阅读说明：本技术 一种共价有机骨架纳米线材料的制备方法及其应用 (Preparation method and application of covalent organic framework nanowire material ) 是由 朱广山 元野 马旭娇 于 2021-08-19 设计创作，主要内容包括：本发明提供了一种共价有机骨架纳米线材料的制备方法及其应用,涉及功能化材料领域。本发明提供的制备方法,包括以下步骤：利用水合肼与1,3,5-三醛苯基三嗪在混合有机溶剂和酸的催化下进行反应,得到共价有机骨架纳米线材料。通过调节有机溶剂中正丁醇的比例实现了纳米线的形态控制。纳米线的形貌尺寸在50-260nm。本发明制得的共价有机骨架纳米线材料具备高的长宽比,更大的比表面积和良好的光电性能。本发明制得的共价有机骨架纳米线材料在光照下和10ppm的铀离子溶液中,对铀的吸附容量高达1000～1300mg g～(-1)。经过5-10次铀的吸附-脱附循环实验后,提取铀的能力可达到首次总吸附量的75～90％。(The invention provides a preparation method and application of a covalent organic framework nanowire material, and relates to the field of functional materials. The preparation method provided by the invention comprises the following steps: hydrazine hydrate and 1,3, 5-trialdehyde phenyl triazine react under the catalysis of a mixed organic solvent and acid to obtain the covalent organic framework nanowire material. The shape control of the nano-wire is realized by adjusting the proportion of n-butyl alcohol in the organic solvent. The shape and size of the nano-wire is 50-260 nm. The covalent organic framework nanowire material prepared by the invention has high length-width ratio, larger specific surface area and good photoelectric property. The covalent organic framework nanowire material prepared by the invention has the adsorption capacity of 1000-1300 mg g to uranium in 10ppm uranium ion solution under illumination ‑1 . After 5-10 times of adsorption-desorption cyclic experiments of uranium, the capacity of extracting uranium can reach 75-90% of the first total adsorption amount.)

1. A covalent organic framework nanowire material, characterized in that the covalent organic framework nanowire material has the following structural formula:

2. the covalent organic framework nanowire material of claim 1, prepared by the following method:

mixing 1,3, 5-trialdehyde benzene triazine and hydrazine hydrate according to a molar ratio of 2: 5-2: 1, adding a mixed organic solvent, wherein the mixed organic solvent is a mixed solution of mesitylene, dioxane and n-butyl alcohol, the volume ratio of mesitylene, dioxane and n-butyl alcohol in the mixed solution is 1-10: 2-20, adding a catalyst acetic acid solution, the volume ratio of the catalyst acetic acid solution to the mixed solution is 1: 15-1: 5, heating at 90-180 ℃ for 1-7 days, cooling to room temperature to obtain a precipitate, collecting the formed precipitate, washing with anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran respectively, filtering, and vacuum drying at room temperature to obtain the covalent organic framework nanowire material.

3. The covalent organic framework nanowire material of claim 2, wherein the concentration of the acetic acid solution is 3 to 9 mol/L.

4. The covalent organic framework nanowire material of any one of claims 1 to 3, wherein the size of the covalent organic framework nanowire is 50 to 260nm, and the specific surface area is 852 to 1641m²·g^-1The average pore diameter was 2.6 nm.

5. Use of a covalent organic framework nanowire material according to claim 4 in the field of uranium solution treatment by photoreduction.

6. The application of the covalent organic framework nanowire material in the field of uranium solution treatment through a photoreduction method according to claim 5 is characterized in that under the illumination condition, the adsorption capacity of the covalent organic framework nanowire material on a 10ppm uranium-containing solution reaches 1000-1300 mg/g, and after 5-10 adsorption-desorption cycles, the amount of extracted uranium reaches 75-90% of the first total adsorption amount.

Technical Field

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

Background

In order to meet the ever-increasing energy demand, the exploitation of ocean uranium resources with a total storage capacity of 45 hundred million tons (about thousand times of terrestrial uranium) has attracted a great deal of attention. Thus, the prior art reports some adsorbtions at presentUranium material and adsorption method. The amino oxime group modified on the adsorbing material has strong uranium binding capacity and certain specific recognition capacity and is considered as the most promising physical adsorbing material, however, the extraction capacity is sharply reduced due to strong electrostatic interaction between very low-concentration uranyl ions and other high-concentration competitive cations, and finally reported adsorption capacity can only reach 700mg g^-1. In practical applications, a large number of associated ions not only compete with uranyl ions for adsorption sites, but also are difficult to effectively diffuse into the pores after entering the internal space of the adsorbent, which results in a drastic reduction in the effective collision rate with the adsorbent material. Therefore, the development of a green, clean and efficient uranium adsorption material is one of the technical problems to be solved at present.

Disclosure of Invention

In order to solve the technical problem, the invention provides a covalent organic framework nanowire material, and the structural formula of the covalent organic framework nanowire material is as follows:

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

mixing 1,3, 5-trialdehyde benzene triazine and hydrazine hydrate according to a molar ratio of 2: 5-2: 1, adding a mixed organic solvent, wherein the mixed organic solvent is a mixed solution of mesitylene, dioxane and n-butyl alcohol, the volume ratio of mesitylene, dioxane and n-butyl alcohol in the mixed solution is 1-10: 2-20, adding a catalyst acetic acid solution, the volume ratio of the catalyst acetic acid solution to the mixed solution is 1: 15-1: 5, heating at 90-180 ℃ for 1-7 days, cooling to room temperature to obtain a precipitate, collecting the formed precipitate, washing with anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran respectively, filtering, and vacuum drying at room temperature to obtain the covalent organic framework nanowire material.

Further, the concentration of the acetic acid solution is 3-9 mol/L.

Further, theThe size of the covalent organic framework nanowire is 50-260nm, and the specific surface area is 852-1641 m²·g^-1The average pore diameter was 2.6 nm.

The invention also provides application of the covalent organic framework nanowire material in the field of uranium solution treatment through a photoreduction method.

Furthermore, under the illumination condition, the adsorption capacity of the covalent organic framework nanowire material to a 10ppm uranium-containing solution reaches 1000-1300 mg-g^-1After 5-10 times of adsorption-desorption circulation, the uranium extraction amount reaches 75-90% of the first total adsorption amount.

The covalent organic framework nanowire material obtained by adjusting the solvent has unique nanowire appearance. In addition, the covalent organic framework nanowire material prepared by the method has strong photoelectric property and good adsorption property and cyclability to uranium under the illumination condition.

The invention utilizes n-butyl alcohol as a regulator, inhibits the growth of the material by utilizing the interaction of the n-butyl alcohol and the skeleton, synthesizes the covalent organic skeleton nanowire material, and the unique morphology and the ordered crystal structure of the material ensure that the covalent organic skeleton nanowire has excellent optical activity and can be used for extracting uranium from water. Under the irradiation of natural light, the covalent organic framework nano-wire releases a large amount of electrons and transmits the electrons to the surface of a material so as to electrostatically attract [ UO ] in water₂]²⁺. The photoactive units in the covalent organic framework nanowire material reduce u (vi) to u (iv). The result shows that the covalent organic framework nanowire prepared by the invention realizes 1000-1300 mg.g in water^-1High uranium extraction capacity. This result completely avoids the limitation of the number of physisorption sites on the adsorption capacity. After 5-10 times of recycling, the adsorption capacity can still keep 75-90% of the first total adsorption capacity.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 is a scanning electron microscope image and a transmission electron microscope image of a covalent organic framework nanowire material prepared in examples 1-6;

FIG. 2 is an infrared spectrum of the covalent organic framework nanowire material prepared in examples 1-6;

FIG. 3 is an X-ray powder diffraction pattern of the covalent organic framework nanowire material prepared in examples 1-6;

FIG. 4 is a nitrogen adsorption isotherm of the covalent organic framework nanowire materials prepared in examples 1-6;

FIG. 5 is a pore size distribution spectrum of the covalent organic framework nanowire prepared in examples 1-6;

FIG. 6 is a thermogravimetric plot of the covalent organic framework nanowire materials prepared in examples 1-6;

fig. 7 is an ultraviolet solid diffuse reflection spectrogram of the covalent organic framework nanowire material obtained in examples 1 to 6, and a small graph in the chart is an energy band gap calculated by a Kubelka-munk transformation equation of the covalent organic framework nanowire material obtained in examples 1 to 6;

FIG. 8 is a photoluminescence spectrum of the covalent organic framework nanowire material prepared in examples 1 to 6;

FIG. 9 is a time resolved PL attenuation spectrum of covalent organic framework nanowire materials prepared in examples 1-6;

FIG. 10 is a photo current response diagram of the covalent organic framework nanowire material prepared in examples 1-6;

FIG. 11 is an electrochemical impedance plot of the covalent organic framework nanowire materials prepared in examples 1-6;

FIG. 12 is a graph of uranium adsorption capacity versus time in light and dark for covalent organic framework nanowire materials prepared in examples 1 and 4;

fig. 13 is a bar graph of the adsorption capacity of the covalent organic framework nanowire material prepared in example 5 to uranium under illumination with pH change;

fig. 14 is a bar graph of 5 times of recycling of the covalent organic framework nanowire material prepared in example 4 by adsorbing uranium.

Detailed Description

The following examples are provided to illustrate the preparation method and application of the covalent organic framework nanowire material provided by the present invention, but they should not be construed as limiting the scope of the present invention.

Example 1

N₃Preparation of-COF-Nws-1 covalent organic framework nanowire material

A suspension was obtained by injecting 1,3, 5-trialdehyde benzotriazine (25mg, 0.065. mu. mol) and 0.45mL of dioxane, 0.45mL of mesitylene, 0.1mL of n-butanol and 0.1mL of a 6mol/L acetic acid solution into a 10mL pressure-resistant glass tube. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 120 ℃ for 72 hours. Taking out the pressure-resistant glass tube, cooling the temperature to room temperature, opening the pressure-resistant glass tube, collecting the formed precipitate, filtering and washing the precipitate by using anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran to obtain a powdery sample, and drying the powdery sample at room temperature and in vacuum to obtain a faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-1, having the formula:

N₃-COF-Nws-1 covalent organic framework nanowire material photoelectric property testing procedure

Example 1 preparation of covalent organic framework nanowires N₃-COF-Nws-1 is prepared into a working electrode, a platinum electrode is used as a counter electrode, and an Ag/AgCl electrode is used as a reference electrode, so that a three-electrode system is constructed. 0.1M Na in 20mL₂SO₄And performing EIS test and photocurrent test in an electrolyte environment. In the preparation of the working electrode, 5mg of covalent organic framework nanowire material N prepared in example 1 was used₃-COF-Nws-1, 50. mu.L Nafion and 1mL n-butanol were mixed and then sonicated for 30 minutes to obtain a slurry. The indium tin oxide glass was then divided into 1cm by 1cm pieces, sonicated in ethanol for 30 minutes, washed and dried for use. Dropping 30l of the slurry on an indium tin oxide glass sheet, and drying for 1h at normal temperature to obtain the working electrode. The working electrode was immersed in the electrolyte for 60s before the measurement was performed. For EIS measurements, the sine wave potential was applied at 5mV and AC amplitude between 0.01Hz-10⁵Hz。

300W xenon lamp with photocurrent test at 420nm cut-off filter (wavelength range 320nm ≤ lambda ≤ 780nm, light intensity 1kW m^-2) In the light, the current was measured when the light was turned on for 40s and turned off for 40 s. The relationship of the applied potential to Ag/AgCl was converted to NHE potential using the following formula: e_NHE＝E_Ag/AgCl+E^θ _Ag/AgCl(E^θ _Ag/AgCl＝0.199eV)。

N₃-COF-Nws-1 covalent organic framework nanowire material uranium adsorption step by photoreduction

Using a 300W xenon lamp (the wavelength range is more than or equal to 320nm and less than or equal to 780nm, the light intensity is 1kW m^-2) As a source of simulated sunlight. It was carried out in a 1000mL photoreactor cooled with circulating water (15. + -. 2 ℃ C.). With HNO₃Or NaOH water solution to adjust the pH value of the solution to 5. 2.5mg of covalent organic framework nanowire material N prepared in example 1₃-COF-Nws-1 was suspended as adsorbent in 500mL of a solution containing U (VI) (10 ppm). Samples were taken periodically and the solids were separated by filtration to give an adsorbed uranium solution for further ICP-MS characterisation to determine the content of u (vi). For comparison, under the corresponding conditions, stirring in the dark and sampling for further characterization. Time (q) is calculated using the following formula_tAdsorption capacity of mg/g): q. q.s_t＝(C_o–C_t) m.times.V, where V is the volume of the treating liquid (L), m is the amount of the adsorbent used (g), and C_oThe initial concentration of uranium (mg/L), C_tIs the uranium concentration (mg/L) after the covalent organic framework nanowire material is adsorbed.

Example 2

N₃Preparation of-COF-Nws-2 covalent organic framework nanowire material

A suspension was obtained by injecting 1,3, 5-trialdehyde benzotriazine (25mg, 0.065. mu. mol) and 0.4mL of dioxane, 0.4mL of mesitylene, 0.2mL of n-butanol and 0.1mL of a 6mol/L acetic acid solution into a 10mL pressure-resistant glass tube. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 120 ℃ for 72 hours. Taking out the pressure-resistant glass tube, cooling to room temperature, opening the pressure-resistant glass tube, and collectingThen filtering the precipitate by using anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran, and washing to obtain a powdery sample. Drying the powder sample at room temperature in vacuum to obtain a faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-2, having the formula:

N₃testing procedure for photoelectric Properties of-COF-Nws-2 covalent organic backbone nanowire Material and example 1N₃The testing steps of the photoelectric properties of the-COF-Nws-1 covalent organic framework nanowire material are consistent and are not repeated.

Example 3

N₃Preparation of-COF-Nws-3 covalent organic framework nanowire material

A suspension was obtained by injecting 1,3, 5-trialdehyde benzotriazine (25mg, 0.065. mu. mol) and 0.3mL of dioxane, 0.3mL of mesitylene, 0.4mL of n-butanol and 0.1mL of a 6mol/L acetic acid solution into a 10mL pressure-resistant glass tube. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 120 ℃ for 72 hours. And taking out the pressure-resistant glass tube, cooling to room temperature, opening the pressure-resistant glass tube, collecting the formed precipitate, filtering with anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran, and washing to obtain a powdery sample. Drying the powder sample at room temperature in vacuum to obtain a faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-3, having the formula:

N₃testing procedure for photoelectric Properties of-COF-Nws-3 covalent organic backbone nanowire Material and example 1N₃The testing steps of the photoelectric properties of the-COF-Nws-1 covalent organic framework nanowire material are consistent and are not repeated.

Example 4

N₃-COF-Nws-4 covalent organylPreparation of framework nanowire materials

A suspension was obtained by injecting 1,3, 5-trialdehyde benzotriazine (25mg, 0.065. mu. mol) and 0.2mL of dioxane, 0.2mL of mesitylene, 0.6mL of n-butanol and 0.1mL of a 6mol/L acetic acid solution into a 10mL pressure-resistant glass tube. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 120 ℃ for 72 hours. And taking out the pressure-resistant glass tube, cooling to room temperature, opening the pressure-resistant glass tube, collecting the formed precipitate, filtering with anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran, and washing to obtain a powdery sample. Drying the powder sample at room temperature in vacuum to obtain a faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-4, having the formula:

N₃-COF-Nws-4 testing procedure for photoelectric Properties of covalent organic backbone nanowire Material and N₃The testing steps of the photoelectric properties of the-COF-Nws-1 covalent organic framework nanowire material are consistent and are not repeated.

The experimental method for uranium adsorption by photoreduction is consistent with the step of uranium adsorption by photoreduction of the covalent organic framework nanowire material in the example 1N3-COF-Nws-1, and is not repeated.

N₃Experimental procedure for adsorption of uranium by photoreduction at different pH values for-COF-Nws-4 covalent organic frameworks nanowire Material adsorbents

Using a 300W xenon lamp (the wavelength range is more than or equal to 320nm and less than or equal to 780nm, the light intensity is 1kW m^-2) As a source of simulated sunlight. It was carried out in a 1000mL photoreactor cooled with circulating water (15. + -. 2 ℃ C.). With HNO₃Or NaOH water solution to regulate the pH value of the solution to 3-9. 2.5mg of covalent organic framework nanowire material N prepared in example 1₃-COF-Nws-4 was suspended as adsorbent in 500mL of a solution containing U (VI) (10 ppm). Samples were taken after 7 days of adsorption and the solid was separated by filtration to give a post-adsorbed uranium solution for further ICP-MS characterisation to determine the content of u (vi). For comparison, under the corresponding conditionsStirred in the dark and sampled for further characterization. Time (q) is calculated using the following formula_tAdsorption capacity of mg/g): q. q.s_t＝(C_o–C_t) m.times.V, where V is the volume of the treating liquid (L), m is the amount of the adsorbent used (g), and C_oThe initial concentration of uranium (mg/L), C_tIs the uranium concentration (mg/L) after the covalent organic framework nanowire material is adsorbed.

N₃Experimental procedure for reusability of-COF-Nws-4 covalent organic backbone nanowire Material adsorbents

With 1M Na₂CO₃And 0.1M H₂O₂Elution with the eluent of (2) elution N₃-COF-Nws-4 covalent organic framework nanowire material adsorbent and then re-used for uranium adsorption capacity determination. For 10mg of adsorbent, bound uranium was eluted for 1h at room temperature using 20mL of elution solution. The elution efficiency (E,%) was determined by the following formula: e ═ C_e×V_e)/((C_o-C_t)×V_t) 100% of C_e(mg/L) is the concentration of the uranium solution in the eluate, V_e(L) is a volume elution solution, C_t(mg/L) is the uranium concentration after uranium adsorption, C_o(mg/L) is the initial uranium concentration, V_t(L) is the volume of water used to effect adsorption. The resulting suspension was filtered and washed with ultrapure water until the supernatant became neutral. After vacuum drying, the resulting material was used for another adsorption experiment.

Example 5

N₃Preparation of-COF-Nws-5 covalent organic framework nanowire material

A suspension was obtained by injecting 1,3, 5-trialdehyde benzotriazine (25mg, 0.065. mu. mol) and 0.1mL of dioxane, 0.1mL of mesitylene, 0.8mL of n-butanol and 0.1mL of a 6mol/L acetic acid solution into a 10mL pressure-resistant glass tube. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 120 ℃ for 72 hours. And taking out the pressure-resistant glass tube, cooling the temperature to room temperature, opening the pressure-resistant glass tube, collecting the formed precipitate, filtering the precipitate by using anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran, and washing the precipitate to obtain a powdery sample. The powder samples were tested at room temperatureDrying in the air to obtain faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-5, having the formula:

N₃testing procedure for photoelectric Properties of-COF-Nws-5 covalent organic backbone nanowire Material and example 1N₃The testing steps of the photoelectric properties of the-COF-Nws-1 covalent organic framework nanowire material are consistent and are not repeated.

Example 6

N₃Preparation of-COF-Nws-6 covalent organic framework nanowire material

A suspension was obtained by injecting 1,3, 5-trialdehyde benzotriazine (25mg, 0.065. mu. mol) and 0.05mL of dioxane, 0.05mL of mesitylene, 0.9mL of n-butanol and 0.1mL of a 6mol/L acetic acid solution into a 10mL pressure-resistant glass tube. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 120 ℃ for 72 hours. And taking out the pressure-resistant glass tube, cooling the temperature to room temperature, opening the pressure-resistant glass tube, collecting the formed precipitate, filtering the precipitate by using anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran, and washing the precipitate to obtain a powdery sample. Drying the powder sample at room temperature in vacuum to obtain a faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-6, having the formula:

N₃testing procedure for photoelectric Properties of-COF-Nws-6 covalent organic backbone nanowire Material and example 1N₃The testing steps of the photoelectric properties of the-COF-Nws-1 covalent organic framework nanowire material are consistent and are not repeated.

Example 7

N₃Preparation of-COF-Nws-7 covalent organic framework nanowire material

1,3, 5-trialdehyde phenyl triazine (20mg,0.052 mu mo) is injected into a 10mL pressure-resistant glass tubeL) and 0.05mL of dioxane, 0.05mL of mesitylene, 0.9mL of n-butanol and 0.2mL of a 6mol/L acetic acid solution. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 120 ℃ for 96 hours. And taking out the pressure-resistant glass tube, cooling to room temperature, opening the pressure-resistant glass tube, collecting the formed precipitate, filtering with anhydrous chloroform, anhydrous acetone and anhydrous tetrahydrofuran, and washing to obtain a powdery sample. Drying the powder sample at room temperature in vacuum to obtain a faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-7, having the formula:

N₃testing procedure for photoelectric Properties of-COF-Nws-7 covalent organic backbone nanowire Material and example 1N₃The testing steps of the photoelectric properties of the-COF-Nws-1 covalent organic framework nanowire material are consistent and are not repeated.

Example 8

N₃Preparation of-COF-Nws-8 covalent organic framework nanowire material

A suspension was obtained by injecting 1,3, 5-trialdehyde benzotriazine (25mg, 0.065. mu. mol) and 0.05mL of dioxane, 0.05mL of mesitylene, 0.9mL of n-butanol and 0.2mL of a 6mol/L acetic acid solution into a 10mL pressure-resistant glass tube. Then hydrazine hydrate (5. mu.L, 50-60% solution) was added to the suspension, and then the pressure-resistant glass tube was sealed and heated at 150 ℃ for 48 hours. And taking out the pressure-resistant glass tube, cooling to room temperature, opening the pressure-resistant glass tube, collecting the formed precipitate, filtering with anhydrous chloroform, 50-60% solution of anhydrous acetone and anhydrous tetrahydrofuran, and washing to obtain a powdery sample. Drying the powder sample at room temperature in vacuum to obtain a faint yellow powder covalent organic framework nanowire material N₃-COF-Nws-8, having the formula:

N₃testing procedure for photoelectric Properties of-COF-Nws-8 covalent organic backbone nanowire Material and example 1N₃The testing steps of the photoelectric properties of the-COF-Nws-1 covalent organic framework nanowire material are consistent and are not repeated.

Structural characterization and Performance analysis

FIG. 1 is a scanning electron microscope image and a transmission electron microscope image of the covalent organic framework nanowire material prepared in examples 1-6, wherein A, C, E, G, I and K in FIG. 1 are respectively N of the covalent organic nanowire material obtained in examples 1-6₃-COF-Nws-1-N₃-COF-Nws-6 scanning electron micrograph, B, D, F, H, J and L in FIG. 1 are respectively the covalent organic nanowire materials N obtained in examples 1-6₃-COF-Nws-1-N₃-COF-Nws-6 transmission electron micrograph. From fig. 1, it follows: the prepared covalent organic framework nanowire material has a linear shape, and the diameter of the nanowire is 50-260 nm. The diameter of the nanowires is tapered as the proportion of n-butanol in the solvent system increases.

FIG. 2 is an IR spectrum of a series of covalent organic framework nanowire materials prepared in examples 1-6, which shows NH₂Characteristic peak of (A) is 3500cm^-1Disappears and C-N is 1619cm^-1And the stretching vibration peak appears. The reaction was demonstrated to occur.

FIG. 3 is an X-ray powder diffraction pattern of a series of covalent organic framework nanowire materials prepared in examples 1-6, and FIG. 3 shows that the amount of n-butanol does not affect the crystal structure of the covalent organic framework nanowire materials of examples 1-6. Also, the increase in n-butanol resulted in a gradual broadening of the diffraction peak at 3.52. This indicates that the X-ray powder diffraction pattern corresponds to the tapered nanowire diameter.

FIG. 4 shows nitrogen adsorption of a series of covalent organic framework nanowire materials prepared in examples 1-6. As can be seen from FIG. 4, the specific surface areas of the crystalline porous framework materials prepared in examples 1 to 6 were 1641, 1200, 1120, 852, 910 and 1082m, respectively²(ii) in terms of/g. Examples 1-4 the specific surface area of the covalent organic framework nanowire materials prepared was gradually reduced. The decrease in crystallinity affects the porosity as the volume ratio of n-butanol in the mixed solvent increases. Fruit of Chinese wolfberryExamples 4-6 the specific surface area of the covalent organic framework nanowire materials was gradually increased. Due to the increased external surface area of the material per unit mass caused by the gradually decreasing diameter of the nanowires.

Fig. 5A-F are pore size distribution spectra of the covalent organic framework nanowire materials prepared in examples 1-6, respectively, and it can be seen from fig. 5 that the average pore size of the covalent organic framework nanowire materials obtained in examples 1-6 is about 2.6 nm.

Fig. 6A-F are thermogravimetric spectra of the covalent organic framework nanowire material prepared in examples 1-6, and the covalent organic framework nanowire material prepared by the present invention has good thermal stability.

FIGS. 7A-F are solid UV diffuse reflectance spectra of the covalent organic framework nanowire materials prepared in examples 1-6. The small graphs in the graphs of FIGS. 7A-F are band gaps calculated by a Kubelka-munk transformation equation of the covalent organic framework nanowire materials prepared in examples 1-6. Fig. 7 was analyzed to evaluate its absorption capacity to determine the band structure of different samples. The proper energy band of visible light absorption is in the range of 1.9-3.1eV, so that the covalent organic framework nanowire material is suitable for photoreduction. The visible light absorption energy band of the covalent organic framework nanowire material obtained in the embodiments 1-6 is in the range of 2.55-2.65eV, so that the covalent organic framework nanowire material prepared by the method is suitable for photoreduction.

FIG. 8 is a photo luminescence spectrum of the covalent organic framework nanowire material prepared in examples 1 to 6. FIG. 8 shows that the fluorescence emission peak has a broad center at 590 nm. Among them, example 4 of the present invention prepares covalent organic framework nanowire material N₃The fluorescence intensity of-COF-Nws-4 is strongest, which indicates that the covalent organic framework nanowire material N prepared by the example 4 in the invention₃The COF-Nws-4 can generate more photogenerated electrons and greatly improve the optical excitation rate.

FIG. 9 is a time-resolved PL attenuation spectrum of the covalent organic framework nanowire material prepared in examples 1-6, wherein example 4 of the present invention prepares covalent organic framework nanowire material N₃The fluorescence lifetime of-COF-Nws-4 is longest and is 1.69 ns. The longer the fluorescence lifetime indicates that the material generates more photogenerated electrons for photoreduction。

FIG. 10 is a photocurrent response experiment of the covalent organic framework nanowire materials prepared in examples 1-6. Photocurrent response results show that example 4 of the present invention prepares covalent organic framework nanowire material N₃-COF-Nws-4 has the strongest photocurrent intensity of 0.15 μ A cm in the covalent organic framework nanowire materials prepared in examples 1-6^-2。

FIG. 11 is an electrochemical impedance spectroscopy experiment of the covalent organic framework nanowire materials prepared in examples 1-6. Electrochemical Impedance Spectroscopy (EIS) analysis revealed that example 4 of the present invention prepares covalent organic framework nanowire material N₃-COF-Nws-4 provided the lowest charge transfer resistance in the covalent organic backbone nanowire materials prepared in examples 1-6. This illustrates covalent organic framework nanowire material N under light excitation₃The electron-hole pair of-COF-Nws-4 has excellent charge separation.

All of the characterizations in FIGS. 7 through 11 illustrate the preparation of covalent organic framework nanowire material N in example 4 of the invention₃the-COF-Nws-4 has the best photoreduction performance and can be used for adsorbing 10ppm uranyl ions.

FIG. 12 shows the covalent organic framework nanowire material N prepared in examples 1 and 4₃-COF-Nws-1 and N₃-COF-Nws-4 adsorption capacity for uranyl ions in light and dark plotted against time. As can be seen from FIG. 12, example 4 of the present invention prepares covalent organic framework nanowire material N₃The absorption amount of-COF-Nws-4 to uranium in 10ppm uranyl ion solution under illumination is high and can reach 1270mg g^-1. And uranium is not substantially adsorbed under dark conditions.

FIG. 13 shows covalent organic framework nanowire material N prepared in example 4₃-COF-Nws-4 has the highest adsorption capacity at pH 5 in 10ppm uranyl ion solution under light and pH range 3-9.

FIG. 14 shows a covalent organic framework nanowire material N prepared in example 4₃The bar chart of 5 times of recycling of uranium adsorption of-COF-Nws-4 in 10ppm uranyl ion solution is shown in FIG. 14The prepared covalent organic framework nanowire material has good recyclable performance, and the adsorption capacity can still keep 81% of that of the first time after 5 times of circulation.

In conclusion, the covalent organic framework nanowire material provided by the invention has the advantages of definite structure, good stability, excellent adsorption performance and good cyclability, and the adsorption capacity to uranium can reach 1000-1300 mg.g^-1After 5-10 times of recycling, the uranium extraction capacity can reach 75-90% of the first total adsorption capacity.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.