0 at 8 min, indicating that 2,4-dichlorophenol is completely degraded. Figure 5 (b) shows the degradation ability of different systems for 2,4-dichlorophenol. When only JLNU-305-Fe is used as the catalyst, at most 55.1% of 2,4-dichlorophenol can be degraded, which is due to the weak adsorption and weak degradation behavior of COF materials. When PDS exists alone in the 2,4-dichlorophenol solution, only 3.6% of 2,4-dichlorophenol is degraded. When JLNU-305-Fe and PDS are added at the same time, the degradation rate of 2,4-dichlorophenol can reach 100% within 8 min, indicating that the degradation process is mainly carried out by the catalyst to activate PDS to generate free radicals. In addition, the degradation rate of JLNU-305 (68.5%) and JLNU-305-PDS system (39.4%) within 8 min is also evaluated, showing that JLNU-305-Fe / PDS has the best degradation performance.

[0034] As Figure 6 (a) shows that the obtained JLNU-305-Fe and PDS system also has excellent degradation effect on high concentration of 2,4-dichlorophenol. Within 30 min, the removal rates of 30 mg / L, 50 mg / L and 100 mg / L of 2,4-dichlorophenol are 98.0%, 95.7% and 86.4%, respectively. Within 150 min, the removal rates of 30 mg / L, 50 mg / L and 100 mg / L of 2,4-dichlorophenol are 100%, 99.6% and 98.6%, respectively, which shows that the pollutants can be completely degraded only with enough time. As Figure 6As shown in (b), a free radical capture experiment was conducted. L-ascorbic acid (L-AA), isopropanol (IPA), furfuryl alcohol (FFA), and methanol (MeOH) were used to capture superoxide radicals, hydroxyl radicals, singlet oxygen radicals, and sulfate radicals, respectively. It was found that L-ascorbic acid and furfuryl alcohol significantly inhibited the degradation of 2,4-dichlorophenol, while isopropanol and methanol had weak inhibitory effects, indicating a synergistic effect of free radicals and non-free radicals in the system. Figure 6 As shown in (c), to investigate the sustained catalytic activity of JLNU-305-Fe, a four-cycle experiment was conducted on 2,4-dichlorophenol using the JLNU-305-Fe / PDS system. The results showed that the final degradation efficiencies of 2,4-dichlorophenol in the four cycles were 100%, 100%, 100%, and 92.9%, respectively. This indicates that the removal capacity of JLNU-305-Fe for 2,4-dichlorophenol is essentially consistent with that of the original catalyst, demonstrating good reusability. Figure 6 As shown in (d), the effect of the JLNU-305-Fe / PDS system on the removal rate of 2,4-dichlorophenol under different experimental conditions is illustrated. It shows that as the catalyst dosage increases from 5 mg to 10 mg, 15 mg, and 20 mg, the degradation rate of 2,4-dichlorophenol increases from 50.3% to 100%, 92.2%, and 93.1% within 8 min, respectively. Figure 6 As shown in (e), the effect of PDS dosage is illustrated. With 5 mg of PDS, the system degrades 85.3% of 2,4-dichlorophenol. However, when the PDS dosage is increased to 15 mg and 20 mg, the degradation rate of 2,4-dichlorophenol decreases. This is because the rapid generation of reactive oxygen species (ROS) leads to quenching reactions between these ROS. In conclusion, adding more catalyst or more PDS may actually cause the system to lose some of its active species. Figure 6 As shown in (f), the degradation performance was also affected by the solution pH. Maintaining a constant pH during the experiment using a buffer solution was more practical than most experiments that only controlled the pH before the reaction. When the pH increased from 4.00 to 6.86, the degradation rate of 2,4-dichlorophenol increased from 60.2% to 97.6%. When the initial pH was further increased to 9.18, the degradation rate of 2,4-dichlorophenol reached 92.7%. This indicates that PDS becomes relatively unstable under acidic conditions and is relatively stable under neutral and alkaline conditions.

[0035] The above embodiments are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes, substitutions and improvements that can be easily conceived by those skilled in the art within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional covalent organic framework material based on Fe doping and bipyridine ligands, comprising the following steps: (1) Mix and grind 14.00-14.50 mg of N,N,N',N'-tetra(p-aminophenyl)p-phenylenediamine and 12.50-13.00 mg of 2,2'-bipyridine-5,5'-dicarboxaldehyde and add the mixture to a high-temperature resistant glass tube. Then add 1-1.2 mL of 1,4-dioxane and 0.1-0.3 mL of 6 mol / L acetic acid mixed solvent. (2) Place the glass tube after adding the mixed solvent in step (1) in liquid nitrogen to freeze, keep the solution in the glass tube in a non-flowing state, evacuate the vacuum to make the pressure in the glass tube 0.10~0.20mmHg, and then seal the glass tube opening; (3) The glass tube sealed in step (2) is reacted at 100-130°C for 3-7 days. After cooling to room temperature, the tube is opened and the reaction product is taken out. The product is filtered and washed with acetone 3-5 times. Then it is soaked in acetone for 3-5 hours. During the soaking period, the acetone is replaced 3-5 times. Finally, it is vacuum dried to obtain the reddish-brown solid product JLNU-305. (4) Soak 50 mg of JLNU-305 obtained in step (3) and 100-110 mg of ferrous sulfate heptahydrate in a mixture of water and ethanol for 24-26 h to obtain a two-dimensional covalent organic framework material based on Fe doping and bipyridine ligand, denoted as JLNU-305-Fe.

2. The method for preparing a two-dimensional covalent organic framework material based on Fe doping and bipyridine ligands as described in claim 1, characterized in that: In step (4), the volume ratio of water to ethanol is 1:

1.

3. A two-dimensional covalent organic framework material based on Fe doping and bipyridine ligands, characterized in that: It is prepared by the method described in claim 1 or 2.

4. The application of the two-dimensional covalent organic framework material based on Fe doping and bipyridine ligand as described in claim 3 in the degradation of organic pollutant 2,4-dichlorophenol by sodium persulfate at room temperature.

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