A core-shell structured Au@CeO 2 nanocatalyst, its preparation method and application

Abstract

The present invention discloses a core-shell structured Au@CeO2 nanocatalyst and its preparation method and application, belonging to the technical field of core-shell structured catalysts. The preparation method of the catalyst comprises the following steps: S1. Add chloroauric acid solution and low-concentration cerium chloride solution into deionized water, stir and mix at 5 °C, then quickly add ammonia water solution, and then quickly add high-concentration cerium chloride solution and continuously stir for 30 min to obtain a mixed solution; S2. Centrifuge the mixed solution to retain the precipitate, wash the precipitate with deionized water and absolute ethanol, and freeze-dry to obtain a catalyst precursor; S3. Carry out cleaning treatment and annealing treatment on the catalyst precursor, and after cooling to room temperature, obtain the core-shell structured Au@CeO2 nanocatalyst; and apply the catalyst to the catalytic synthesis of boron dipyrromethene-based fluorescent dyes, which shows excellent catalytic performance and recycling performance and can significantly improve the yield of boron dipyrromethene-based fluorescent dyes.

Description

Technical Field

[0001] The present invention belongs to the technical field of core-shell structure catalysts, and particularly relates to a core-shell structure Au@CeO 2 nano-catalyst and its preparation method and application. Background Art

[0002] Fluoroboron dipyrrole-based fluorescent dyes are compounds with a fluoroboron dipyrrole backbone. They have the advantages of high fluorescence quantum yield, good photostability, and easy chemical modification, and are widely used in various fields such as biology, materials, and medicine. Introducing a conjugated structure or constructing an electron donor-electron acceptor unit into the fluoroboron dipyrrole structure can improve the photophysical properties of the fluoroboron dipyrrole-based fluorescent dyes; the aniline group has good photophysical properties and a small molecular weight, making it easy to chemically couple; introducing the aniline group into the fluoroboron dipyrrole structure can expand the conjugated system of the fluoroboron dipyrrole molecule, which helps to increase its fluorescence quantum yield and molar extinction coefficient, thereby enhancing the fluorescence intensity; by introducing a phenylamino group, the fluoroboron dipyrrole-based fluorescent dyes can be further functionally modified to introduce targeting groups, reactive groups, etc., thus expanding their application scope.

[0003] Chinese Patent with Publication No. CN113308130B discloses a preparation method of a fluoroboron dipyrrole fluorescent dye. A intermediate containing a fluoroboron dipyrrole structure, allylboronic acid pinacol ester, potassium carbonate, tetrakis(triphenylphosphine)palladium, and an organic solvent are mixed. The molar ratio of the intermediate, allylboronic acid pinacol ester, potassium carbonate, and tetrakis(triphenylphosphine)palladium is 1:1.4 - 1.6:5.8 - 6.2:0.06 - 0.08. It is heated to 100°C and stirred for reaction for 12 h under a nitrogen atmosphere; after the reaction is completed, it is cooled to room temperature, and after post-treatments such as extraction, washing, drying, column chromatography, and drying, a black solid fluoroboron dipyrrole fluorescent dye is obtained, with a yield of 65%. This preparation method uses tetrakis(triphenylphosphine)palladium as a catalyst, and its catalytic effect is average and the catalytic selectivity is insufficient, resulting in a low reaction yield; moreover, the stability of tetrakis(triphenylphosphine)palladium is poor and it is easily decomposed and inactivated at high temperatures, resulting in a large amount of residual palladium in the waste liquid and difficult recycling.

[0004] The specific chemical reaction formula is as follows:

[0005]

[0006] There are also reports in the prior art on using nano-gold catalysts in cross-coupling reactions. However, the service life of nano-gold catalysts is a key factor affecting their catalytic performance. After long-term reaction use, the gold particles are prone to loss or aggregation, resulting in a decrease in activity or even inactivation.

[0007] Therefore, how to prepare a catalyst with good catalytic performance, high conversion rate, stable performance and capable of being recycled and reused, and apply it to the efficient synthesis of fluoroboron dipyrrole fluorescent dyes is of great significance. Summary of the Invention

[0008] The purpose of the present invention is to provide a core-shell structured Au@CeO 2 nano-catalyst and its preparation method and application to solve the problems in the background technology.

[0009] The purpose of the present invention can be achieved through the following technical solutions:

[0010] A preparation method of a core-shell structured Au@CeO 2 nano-catalyst, comprising the following steps:

[0011] S1. Add chloroauric acid solution and low-concentration cerium chloride solution into deionized water, magnetically stir at a speed of 1200 r / min in an ice-water bath at 5 °C for 30 min, then quickly add ammonia water solution, and the mixed solution immediately turns black. Then quickly add high-concentration cerium chloride solution and continuously stir for 30 min to obtain a mixed solution; Au 3+ and Ce 3+ generate nano-gold particles and a large amount of Ce 4+ through an oxidation-reduction reaction. After adding an appropriate amount of ammonia water, Ce 4+ is hydrolyzed and converted into cerium dioxide and quickly assembled around the nano-gold particles to form a precipitate. After quickly adding high-concentration cerium chloride solution, the supplemented Ce 3+ absorbs OH - to form relatively stable [Ce(OH) 2 + and [Ce(OH)] 2+ ions. The OH - in the solution decreases, and the free cerium dioxide particles not assembled with the nano-gold particles preferentially dissolve and release OH - until equilibrium is reached, making the boundary of the core-shell structured Au@CeO 2 become clear, thereby obtaining a core-shell structured Au@CeO 2 with a complete structure and monodispersity;

[0012] S2. Place the mixed solution in a centrifuge tube and centrifuge at a speed of 12000 r / min for 30 min. After centrifugation, remove the upper solution in the centrifuge tube, retain the precipitate at the bottom of the centrifuge tube, wash it 3 times with deionized water, centrifuge for 30 min to remove the upper solution, then wash it at least 3 times with absolute ethanol, centrifuge for 30 min to remove the upper solution, completely remove other impurities such as organic matters in the precipitate, and freeze-dry for 12 h to obtain a catalyst precursor;

[0013] ​S3. Clean the catalyst precursor, then heat it to 100 °C at a heating rate of 1 °C / min for annealing treatment for 12 h. After cleaning again, heat it to 300 °C at a heating rate of 1 °C / min for annealing treatment for 6 h. After cooling to room temperature, a core-shell structured Au@CeO 2 nano-catalyst is obtained. The two annealing treatments enhance the interaction between gold particles and cerium oxide, thereby improving the stability and activity of the catalyst.

[0014] Furthermore, the dosage ratio of the chloroauric acid solution, low-concentration cerium chloride solution, deionized water, ammonia water solution and high-concentration cerium chloride solution is 2 mL: 4 mL: 100 mL: 6 mL: 5 mL.

[0015] Furthermore, the concentration of the chloroauric acid solution is 0.02 mol / L, the concentration of the low-concentration cerium chloride solution is 0.01 mol / L, the concentration of the ammonia water solution is 0.33 mol / L, and the concentration of the high-concentration cerium chloride solution is 0.05 mol / L.

[0016] Furthermore, the cleaning treatment is as follows: ultrasonically disperse the object to be treated in ethanol, then perform centrifugal separation, and then dry it at 25 °C.

[0017] A core-shell structured Au@CeO 2 nano-catalyst is prepared by the above preparation method; the core-shell structured Au@CeO 2 nano-catalyst has a nano-gold particle as the core and cerium oxide as the shell. The particle size of the core is 10 nm, and the particle size of the shell is 40 nm.

[0018] An application of a core-shell structured Au@CeO 2 nano-catalyst in the catalytic synthesis of fluoroboron dipyrrole-based fluorescent dyes, including the following steps:

[0019] Under argon protection, ultrasonically mix a fluoroboron dipyrrole-based compound, an aminophenylboronic acid pinacol ester-based compound, a core-shell structured Au@CeO 2 nano-catalyst, sodium acetate and toluene for 30 min to uniformly disperse the fluoroboron dipyrrole-based compound, the aminophenylboronic acid pinacol ester-based compound, the core-shell structured Au@CeO 2 nano-catalyst and sodium acetate in toluene, and carry out a Suzuki coupling reaction at 100 - 120 °C with a magnetic stirring speed of 1200 r / min for 12 - 18 h. After the reaction is completed, use ethyl acetate as an extraction agent to extract the reaction product to obtain a fluoroboron dipyrrole-based fluorescent dye. The present invention optimizes conditions such as the type of catalyst, dosage, type of solvent, reaction time, etc., and greatly improves the yield of the fluoroboron dipyrrole-based fluorescent dye.

[0020] Further, the usage ratio of the boron dipyrromethene compound, aminophenylboronic acid pinacol ester compound, core-shell structured Au@CeO 2 nano-catalyst, sodium acetate and toluene is 0.1 mmol: 0.4 mmol: 5 - 8 mg: 0.4 mmol: 2 mL.

[0021] Further, the general structural formula of the boron dipyrromethene compound is:

[0022]

[0023] Wherein, R1 is any one of H, CH 3 , OCH 3 , F, Cl, Br, COOH, NH 2 ; R2 and R3 are any one of H, OCH 3 , Cl.

[0024] Further, the general structural formula of the aminophenylboronic acid pinacol ester compound is:

[0025]

[0026] Wherein, R4 is any one of H, CH 3 , OCH 3 , F, Cl, Br, COOH, NH 2 , NO 2 , CF 3 ; R5 is any one of H, CH 3 .

[0027] Further, the general structural formula of the boron dipyrromethene fluorescent dye is as follows:

[0028]

[0029] Wherein, R1 is any one of H, CH 3 , OCH 3 , F, Cl, Br, COOH, NH 2 ; R2 and R3 are any one of H, OCH 3 , Cl; R4 is any one of H, CH 3 , OCH 3 , F, Cl, Br, COOH, NH 2 , NO 2 , CF 3 ; R5 is any one of H, CH 3 .

[0030] Beneficial effects:

[0031] The present invention directly undergoes a redox reaction between chloroauric acid and cerium chloride in deionized water by a one-pot method, and after the reaction is completed, by adding an appropriate amount of Ce 3+ and annealing treatment, the prepared core-shell structured Au@CeO 2 nano-catalyst has a more complete structure, and is more excellent in dispersibility, stability and catalytic activity; moreover, the preparation method of the present invention is simple and easy to operate, has low requirements for production equipment, has mild reaction conditions, and is safe, environmentally friendly;

[0032] The present invention uses the core-shell structured Au@CeO 2 nano-catalyst to catalyze the coupling reaction of boron dipyrromethene compounds and pinacol aminophenylboronic esters under alkaline conditions. The core-shell structured Au@CeO 2 nano-catalyst plays a role of heterogeneous catalysis during the reaction process, and has the advantages of high catalytic activity, strong selectivity, good stability, and recyclability, can significantly improve the yield, and can be widely applied to the actual production of catalytic synthesis of boron dipyrromethene fluorescent dyes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below in conjunction with the drawings.

[0034] Figure 1 is the transmission electron microscope (TEM) image of the core-shell structured Au@CeO 2 nano-catalyst of the present invention;

[0035] Figure 2 is the bar graph of the final yield of the core-shell structured Au@CeO 2 nano-catalyst prepared in Example 1 for recycling 5 times in the conditions of Example 2 for catalytic synthesis of boron dipyrromethene fluorescent dyes;

[0036] Figure 3 is the line graph of the yield monitored in real time by GC-MS for Example 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0038] Example 1

[0039] This example provides a core-shell structured Au@CeO 2 nano-catalyst, which is prepared by the following preparation method:

[0040] S1. Add 2 mL of chloroauric acid solution with a concentration of 0.02 mol / L and 4 mL of cerium chloride solution with a low concentration of 0.01 mol / L to 100 mL of deionized water. Magnetically stir the mixture at a speed of 1200 r / min in an ice-water bath at 5 °C for 30 min. Then quickly add 6 mL of ammonia water solution (prepared by dissolving 0.1 mL of ammonia water with a concentration of 20 mol / L in 6 mL of water). The mixed solution immediately turns black. After stirring for 25 s, quickly add 5 mL of cerium chloride solution with a high concentration of 0.05 mol / L and continue stirring for 30 min to obtain a mixed solution;

[0041] S2. Place the mixed solution in a centrifuge tube and centrifuge it at a speed of 12000 r / min for 30 min. After centrifugation, remove the upper layer solution in the centrifuge tube, retain the precipitate at the bottom of the centrifuge tube, wash it 3 times with deionized water, centrifuge for 30 min to remove the upper layer solution, then wash it at least 3 times with absolute ethanol, centrifuge for 30 min to remove the upper layer solution, completely remove other impurities such as organic matter in the precipitate, and freeze-dry for 12 h to obtain a catalyst precursor;

[0042] S3. Ultrasonically disperse the catalyst precursor in ethanol, then centrifuge and separate it, dry it at 25 °C, then heat it to 100 °C at a heating rate of 1 °C / min for annealing treatment for 12 h, ultrasonically disperse it in ethanol again, then centrifuge and separate it, dry it at 25 °C, and then heat it to 300 °C at a heating rate of 1 °C / min for annealing treatment for 6 h. After cooling to room temperature, obtain a core-shell structured Au@CeO 2 nano-catalyst.

[0043] Characterize the core-shell structured Au@CeO 2 nano-catalyst by transmission electron microscopy. As Figure 1 shown, the core-shell structured Au@CeO 2 nano-catalyst prepared by the present invention is uniformly dispersed, has uniform size, no agglomeration phenomenon. CeO 2 acts as the shell, and its particle size is about 40 nm. Au acts as the core, and its particle size is about 10 nm.

[0044] Comparative Example 1

[0045] Compared with Example 1, the difference in this comparative example is that in step S1, the high-concentration cerium chloride solution is not added. The other raw materials and steps are the same, denoted as Au@CeO 2 (1).

[0046] Comparative Example 2

[0047] Compared with Example 1, the difference in this comparative example is that the two annealing treatment operations in step S3 are not carried out. The other raw materials and steps are the same, denoted as Au@CeO2 (2).

[0048] The present invention provides an application of a core-shell structured Au@CeO 2 nano-catalyst in the catalytic synthesis of BODIPY fluorescent dyes, comprising the following steps:

[0049] Under argon protection, 0.1 mmol of a BODIPY compound, 0.4 mmol of an aminophenylboronic acid pinacol ester compound, 5 - 8 mg of the core-shell structured Au@CeO 2 nano-catalyst prepared in Example 1, 0.4 mmol of sodium acetate and 2 mL of toluene are added to a 100 mL reaction tube and ultrasonically mixed for 30 min, and then magnetically stirred at 100 - 120 °C at a rotation speed of 1200 r / min for 12 - 18 h. After the reaction, ethyl acetate is used as an extractant to extract the reaction product to obtain a BODIPY fluorescent dye.

[0050] The specific chemical reaction formula is as follows:

[0051]

[0052] Among them, R1 is any one of H, CH 3 , OCH 3 , F, Cl, Br, COOH, NH 2 ; R2 and R3 are any one of H, OCH 3 , Cl; R4 is any one of H, CH 3 , OCH 3 , F, Cl, Br, COOH, NH 2 , NO 2 , CF 3 ; R5 is any one of H, CH 3 .

[0053] Example 2

[0054] The BODIPY fluorescent dye is prepared by the following steps:

[0055] Under argon protection, 0.1 mmol of a BODIPY compound (R1 is OCH 3 , R2 and R3 are H), 0.4 mmol of an aminophenylboronic acid pinacol ester compound (R4 and R5 are H), 5 mg of the core-shell structured Au@CeO 2A nanocatalyst, 0.4 mmol of sodium acetate, and 2 mL of toluene were added to a 100 mL reaction tube and ultrasonically mixed for 30 min, and then magnetically stirred at 1200 r / min at 100 °C for 12 h. After the reaction, ethyl acetate was used as an extractant to extract the reaction product to obtain a boron dipyrromethene fluorescent dye.

[0056] The yield of the boron dipyrromethene fluorescent dye in this example was continuously monitored using a gas chromatograph and a gas chromatography-mass spectrometry (GC-MS) instrument, and the final yield was recorded as 82%.

[0057] The core-shell structured Au@CeO 2 nanocatalyst used in the reaction of Example 2 was recovered by centrifugal filtration and then recycled under the same reaction conditions 4 times, and the final yield of the boron dipyrromethene fluorescent dye obtained after each cycle was recorded.

[0058] As Figure 2 shown, after 5 recycling cycles, the core-shell structured Au@CeO 2 nanocatalyst prepared in the present invention still achieved a final yield of 72% when catalyzing the synthesis of the boron dipyrromethene fluorescent dye, indicating that the core-shell structured Au@CeO 2 nanocatalyst prepared in the present invention has good catalytic activity, stability, and recycling performance.

[0059] Comparative Example 3

[0060] This comparative example was different from Example 2 in that after the reaction proceeded for 2 h, centrifugal filtration was carried out to remove the core-shell structured Au@CeO 2 nanocatalyst, and the filtrate was continued to react under the same reaction conditions until 12 h, and real-time monitoring was carried out by GC-MS.

[0061] As Figure 3 shown, from the monitoring results, it can be seen that no further formation of the boron dipyrromethene fluorescent dye was observed in Comparative Example 3, indicating that the core-shell structured Au@CeO 2 nanocatalyst has good stability and heterogeneous catalytic characteristics, and metal Au did not leach out from the catalyst. The core-shell structured Au@CeO 2 nanocatalyst prepared in the present invention for catalyzing the synthesis of the boron dipyrromethene fluorescent dye is a real heterogeneous catalytic process.

[0062] Examples 3 - 25

[0063] This group of examples was the same as Example 2 in terms of reaction conditions, only changing the reaction substrates, as shown in Table 1 specifically.

[0064] Table 1

[0065]

[0066]

[0067] As can be seen from the data in Table 1, the core-shell structure Au@CeO 2 nano-catalyst is widely used in the catalytic synthesis of BODIPY fluorescent dyes, has good functional group tolerance, and has good conversion rate and selectivity. Whether for ortho-, meta-, or para-BODIPY fluorescent dyes, or for BODIPY fluorescent dyes with electron-donating groups or electron-withdrawing groups, it has good catalytic activity and stability, and the catalytic effect is excellent.

[0068] Examples 26 - 28

[0069] Compared with Example 2, the reaction substrates in this group of examples are the same, and only one of the types or amounts of the catalyst, solvent, and base, as well as the reaction conditions, is changed, as specifically shown in Table 2 below.

[0070] Comparative Examples 4 - 17

[0071] Compared with Example 2, the reaction substrates in this group of comparative examples are the same, and only one of the types or amounts of the catalyst, solvent, and base, as well as the reaction conditions, is changed, as specifically shown in Table 2.

[0072] Table 2

[0073]

[0074]

[0075] As can be seen from the data in Table 2, under the catalysts, solvents, bases, and reaction conditions defined within the scope of the present invention, the catalytic synthesis of BODIPY fluorescent dyes has a higher yield. The catalytic performances of the existing Au@HT (nano-gold catalyst supported on hydrotalcite), Au@HAP (nano-gold catalyst supported on hydroxyapatite), Au@SiO 2 (nano-gold catalyst coated with silica) and the catalysts prepared in Comparative Examples 1 - 2 are all inferior to the core-shell structure Au@CeO 2 nano-catalyst prepared in the present invention.

[0076] It should be noted that in this article, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0077] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a core-shell structure Au@CeO2 nanocatalyst, characterized in that: The steps include: S1. Add tetrachloroauric acid solution and low-concentration cerium chloride solution into deionized water, stir magnetically for 30 min at 5°C, then quickly add ammonia solution and stir for 25 s, then quickly add high-concentration cerium chloride solution and continue stirring for 30 min to obtain a mixed solution; the concentration of the tetrachloroauric acid solution is 0.02 mol / L, the concentration of the low-concentration cerium chloride solution is 0.01 mol / L, the concentration of the ammonia solution is 0.33 mol / L, and the concentration of the high-concentration cerium chloride solution is 0.05 mol / L; S2, centrifuging the mixed solution to retain the precipitate, washing the precipitate with deionized water and anhydrous ethanol for multiple times, and freeze-drying to obtain a catalyst precursor; S3. The catalyst precursor is cleaned, then heated to 100° C. and annealed for 12 h. After cleaning again, it is heated to 300° C. and annealed for 6 h. After cooling to room temperature, a core-shell structured Au@CeO2 nanocatalyst is obtained.

2. The method for preparing a core-shell Au@CeO2 nanocatalyst according to claim 1, characterized in that: The dosage ratio of the tetrachloroauric acid solution, the low-concentration cerium chloride solution, the deionized water, the ammonia solution and the high-concentration cerium chloride solution is 2 mL: 4 mL: 100 mL: 6 mL: 5 mL.

3. The method for preparing a core-shell Au@CeO2 nanocatalyst according to claim 1, characterized in that: The cleaning process is as follows: ultrasonically dispersing the treated object in ethanol, then centrifugally separating the object, and then drying the object at 25°C.

4. A core-shell structure Au@CeO2 nanocatalyst, characterized in that: The core-shell structured Au@CeO2 nanocatalyst is prepared by the preparation method according to any one of claims 1 to 3, wherein the core-shell structured Au@CeO2 nanocatalyst has nano-gold particles as the core and cerium oxide as the shell, the particle size of the core is 10 nm, and the particle size of the shell is 40 nm.

5. The use of a core-shell structure Au@CeO2 nanocatalyst according to claim 4, characterized in that: The following steps are involved: Under argon protection, fluoroboron dipyrrole compounds, aminophenylboronic acid pinacol ester compounds, core-shell structure Au@CeO2 nanocatalysts, sodium acetate and toluene are ultrasonically mixed and stirred at 100-120°C for 12-18h. After the reaction, the reaction product is extracted with ethyl acetate to obtain fluoroboron dipyrrole fluorescent dyes.

6. The use of a core-shell structure Au@CeO2 nanocatalyst according to claim 5, characterized in that: The dosage ratio of the fluoroborane dipyrrole compound, the aminophenylboronic acid pinacol ester compound, the core-shell structure Au@CeO2 nanocatalyst, sodium acetate and toluene is 0.1mmol:0.4mmol:5-8mg:0.4mmol:2mL.

7. The use of a core-shell structure Au@CeO2 nanocatalyst according to claim 5, characterized in that: The general structural formula of the fluoroborane dipyrrole compound is: Wherein, R1 is any one of H, CH3, OCH3, F, Cl, Br, COOH, and NH2; and R2 and R3 are any one of H, OCH3, and Cl.

8. The use of a core-shell structure Au@CeO2 nanocatalyst according to claim 5, characterized in that: The general structural formula of the aminophenylboronic acid pinacol ester compound is: Wherein, R4 is any one of H, CH3, OCH3, F, Cl, Br, COOH, NH2, NO2, and CF3; and R5 is any one of H and CH3.

9. The use of a core-shell structure Au@CeO2 nanocatalyst according to claim 5, characterized in that: The general structural formula of the fluoroboron dipyrrole fluorescent dye is as follows: Wherein, R1 is any one of H, CH3, OCH3, F, Cl, Br, COOH, and NH2; R2 and R3 are any one of H, OCH3, and Cl; R4 is any one of H, CH3, OCH3, F, Cl, Br, COOH, NH2, NO2, and CF3; and R5 is any one of H and CH3.

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