A method for preparing carboxylic acid functionalized two-dimensional covalent organic framework nanosheets in an alcoholamine-propylene carbonate solution

Abstract

The invention discloses a method for preparing a carboxylic acid functionalized two-dimensional covalent organic framework nanosheet in an alcoholamine-propylene carbonate solution. The specific steps are: using propylene carbonate as a solvent and an alcoholamine compound as a solute to prepare an alcoholamine-propylene carbonate solution system, and using the system as a dispersing stabilizing liquid for exfoliating bulk materials; adding bulk materials QL-COF-2, HOOC-COF1 or TpPa-(COOH) 2 The nanosheets are placed in a dispersion stabilizing liquid, wherein the alcoholamine compound is used as an intercalating agent to enter the interlayer of the bulk material, and the nanosheets are peeled off under the assistance of ultrasound, and the dispersion liquid is centrifuged and washed and dried to obtain carboxylic acid functionalized two-dimensional covalent organic framework nanosheets. The present invention can simply, efficiently and on a large scale prepare carboxylic acid functionalized two-dimensional covalent organic framework nanosheets; the present invention can stably exist for a long time in the alcoholamine-propylene carbonate solution system, and the nanosheets obtained during the ultrasound assistance process are not easy to precipitate.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of nano functional materials, and particularly relates to a method for preparing carboxylic acid functionalized two-dimensional covalent organic framework nanosheets in an alcoholamine-propylene carbonate solution. Background Art

[0002] Covalent organic frameworks (COFs) are a class of porous crystalline materials with highly ordered two-dimensional (2D) or three-dimensional (3D) network structures. Among them, 2D COFs are generally considered to be a new type of layered stacking materials. They not only exhibit a two-dimensional extended layered structure, but also have a periodic columnar π array, which gives them excellent optical, electrical and optoelectronic properties. Carboxylic acid-functionalized two-dimensional covalent organic framework nanosheets show great application prospects due to their hydrophilic carboxylic acid functional groups and more abundant surface active sites. However, there are currently few liquid phase exfoliation methods for carboxylic acid-functionalized two-dimensional covalent organic framework nanosheets, and the yield is low and the quality is poor. Therefore, it is of great significance to prepare carboxylic acid-functionalized two-dimensional covalent organic framework nanosheets by liquid phase exfoliation of bulk materials with high efficiency and high quality. Summary of the invention

[0003] The technical problem solved by the present invention is to provide an efficient and green method for preparing carboxylic acid functionalized two-dimensional covalent organic framework nanosheets in an alcoholamine-propylene carbonate solution. The method uses propylene carbonate (PC) as a solvent, can better prevent the agglomeration of nanosheets during the ultrasonic-assisted action process, and utilizes the hydrogen bond interaction formed between the specific carboxyl functional groups in COFs and the amino groups in the alcoholamine compounds to further improve the selectivity of the nanosheets, effectively solving the key technical problems of low nanosheet yield, poor quality and low selectivity in the traditional liquid phase exfoliation method.

[0004] The present invention adopts the following technical solution to solve the above technical problems: a method for preparing carboxylic acid functionalized two-dimensional covalent organic framework nanosheets in an alcoholamine-propylene carbonate solution, characterized in that the specific steps are:

[0005] Step S1, using propylene carbonate as a solvent and an alcoholamine compound as a solute to prepare an alcoholamine-propylene carbonate solution system, and using the alcoholamine-propylene carbonate solution system as a dispersing stabilizing liquid for exfoliating bulk materials, wherein the alcoholamine compound is one or more of ethanolamine, propanolamine, butanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-butylethanolamine or N-butyldiethanolamine;

[0006] Step S2, placing the bulk material QL-COF-2, HOOC-COF1 or TpPa-(COOH)2 in the dispersed stabilizing liquid obtained in step S1, wherein the alcohol amine compound enters the interlayer of the bulk material as an intercalating agent, and peels off under the assistance of ultrasound, and then centrifuges the dispersion liquid for washing and drying to obtain carboxylic acid functionalized two-dimensional covalent organic framework nanosheets;

[0007] The synthetic route of the bulk material QL-COF-2, HOOC-COF1 or TpPa-(COOH)2 is:

[0008]

[0009]

[0010] It is further defined that the concentration of the dispersion stabilizing liquid in step S1 is 0.5-2 mol / L.

[0011] It is further defined that the feeding ratio of the block material to the dispersion stabilizing liquid in step S2 is 1 mg: 1-1.2 mL.

[0012] It is further defined that the temperature of the ultrasound-assisted effect in step S2 is 20-30°C.

[0013] It is further defined that the ultrasonic power of the ultrasonic-assisted action in step S2 is 280-420 W, and the ultrasonic-assisted action time is 7-11 h.

[0014] It is further defined that the centrifugal washing in step S2 includes two processes: low-speed centrifugation and high-speed centrifugation, wherein the low-speed centrifugation speed is 1500~2500rpm, the low-speed centrifugation time is 5~15min, centrifugation is performed twice, the upper dispersion is taken and high-speed refrigerated centrifugation is performed again, the high-speed centrifugation speed is 10000~20000rpm, the high-speed centrifugation time is 3~10min, the bottom precipitate is collected and washed with secondary water at least 10 times, and washed with ethanol at least 3 times to remove residual alcoholamine compounds and propylene carbonate, and finally the washed precipitate is vacuum dried at 30~50°C to obtain pure carboxylic acid functionalized two-dimensional covalent organic framework nanosheets.

[0015] Compared with the existing technology, the excellent effects of the present invention are embodied in:

[0016] The present invention can prepare carboxylic acid functionalized two-dimensional covalent organic framework nanosheets simply, efficiently and on a large scale; the yield of the carboxylic acid functionalized two-dimensional covalent organic framework nanosheets obtained by exfoliation of the present invention is as high as 45.4%, and the selectivity of nanosheets with a lateral size between 1-2 μm and a thickness less than 2 nm is as high as 81.3%. The present invention can stably exist for a long time in an alcoholamine-propylene carbonate solution system, and the alcoholamine-propylene carbonate solution system has good dispersion stability, can effectively prevent the agglomeration of nanosheets, and the nanosheets obtained in the process of ultrasound-assisted action are not easy to flocculate.

[0017] The present invention is universal for the preparation of two-dimensional covalent organic framework nanosheets containing carboxylic acid functional groups. The amine-propylene carbonate solution system is used in two other two-dimensional covalent organic framework materials functionalized with carboxylic acids having different bonding modes, and it is found that both have good stripping effects.

[0018] The QL-COF-2 nanosheets prepared by the present invention have more excellent photocatalytic CO2 reduction activity. The peeled QL-COF-2 nanosheets are used as photocatalysts in the photocatalytic CO2 reduction reaction. The CO yield is 2.3 times that of the corresponding bulk material, and the QL-COF-2 nanosheets have good cyclic stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FT-IR spectra and XRD spectra of bulk materials QL-COF-2, HOOC-COF1, TpPa-(COOH)2 and corresponding nanosheets obtained by liquid phase exfoliation of the present invention.

[0020] Figure 2 AFM and thickness statistics of QL-COF-2, HOOC-COF1, and TpPa-(COOH)2 nanosheets prepared by liquid phase exfoliation in a propanolamine-propylene carbonate solution of the present invention.

[0021] Figure 3 This is a SEM comparison picture of QL-COF-2, HOOC-COF1, TpPa-(COOH)2 nanosheets and their corresponding bulk materials prepared by liquid phase exfoliation in a propanolamine-propylene carbonate solution of the present invention.

[0022] Figure 4 TEM comparison diagram of QL-COF-2 nanosheets prepared by liquid phase exfoliation in a propanolamine-propylene carbonate solution and their corresponding bulk materials.

[0023] Figure 5 This is a diagram showing the photocatalytic performance of the QL-COF-2 nanosheets prepared in the present invention and its corresponding bulk material.

[0024] Figure 6This is a comparison chart of the photoelectric properties of the QL-COF-2 nanosheets prepared in the present invention and its corresponding bulk material. DETAILED DESCRIPTION

[0025] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention.

[0026] The synthesis of bulk materials QL-COF-2, HOOC-COF1 or TpPa-(COOH)2 refers to the following synthesis route:

[0027]

[0028] . Example 1

[0029] Preparation of QL-COF-2 nanosheets:

[0030] Step S1, weigh 5 mg of block material QL-COF-2, disperse it in 5 mL of a prepared 1 mol / L propanolamine-propylene carbonate solution, and perform water bath ultrasound for 9 h at an ultrasound power of 360 W to obtain a brown-yellow suspension.

[0031] Step S2, transfer the brown-yellow suspension obtained in step S1 into a 5 mL centrifuge tube, and centrifuge it twice at a speed of 2000 rpm, each time for 10 minutes, and collect the supernatant obtained, which is the QL-COF-2 nanosheet dispersion obtained by peeling; then centrifuge the obtained QL-COF-2 nanosheet dispersion at a speed of 18000 rpm for 5 minutes, and the precipitate after centrifugation is the QL-COF-2 nanosheet, and then wash the QL-COF-2 nanosheet with ethanol for more than 10 times to remove residual propanolamine and propylene carbonate, and finally place the washed precipitate in a vacuum drying oven at 40°C and dry it overnight to obtain a relatively pure QL-COF-2 nanosheet. Example 2

[0032] Preparation of HOOC-COF1 nanosheets:

[0033] Step S1, weigh 5 mg of block material HOOC-COF1, disperse it in 5 mL of a prepared 1 mol / L propanolamine-propylene carbonate solution, and perform water bath ultrasound for 9 h at an ultrasound power of 360 W to obtain a light brown suspension.

[0034] Step S2, transfer the light brown suspension obtained in step S1 into a 5 mL centrifuge tube, and centrifuge it twice at a speed of 2000 rpm, each time for 10 minutes, and the collected supernatant is the HOOC-COF1 nanosheet dispersion obtained by peeling; then centrifuge the obtained HOOC-COF1 nanosheet dispersion at a speed of 18000 rpm for 5 minutes, and the precipitate after centrifugation is the HOOC-COF1 nanosheet, and then wash the HOOC-COF1 nanosheet with ethanol for more than 10 times to remove residual propanolamine and propylene carbonate, and finally place the washed precipitate in a vacuum drying oven at 40° C. and dry it overnight to obtain a relatively pure HOOC-COF1 nanosheet. Example 3

[0035] Preparation of TpPa-(COOH)2 nanosheets:

[0036] Step S1, weigh 5 mg of block material TpPa-(COOH)2, disperse it in 5 mL of 1 mol / L propanolamine-propylene carbonate solution, and perform water bath ultrasound for 9 h at an ultrasound power of 360 W to obtain a dark red suspension.

[0037] Step S2, transfer the dark red suspension obtained in step S1 into a 5 mL centrifuge tube and centrifuge it twice at a speed of 2000 rpm, each time for 10 minutes, and the collected supernatant is the TpPa-(COOH)2 nanosheet dispersion obtained by peeling; then centrifuge the obtained TpPa-(COOH)2 nanosheet dispersion at a speed of 18000 rpm for 5 minutes, and the precipitate after centrifugation is the TpPa-(COOH)2 nanosheet, and then wash the TpPa-(COOH)2 nanosheet with ethanol for more than 10 times to remove residual propanolamine and propylene carbonate, and finally place the washed precipitate in a vacuum drying oven at 40°C and dry it overnight to obtain a relatively pure TpPa-(COOH)2 nanosheet.

[0038] Table 1 shows the optimal exfoliation conditions of QL-COF-2 nanosheets obtained by optimizing the concentration of amine compounds, ultrasonic power and ultrasonic time by the control variable method and the corresponding nanosheet yield. When propanolamine is used as the intercalation agent, the yield of QL-COF-2 nanosheets obtained by exfoliation is as high as 45.4%.

[0039] Table 1

[0040]

[0041] Figure 1The FT-IR spectra and XRD spectra of the QL-COF-2, HOOC-COF1, and TpPa-(COOH)2 nanosheets obtained by the present invention and their corresponding bulk materials are shown in Figure 2. In the infrared spectrum, the QL-COF-2 nanosheets obtained by the present invention have a peak at 1704 cm -1 、1602cm -1 and 1620cm -1 The characteristic peaks at 1621 cm-1 in the infrared spectrum of HOOC-COF1 nanosheets are present. -1 The C=N characteristic peak at 1560 cm -1 )、CN(1213cm -1 ), HO-C=O (1701cm -1 ) characteristic peaks exist, indicating that the chemical bond connection mode of the QL-COF-2, HOOC-COF1, and TpPa-(COOH)2 nanosheets obtained by exfoliation remains unchanged. However, the XRD characteristic peaks of QL-COF-2, HOOC-COF1, and TpPa-(COOH)2 nanosheets after exfoliation are greatly weakened or disappear, because the layered stacking of the bulk material is destroyed after exfoliation, thus forming a few-layer nanosheet.

[0042] Figure 2 The AFM and thickness statistics of QL-COF-2, HOOC-COF1, and TpPa-(COOH)2 nanosheets prepared in the propanolamine-propylene carbonate solution of the present invention. The lateral size of the three carboxylic acid functionalized two-dimensional covalent organic framework nanosheets is 1-2μm, and the selectivity of nanosheets with a thickness less than 2nm is 81.3%, 72%, and 79.4%, respectively. The more carboxylic acid functional groups contained in the QL-COF-2, HOOC-COF1, and TpPa-(COOH)2 nanosheets, the higher the proportion of nanosheets with a thickness less than 2nm, which corresponds to the variation law of the yield of the nanosheets obtained by stripping (45.4%, 18.2%, and 26.1%), indicating that the stripping yield and quality of the nanosheets are related to the number of carboxylic acids on the bulk material.

[0043] Figure 3The present invention is a SEM comparison diagram of QL-COF-2, HOOC-COF1, TpPa-(COOH)2 nanosheets and their corresponding bulk materials prepared in a propanolamine-propylene carbonate solution. The morphology of the QL-COF-2 nanosheet after stripping is almost the same as the bulk, both of which are disorderly and tightly packed spheres, but the size of the spheres is significantly reduced after stripping. There are indeed different changes for HOOC-COF1 and TpPa-(COOH)2 nanosheets. The bulk material HOOC-COF1 is a tightly packed rod-like morphology, and the HOOC-COF1 nanosheets obtained after liquid phase stripping are in the form of sheets. The morphology of the bulk material TpPa-(COOH)2 is nanowire-like, and the TpPa-(COOH)2 nanosheets after stripping are stacked in fragments. This phenomenon is also observed in other alcoholamine-propylene carbonate solution systems.

[0044] Figure 4 The TEM comparison diagram of the QL-COF-2 nanosheets and the corresponding bulk materials prepared in the propanolamine-propylene carbonate solution of the present invention. The QL-COF-2 nanosheets are stacked in thin sheets, and compared with the unpeeled bulk materials, the nanosheets are more transparent and thinner. This shows that the thinner QL-COF-2 nanosheets were successfully obtained in the alcoholamine-propylene carbonate solution system.

[0045] Figure 5 The present invention is a comparison of the CO yield of the QL-COF-2 nanosheets prepared in the propanolamine-propylene carbonate solution and the corresponding bulk material during the photocatalytic CO2 reduction reaction, as well as the cyclic stability of the QL-COF-2 nanosheets. Compared with the bulk material QL-COF-2, the QL-COF-2 nanosheets have better photocatalytic activity and cyclic stability.

[0046] Figure 6 The present invention prepares QL-COF-2 nanosheets and their corresponding bulk materials in a propanolamine-propylene carbonate solution, and the transient photocurrent curve and electrochemical impedance diagram. The transient photocurrent intensity generated by the QL-COF-2 nanosheets is higher than that of the corresponding bulk materials, which indicates that the photocurrent response ability of the QL-COF-2 nanosheets after stripping is stronger than that of the bulk materials, and the photogenerated electron-hole pairs can be effectively separated. In addition, the QL-COF-2 nanosheets have a lower electrochemical impedance than the corresponding bulk materials, indicating that the QL-COF-2 nanosheets have good photogenerated electron ability and a small charge transfer resistance, and can effectively separate photogenerated electron-hole pairs, reduce their recombination rate, and thus improve the photocatalytic performance of the QL-COF-2 nanosheets.

[0047] The present invention utilizes amine-propylene carbonate solution to disperse and stabilize block carboxylic acid functionalized two-dimensional covalent organic framework materials, and then obtains high-yield, high-quality carboxylic acid functionalized two-dimensional covalent organic framework nanosheets by ultrasonic-assisted exfoliation. The QL-COF-2 nanosheets prepared by the present invention have better photocatalytic CO2 reduction performance than their corresponding block materials. The technical advantages of the present invention are: (1) the preparation process of the present invention is simple and efficient, and it is easy to operate on a large scale; (2) during the stripping process of the present invention, the bulk material can stably exist in the amine-propylene carbonate solution system and is not easy to precipitate. The amine-propylene carbonate solution system has good dispersion stability and can effectively prevent the agglomeration of nanosheets; (3) the yield of QL-COF-2 nanosheets obtained by stripping of the present invention is as high as 45.6%, and the lateral size is about 1 μm; (4) the present invention has good universality for two-dimensional covalent organic framework materials containing carboxylic acid functional groups, and the yield and quality of the nanosheets obtained by stripping are related to the number of carboxylic acid functional groups contained in the corresponding bulk material; (5) the QL-COF-2 nanosheets prepared by the present invention can be used as a catalyst in the photocatalytic CO2 reduction reaction, and the CO yield generated is 2.3 times that of the corresponding bulk material.

[0048] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing carboxylic acid functionalized two-dimensional covalent organic framework nanosheets in an amine-propylene carbonate solution, characterized in that The specific steps are: Step S1, using propylene carbonate as a solvent and an alcoholamine compound as a solute to prepare an alcoholamine-propylene carbonate solution system, using the alcoholamine-propylene carbonate solution as a dispersion stabilizing liquid for exfoliating bulk materials, wherein the concentration of the dispersion stabilizing liquid is 0.5 to 2 mol / L, wherein the alcoholamine compound is one or more of ethanolamine or propanolamine; Step S2, placing the bulk material QL-COF-2, HOOC-COF1 or TpPa-(COOH)2 in the dispersed stabilizing liquid obtained in step S1, wherein the feeding ratio of the bulk material to the dispersed stabilizing liquid is 1 mg: 1-1.2 mL, and the amine compound is used as an intercalating agent to enter the interlayer of the bulk material, and the peeling is performed under the assistance of ultrasound at 20-30° C., wherein the ultrasonic power is 280-420 W, and the ultrasonic assistance time is 7-11 h, and then the dispersion liquid is centrifuged, washed, and dried to obtain a carboxylic acid functionalized two-dimensional covalent organic framework nanosheet; The synthetic route of the bulk material QL-COF-2, HOOC-COF1 or TpPa-(COOH)2 is:

2. The method for preparing carboxylic acid functionalized two-dimensional covalent organic framework nanosheets in an alcoholamine-propylene carbonate solution according to claim 1, characterized in that: The centrifugal washing in step S2 includes two processes: low-speed centrifugation and high-speed centrifugation. The low-speed centrifugation speed is 1500-2500 rpm, the low-speed centrifugation time is 5-15 minutes, and the centrifugation is performed twice. The upper layer of the dispersion is taken and high-speed refrigerated centrifugation is performed again. The high-speed centrifugation speed is 10000-20000 rpm, and the high-speed centrifugation time is 3-10 minutes. The bottom precipitate is collected and washed with secondary water for at least 10 times and ethanol for at least 3 times to remove residual alcoholamine compounds and propylene carbonate. Finally, the washed precipitate is vacuum dried at 30-50° C. to obtain pure carboxylic acid functionalized two-dimensional covalent organic framework nanosheets.

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