CN113198425B

CN113198425B - Covalent organic framework material and preparation method and application thereof

Info

Publication number: CN113198425B
Application number: CN202110528898.XA
Authority: CN
Inventors: 吕文英; 金毓瀚; 庄晓钦
Original assignee: Guangdong University of Technology
Current assignee: Guangdong University of Technology
Priority date: 2021-05-14
Filing date: 2021-05-14
Publication date: 2022-08-19
Anticipated expiration: 2041-05-14
Also published as: CN113198425A

Abstract

The invention relates to the technical field of adsorption materials, in particular to a covalent organic framework material and a preparation method and application thereof. The invention discloses a novel covalent organic framework material which has the advantages of large specific surface area, high adsorptivity to hexavalent chromium and good cyclic adsorption performance. According to experimental data, after the adsorption is carried out for 300min, the removing amount of Cr (VI) by the Tp-DGCl adsorbent is 333.33mg/L, and the removing rate of hexavalent chromium ions can still reach 83.7% by the sixth adsorption.

Description

Covalent organic framework material and preparation method and application thereof

Technical Field

The invention relates to the technical field of adsorption materials, in particular to a covalent organic framework material and a preparation method and application thereof.

Background

Since the 21 st century, with the continuous development of economic society and the continuous acceleration of industrialization process in China, the problem of environment damage caused by economic development is very prominent, wherein serious heavy metal water environment pollution brings great influence to the life of people. Heavy metal pollutants have the characteristics of wide sources, difficult degradation, easy enrichment and the like, so that how to effectively remove heavy metal ions in water becomes an environmental problem which cannot be ignored at present.

Hexavalent chromium is an inhalation poison, skin allergy may be caused by human skin contact, genetic gene defects may be caused in severe cases, and human inhalation may be carcinogenic, so hexavalent chromium has a long-lasting risk to the environment. Hexavalent chromium is very easy to enter human body through alimentary canal, respiratory tract, human skin and mucosa, and the ingestion of large dose of hexavalent chromium can seriously damage the kidney and liver of human body. Hexavalent chromium is easily enriched in the environment and human body, so a method for effectively removing hexavalent chromium in wastewater needs to be found, and the harm to the human body and the environment is reduced.

The covalent organic framework material (COF) is a novel material of a crystal grid which is connected by light elements (C, O, N, B and the like) through covalent bonds and has permanent pore channels, has low density, high specific surface area and good chemical stability, brings rich application prospects for the COF material, but the synthetic COF material has poor absorption effect on hexavalent chromium ions.

Disclosure of Invention

In view of the above, the invention provides a covalent organic framework material, and a preparation method and an application thereof, and the covalent organic framework material has a large specific surface area, a good absorption effect on hexavalent chromium ions, and good cycle performance.

The specific technical scheme is as follows:

the invention provides a covalent organic framework material, which has a structural unit shown as a formula (I);

the covalent organic framework material with the structure provided by the invention has large specific surface area and good adsorption effect on Cr (VI).

The invention also provides a preparation method of the covalent organic framework material, which comprises the following steps:

and (2) carrying out polymerization reaction on the trialdehyde phloroglucinol and 1, 3-diaminoguanidine hydrochloride in a solvent to obtain the covalent organic framework material.

The reaction route is as follows:

the preparation mechanism of the covalent organic framework material is as follows:

the three aldehyde group phloroglucinol and 1, 3-diamino guanidine hydrochloride are polymerized under high temperature and closed condition, and then the tautomerism of hydroxyl and aldehyde group is generated in a reaction container to obtain the compound.

The invention adopts a simple heating synthesis method to prepare the covalent organic framework material, has simple process and is easy to realize industrial production.

In the invention, the molar ratio of the trialdehyde phloroglucinol to the 1, 3-diaminoguanidine hydrochloride is 1: (0.5 to 3), preferably 1: 0.75, 1: 1.5 or 1: 3;

in the invention, the solvent is water and 1, 4-dioxane, and the volume ratio of the water to the 1, 4-dioxane is 1: 4.

the temperature of the polymerization reaction is 110-130 ℃, the time is 18-30 hours, and the reaction is preferably carried out for 24 hours at 120 ℃.

The invention also provides the application of the covalent organic framework material or the covalent organic framework material prepared by the preparation method in heavy metal ion adsorption.

The invention also provides a method for treating heavy metals in sewage, which comprises the following steps:

and mixing the covalent organic framework material or the covalent organic framework material prepared by the preparation method with sewage containing heavy metal ions for adsorption.

In the present invention, the adsorption time is 4 to 6 hours, preferably 6 hours;

the mass ratio of the heavy metal ions to the covalent organic framework material is 1 (1-2.3). The covalent organic framework material provided by the application is adsorbed by 8 times of cycles, and the total adsorption amount is about 2266 mg/g.

According to the technical scheme, the invention has the following advantages:

the invention provides a novel covalent organic framework material which has the advantages of large specific surface area, high adsorptivity to hexavalent chromium and good cyclic adsorption performance. According to experimental data, after the adsorption is carried out for 300min, the removing amount of Cr (VI) by the Tp-DGCl adsorbent is 333.33mg/L, and the removing rate of hexavalent chromium ions can still reach 83.7% by the sixth adsorption.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

FIG. 1 is an SEM image of covalent organic framework materials prepared in example 1, comparative example 1 and comparative example 2 of the present invention, wherein a, b and c correspond to example 1, comparative example 1 and comparative example 2, respectively;

FIG. 2 is an XRD characterization of the covalent organic framework material prepared in example 1 of the present invention;

FIG. 3 is a TEM representation of a covalent organic framework material prepared according to example 1 of the present invention;

FIG. 4 is a BET characterization of the covalent organic framework material prepared in example 1 of the present invention;

FIG. 5 is a graphical representation of an infrared spectrum of a covalent organic framework material prepared in example 1 of the present invention;

FIG. 6 is a XPS characterization of covalent organic framework materials prepared in example 1 of the present invention before and after adsorption;

FIG. 7 is a schematic diagram showing the adsorption kinetics of Cr (VI) by the covalent organic framework material prepared in example 1 of the present invention;

FIG. 8 is a graph of the degradation rate of Cr (VI) in five cycles of the covalent organic framework material prepared in example 1 of the present invention.

Detailed Description

In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it should be apparent that the embodiments described below are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

Example 1

The embodiment is a preparation method of a covalent organic framework material Tp-DGCl, and the specific preparation steps are as follows:

1. weighing 4.759 x 10 ^-4 mol trialdehyde phloroglucinol, 7.198 x 10 ^-4 Putting mol 1, 3-diaminoguanidine hydrochloride into a standard glass throttle reaction tube with the specification of 25mL, adding 4mL ultrapure water and 12mL1, 4-dioxane into the reaction tube, sealing the reaction tube, putting the reaction tube into an oil bath kettle, heating the reaction tube at 120 ℃ for 24 hours, and fully cooling the reaction tube after the reaction is finished to obtain an intermediate product.

2. And (3) fully washing the intermediate product with methanol, ultrapure water and acetone in sequence, and drying the intermediate product with an oven to obtain the covalent organic framework material Tp-DGCl with the structure shown in the formula (I).

Example 2

1. Weighing 4.759 x 10 ^-4 mol trialdehyde phloroglucinol, 14.396 x 10 ^-4 Putting mol 1, 3-diaminoguanidine hydrochloride into a standard glass throttle reaction tube with the specification of 25mL, adding 4mL ultrapure water and 12mL1, 4-dioxane into the reaction tube, sealing the reaction tube, putting the reaction tube into an oil bath kettle, heating the reaction tube at 120 ℃ for 24 hours, and fully cooling the reaction tube after the reaction is finished to obtain an intermediate product.

2. And (3) fully washing the intermediate product with methanol, ultrapure water and acetone in sequence, and drying the intermediate product with an oven to obtain the covalent organic framework material Tp-DGCl.

Example 3

1. Weighing 4.759 x 10 ^-4 mol trialdehyde phloroglucinol, 3.599 x 10 ^-4 And (2) putting the mol 1, 3-diaminoguanidine hydrochloride into a standard glass throttle reaction tube with the specification of 25mL, adding 4mL of ultrapure water and 12mL of 1, 4-dioxane into the reaction tube, sealing the reaction tube, putting the reaction tube into an oil bath kettle, heating the reaction tube at the temperature of 120 ℃ for 24 hours, and fully cooling the reaction tube after the reaction is finished to obtain an intermediate product.

Comparative example 1

The embodiment is a preparation method of a covalent organic framework material TPODH, and the preparation method comprises the following specific steps:

1. 0.0180g of ODH (oxalyl dihydrazide) and 0.0210g of Tp (trialdehyde phloroglucinol) were weighed into an ampoule of 10mm X8 mm (outer diameter (od) X inner diameter (id)), 0.5mL of anhydrous 1, 4-dioxane and 0.5mL of mesitylene, and then subjected to sonication for 45 minutes, followed by addition of 0.4mL of an aqueous acetic acid solution. The bottle was heated at-196.15 deg.C (N) ₂ Liquid bath), stopping freezing when the internal pressure is evacuated to below 5Pa, and then obtaining an intermediate product by flame sealing.

2. The intermediate was reacted at 120 ℃ for 72 hours to give a brown solid, which was isolated by filtration and washed with anhydrous DMF and THF, and the resulting powder was immersed in anhydrous THF for 24h and then dried under vacuum at 100 ℃ overnight to give the covalent organic framework material TPODH.

Comparative example 2

The embodiment is a preparation method of a covalent organic framework material BT-DGCL, and the specific preparation steps are as follows:

1. weighing 2.00g of trimesic aldehyde and 2.32g of diaminoguanidine hydrochloride, placing the weighed materials in a 500mL pressure vessel with a polytetrafluoroethylene screw cap, adding 38mL of ultrapure water and 124mL of 1, 4-dioxane, heating the reaction mixture at 120 ℃ for 24 hours, and then cooling to room temperature to obtain an intermediate product.

2. The resulting intermediate was filtered, washed extensively with deionized water, MeOH and acetone, and then dried under vacuum at 70 ℃ for 12 hours to yield the covalent organic framework material BT-DGCL.

Comparative example 3

The comparative example is the preparation of covalent organic framework material Tp-TAB, and the specific preparation steps are as follows:

1. weighing 0.2mol of triaminobenzene and 0.15mol of trialdehyde phloroglucinol into a standard glass gate reaction tube with the specification of 10mL, adding 1.5mL of tetrahydrofuran, 2mL of 1, 4-dioxane and 0.8mL of N-butyl alcohol into the reaction tube, and placing the reaction tube at the temperature of-196.15 ℃ (N is ₂ Liquid bath), stopping freezing when the internal pressure is evacuated to below 5Pa, and then obtaining an intermediate product by flame sealing.

2. The intermediate product is reacted and heated at 120 ℃ for 72 hours to obtain red solid, which is filtered and separated, washed by 1, 4-dioxane, tetrahydrofuran and methanol, and then vacuum dried at 60 ℃ for 12 hours to obtain the covalent organic framework material Tp-TAB.

Test example 1

1. SEM analysis was performed on Tp-DGCl prepared in example 1, HIM analysis was performed on TPODH in comparative example 1, and SEM analysis was performed on BT-DGCL in comparative example 2, with the results shown in FIG. 1. As can be seen from fig. 1, the synthesized COF contains a large number of aggregates of short nanofibers. These nanofiber morphologies can facilitate their potential applications in the fields of adsorption, catalysis, and sensors.

2. The Tp-DGCl prepared in example 1 was characterized by infrared spectroscopy and XRD, and the results are shown in fig. 2 and 5. FIG. 5 is a characterization of the IR spectrum of COF comparing monomeric trihalophloroglucinol (Tp) and 1, 3-diaminoguanidine hydrochloride (DG) _Cl ) The infrared spectrogram proves that the synthesized material has the peak of 1585cm ^-1 A characteristic peak of C ═ C appears at 1622cm ^-1 The characteristic peak of C ═ O appears, and therefore, the successful synthesis of the material can be proved. XRD analysis of the Cu Ka radiation in FIG. 2 clearly reveals the crystal properties of Tp-DGCl, which is shown in FIG. 2 to be similar in crystal structure to BT-DGCl prepared in comparative example 2, confirming the successful preparation of Tp-DGCl. The results show that a broad peak exists at 27.1 ° corresponding to the (001) reflection of the sheet material, mainly due to poor pi-pi stacking between layers of material with a d-spacing value of 3.2A. The presence of loosely bound chloride ions and the positive charge of the guanidine units can reduce crystallinity by interfering with pi-pi stacking. The thermogravimetric curves in the figure were used to estimate the thermal stability of Tp-DGCl, and the results show that Tp-DGCl has excellent thermal stability below 274 degrees, which further demonstrates the efficient condensation of aldehyde with DGCl in the synthesis of Tp-DGCl.

3. TEM analysis of Tp-DGCl prepared in example 1 is shown in FIG. 3. As can be seen from FIG. 3, the Tp-DGCl surface contains many tentacle-like substances, indicating that the Tp-DGCl has a large specific surface area, which is favorable for the adsorption of substances.

4. Tp-DGCl prepared in example 1 was subjected to BET characterization, and the results are shown in FIG. 4, in comparison with those reported4m of BT-DGCl prepared in comparative example 2 ² The application of the ketone-alcohol tautomerism improves the specific surface area of Tp-DGcl greatly, because the ketone-alcohol tautomerism can convert benzene rings in the Tp-DGcl into aromatic hydrocarbon structures, the pi-pi stacking effect is weakened, and the interlayer spacing is enlarged, so that the specific surface area is increased. This also confirms the significant effect of the method applied to build the Tp-DGcl framework on increasing its specific surface area, ketone-thiol tautomerism.

Test example 2

In this example, Tp-DGCl prepared in example 1 is used to adsorb hexavalent chromium ions, and the specific steps are as follows:

(1) preparing 100mL K with Cr (VI) concentration of 200mg/L at 25 DEG C ₂ Cr ₂ O ₇ 25mg of Tp-DGCl prepared in example 1 was added to the solution, and the solution was adsorbed on a six-stage stirrer for 6 hours by adding a rotor.

(2) 2mL of sample solution were taken at regular intervals with a syringe and filtered using a 0.45 μm polyethersulfone membrane (no effect on Cr (VI) concentration).

(3) When the reaction is completed in 6 hours, the stirring is stopped.

(4) The reaction was poured into a sand-core funnel containing water-phase filter paper and filtered with suction.

(5) And drying the obtained COF after adsorption in a vacuum drying oven at 70 ℃ to obtain a sample after adsorption.

XPS analysis was performed on the collected samples, and the results are shown in fig. 6. The panel in fig. 6 shows the pore size adsorption distribution of the sample before adsorption, and the pore size of most micropores contained in the COF was 38A. The other figure is a BET adsorption closed curve, and the adsorption type of COF is judged to be type II through the adsorption closed curve, which shows that the surface of the adsorbate has stronger interaction, the adsorption quantity rapidly rises under lower relative pressure, and the curve is convex upwards. As can be seen from FIG. 6, Cr (VI) was successfully adsorbed on Tp-DGCl as demonstrated by COF spectrum, with peak binding energies of 576.93eV and 586.50 eV. With pure K ₂ Cr ₂ O ₇ (579.88eV ( Cr 2p 3/2) and 589.10eV ( Cr 2p 1/2)) undergo large energy shifts (2.95eV and 2.6eV), indicating that Tp-DGCl compares with that of Tp-DGClCr (VI) has remarkable strong affinity. As shown in FIG. 6, the Cl 2p 3/2 and Cl 2p 1/2 XPS data for Tp-DGCl and Tp-DGCr standards were plotted. It can be seen that the material peaks after adsorption at 197.24eV and 198.81eV are very weak, indicating that Cl elements have been removed from the material, indicating Tp-DGCl and Cr of the material ₂ O ₇ ^2- Ion exchange was performed.

The collected hexavalent chromium samples were analyzed by UV-visible spectroscopy. The maximum adsorption value of Cr (VI) was 540 nm.

As can be seen from FIG. 7, after the adsorption is carried out for 300min, the removal amount of Tp-DGCl on Cr (VI) prepared in example 1 is 333.33mg/g, which is higher than that of most of the reported adsorbents, and the Tp-DGCl has a good adsorption effect on Cr (VI). The mass of the material prepared in example 3 after washing is less, about 0.4 times that of the material prepared in example 2, and the adsorption effect is poor, and the average adsorption amount of Cr (VI) in example 3 is only 240mg/g after three times of repeated adsorption experiments. After being washed, the material prepared in the example 3 has similar quality and adsorption effect to the material prepared in the original example 1, and the average adsorption amount of the material prepared in the example 3 to Cr (VI) is 328mg/g through three times of repeated adsorption experiments.

The materials prepared in the comparative examples 1 to 3 can be obtained by repeating the adsorption experiment for three times, the average adsorption amount of the material prepared in the comparative example 1 to Cr (VI) is only 0.98mg/g, the average adsorption amount of the material prepared in the comparative example 2 to Cr (VI) is only 200mg/g, and the average adsorption amount of the material prepared in the comparative example 3 to Cr (VI) is only 154 mg/g. It can be observed that the covalent organic framework material synthesized in comparative example 1 does not contain hydroxyl groups and guanidine groups, the covalent organic framework material synthesized in comparative example 2 contains only guanidine groups, and the covalent organic framework material synthesized in comparative example 3 contains only hydroxyl groups. The covalent organic framework materials prepared in comparative examples 1, 2 and 3 have poor adsorption effect on Cr (VI). Compared with the comparative examples 1 to 3, the hydroxyl and aldehyde groups in the raw materials for preparing the covalent organic framework materials in the examples 1 to 3 are subjected to tautomerism in the reaction process, so that adsorption sites are increased, and the adsorption effect on Cr (VI) is remarkably improved by the synergy of the hydroxyl and aldehyde groups and the guanidine groups.

Test example 3

The embodiment detects the absorption cycle utilization rate of the Tp-DGCl to hexavalent chromium ions

The Tp-DGCl adsorbent reacted in the Cr (VI) solution adsorbed in example 2 was filtered, 0.5M NaOH and 1.0M HCl were used for desorption and recovery of the material, respectively, and washed three times with methanol, three times with ultrapure water, three times with acetone, and then dried in an oven at 70 ℃ overnight. 100mg of Tp-DGCl after reaction drying was weighed out and the experimental example 2, steps (1), (2), (3) and (4), was repeated, wherein K was 10mg/L ₂ Cr ₂ O ₇ 40mL of the solution was added 10mg of Tp-DGCl prepared in example 1. The test was repeated 5 times in total, and the amount of Cr (VI) solution removed after the cycle test was measured, and the results are shown in FIG. 8. As can be seen from FIG. 8, in the 5 th cycle test, the removal rate of Cr (VI) by the Tp-DGCl adsorbent can still reach 83.7%, that is, the concentration of hexavalent chromium in the adsorbed solution meets the national standard. This indicates that Tp-DGCl is a reliable reusable hexavalent chromium adsorbent.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. The application of a covalent organic framework material in heavy metal ion adsorption is characterized in that the covalent organic framework material has a structural unit shown as a formula (I);

the heavy metal ions are hexavalent chromium ions.

2. Use according to claim 1, wherein said covalent organic framework material is prepared by a process comprising the steps of:

3. Use according to claim 2, wherein the molar ratio of the triphenolide to the 1, 3-diaminoguanidine hydrochloride is 1: (0.5-3).

4. Use according to claim 2, wherein the solvent is water with 1, 4-dioxane;

the volume ratio of the water to the 1, 4-dioxane is 1: 4.

5. use according to claim 2, wherein the polymerization is carried out at a temperature of between 110 ℃ and 130 ℃ and for a time of between 18h and 30 h.

6. The method for treating heavy metals in sewage is characterized by comprising the following steps:

the covalent organic framework material of claim 1 is mixed with sewage containing heavy metal hexavalent chromium ions for adsorption.

7. The process according to claim 6, characterized in that the adsorption time is comprised between 4 and 6 hours.

8. The treatment method according to claim 6, wherein the mass ratio of the heavy metal hexavalent chromium ions to the covalent organic framework material is 1 (1-2.3).