Gold nanocluster-porous organic framework composite catalyst and preparation method thereof

Abstract

The invention provides a gold nanocluster-porous organic framework composite catalyst and a preparation method thereof.The method comprises the steps that thiophene derivative monomers with electrochemical activity are subjected to in-situ polymerization through an electrochemical synthesis method to obtain a rigid porous organic framework, and meanwhile gold nanoclusters are doped in the porous organic framework in an in-situ confinement mode; the confinement effect of the rigid porous organic framework can greatly increase the contact area of the nanoclusters and a catalytic reaction substrate, can effectively avoid agglomeration caused by mutual contact of the nanoclusters in the reaction process, and can improve the catalytic activity and stability of the nanoclusters at the same time. The preparation method of the gold nanocluster-porous organic framework composite catalyst has the advantages of controllable product thickness and mild reaction conditions, other catalysts do not need to be added, the method is environment-friendly and pollution-free, and on the basis of keeping the original performance of the Au25 catalyst, the preparation method of the gold nanocluster-porous organic framework composite catalyst can be used for preparing the gold nanocluster-porous organic framework composite catalyst by accurately regulating the surface properties of the catalyst. The catalytic activity and the stability are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a gold nanocluster-porous organic skeleton composite catalyst and a preparation method thereof. Background Art

[0002] Gold clusters are relatively stable aggregates consisting of a few to several hundred gold atoms. Protected by a molecular layer, gold clusters can emit visible light or near-infrared light at specific wavelengths, showing unique fluorescence properties that are different from bulk gold. For more than 50 years, researchers have made excellent achievements in the field of catalysis by utilizing the unique physical and chemical properties of gold clusters.

[0003] However, gold nanocluster catalysts are easily deactivated by temperature. This is mainly because gold nanoclusters will undergo thermal weight loss at high temperatures, and the ligands will begin to fall off. This ligand shedding will cause the structure of the gold nanoclusters to change, thereby reducing their catalytic activity. In addition, the deactivation of nanocluster catalysts is also related to the aggregation and growth of gold nanoparticles. In a highly dispersed nanoscale state, gold particles have a higher surface energy and thus have catalytic activity. Since substances are more stable in low energy states, gold nanoparticles tend to transform to low energy states. When conditions change, gold nanoparticles will aggregate and grow with each other, thereby reducing their surface energy and resulting in reduced catalytic activity, which is the so-called "sintering deactivation." That is, nanoclusters have good surface activity under high dispersion, but the catalytic activity is lost after agglomeration. Therefore, maintaining the stability of the cluster structure and preventing it from aggregating during the reaction is crucial to improving the activity and stability of the catalyst. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a gold nanocluster-porous organic skeleton composite catalyst and a preparation method thereof in view of the deficiencies of the above-mentioned prior art. The method is to obtain a rigid porous organic skeleton by in situ polymerization of electrochemically active thiophene derivative monomers through an electrochemical synthesis method, and at the same time, in situ "one-pot" confined doping of gold nanoclusters into the porous organic skeleton, which is beneficial to greatly increase the contact area between the nanoclusters and the catalytic reaction substrate, and can effectively prevent the nanoclusters from contacting each other and agglomerating during the reaction, and can simultaneously improve the catalytic activity and stability of the nanoclusters.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for preparing a gold nanocluster-porous organic framework composite catalyst comprises the following steps:

[0007] S1. The monomer with electrochemical active sites and Au 25The nanoclusters are mixed, solvent is added to fully dissolve them, electrolyte is added, sealed, and then sonicated to obtain a uniform solution;

[0008] S2. The solution obtained in S1 is subjected to electrochemical polymerization by cyclic voltammetry in a three-electrode system, wherein the three-electrode system consists of a reference electrode, a working electrode and an auxiliary electrode, and the reference electrode is Ag / Ag + The electrode is a working electrode of nickel foam and an auxiliary electrode of a conductive metal sheet; under an electrochemical reaction, monomers with electrochemically active sites are polymerized to form a rigid porous organic skeleton, and gold nanoclusters are in-situ confinedly doped in the porous organic skeleton. At this time, a layer of yellow-black product is evenly attached to the working electrode, and the obtained yellow-black product is washed with dichloromethane and then dried at 60° C. for 12 to 18 hours to obtain a gold nanocluster-porous organic skeleton composite catalyst.

[0009] Preferably, the monomer having electrochemically active sites in S1 is a thiophene derivative monomer, including tri[4-(2-thienyl)phenyl]amine or 1,3,5-triphenylthiophene.

[0010] Preferably, the electrolyte in S1 includes tetrabutylammonium perchlorate, lithium perchlorate or tetrabutylammonium hexafluorophosphate.

[0011] Preferably, the monomer having electrochemically active sites described in S1, Au 25 The molar ratio of nanoclusters to electrolyte was 25:1:25.

[0012] Preferably, the solvent in S1 is one or more of dichloromethane, propylene carbonate or N,N′-dimethylformamide;

[0013] Preferably, the solvent is a mixed solvent of dichloromethane and propylene carbonate, and the volume ratio of dichloromethane to propylene carbonate is 4:1.

[0014] Preferably, the ultrasonic power in S1 is 500-800W, and the time is 10-20min.

[0015] Preferably, the auxiliary electrode conductive metal sheet S2 comprises a Ti sheet or a stainless steel sheet.

[0016] Preferably, the electrochemical polymerization conditions in S2 are: scanning voltage is 0-1.7-0V, scanning speed is 0.01V / s, and scanning number of circles is 10-20 circles.

[0017] The gold nanocluster-porous organic skeleton composite catalyst prepared by the method is spherical and has a particle size of 200-500 nm.

[0018] The present invention has significant technical effects due to the adoption of the above technical solution:

[0019] 1. The present invention provides a gold nanocluster-porous organic skeleton composite catalyst and a preparation method thereof. The method comprises the following steps: in situ polymerizing electrochemically active thiophene derivative monomers through an electrochemical synthesis method to obtain a rigid porous organic skeleton, and at the same time, in situ "one-pot" confined doping of gold nanoclusters into the porous organic skeleton. The confinement effect of the rigid porous organic skeleton can greatly increase the contact area between the nanoclusters and the catalytic reaction substrate, and can effectively prevent the nanoclusters from contacting each other and agglomerating during the reaction, thereby improving the catalytic activity and stability of the nanoclusters.

[0020] 2. Compared with the traditional method of chemical modification of nanoclusters, the electrochemical synthesis method of the present invention is a simple, rapid and scalable film-forming method, which can prepare porous polymer materials in a short time. It has the advantages of controllable product thickness and mild reaction conditions, and no need to add other catalysts. It is environmentally friendly and pollution-free. It can quickly polymerize in situ to obtain gold nanoclusters@porous organic skeleton composite materials while maintaining Au 25 On the basis of the original performance of the catalyst, its catalytic activity and stability can be further improved by precisely controlling the surface properties of the catalyst.

[0021] The present invention is further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the Fourier transform infrared spectra of the TTPA and PTTPA samples of Example 2;

[0023] Figure 2 The Au of Example 2 25 and Au 25 @Fourier transform infrared spectrum of PTPA sample;

[0024] Figure 3 The Au of Example 2 25 、Au 25 @UV absorption spectra of PTTPA and PTTPA samples;

[0025] Figure 4 The Au of Example 2 25 @SEM image of PTPA sample;

[0026] Figure 5 The Au of Example 2 25 @Thermogravimetric analysis of PTPA and PTPA samples;

[0027] Figure 6 The Au in the 0.5M KOH alkaline solution of Example 2 25 and Au 25@PTTPA oxygen reduction test curve under O2-saturation. DETAILED DESCRIPTION

[0028] Example 1

[0029] A method for preparing a gold nanocluster-porous organic framework composite catalyst, characterized in that it comprises the following steps:

[0030] S1. The monomer with electrochemical active sites and Au 25 The nanoclusters are mixed, a solvent is added to fully dissolve them, and then an electrolyte is added, the opening is sealed, and ultrasonication is performed at a power of 500 to 800 W for 10 to 20 min to obtain a uniform solution.

[0031] The monomer having electrochemically active sites is a thiophene derivative monomer, including tris[4-(2-thienyl)phenyl]amine or 1,3,5-triphenylthiophene;

[0032] The electrolyte includes tetrabutylammonium perchlorate, lithium perchlorate or tetrabutylammonium hexafluorophosphate;

[0033] The monomer having electrochemical active sites, Au 25 The molar ratio of nanoclusters to electrolyte was 25:1:25.

[0034] The solvent is one or more of dichloromethane, propylene carbonate or N,N′-dimethylformamide; preferably a mixed solvent of dichloromethane and propylene carbonate, wherein the volume ratio of dichloromethane to propylene carbonate is 4:1.

[0035] S2. The solution obtained in S1 is subjected to electrochemical polymerization by cyclic voltammetry in a three-electrode system, wherein the three-electrode system consists of a reference electrode, a working electrode and an auxiliary electrode, wherein the reference electrode is Ag / Ag + The electrode is a nickel foam electrode, and the auxiliary electrode is a conductive metal sheet (including a Ti sheet or a stainless steel sheet); the electrochemical polymerization conditions are as follows: the scanning voltage is 0-1.7-0V, the scanning speed is 0.01V / s, and the number of scanning circles is 10-20 circles; under the electrochemical reaction, the monomers with electrochemically active sites are polymerized to form a rigid porous organic skeleton, and the gold nanoclusters are in-situ confined and doped in the porous organic skeleton. At this time, a layer of yellow-black product is evenly attached to the working electrode, and the obtained yellow-black product is washed with dichloromethane, and then placed at 60°C for drying for 12-18h to obtain a gold nanocluster-porous organic skeleton composite catalyst.

[0036] Example 2

[0037] This example uses the method of Example 1 to prepare Au 25 @PTTPA composite catalyst, comprising the following steps:

[0038] S1. Weigh 0.0735 g of tris[4-(2-thienyl)phenyl]amine (TTPA) monomer and 30 mg of Au using an analytical balance. 25 The nanoclusters were added to a 50 mL beaker, and a mixed solvent of 12 mL of dichloromethane and 3 mL of propylene carbonate was added to fully dissolve them. Then, 0.0503 g of tetrabutylammonium perchlorate electrolyte was added, and the beaker was sealed with a sealing film. Ultrasonication was performed at a power of 800 W for 10 min to obtain a uniform solution.

[0039] S2. The solution obtained in S1 is subjected to electrochemical polymerization. The electrochemical polymerization system is a three-electrode system, and the reference electrode is Ag / Ag + Electrode, the working electrode is nickel foam, the auxiliary electrode is Ti sheet. Before use, the nickel foam of the working electrode is ultrasonically cleaned with water, acetone and ethanol, the Ti sheet of the electrode is polished with sandpaper to remove the surface oxide layer, and then ultrasonically cleaned with water, acetone and ethanol. A CHI760 series electrochemical workstation (Shanghai Chenhua) was used, and cyclic voltammetry (CV) was selected. The scanning voltage was 0~1.7~0V, the scanning speed was 0.01V / s, and the number of scanning circles was 20 circles. The tri[4-(2-thienyl)phenyl]amine monomer was polymerized, and a layer of yellow-black product was evenly attached to the working electrode. The obtained yellow-black product was washed with dichloromethane 5 times to wash away the unreacted tri[4-(2-thienyl)phenyl]amine monomer, electrolyte and Au. 25 After the completion, the nanoclusters were placed in a forced air drying oven (Shanghai Fuma Experimental Equipment Co., Ltd.) at 60 °C for 12 h to obtain Au 25 @PTTPA composite catalyst.

[0040] The Fourier transform infrared spectroscopy test results of TTPA monomer and PTTPA are as follows Figure 1 Infrared spectrometer, instrument model: Bruker Foucus D8, instrument manufacturer: Bruker, Germany, infrared scanning range from 400cm –1 ~4000cm –1 The results show that for PPTA, 826cm -1 The sharp absorption band at 692 cm-1 belongs to the unique vibration of 1,4-substituted benzene ring, which red-shifts after polymerization. -1 The reduction of the out-of-plane CH bending vibration at the , and the obvious weakening of the peak value, indicate that most active sites are involved, which also means that the monomers are effectively polymerized, the degree of polymerization of the system is high, and a cross-linked network structure is formed;

[0041] Au 25 and Au 25 @PTTPA sample Fourier transform infrared spectrum test results are as follows Figure 2As shown, the characteristic peaks of PTTPA are located at 500-1800 cm -1 The Au prepared in this example 25 The absorption peak of @PTTPA is located at 1495cm -1 、1367cm -1 、1213cm -1 、1180cm -1 、1022cm -1 The positions are consistent with the infrared absorption peaks of PTTPA. -1 、2362cm -1 The characteristic peak at 25 This is consistent with the above, which proves that Au 25 Successfully doped and embedded into PTTPA.

[0042] Au 25 、PTTPA、Au 25 @PTTPA UV absorption spectrum Figure 3 , UV-Vis spectrophotometer, instrument model: 752N, instrument manufacturer: Shanghai Precision Scientific Instrument Co., Ltd., wavelength scanning range from 300 to 800nm. From the comparison in the figure, it can be seen that the blue curve is the characteristic peak of PTTPA, which is similar to Au 25 Compared with @PTTPA, the peak has a blue shift, proving that Au 25 Embedded in PTTPA, the conjugation degree of the PTTPA backbone changes.

[0043] Scanning electron microscope, instrument model: JSM-7500F, instrument manufacturer: Hitachi, Japan. The specific operation of this experiment is to cut the obtained samples into appropriate sizes and directly paste them on the conductive glue for testing. 25 @PTTPA sample scanning electron microscope test results are as follows Figure 4 As shown. It can be seen from the figure that the prepared Au 25 @PTTPA samples have uniform morphology, mostly spherical, and uniform particle size, about 500nm.

[0044] PTTPA、Au 25 @The thermal stability curve of PTPA sample is as follows Figure 5 As shown, the thermogravimetric analyzer, instrument model: DZ-TGA101, instrument manufacturer: Suzhou Jianzhuo Instrument Technology Co., Ltd., the test was carried out in N2 atmosphere, and the test temperature range was 50~800℃. It can be found that when the temperature is between 50~200℃, Au 25 @PTTPA weight loss is not obvious, when the temperature exceeds 200℃, Au 25@PTTPA began to lose weight significantly, and the weight loss ratio was greater than that of PTTPA material, indicating that in addition to the destruction of the polymer structure, Au 25 The ligands of the clusters also began to fall off. 25 After the cluster is heated to 100°C, the ligand will fall off significantly, indicating that the method of electropolymerization confinement of the present invention has greatly improved the thermal stability of the cluster. In addition, when the temperature rises to 600°C, PTTPA begins to lose weight rapidly, which is attributed to the destruction of the monomer structure, indicating that Au is generated by electropolymerization. 25 @PTTPA material not only helps to improve the thermal stability of the cluster, but also plays a certain protective role for the monomer structure.

[0045] Disc potentiometer, instrument model: Pine research-AFMSRCE, instrument manufacturer: Physical and Chemical Corporation, test conditions: 0.5M KOH alkaline solution, oxygen was introduced for 30 minutes before the test to ensure that the solution was oxygen saturated. The oxygen reduction (ORR) test results are shown in Figure 6 Before modification, Au 25 The maximum ORR current density is 0.95 mA cm –2 , the starting voltage is -0.25V (vs Ag / AgCl), after confined doping, Au 25 The maximum current density of @PTTPA increased to 1.31 mA cm –2 , and the starting voltage becomes -0.2V (vs Ag / AgCl). This test result shows that the electrochemical synthesis of Au provided by the present invention 25 @PTTPA composite catalyst can improve the catalytic performance of Au 25 Catalytic activity and stability of nanoclusters.

[0046] Example 3

[0047] This example uses the method of Example 1 to prepare Au 25 @PTTB composite catalyst, comprising the following steps:

[0048] S1. Weigh 0.0487 g 1,3,5-triphenylthiophene (TTB) monomer and 30 mg Au using an analytical balance. 25 The nanoclusters were added to a 50 mL beaker, and 12 mL of dichloromethane and 3 mL of propylene carbonate were added to fully dissolve them. Then, 0.0503 g of lithium perchlorate electrolyte was added, and the beaker was sealed with a sealing film. Ultrasonication was performed at a power of 500 W for 20 min to obtain a uniform solution.

[0049] S2. The solution obtained in S1 is subjected to electrochemical polymerization. The electrochemical polymerization system is a three-electrode system, and the reference electrode is Ag / Ag + Electrode, the working electrode is nickel foam, the auxiliary electrode is stainless steel sheet. Before use, the nickel foam of the working electrode is ultrasonically cleaned with water, acetone, and ethanol, the stainless steel sheet is polished with sandpaper to remove the surface oxide layer, and then ultrasonically cleaned with water, acetone, and ethanol. A CHI760 series electrochemical workstation (Shanghai Chenhua) was used, and cyclic voltammetry (CV) was selected. The scanning voltage was 0-1.7-0V, the scanning speed was 0.01V / s, and the number of scanning circles was 10 circles. 1,3,5-triphenylthiophene monomer polymerized, and a layer of light yellow product was evenly attached to the working electrode. The obtained light yellow product was washed 3 times with dichloromethane to wash away the unreacted 1,3,5-triphenylthiophene monomer, electrolyte, and Au. 25 After the completion, the nanoclusters were placed in a forced air drying oven (Shanghai Fuma Experimental Equipment Co., Ltd.) at 60 ° C for 18 h to obtain Au 25 @PTTB composite catalyst.

[0050] The present invention uses an electrochemical synthesis method to in-situ polymerize electrochemically active thiophene derivative monomers to obtain a rigid porous organic skeleton, and at the same time in-situ confinement dopes gold nanoclusters in the porous organic skeleton. The obtained gold nanocluster-porous organic skeleton composite catalyst is uniformly distributed spherical particles with a particle size of 200-500nm. The confinement effect of the porous organic skeleton can greatly increase the contact area between the nanoclusters and the catalytic reaction substrate, can effectively prevent the nanoclusters from contacting each other and agglomerating during the reaction process, and can simultaneously improve the catalytic activity and stability of the nanoclusters.

[0051] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a gold nanocluster-porous organic framework composite catalyst, characterized in that: The following steps are involved: S1. The monomer with electrochemical active sites and Au 25 The nanoclusters are mixed, solvent is added to fully dissolve them, electrolyte is added, sealed, and then sonicated to obtain a uniform solution; S2. The solution obtained in S1 is subjected to electrochemical polymerization by cyclic voltammetry in a three-electrode system, wherein the three-electrode system consists of a reference electrode, a working electrode and an auxiliary electrode, and the reference electrode is Ag / Ag + The electrode is a working electrode of nickel foam and an auxiliary electrode of a conductive metal sheet; under an electrochemical reaction, monomers with electrochemically active sites are polymerized to form a rigid porous organic skeleton, and gold nanoclusters are in-situ confinedly doped in the porous organic skeleton. At this time, a layer of yellow-black product is evenly attached to the working electrode, and the obtained yellow-black product is washed with dichloromethane and then dried at 60° C. for 12 to 18 hours to obtain a gold nanocluster-porous organic skeleton composite catalyst.

2. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 1, characterized in that: The monomer having electrochemically active sites described in S1 is a thiophene derivative monomer, including tri[4-(2-thienyl)phenyl]amine or 1,3,5-triphenylthiophene.

3. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 1, characterized in that: S1 The electrolyte includes tetrabutylammonium perchlorate, lithium perchlorate or tetrabutylammonium hexafluorophosphate.

4. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 1, characterized in that: S1: monomers with electrochemically active sites, Au 25 The molar ratio of nanoclusters to electrolyte was 25:1:

25.

5. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 1, characterized in that: S1 The solvent is one or more of dichloromethane, propylene carbonate or N,N′-dimethylformamide.

6. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 5, characterized in that: The solvent is a mixed solvent of dichloromethane and propylene carbonate, and the volume ratio of the dichloromethane to propylene carbonate is 4:

1.

7. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 1, characterized in that: S1: The ultrasonic power is 500-800W, and the time is 10-20min.

8. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 1, characterized in that: S2 The auxiliary electrode conductive metal sheet includes a Ti sheet or a stainless steel sheet.

9. The method for preparing a gold nanocluster-porous organic framework composite catalyst according to claim 1, characterized in that: The electrochemical polymerization conditions described in S2 are: scanning voltage is 0-1.7-0V, scanning speed is 0.01V / s, and scanning number of circles is 10-20 circles.

10. A gold nanocluster-porous organic framework composite catalyst prepared by the method according to any one of claims 1 to 9, characterized in that: The gold nanocluster-porous organic skeleton composite catalyst is spherical, and the particle size is 200-500nm.

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