A palladium single atom catalyst and its preparation method and application

Abstract

The present invention relates to the technical field of photocatalyst materials, and specifically discloses a palladium single-atom catalyst and a preparation method and application thereof. The catalyst preparation method comprises the following steps: S1, reacting tetrakis(4-carboxyphenyl)porphine in a weakly acidic environment, self-assembling to form a nanosheet material, and obtaining a precursor X; S2, reacting the precursor X and palladium acetate in a solvent, and obtaining a palladium single-atom catalyst after centrifugation, washing and drying. The carboxyl groups on the surface of the nanosheet material capture Pd ions, and Pd 2+ The H + The carboxylate ion and the replaced H + The combination forms acetic acid, and according to the principle of strong acid to weak acid, the reaction is irreversible, forming Pd single atoms, thereby achieving the loading of Pd single atoms. The palladium single atom catalyst provided by the present invention has higher dispersibility and 100% atomic utilization, so that the catalyst can achieve better catalytic effect at a lower Pd loading.

Description

Technical Field

[0001] The invention belongs to the technical field of photocatalyst materials, and specifically relates to a palladium single-atom catalyst and a preparation method and application thereof. Background Art

[0002] Advanced oxidation technology relies on modern electrical, magnetic, acoustic, optical and other scientific and technological means to generate free radicals or charged ions with strong oxidizing ability, oxidizing and degrading organic pollutants in wastewater into low-toxic or non-toxic small molecules, or even directly degrading them into CO2 and H2O. The Fenton process is a process that uses H2O2 and Fe 2+ Advanced oxidation technology that produces hydroxyl radicals (•OH) through ion reactions is widely used in wastewater treatment. However, the traditional Fenton process consumes a large amount of H2O2 as an oxidant, which poses a safety hazard in the storage and transportation of H2O2. 3+ Fe 2+ The transformation is a slow rate-controlling step, which limits the efficiency of the Fenton reaction; the generated •OH is electrophilic and has low reaction activity with aromatic organic matter with strong chemical bonds, which makes it difficult for the organic matter to be effectively mineralized and the treatment effect is poor.

[0003] As a new advanced oxidation technology, the self-Fenton process (PSF) based on in-situ photosynthesis of H2O2 has the advantages of strong oxidation ability and green and mild reaction conditions, providing a new idea for the deep treatment of difficult-to-degrade organic wastewater. By in-situ photosynthesis of H2O2, the problem of large consumption of H2O2 in the traditional Fenton process is avoided, the operating cost is reduced and the safety is improved. In the PSF process, the electrons and holes generated on the surface of the photocatalyst participate in the reaction, which can accelerate the Fe 3+ To Fe 2+ The PSF process based on in situ photosynthesis of H2O2 can synergize the advantages of photocatalysis and Fenton reaction and significantly improve the degradation efficiency of organic pollutants, but the design of high-performance photocatalysts remains challenging.

[0004] Scholars at home and abroad have conducted a lot of research and constructed various photocatalysts, using strategies such as element doping and heterojunction engineering to improve photocatalytic performance, but the effect is limited. In view of this, researchers are in urgent need of providing a high-performance photocatalyst. Summary of the invention

[0005] The purpose of the present invention is to provide a palladium single atom catalyst and its preparation method and application in view of the deficiencies in the prior art, taking advantage of the higher dispersibility and 100% atomic utilization of Pd single atoms, so that the catalyst can achieve better catalytic effect at a lower Pd loading.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] The first object of the present invention is to provide a method for preparing a palladium single-atom catalyst, comprising the following steps:

[0008] S1, reacting tetrakis(4-carboxyphenyl)porphine in a weakly acidic environment to self-assemble into a nanosheet material to obtain a precursor X;

[0009] S2. The precursor X and palladium acetate are reacted in a solvent, and after centrifugation, washing and drying, a palladium single atom catalyst is obtained.

[0010] Furthermore, in step S1, tetrakis(4-carboxyphenyl)porphine is reacted in a weakly acidic environment and stirred in a closed reactor at 130° C. for at least 48 hours.

[0011] Furthermore, in step S2, the solvent is dichloromethane.

[0012] Furthermore, the mass ratio of tetrakis(4-carboxyphenyl)porphine to palladium acetate is 1.2:(10~30).

[0013] The second object of the present invention is to provide a palladium single-atom catalyst prepared by the above-mentioned preparation method.

[0014] Furthermore, the mass percentage of palladium atoms in the catalyst is 0.53% to 1.45%.

[0015] The third object of the present invention is to provide the use of the above-mentioned palladium single-atom catalyst in synthesizing hydrogen peroxide using sunlight.

[0016] Furthermore, the intensity of the sunlight is 100 mW / cm 2 .

[0017] The fourth object of the present invention is to provide the application of the above-mentioned palladium single-atom catalyst in removing pollutants from water bodies.

[0018] Furthermore, the pollutant includes any one of bisphenol A, 4-chlorophenol, rhodamine B and ciprofloxacin.

[0019] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0020] (1) The present invention provides a method for preparing a palladium single-atom catalyst, wherein tetrakis(4-carboxyphenyl)porphine is reacted in a weakly acidic environment to self-assemble into a nanosheet material, and then the carboxyl groups on the surface of the nanosheet material are used to capture Pd ions. The divalent Pd ions (Pd 2+ ) + The carboxylate ion and the replaced H + Combined to form acetic acid, this process follows the principle of strong acid to produce weak acid, the reaction is irreversible, forming Pd single atoms, thereby realizing the loading of Pd single atoms.

[0021] (2) The palladium single atom catalyst provided by the present invention, in which the Pd single atom is directly bonded to the nanosheet material, has a shorter electron transfer path and can greatly improve the electron-hole separation efficiency of the catalyst.

[0022] (3) In the palladium single atom catalyst provided by the present invention, the Pd single atom is directly bonded to the substrate material to form an intermediate valence state between 0 and +2. Its special electronic structure helps to modulate the adsorption of the substrate and improve the catalytic efficiency and selectivity.

[0023] (4) The palladium single atom catalyst provided by the present invention has higher dispersibility and 100% atomic utilization of Pd single atoms, so that the catalyst can achieve better catalytic effect at a lower Pd loading.

[0024] (5) The preparation method provided by the present invention requires low raw material cost, simple process operation, meets environmental protection requirements, and has promising application prospects in the field of photocatalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 TEM image of the precursor X prepared in the present invention;

[0026] Figure 2 This is a transmission electron microscope image of catalyst A prepared in Example 1 of the present invention;

[0027] Figure 3 This is a transmission electron microscope image of catalyst B prepared in Example 2 of the present invention;

[0028] Figure 4 This is a transmission electron microscope image of catalyst C prepared in Example 3 of the present invention;

[0029] Figure 5 It is a transmission electron microscope image of catalyst D prepared in comparative example 1;

[0030] Figure 6 This is an energy spectrum scanning analysis diagram of the catalyst B prepared in Example 2, in which a is a distribution diagram of palladium (Pd) elements, b is a distribution diagram of nitrogen (N) elements, c is a distribution diagram of carbon (C) elements, and d is a distribution diagram of oxygen (O) elements;

[0031] Figure 7 : is a comparison result diagram of X-ray photoelectron spectroscopy of catalyst B and catalyst D;

[0032] Figure 8 This is a graph showing the impedance test results of catalyst B prepared in Example 2;

[0033] Fig. 9 This is a photocurrent density test result diagram of catalyst B prepared in Example 2;

[0034] Fig.10 This is a performance comparison chart of precursor X, catalyst B and catalyst D in photosynthetic hydrogen peroxide. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention clearer, the specific embodiments of the present invention are further described in detail below in conjunction with specific examples and drawings. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0036] Example 1

[0037] This embodiment provides a method for preparing a palladium single atom catalyst:

[0038] 1.2 g of tetrakis(4-carboxyphenyl)porphine was weighed and added to 35 mL of ultrapure water, and 0.5 mL of hydrochloric acid with a concentration of 0.01 mol / L was added. The mixture was stirred in a closed reactor at 130° C. for 48 hours. The product was centrifuged, washed and dried to obtain a precursor X.

[0039] 1.0 g of the precursor X was weighed and added to 50 mL of dichloromethane, followed by 10 mg of palladium acetate, and the mixture was heated to 60° C. and refluxed for 12 hours. After the reaction, the target catalyst was obtained by centrifugation, washing and drying, which was marked as catalyst A.

[0040] Example 2

[0041] This embodiment provides a method for preparing a palladium single atom catalyst:

[0042] The process is basically the same as Example 1, except that 20 mg of palladium acetate is added to obtain the target catalyst, which is marked as catalyst B.

[0043] Example 3

[0044] This embodiment provides a method for preparing a palladium single atom catalyst:

[0045] The process is basically the same as Example 1, except that 30 mg of palladium acetate is added to obtain the target catalyst, which is marked as catalyst C.

[0046] Comparative Example 1

[0047] 1.0 g of the precursor X was weighed and added into 50 mL of ultrapure water, followed by the addition of 20 mg of palladium chloride, and the mixture was heated to 60° C. for 12 hours. After the reaction, the mixture was centrifuged, washed and dried to obtain a catalyst D.

[0048] Characterization results

[0049] After the above-prepared catalysts A, B, C and D were digested, the Pd content therein was determined by ICP-AES, and the results are shown in Table 1. It can be seen that A, B, C and D all contain different amounts of Pd, and the Pd loading is close to the theoretical value. It is proved that the methods in Examples 1-3 and Comparative Example 1 can load Pd onto the precursor.

[0050] Table 1. Pd content statistics

[0051]

[0052] like Figure 1 , which is a transmission electron microscope image of the precursor X, it can be seen from the image that tetrakis(4-carboxyphenyl)porphine forms a sheet-like material through self-assembly.

[0053] like Figure 2-Figure 4 As shown, they are transmission electron micrographs of the catalysts prepared in Examples 1 to 3, respectively. It can be seen from the figures that after the reaction with palladium acetate, the surface of the material is the same as that of the precursor X, and no Pd particles are observed.

[0054] like Figure 5 As shown in FIG. 1 , it is a transmission electron microscope image of catalyst D prepared in comparative example 1. It can be seen from the figure that after the reaction with palladium chloride, a large number of Pd particles appear on the surface of the material. This shows that the method adopted by the present invention, using palladium acetate as a reactant, can avoid the aggregation of Pd on the catalyst surface and obtain atomically dispersed Pd, which cannot be achieved by methods other than the present invention.

[0055] like Figure 6 As shown, this is the energy spectrum surface scanning analysis diagram of catalyst B prepared in Example 2. It can be seen from the figure that the Pd element is evenly distributed on the surface of the catalyst, proving that Pd is successfully loaded on the catalyst surface and presents atomic-level dispersion.

[0056] like Figure 7As shown in the figure, it is a comparison result of the X-ray photoelectron spectra of catalyst B and catalyst D. It can be seen from the figure that catalyst D presents a mixed valence state, which is 0-valence Pd inside the Pd particles and +2-valence Pd on the particle surface. Catalyst B presents a single valence state between 0 and +2. This further proves that the method provided by the present invention can prepare Pd single atoms with monodisperse and single valence state.

[0057] like Figure 8 and Fig. 9 The photoelectrochemical test results of catalyst B prepared in Example 2 are shown. The photoelectrochemical test was carried out on a three-electrode system connected to an electrochemical workstation, and the light source was a 300 W xenon lamp. When preparing the working electrode, 5 mg of the sample was dispersed in a mixture of 500 μL of isopropanol and 490 μL of ultrapure water; then, 10 μL of Nafion solution was added and the mixture was shaken; then 40 μL of the mixed sample suspension was dropped on a conductive glass (1.0×1.0 cm 2 ) and dried naturally to obtain the working electrode. The electrolyte used in the photoelectrochemical test was a 0.2 M sodium sulfate (Na2SO4) aqueous solution. The counter electrode was a platinum sheet and the reference electrode was an Ag / AgCl electrode. The photocurrent density test was measured by a 10 s pulse switching process. Figure 8 This is the impedance test result diagram. Fig. 9 The photocurrent density test results are shown in Figure 2. As can be seen from the figure, catalyst B has lower impedance and higher photocurrent density, which proves that the catalyst loaded with Pd single atoms can effectively promote the separation of electrons and holes and improve the photocatalytic performance. Similarly, catalysts A and C have similar photoelectric properties as mentioned above.

[0058] In order to better illustrate the catalytic performance of the palladium single-atom catalyst provided by the present invention, the following studies were conducted:

[0059] Example 4

[0060] Used for photosynthesis of hydrogen peroxide.

[0061] Experimental steps for photosynthetic hydrogen peroxide:

[0062] Weigh 20 mg of photocatalyst, add it into 50 mL of pure water, and use a xenon lamp light source at 100 mW / cm 2 The reaction was carried out under a light intensity of , and the concentration of hydrogen peroxide was determined by iodine titration.

[0063] The results are as follows Fig.10The figure shows the performance comparison of precursor X, catalyst B and catalyst D in photosynthetic hydrogen peroxide. As can be seen from the figure, the order of photocatalytic performance is: B>D>X, which proves the high performance of the single atom catalyst. The high performance of catalyst B has two reasons. One is that the loading of Pd single atoms improves the electron-hole separation ability of the photocatalyst, and the other is that Pd single atoms have better adsorption and activation ability for water and oxygen.

[0064] Example 5

[0065] Experiment on removing the pollutant bisphenol A from water.

[0066] Photo-Fenton experimental steps:

[0067] Weigh 20 mg of photocatalyst, add it to 50 mL of water containing organic pollutants, add 5 mg of FeCl3, and use a xenon lamp light source at 100 mW / cm 2 The reaction was carried out under a light intensity of for 30 minutes, and the changes in the pollutant content were determined by liquid chromatography, ultraviolet spectrophotometry, etc.

[0068] The experimental results are shown in Table 2, which is a statistical table of the degradation efficiency of different catalysts for bisphenol A. The main reasons for the high performance of catalyst B are twofold: first, catalyst B is more efficient in photosynthesizing hydrogen peroxide; second, the Pd single atom in catalyst B helps to adsorb and activate organic pollutants.

[0069] Table 2. Statistical table of degradation efficiency of bisphenol A by different catalysts

[0070]

[0071] The Pd content of the catalyst before and after the reaction was determined by ICP-AES, and the results are shown in Table 3. It can be seen that the Pd content in the catalyst did not change before and after the reaction, indicating that catalyst B has good stability.

[0072] Table 3. Changes in Pd content of catalyst before and after reaction

[0073]

[0074] Example 6

[0075] Study on the degradation efficiency of removing different pollutants from water bodies.

[0076] The experimental method is the same as that of Example 5, and the pollutants are bisphenol A, 4-chlorophenol, rhodamine B and ciprofloxacin.

[0077] The experimental results are shown in Table 4, which is a statistical table of the degradation effect of catalyst B on different pollutants, proving that catalyst B has a good degradation effect on different types of pollutants in the photo-Fenton process.

[0078] Table 4. Statistical table of degradation effects of different pollutants

[0079]

[0080] In the absence of conflict, the above embodiments and features in the embodiments may be combined with each other.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a palladium single-atom catalyst, characterized in that: The following steps are involved: S1, using tetrakis(4-carboxyphenyl)porphine to react in a weakly acidic environment, stirring the reaction in a closed reactor at 130° C. for at least 48 hours, and self-assembling to form a nanosheet material to obtain a precursor X; S2. The precursor X and palladium acetate are reacted in a solvent, wherein the mass ratio of tetrakis(4-carboxyphenyl)porphine to palladium acetate is 1.2:(10-30). After centrifugation, washing and drying, a palladium single atom catalyst is obtained.

2. The preparation method according to claim 1, characterized in that In step S2, the solvent is dichloromethane.

3. A palladium single atom catalyst prepared by the preparation method described in any one of claims 1 to 2.

4. The palladium single atom catalyst according to claim 3, characterized in that The mass percentage of palladium atoms in the catalyst is 0.53%~1.45%.

5. Use of the palladium single atom catalyst as claimed in claim 3 or 4 in synthesizing hydrogen peroxide using sunlight.

6. The use according to claim 5, characterized in that The intensity of the sunlight is 100 mW / cm 2 .

7. Use of the palladium single atom catalyst as described in claim 3 or 4 in removing pollutants from water.

8. The use according to claim 7, characterized in that The pollutant includes any one of bisphenol A, 4-chlorophenol, rhodamine B and ciprofloxacin.

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