CN115260510A

CN115260510A - Method for preparing COF-316 nanosheet through chemical stripping

Info

Publication number: CN115260510A
Application number: CN202210764695.5A
Authority: CN
Inventors: 魏金枝; 谢陆航; 张凤鸣
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2022-06-30
Filing date: 2022-06-30
Publication date: 2022-11-01

Abstract

The invention provides a novel method for preparing COF-316 nanosheets by chemical stripping, which aims to solve the problems that the COF-316 nanosheets constructed by the traditional ultrasonic method are low in yield and poor in controllability, and the use of a large amount of catalysts is limited. According to the invention, metal nickel ions are added in situ in the process of synthesizing COF-316 to obtain COF-316-Ni. And (3) soaking the obtained COF-316-Ni in an HCl solution, centrifuging, washing, and freeze-drying to obtain yellow powder which is marked as COF-316 nanosheet. The preparation method is simple in preparation process and has high nanosheet stripping efficiency. Compared with a bulk COF-316 material, the COF-316 nanosheet material prepared by the chemical stripping method provided by the invention has more excellent photocatalytic carbon dioxideThe original performance, the rate of reducing carbon dioxide into carbon monoxide can reach 33.9 mu mol g^‑1·h^‑11.67 times that of bulk COF-316.

Description

Method for preparing COF-316 nanosheet through chemical stripping

Technical Field

The invention belongs to the field of preparation of covalent organic framework materials, and particularly relates to a preparation method of a COF-316 nanosheet.

Background

The rapid development of human society consumes a large amount of fossil fuels, indirectly causes a series of environmental problems such as emission of a large amount of smoke and exhaust gas, and CO in the air caused by the combustion of a large amount of these fossil fuels₂The problems of the aggravation of greenhouse effect and the rise of sea level caused by the rise of concentration seriously affect the survival of human beings and the further development of industry. Based on this, researchers have made a lot of efforts to find green methods for obtaining new energy. Wherein the development of new energy or the reduction of waste emissions has become the most feasible solution at present. Catalytic conversion of CO₂The reduction into carbon-based fuel with high added value is also another effective way for obtaining new energy. The catalytic conversion mode can relieve CO in the air₂The problem of too high concentration can reduce the influence of greenhouse effect, and can also reduce CO₂Is converted into energy with high added value by means of catalytic conversion. However, the research on catalysis still faces many challenges, such as limited light absorption, low electron-hole separation efficiency, slow interface charge kinetics, low catalytic activity, and photo-corrosion, which limit the wide application. Thus, high efficiency catalytic conversion of CO₂The research and development of the reduction novel catalyst have important practical significance and scientific significance.

Covalent Organic Frameworks (COFs) are porous crystalline materials formed by covalent connection through reversible reactions, and are widely applied to various fields such as gas adsorption and separation, catalysis, sensing, photoelectricity and the like due to the advantages of high specific surface area, adjustable periodic pore channels, ordered structures, functionalized frameworks and the like. The uniform structural characteristics of COFs also show that the COFs have huge potential and advantages in energy storage and conversion. For example, the redox/catalytic site can be accurately anchored at a specific site of the framework, the electronic structure can be easily controlled, and the structure-activity relationship between the structure and the performance can be researched as a platform. During the past few years, COFs have been extensively studied in the field of electrochemical storage and conversion. However, the layer-by-layer stacking structure of two-dimensional COFs makes active sites deeply embedded and difficult to reach by ion diffusion, and the boundaries between some defects and particles severely limit the transmission of electrons and ions and the application thereof. It is worth noting that for COF nano-sheets containing a single layer or few layers, the COF nano-sheets have uniform chemical, physical, electronic and optical properties, and can minimize the ion transmission path from reaching active sites, so that finding a reasonable method for preparing the nano-sheets is of great significance for improving the photocatalytic carbon dioxide reduction efficiency.

Disclosure of Invention

The invention aims to solve the problems of low reduction efficiency of COF-316 photocatalytic carbon dioxide and low preparation efficiency of COF-316 nanosheets, and provides a method for preparing COF-316 nanosheets by a chemical stripping method.

The preparation method of the COF-316 nanosheet material is completed according to the following steps:

step 1, sequentially adding 2,3,6,7,10, 11-hexahydroxy triphenyl (HHTP), tetrafluoroterephthalonitrile (TFPN), nickel acetate (CH 3 COONi), 1.4mL dioxane, 0.6mL LDMF and 78 mu L triethylamine into a Schlenk tube. Carrying out ultrasonic treatment on the obtained solution for 30min to ensure that the solution is uniformly dispersed;

and 2, placing the sample-filled Stirling tube into liquid N2 at-196 ℃ for rapid freezing treatment, and performing four freezing-air extraction-thawing processes to ensure that the air in the tube is completely discharged. Finally, the Schwann tube is sealed in a vacuum state and is placed in an oven to be heated. Filtering the obtained product, and washing with DMF, etOH and deionized water respectively to obtain dark green solid powder which is marked as COF-316-Ni;

and 3, soaking the COF-316-Ni obtained in the step 2 in an HCl solution, centrifuging the dispersion liquid, centrifuging the centrifuged clear liquid, washing the centrifuged lower-layer product with deionized water, and freeze-drying to obtain yellow powder, which is recorded as COF-316NSs.

Weighing the mixture in a molar ratio of 1:1.5:0.4-0.5 of 2,3,6,7,10, 11-hexahydroxytriphenyl, tetrafluoroterephthalonitrile and nickel acetate are placed in a Schlenk tube;

in the step 2, the temperature of the oven is 120 ℃, and the reaction time is 72 hours;

in the step 3, the concentration of hydrochloric acid is 3mol/L, and the soaking time is 5h;

in the step 3, the rotating speed of the centrifugal treatment of the dispersion liquid is 2000r/min, and the centrifugal time is 10min. The rotating speed of the centrifugal clear liquid is 8000r/min, and the centrifugal time is 10min.

The invention has the beneficial effects that:

the invention uses a new method to prepare the COF-316 nanosheet material, the nanosheet material has high yield, has higher photocatalytic carbon dioxide reduction performance compared with pure COF-316, has the rate of reducing carbon dioxide into carbon monoxide which can reach 33.9 mu mol g < -1 > h < -1 >, and is 1.67 times of that of a bulk COF-316 material.

Drawings

FIG. 1 is a flow chart of the preparation of embodiment 1 of the present invention;

FIG. 2 is an X-ray powder diffraction pattern of an embodiment 1 of the present invention;

FIG. 3 is a chart of an infrared absorption spectrum of embodiment 1 of the present invention;

FIG. 4 is a transmission electron microscope photograph of an embodiment 1 of the present invention;

FIG. 5 is a graph comparing the yields of the COF-316 photocatalytic carbon dioxide reduction of example 1 of the present invention.

Detailed Description

The present invention is further illustrated in detail below with reference to examples, which are intended only to illustrate the process of the present invention in order to facilitate a better understanding of the present invention and therefore should not be construed as limiting the scope of the present invention.

Example 1: the preparation of the nanosheet material of the present embodiment is completed according to the following steps:

step one, preparing COF-316-Ni: 2,3,6,7,10, 11-hexahydroxy-triphenylene (HHTP, 30mg, 0.0928mmol), tetrafluoroterephthalonitrile (TFPN, 27.6mg, 0.138mmol), nickel acetate (CH 3COONi,11.4mg,0.046 mmol), 1.4mL dioxane, 0.6mL LDMF,78 μ L triethylamine were sequentially added to the Schlenk tube. The obtained solution was subjected to ultrasonic treatment for 30min to disperse it uniformly. The sample-filled Schlenk tube was placed in liquid N2 at-196 ℃ for rapid freezing and four freeze-pump-thaw cycles were performed to ensure complete evacuation of the air in the tube. Finally, the Schlenk tube is sealed in a vacuum state and is placed in an oven at 120 ℃ to be heated for 72h. Filtering the obtained product, and washing with DMF, etOH and deionized water respectively to obtain dark green solid powder which is marked as COF-316-Ni;

step two, preparing a COF-316 nano sheet: soaking the obtained COF-316-Ni in 3M HCl solution for 5h, centrifuging the dispersion liquid at the rotating speed of 2000r/min for 10min, centrifuging the centrifuged clear liquid at the rotating speed of 8000r/min for 10min, washing the centrifuged lower-layer product with deionized water, and performing freeze-drying treatment to obtain yellow COF-316NSs;

a characterization of COF-316 nanoplatelets prepared by chemical stripping:

XRD test is carried out on the obtained COF-316 nano-sheet material, and as can be seen from figure 2, the COF-316 has obvious characteristic peaks at 4.47 degrees, 9.08 degrees and 27.66 degrees, which proves that the COF-316 material is successfully synthesized. In addition, all characteristic peaks of the COF-316NSs are consistent with those of the COF-316, and the fact that the crystal structure of the COF-316 is not changed in the stripping process is proved.

The obtained COF-316 nanosheet material was subjected to FT-IR test, and as can be seen from FIG. 3, in order to prove the formation of C-O-C bond in the COF-316, infrared spectrum tests were respectively carried out on the monomers HHTP, TFPN and COF-316, and the results are shown in the figure. Wherein, COF-316 respectively presents characteristic peaks at the positions of a map 1020 and a 1262cm-1, which respectively correspond to C-O symmetrical and asymmetrical stretching vibration peaks; and the O-H stretching vibration peak originally existing at 3200cm-1 of the HHTP monomer is completely disappeared, thereby proving that the-OH functional groups in the HHTP monomer are completely converted into C-O-C bonds. In addition, the COF-316NSs and the COF-316 present the same characteristic peak, and the fact that the nanosheet stripping does not destroy the original structure of the COF-316 is confirmed.

The obtained COF-316 nanosheets are subjected to TEM testing, and a Tyndall effect diagram of the COF-316NSs-1 can be seen from FIG. 4. By vertically injecting laser into the COF-316NSs dispersion, a bright 'path' phenomenon appearing in the solution can be observed, and the dispersion is identified as a colloidal solution; it can be seen from the TEM image that the morphology exhibits lamellae of a size of about 300 nm.

To verify the beneficial effects of the present invention, the following tests were performed:

in order to examine the photocatalytic carbon dioxide reduction effect of the nanosheet material, the photocatalytic carbon dioxide reduction performance thereof was tested as follows. The test procedure was as follows: the total capacity of the device is about 100mL by adopting a gas-liquid photocatalytic reaction device. Before testing the samples, they were pre-treated as follows: 10mg of catalyst was dispersed ultrasonically in a mixture of 40mL acetonitrile and 10mL water. And pouring the pretreated dispersion liquid into the device, introducing 99.9% of CO2 gas into the device, and sealing the reaction device after 30 min. The reaction system was placed under a 300W Xe lamp (filter. Lamda. >420 nm) and the condensing unit was turned on to ensure that the system was at room temperature. And (3) collecting the gas sample in the system once every 1h by self-opening a light source for timing, injecting the gas sample into an FID detection port of a GC7920 gas chromatograph, and determining the content of the CO gas. The number of sample tests was five times, and the photocatalytic reaction amounted to five hours. As shown in FIG. 5, the rate of reducing carbon dioxide into carbon monoxide can reach 33.9 mu mol g-1. Multidot.h-1, which is 1.67 times of that of the bulk COF-316 material.

Claims

1. A method for preparing COF-316 nanosheets by chemical stripping, characterized in that the method comprises the steps of:

step 1, sequentially adding 2,3,6,7,10, 11-hexahydroxy triphenyl, tetrafluoroterephthalonitrile, nickel acetate, 1.4mL dioxane, 0.6mLDMF and 78 mu L triethylamine into a Schlenk tube;

and 2, carrying out ultrasonic treatment on the obtained solution for 30min to uniformly disperse the solution. Placing the sample-filled Schlenk tube in a liquid N at-196 deg.C₂The quick freezing treatment is carried out, and four freezing-air extraction-thawing processes are carried out to ensure that the air in the pipe is completely discharged. Finally, the Schwann tube is sealed in a vacuum state. It was heated in an oven at 120 ℃ for 72h. Filtering the obtained product, and washing with DMF, etOH and deionized water respectively to obtain dark green solid powder, which is marked as COF-316-Ni;

and 3, soaking the COF-316-Ni obtained in the step 2 in an HCl solution, centrifuging the dispersion liquid, washing a centrifuged lower-layer product with deionized water, and performing freeze-drying treatment to obtain yellow powder, namely COF-316NSs.

2. A preparation of nanosheet material of claim 1, wherein in step 1, the molar ratio of 1:1.5:0.4-0.5 of 2,3,6,7,10, 11-hexahydroxytriphenyl, tetrafluoroterephthalonitrile and nickel acetate are placed in a Schlenk tube.

3. A nanosheet material of claim 1, wherein the hydrochloric acid concentration in step 3 is 3mol/L and the soaking time is 5h.

4. A nanosheet material of claim 1, wherein the dispersion is centrifuged in step 3 at a speed of 2000r/min for a period of 10min.

5. A nanosheet material of claim 1, wherein the centrifugation of the centrifuged supernatant in step 3 is carried out at a rotation rate of 8000r/min for a centrifugation time of 10min.