A covalent organic framework composite adsorption material and its preparation method and application

Abstract

The present invention discloses a covalent organic framework composite adsorption material and a preparation method and application thereof, belonging to the field of environmental protection technology. The composite adsorption material comprises a metal oxide and a covalent organic framework material loaded with the metal oxide, wherein the synthesis raw materials of the covalent organic framework material comprise melamine and terephthalaldehyde. The synthesis method of the present invention is simple and easy to operate, with low raw material cost and high composite material yield. At the same time, the material has high adsorption efficiency, and exhibits efficient adsorption and fixation performance for fluoride ions due to the synergistic effect of abundant adsorption active sites and electrostatic attraction.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technology, in particular to the field of wastewater treatment technology, and specifically to a covalent organic framework composite adsorption material and a preparation method and application thereof. Background Art

[0002] Covalent organic frameworks (COFs) are organic building blocks linked together by covalent bonds to form a porous skeleton with a periodic structure. They are considered to be very attractive candidates for adsorption materials because of their large surface area, high porosity and well-organized channel structure. At present, progress has been made in gas adsorption separation and metal / non-metal ion adsorption. In order to further improve the adsorption performance and broaden the scope of application, research on composite materials formed by combining COF with other materials in the field of adsorption has also gradually been carried out. At present, some researchers have successfully combined COF with nanomaterials (such as nanoparticles, nanofibers, etc.) to form composite materials with larger specific surface area and better adsorption performance. For example, Li et al. combined Ti-MOFs and covalent organic frameworks (COFs) with triazine skeletons through covalent bonds to construct MOFs@COFs. Although Z-scheme heterojunction composites achieve efficient synergistic adsorption and degradation of bisphenols, the material's preparation method is relatively complex, requiring specific synthesis conditions and a long synthesis time, which limits its promotion in practical applications. Yu et al. synthesized a new magnetic covalent organic framework (COF) composite (Fe3O4@TpPa-NO2) composed of a magnetic Fe3O4 core and a TpPa-NO2 COF shell, and used it for the adsorption of Pb(II) in aqueous solution. However, its stability and recyclability in practical applications need to be further improved. Therefore, in order to achieve large-scale preparation and application of COF composites, it is necessary to develop a simplified and economical preparation method for covalent organic framework composites, and further improve its stability and recyclability to ensure its long-term stability and high performance in practical applications.

[0003] Fluoride ions in wastewater are harmful substances that can have serious impacts on the environment and human health. Therefore, removing fluoride ions from wastewater is a major environmental issue. Currently, there are no technical solutions for adsorbing fluoride ions using covalent organic framework composites. Summary of the Invention

[0004] In response to the above problems, the present invention provides a covalent organic framework composite adsorption material and a preparation method and application thereof.

[0005] The purpose of the present invention is achieved by adopting the following technical solutions:

[0006] A covalent organic framework composite adsorption material comprises a metal oxide and a covalent organic framework material loaded with the metal oxide. The synthetic raw materials of the covalent organic framework material comprise melamine and terephthalaldehyde.

[0007] Melamine is a rigid triazine ring with three active amino groups and is considered an ideal precursor for preparing complex organic frameworks. COFs synthesized from melamine and terephthalaldehyde are low-cost and have a simple preparation route.

[0008] Nano-metal oxides are rich in functional groups on their surface and are highly stable in adsorbing fluoride from aqueous solutions. The increase in the surface area of ​​metal oxide nanoparticles is highly conducive to the adsorption of fluoride. Their high adsorption capacity, non-toxicity, limited solubility in water and good desorption potential make them potential application materials for defluorination.

[0009] In some preferred embodiments, the metal oxide is at least one of iron oxide, titanium oxide, aluminum oxide, and magnesium oxide.

[0010] In particular, aluminum oxides and hydroxides have been used to repair fluoride-containing water. The Al site of alumina is one of the main adsorption sites and has high activity under acidic conditions, giving the material a higher affinity for fluorine. At the same time, alumina has a positively charged surface and produces electrostatic attraction, which is more conducive to the adsorption of negatively charged fluoride ions. In the recycling experiment, the alumina-composite COF material showed better regeneration performance than other composite materials.

[0011] In other preferred embodiments, the particle size of the metal oxide is 20 nm-5 mm, and a more preferred particle size is 20 nm.

[0012] The second aspect of the present invention is to provide a method for preparing the covalent organic framework composite adsorption material, specifically by using a solvent thermal method.

[0013] In some preferred embodiments, the solvent used in the solvothermal method is ultrapure water, ethanol, N,N-dimethylformamide or dimethyl sulfoxide, more preferably dimethyl sulfoxide.

[0014] In some preferred embodiments, the solvothermal method comprises the following steps:

[0015] The metal oxide, melamine and terephthalaldehyde are dispersed and dissolved in a dimethyl sulfoxide solvent, and heated in a sealed high-pressure reactor for reaction. After the reaction is completed, the reaction is cooled, the precipitate is separated, washed and dried to obtain the powdered covalent organic framework composite adsorption material.

[0016] In some preferred embodiments, the dispersing and dissolving is carried out under ultrasonic conditions, and the preferred ultrasonic time is 30 min.

[0017] In some preferred embodiments, the molar ratio of the melamine to the terephthalaldehyde is 1:(0.5-1), and a more preferred molar ratio is 3:2; the mass ratio of the metal oxide to the sum of the melamine and the terephthalaldehyde is (0.1-3):1, and a more preferred mass ratio is 1:2.

[0018] In some preferred embodiments, the reaction temperature of the heating reaction is 120-200° C., more preferably 180° C.; the reaction time is 12-72 h, more preferably 18 h.

[0019] In some preferred embodiments, the washing solvents are anhydrous ethanol and acetone, and the preferred washing method is to wash with anhydrous ethanol and acetone three times each.

[0020] The third aspect of the present invention is to provide an application method of the covalent organic framework composite adsorption material, specifically, an application as an adsorption and defluorination material.

[0021] The beneficial effects of the present invention are:

[0022] The present invention uses melamine and terephthalaldehyde as raw materials to synthesize a covalent organic framework, and loads metal oxide to successfully prepare a covalent organic framework / metal oxide composite material. The synthesis method is simple and easy to operate, the raw material cost is low, and the composite material yield is high. At the same time, the material has high adsorption efficiency. Due to the synergistic effect of abundant adsorption active sites and electrostatic attraction, it exhibits efficient adsorption and fixation performance for fluoride ions, and shows high selectivity for fluoride ions in anti-anion competition experiments. At the same time, adsorption regeneration experiments also verify its excellent cyclic regeneration performance. Compared with traditional covalent organic frameworks, it exhibits better material stability and wide application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is further described with reference to the accompanying drawings. However, the embodiments in the accompanying drawings do not constitute any limitation to the present invention. A person skilled in the art can obtain other drawings based on the following drawings without creative effort.

[0024] Figure 1 is a SEM image of the COF material described in Example 1;

[0025] Figure 2 is a SEM image of the Al2O3-COF material described in Example 2;

[0026] Figure 3 is the fluoride ion adsorption capacity of the adsorption materials described in Example 2 and Comparative Examples 1-6 at different pH values;

[0027] Figure 4 is the infrared spectrum of the Al2O3-COF material before and after adsorption described in Example 2;

[0028] Figure 5 is the XRD pattern of the Al2O3-COF material before and after adsorption described in Example 2;

[0029] Figure 6 is the XPS graph of the Al2O3-COF material before and after adsorption described in Example 2;

[0030] Figure 7 is the fluoride ion adsorption capacity of the Al2O3-COF material described in Example 2 in the presence of coexisting anions at different concentrations;

[0031] Figure 8 It is the regeneration adsorption capacity of the Al2O3-COF material described in Example 2 within 5 cycles. DETAILED DESCRIPTION

[0032] The present invention is further described with reference to the following examples.

[0033] Example 1

[0034] A covalent organic framework (COF) material, the preparation method of which comprises the following steps:

[0035] 0.94 g of melamine and 1.5 g of terephthalaldehyde were weighed separately and dissolved in 46 mL of dimethyl sulfoxide (DMSO) solvent. The mixture was ultrasonically treated for 30 minutes, then placed in a 100 mL stainless steel autoclave and heated in an oven at 180°C for 18 hours. After heating was completed, the mixture was cooled to room temperature and washed three times with anhydrous ethanol and acetone respectively. The mixture was then dried in a vacuum drying oven at 60°C for 24 hours to obtain the COF material.

[0036] Example 2

[0037] A covalent organic framework composite adsorption material (Al2O3-COF), the preparation method of which comprises the following steps:

[0038] 1.2 g of Al2O3 (20 nm level), 0.94 g of melamine, and 1.5 g of terephthalaldehyde were weighed separately and dispersed and dissolved in 46 mL of dimethyl sulfoxide (DMSO) solvent. The mixture was ultrasonically treated for 30 min, then placed in a 100 mL stainless steel autoclave and heated in an oven at 180°C for 18 h. After heating was completed and cooled to room temperature, the material was washed three times with anhydrous ethanol and acetone respectively, and dried in a vacuum drying oven at 60°C for 24 h to obtain the powdered covalent organic framework composite adsorption material.

[0039] Comparative Example 1

[0040] According to the present invention, 1.2 g of pure Al2O3 (20 nm level) is used as comparative example 1.

[0041] Comparative Example 2

[0042] According to the present invention, 1.2 g of pure Al2O3 (30 nm level) was used as comparative example 2.

[0043] Comparative Example 3

[0044] According to the present invention, 1.2 g of pure Al2O3 (40-60 nm level) was used as comparative example 3.

[0045] Comparative Example 4

[0046] According to the present invention, 1.2 g of pure Al2O3 (60-80 nm level) was used as comparative example 4.

[0047] Comparative Example 5

[0048] According to the present invention, 1.2 g of pure Al2O3 (80-100 nm level) is used as comparative example 5.

[0049] Comparative Example 6

[0050] According to the present invention, 1.2 g of pure Al2O3 (3-5 mm grade) was used as comparative example 6.

[0051] Experimental example

[0052] (1) The scanning electron microscope image of the COF material described in Example 1 is shown in the attached Figure 1 The scanning electron microscope image of the Al2O3-COF material described in Example 2 is shown in the attached Figure 2 .

[0053] (2) Using the uncompounded Al2O3 comparative examples (1-6) as a comparison, the adsorption performance of the Al2O3-COF material described in Example 2 for fluoride ions under different pH conditions was measured. The fluoride ion adsorption capacity of the Al2O3-COF material described in Example 2 and the uncompounded 20nm-5mm grade Al2O3 under different pH conditions is shown in the attached Figures. Figure 3 .

[0054] (3) The infrared spectra of the Al2O3-COF material before and after adsorption in Example 2 are shown in the attached Figure 4 , of which 3408cm -1 and 1694cm -1 The peaks of 500-800 cm represent the stretching vibration and bending vibration of the primary amine group of melamine. -1 The absorption peak represents the aluminum species, reflecting the good composite of Al2O3 and COF.

[0055] (4) The X-ray diffraction patterns of the Al2O3-COF material before and after adsorption in Example 2 are shown in the attached Figure 5 .

[0056] (5) The X-ray photoelectron spectrum of the Al2O3-COF material before and after adsorption in Example 2 is shown in the attached figure. Figure 6 , where: (a) full spectrum before and after adsorption; (b) Al 2p before adsorption; (c) Al 2p after adsorption; (d) N 1s before adsorption; (e) N1s after adsorption; (f) F 1s after adsorption.

[0057] (6) The Al2O3-COF material described in Example 2 coexists with anions (PO4 3- 、Cl - Br - 、NO3 - 、SO4 2- The fluoride ion adsorption capacity in the presence of Figure 7 .

[0058] (7) After adsorbing fluoride ions, the Al2O3-COF material described in Example 2 was desorbed and regenerated in a 0.005 mol / L alum solution. The regenerated adsorption performance was measured. The adsorption performance retention during the five cycles was shown in the attached figure. Figure 8 .

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. Application of a covalent organic framework composite adsorption material as a fluorine removal material, characterized in that: The covalent organic framework composite adsorption material comprises a metal oxide and a covalent organic framework material loaded with the metal oxide, the synthetic raw materials of the covalent organic framework material comprise melamine and terephthalaldehyde, and the metal oxide is aluminum oxide; The preparation method comprises the following steps: The metal oxide, melamine and terephthalaldehyde are dispersed and dissolved in a dimethyl sulfoxide solvent, and heated in a sealed high-pressure reactor for reaction. After the reaction is completed, the mixture is cooled, the precipitate is separated, and the powdered covalent organic framework composite adsorption material is obtained after washing and drying. The particle size of the metal oxide is 20 nm-5 mm; the molar ratio of the melamine to the terephthalaldehyde is 1:(0.5-1), and the mass ratio of the metal oxide to the sum of the melamine and the terephthalaldehyde is (0.1-3):

1.

2. The use of a covalent organic framework composite adsorption material as a fluorine removal material according to claim 1, characterized in that: The reaction temperature of the heating reaction is 120-200° C., and the reaction time is 12-72 hours.

3. The use of a covalent organic framework composite adsorption material as a fluorine removal material according to claim 1, characterized in that: The washing solvents are anhydrous ethanol and acetone.

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