Disclosure of Invention
In order to overcome the problems of the prior art, the present invention provides a covalent organic framework composite material; the second purpose of the invention is to provide a preparation method of the covalent organic framework composite material; the invention also aims to provide application of the covalent organic framework composite material.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
in a first aspect, the present invention provides a covalent organic framework composite, said composite comprising an inner core and a coating layer;
the inner core comprises a covalent organic framework material which takes 1,3, 5-tri (4-aminophenyl) benzene and 2,3,5, 6-tetrafluoro-p-benzaldehyde as repeating structural units;
the coating layer comprises chitosan gel.
Preferably, the covalent organic framework material is a covalent organic framework of 1,3, 5-tris (4-aminophenyl) benzene and 2,3,5, 6-tetrafluoro-p-benzaldehyde connected with a repeating structural unit through an imine bond.
Preferably, the covalent organic framework material has the following structural formula:
preferably, the covalent organic framework material has a spherical structure.
Preferably, the diameter of the spherical structure is 200nm-800 nm.
A second aspect of the invention provides a method for preparing such a covalent organic framework composite, comprising the steps of:
1) mixing 1,3, 5-tri (4-aminophenyl) benzene and 2,3,5, 6-tetrafluoro-p-benzaldehyde, and reacting to obtain a covalent organic framework material;
2) and mixing the covalent organic framework material with chitosan and sodium tripolyphosphate, and reacting to obtain the covalent organic framework composite material.
Preferably, in this preparation method, the molar ratio of the 1,3, 5-tris (4-aminophenyl) benzene to the 2,3,5, 6-tetrafluoro-p-benzaldehyde is 1 (1.2-1.8), and more preferably, the molar ratio of the 1,3, 5-tris (4-aminophenyl) benzene to the 2,3,5, 6-tetrafluoro-p-benzaldehyde is 1 (1.3-1.7); still more preferably, the molar ratio of the 1,3, 5-tri (4-aminophenyl) benzene to the 2,3,5, 6-tetrafluoro-p-benzaldehyde is 1 (1.4-1.6).
Preferably, in this preparation method, the reaction in step 1) further comprises a catalyst.
Preferably, in the preparation method, the catalyst comprises at least one of formic acid, acetic acid, propionic acid, p-dibenzoic acid and 5-glutaric acid; further preferably, the catalyst comprises at least one of acetic acid, propionic acid and p-dibenzoic acid; most preferably, the catalyst is acetic acid.
Preferably, in this preparation method, the solvent for the reaction in step 1) comprises at least one of benzene, toluene, chlorobenzene, o-dichlorobenzene, and N, N-dimethylacetamide; further preferably, the solvent for the reaction in step 1) comprises at least one of ortho-dichlorobenzene and N, N-dimethylacetamide.
Preferably, in the preparation method, the reaction temperature in the step 1) is 10-40 ℃; further preferably, the reaction temperature in the step 1) is 20-30 ℃; most preferably, the reaction temperature in step 1) is 25 ℃.
Preferably, in the preparation method, the reaction time of the step 1) is 40-80 h; further preferably, the reaction time in step 1) is 48h to 72 h.
Preferably, in this preparation method, the reaction in step 1) further comprises a washing step.
Preferably, the washing step detergent in step 1) comprises at least one of tetrahydrofuran, methanol and acetone.
Preferably, in the preparation method, the chitosan in the step 2) is a chitosan aqueous solution with the mass concentration of 3 mg/mL-6 mg/mL; further preferably, the chitosan in the step 2) is a chitosan aqueous solution with the mass concentration of 4 mg/mL-5 mg/mL; still more preferably, the chitosan in the step 2) is a chitosan aqueous solution with the mass concentration of 4 mg/mL-4.5 mg/mL.
Preferably, in the preparation method, the reaction temperature in the step 2) is 10-40 ℃; further preferably, in the preparation method, the reaction temperature in the step 2) is 20-30 ℃; most preferably, in this preparation method, the reaction temperature in step 2) is 25 ℃.
Preferably, in the preparation method, the reaction time of the step 2) is 0.8h-1.5 h; further preferably, in the preparation method, the reaction time of the step 2) is 0.9h-1.2 h.
Preferably, in this preparation method, the reaction in step 2) further comprises a washing step.
Preferably, the washing step detergent of step 2) comprises at least one of methanol and ethanol.
A third aspect of the invention provides the use of a covalent organic framework composite according to the first aspect of the invention in the field of adsorption.
Preferably, the adsorption field is adsorption of fluorine-containing substances; more preferably, the adsorption field is the adsorption of perfluoro and polyfluoroalkyl compounds; still more preferably, the adsorption field is adsorption of perfluorooctanesulfonic acid (PFOS).
Preferably, the application method is to mix the covalent organic framework composite material with a fluorine-containing substance.
Preferably, the mass ratio of the valence organic framework composite material to the fluorine-containing substance in the adsorption process is 1 (0-7), but not 0; further preferably, the mass ratio of the valence organic framework composite material to the fluorine-containing substance in the adsorption process is 1 (0.1-6); still further preferably, the mass ratio of the valence organic framework composite material to the fluorine-containing substance in the adsorption process is 1 (0.1-5).
Preferably, the fluorine-containing substance is an aqueous solution with the mass concentration of 0mg/L-800mg/L, but 0 is not taken; more preferably, the fluorine-containing substance is an aqueous solution with the mass concentration of 1mg/L-700 mg/L; still more preferably, the fluorine-containing substance is an aqueous solution having a mass concentration of 10mg/L to 600 mg/L.
Preferably, in the adsorption process, the time for mixing the covalent organic framework composite material and the fluorine-containing substance is 0.5h-24 h.
The invention has the beneficial effects that:
the covalent organic framework composite material is obtained by reacting 1,3, 5-tri (4-aminophenyl) benzene and 2,3,5, 6-tetrafluoro-p-benzaldehyde to obtain a covalent organic framework material, and further coating the covalent organic framework material by chitosan gel. The preparation method disclosed by the invention is simple, efficient, safe and pollution-free. The covalent organic framework composite material prepared by the invention has excellent adsorption effect and can be widely applied to the adsorption field.
Specifically, the covalent organic framework composite material prepared by the invention has the following advantages:
1. the invention designs a covalent organic framework composite material with high adsorption performance aiming at PFASs, the composite material is prepared by the Schiff base reaction of two monomers of 1,3, 5-tri (4-aminophenyl) benzene and 2,3,5, 6-tetrafluoro-p-benzaldehyde at room temperature through a catalyst to form a covalent organic framework material with an imine bond connecting with a repeating structural unit, and further introduces an outer layer of chitosan gel through the cross-linking reaction of chitosan and sodium tripolyphosphate, thereby obviously improving the hydrophilicity, the adsorption rate and the adsorption capacity of COFs, meanwhile, the PFASs are adsorbed with high selectivity and high efficiency through the size selection effect, hydrophobic interaction, electrostatic interaction, fluorine-fluorine bond interaction and hydrogen bond interaction of the covalent organic framework composite material, so that the covalent organic framework composite material with high crystallinity, high porosity and high specific surface area is obtained.
2. The preparation method disclosed by the invention is simple and efficient, safe and pollution-free, does not need harsh experimental conditions, and can be synthesized only under room temperature conditions.
3. The covalent organic framework composite material prepared by the invention has excellent adsorption effect on perfluoro and polyfluoroalkyl compounds, the adsorption capacity on perfluorooctane sulfonate (PFOS) under experimental conditions can reach 4.99g/g, and the PFOS adsorption rate in 18h can reach 99.99%; meanwhile, the composite material has excellent recycling performance, and the adsorption effect of recycling is not obviously reduced; the covalent organic framework composite material prepared by the invention can be widely applied to the field of adsorption, in particular to the adsorption of pollutants such as perfluoro and polyfluoroalkyl compounds in the environment.
Detailed Description
The following description of the embodiments of the present invention is provided in connection with the accompanying drawings and examples, but the invention is not limited thereto. It is noted that the following processes, if not described in particular detail, are all realizable or understandable by those skilled in the art with reference to the prior art, and the reagents or equipment used are not indicated to the manufacturer, but are regarded as conventional products available commercially.
FIG. 1 is a chemical reaction scheme for the preparation of covalent organic frameworks according to the invention. The invention will be further described with reference to specific embodiments in the following, with reference to fig. 1.
Example 1
The covalent organic framework material of this example was prepared as follows:
uniformly mixing 28.1mg (0.08mmol) of 1,3, 5-tri (4-aminophenyl) benzene and 24.6mg (0.12mmol) of 2,3,5, 6-tetrafluoro-p-benzaldehyde in a reaction kettle, then adding 10mL of o-dichlorobenzene, carrying out ultrasonic treatment until the o-dichlorobenzene is completely dissolved, adding 0.8mL of glacial acetic acid aqueous solution with the concentration of 12mol/L as a reaction catalyst, and immediately carrying out violent shaking on a reaction system for 0.5-1 min. The reaction was then allowed to stand at room temperature for 60h, during which a yellow precipitate continuously precipitated. And transferring the system into a glass centrifuge tube after the precipitate is completely separated out, centrifuging to remove supernatant, washing the precipitate with 10mL of tetrahydrofuran, 10mL of methanol and 10mL of acetone in sequence respectively, and then drying the washed precipitate in vacuum at 100 ℃ for 12h to obtain light yellow powdery solid, namely the target product covalent organic framework material.
The resulting covalent organic framework material was subjected to scanning electron microscopy and figure 2 is a scanning electron microscopy image of the covalent organic framework material obtained in example 1. As can be seen from FIG. 2, the covalent organic framework material prepared in this example has a uniform spherical structure, and has a full particle size with a particle diameter of 200nm-800 nm.
The resulting covalent organic framework material was subjected to X-ray powder diffraction, and fig. 3 is an X-ray powder diffraction pattern of the covalent organic framework material obtained in example 1. As can be seen from fig. 3, the covalent organic framework material prepared in this example has high purity and good crystal form.
The covalent organic framework composite of this example was prepared as follows:
adding 10mg of the covalent organic framework material prepared in the step of example 1 into 20mL of chitosan aqueous solution with the concentration of 4mg/mL (containing 2% of acetic acid by mass fraction), carrying out ultrasonic oscillation for 30min, adding 10mL of sodium tripolyphosphate solution with the concentration of 0.5mg/mL after uniform dispersion, mixing uniformly, and carrying out polymerization reaction for 1h at room temperature under the condition of ultrasonic oscillation. And after the reaction is finished, transferring the reaction system into a glass centrifuge tube, centrifuging to remove supernatant, continuously washing the precipitate for 5 times (10mL multiplied by 5 times) by using 10mL of methanol, and then drying in vacuum at 120 ℃ for 12 hours to obtain light yellow powdery solid, namely the covalent organic framework composite material.
The resulting covalent organic framework composite was subjected to fourier transform infrared spectroscopy testing, and fig. 4 is a fourier transform infrared spectroscopy plot of the covalent organic framework composite obtained in example 1.
The obtained covalent organic framework composite material is subjected to X-ray photoelectron spectroscopy analysis, and FIG. 5 is an X-ray photoelectron spectroscopy analysis chart of the covalent organic framework composite material obtained in example 1. As can be seen in fig. 5, the covalent organic framework composite contains O, N, F, C and P elements.
And (3) carrying out an adsorption performance test on the obtained covalent organic framework composite material, wherein the test steps are as follows:
2mg of the activated chitosan gel-coated covalent organic framework material was dispersed in 20mL of an aqueous solution containing 500mg/L of perfluorooctanesulfonic acid (PFOS), and the mixture was stirred at 500rpm at room temperature to be adsorbed. After 18 hours, 200. mu.L of the upper aqueous solution was collected and passed through a 0.22 μm aqueous membrane, UPLC-MS/MS analysis was performed and PFOS removal rate and adsorption capacity were calculated.
The PFOS removal rate calculation formula is as follows:
PFOS removal rate ═ C0-Ct)/C0×100% (1)
In formula (1): c0And Ct(mg/L) are the concentrations of the PFOS solution at the initial reaction time and the given time (t), respectively;
the adsorption capacity calculation formula is as follows:
qe=(C0-Ce)×V/m (2)
in formula (2): v (L) is the volume of the solution; c0And Ce(mg/L) are the concentrations of the PFOS solution at the initial reaction time and at the equilibrium reaction time, respectively; m (g) is the mass of adsorbent; q. q.se(mg/g) represents the amount of adsorption at equilibrium.
Experimental results show that the removal rate of PFOS (perfluorooctanoic acid) by the covalent organic framework material coated by chitosan gel is as high as 99.99% within 18h, and the adsorption capacity is as high as 4.99 g/g.
The desorption and cycling experimental procedure for the covalent organic framework composite material of this example is as follows:
this section studies the adsorption-desorption cycling experiments of the covalent organic framework composite material for PFOS. Stirring the PFOS-loaded covalent organic framework composite material in 5mL of methanol solution until the PFOS is completely released, then centrifuging and collecting powder, activating by using methanol, drying in vacuum, and then adsorbing the PFOS again. The adsorption of the covalent organic framework wrapped by the chitosan gel to the PFOS shows good repeatability, and the PFOS removal rate is still kept above 90% after the chitosan gel is repeatedly used for 3 times.
The above examples are preferred embodiments of the present invention, but the present invention is not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.