Method for preparing molten salt assisted polyphthalocyanine photocatalyst and synthesizing hydrogen peroxide by using molten salt assisted polyphthalocyanine photocatalyst

Abstract

The invention belongs to the technical field of photocatalysis, and particularly discloses a method for preparing a molten salt assisted polyphthalocyanine photocatalyst and synthesizing hydrogen peroxide from the molten salt assisted polyphthalocyanine photocatalyst, and the preparation method comprises the following steps: weighing pyromellitic dianhydride, 2, 3-naphthalene dicarboxylic anhydride, ammonium chloride, alkali chloride, urea and ammonium molybdate tetrahydrate, and putting into a ceramic crucible; putting the ceramic crucible into a muffle furnace, and heating to obtain a crude product; extracting the obtained crude product; ball-milling the product for 6 hours; and weighing a sample, and drying by ultrasonic treatment to obtain a final product. According to the method for preparing the molten salt-assisted polyphthalocyanine photocatalyst and synthesizing hydrogen peroxide by using the molten salt-assisted polyphthalocyanine photocatalyst, the catalyst Li-K-PPc-n is successfully prepared by adopting a strategy of synthesizing edge-functionalized polyphthalocyanine under the assistance of potassium-lithium blended molten salt, and the photocatalytic performance of the material is further optimized through treatment means such as ball milling and cell disruption; the yield of photocatalytic synthesis of H2O2 is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysis, in particular to a method for preparing a molten salt-assisted polyphthalocyanine photocatalyst and synthesizing hydrogen peroxide therefrom. Background Art

[0002] Using solar energy to drive artificial photosynthesis, providing energy for electrons and holes in photocatalysts, and then converting water and O2 into hydrogen peroxide (H2O2) through redox reactions, is an advanced technology that is extremely economical and environmentally friendly. Photocatalytic technology has significant advantages such as environmental friendliness, energy conservation and sustainability, and excellent catalytic performance, providing a new way to achieve green production of H2O2. Phthalocyanine-based covalent organic polymers (COPs) have attracted much attention due to their unique π-conjugated structure. This structure not only significantly improves the material's ability to absorb visible light, but also effectively promotes the separation and migration of photogenerated carriers, thereby improving photocatalytic performance. Therefore, COPs are considered to be a very promising catalyst for the artificial photocatalytic synthesis of hydrogen peroxide.

[0003] In recent years, the application of melt methods in photocatalysis has made significant progress, providing new ideas and methods for the development of high-performance photocatalysts. For example, in the synthesis of carbon nitride-based photocatalysts, melt methods have successfully overcome the problems of low crystallinity, high structural defect density, small specific surface area, and insufficient light absorption capacity in traditional methods, thereby significantly improving the photocatalytic activity of carbon nitride-based photocatalysts. Furthermore, melt methods have also demonstrated unique advantages in the synthesis of covalent organic frameworks (COFs). COFs synthesized via this method not only have higher crystallinity and specific surface area but also significantly enhance the chemical stability of the materials. Similarly, melt methods have achieved significant breakthroughs in the synthesis of metal oxide-based photocatalysts. This method not only reduces synthesis temperature, energy consumption, and byproduct formation, but also significantly improves the crystallinity and chemical stability of the catalysts. However, despite the numerous achievements of melt methods in photocatalysis, there have been no reports on the molten salt-assisted synthesis of polyphthalocyanines. Given the enormous potential of polyphthalocyanines in photocatalysis, it is believed that molten salt-assisted synthesis strategies will provide new ideas and research directions for the modification of polyphthalocyanines and the improvement of their photocatalytic performance.

[0004] This method uses a eutectic mixture of potassium chloride (KCl) and lithium chloride (LiCl) as a molten salt system to achieve low-temperature melt synthesis of edge-functionalized polyphthalocyanine (Li-K-PPc-n) by lowering its melting point. This method aims to significantly increase the yield of polyphthalocyanine (PPc-n) in the photocatalytic synthesis of H2O2. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a molten salt-assisted polyphthalocyanine photocatalyst and synthesizing hydrogen peroxide from it. A strategy of synthesizing edge-functionalized polyphthalocyanine using a potassium-lithium blended molten salt as an aid has been successfully employed to prepare the catalyst Li-K-PPc-n. Treatments such as ball milling and cell disruption have been employed to further optimize the photocatalytic performance of the material and improve its yield in photocatalytically synthesizing H2O2.

[0006] To achieve the above object, the present invention provides a method for preparing a molten salt-assisted polyphthalocyanine photocatalyst, comprising the following steps:

[0007] S1. Weigh pyromellitic anhydride, 2,3-naphthalene dicarboxylic anhydride, ammonium chloride, alkali metal chloride, urea, and ammonium molybdate tetrahydrate, mix them evenly in a mortar and grind them for 30 minutes, then transfer the mixture into a ceramic crucible;

[0008] S2. Place the ceramic crucible in a muffle furnace, heat to 220°C at a heating rate of 5°C / min, and maintain at this temperature for 7 hours to obtain a crude product;

[0009] S3. The crude product was placed in a Soxhlet extractor and extracted with a mixed solvent at a temperature of 120° C. for 48 hours.

[0010] S4. After the extraction is completed, the product is placed in a vacuum drying oven to dry overnight, and the dried sample is placed in a ball mill filled with zirconium dioxide balls and ball milled at a speed of 500 rpm for 6 h;

[0011] S5. Weigh the sample and disperse it in deionized water. Use an ultrasonic cell disruptor to treat it for 1 hour to achieve uniform dispersion of the sample. Centrifuge and wash the ultrasonically treated solution three times. Place the washed sample in a vacuum drying oven again and dry it overnight to obtain the final product.

[0012] Preferably, in step S1, the alkali metal chloride includes potassium chloride and lithium chloride.

[0013] Preferably, in step S3, the mixed solvent is a mixed solvent of water, ethanol and tetrahydrofuran, and the volume ratio of water, ethanol and tetrahydrofuran is 1:1:1.

[0014] Preferably, in step S5, acetone solution is used for centrifugal washing.

[0015] The present invention also provides a molten salt-assisted polyphthalocyanine photocatalyst, which is prepared by a preparation method of the molten salt-assisted polyphthalocyanine photocatalyst.

[0016] The present invention also provides a method for synthesizing hydrogen peroxide using a molten salt-assisted polyphthalocyanine photocatalyst, which is achieved by using a photocatalyst and comprises the following steps:

[0017] At room temperature, the photocatalyst, deionized water and sacrificial agent were evenly dispersed in a glass photocatalytic reactor. In the dark, O2 was introduced into the solution at a flow rate of 300 mL / min and stirred for 30 minutes to achieve O2 adsorption-desorption equilibrium. The solution was illuminated by a 300W xenon lamp equipped with a 400nm filter to generate hydrogen peroxide.

[0018] Preferably, the sacrificial agent is ethanol.

[0019] The advantages and beneficial effects of the method for preparing the polyphthalocyanine photocatalyst and synthesizing hydrogen peroxide using the molten salt-assisted method of the present invention are:

[0020] 1. This study successfully prepared the catalyst Li-K-PPc-n by using a potassium-lithium blend molten salt-assisted synthesis of edge-functionalized polyphthalocyanine. Ball milling and cell disruption were used to further optimize the material's photocatalytic performance. This study demonstrates that this molten salt-assisted synthesis of edge-functionalized polyphthalocyanine can successfully improve its photocatalytic yield of H2O2.

[0021] 2. The Li-K-PPc-n of the present invention has a low degradation rate for H2O2 and good cyclic stability. When ethanol is used as a sacrificial agent and the solution pH is 3, the yield of H2O2 photocatalytic synthesis is increased.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is a structural diagram of the Li-K-PPc-n photocatalyst of the present invention, wherein (a) is an XRD pattern, (b) is an FT-IR pattern, and (c) is a Raman pattern;

[0024] Figure 2 These are SEM images of the photocatalyst of the present invention at a scale of 2 μm, where (a) is K-PPc-n, (b) is Li-PPc-n, and (c) is Li-K-PPc-n;

[0025] Figure 3 These are the N2 adsorption-desorption isotherms and pore size distribution diagrams of Li-PPc-n, K-PPc-n, and Li-K-PPc-n of the present invention, wherein (a) is the adsorption-desorption isotherm of Li-PPc-n, (b) is the pore size distribution diagram of Li-PPc-n, (c) is the adsorption-desorption isotherm of K-PPc-n, (d) is the pore size distribution diagram of K-PPc-n, (e) is the adsorption-desorption isotherm of Li-K-PPc-n, and (f) is the pore size distribution diagram of Li-K-PPc-n;

[0026] Figure 41 are XPS spectra of K-PPc-n and Li-K-PPc-n of the present invention, wherein (a) is the C1s diagram of K-PPc-n, (b) is the C1s diagram of Li-K-PPc-n, (c) is the N1s diagram of K-PPc-n, (d) is the N1s diagram of Li-K-PPc-n, (e) is the K 2p diagram of K-PPc-n, and (f) is the K 2p diagram of Li-K-PPc-n;

[0027] Figure 5 are TGA graphs of K-PPc-n, Li-PPc-n and Li-K-PPc-n of the present invention;

[0028] Figure 6 are UV-vis DRS diagrams and Tauc diagrams of K-PPc-n, Li-PPc-n and Li-K-PPc-n of the present invention, wherein (a) is the UV-vis DRS diagram of K-PPc-n, Li-PPc-n and Li-K-PPc-n, (b) is the Tauc diagram of K-PPc-n, (c) is the Tauc diagram of Li-PPc-n, and (d) is the Tauc diagram of Li-K-PPc-n;

[0029] Figure 7 PL spectra of K-PPc-n, Li-PPc-n, Li-K-PPc-n and PPc-n of the present invention;

[0030] Figure 8 1 are the EIS and TPC diagrams of K-PPc-n, Li-PPc-n and Li-K-PPc-n of the present invention, wherein (a) is the EIS diagram and (b) is the TPC diagram;

[0031] Figure 9 : are the Mott-Schottky plots of K-PPc-n, Li-PPc-n, and Li-K-PPc-n of the present invention, wherein (a) is K-PPc-n, (b) is Li-PPc-n, and (c) is Li-K-PPc-n;

[0032] Figure 10 Schematic diagram of the energy band structure of K-PPc-n, Li-PPc-n and Li-K-PPc-n of the present invention;

[0033] Figure 112 is a comparison chart of the performance and yield of the photocatalytic synthesis of H2O2 by K-PPc-n, Li-PPc-n and Li-K-PPc-n of the present invention, wherein (a) is a performance comparison chart in a pure water environment, (b) is a performance comparison chart in an environment where ethanol is used as a sacrificial agent, (c) is a performance comparison chart in an environment where ethanol is used as a sacrificial agent and the solution pH is 3, and (d) is a comparison chart of the yield of photocatalytic synthesis of H2O2 by K-PPc-n, Li-PPc-n and Li-K-PPc-n after 100 minutes of illumination;

[0034] Figure 12 2 is a graph comparing the photocatalytic degradation performance of PPc-n and Li-K-PPc-n for H2O2 under illumination and oxygen-free (argon-filled) conditions of the present invention, wherein (a) is a graph showing the photocatalytic degradation of H2O2 by PPc-n and Li-K-PPc-n under illumination and oxygen-free conditions, (b) is a graph showing the photocatalytic cycle experiment of Li-K-PPc-n, and (c) is a graph showing the photocatalytic synthesis of H2O2 yields by Li-K-PPc-n under the action of different quenchers;

[0035] Figure 13 It is the EPR diagram of Li-K-PPc-n of the present invention under dark conditions and when illuminated for 5 minutes. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0037] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0038] Unless otherwise defined, the reagents, equipment and other materials used in the present invention are all commercially available.

[0039] Example 1

[0040] The preparation method of molten salt-assisted polyphthalocyanine photocatalyst (K-PPc-n) comprises the following steps:

[0041] S1. Weigh pyromellitic anhydride (0.87 g), 2,3-naphthalene dicarboxylic anhydride (0.2 g), ammonium chloride (0.5 g), urea (2.05 g), potassium chloride (0.182 g) and ammonium molybdate tetrahydrate (12.5 mg), mix well in a mortar and grind for 30 min, then transfer the mixture to a ceramic crucible.

[0042] S2. Place the ceramic crucible in a muffle furnace, heat to 220°C at a heating rate of 5°C / min, and maintain at this temperature for 7 hours to obtain a crude product.

[0043] S3. The obtained crude product was placed in a Soxhlet extractor and extracted with a mixed solvent of water, ethanol and tetrahydrofuran (volume ratio of 1:1:1, 60 mL each) at a temperature of 120° C. for 48 h.

[0044] S4. After the extraction is completed, the product is placed in a vacuum drying oven at 70°C and dried overnight. The dried sample is placed in a ball mill filled with zirconium dioxide balls, and the ball mill is placed in a planetary ball mill and ball milled at a speed of 500 rpm for 6 h.

[0045] S5. Weigh 0.2 g of the sample and disperse it in 15 mL of deionized water. Use an ultrasonic cell disrupter for 1 hour to achieve uniform dispersion of the sample. Subsequently, the ultrasonically treated solution is centrifuged and washed three times (using acetone solution for the washing operation). The washed sample is again placed in a vacuum drying oven at 70°C overnight to obtain the final product.

[0046] A method for preparing a molten salt-assisted polyphthalocyanine photocatalyst (Li-PPc-n) comprises the following steps:

[0047] Weigh pyromellitic anhydride (0.87 g), 2,3-naphthalene dicarboxylic anhydride (0.2 g), ammonium chloride (0.5 g), urea (2.05 g), lithium chloride (0.182 g), and ammonium molybdate tetrahydrate (12.5 mg). Mix thoroughly in a mortar and pestle, grind for 30 minutes, and then transfer the mixture to a 50 mL ceramic crucible. The remaining steps are identical to those for the preparation of K-PPc-n.

[0048] The preparation method of a molten salt-assisted polyphthalocyanine photocatalyst (Li-K-PPc-n) includes the following steps: weighing pyromellitic anhydride (0.87 g), 2,3-naphthalene dicarboxylic anhydride (0.2 g), ammonium chloride (0.5 g), urea (2.05 g), potassium chloride (0.091 g), lithium chloride (0.091 g), and ammonium molybdate tetrahydrate (12.5 mg), mixing the above materials in a mortar and grinding them for 30 minutes, and then transferring the mixture to a 50 mL ceramic crucible. The remaining steps are the same as those for the preparation of K-PPc-n.

[0049] The method for synthesizing hydrogen peroxide using a molten salt-assisted polyphthalocyanine photocatalyst comprises the following steps:

[0050] At room temperature, 10 mg of K-PPc-n, Li-PPc-n, and Li-K-PPc-n photocatalysts were uniformly dispersed with 20 ml of deionized water and 10 ml of sacrificial agent (ethanol) in a glass photocatalytic reactor. In the dark, O2 was introduced into the solution at a flow rate of 300 mL / min and stirred for 30 minutes to achieve O2 adsorption-desorption equilibrium. The solution was illuminated with a 300 W xenon lamp equipped with a 400 nm filter to generate hydrogen peroxide.

[0051] Test Example 1

[0052] The performance of the photocatalyst prepared in Example 1 was tested and characterized.

[0053] 1. Test method.

[0054] X-ray diffraction (XRD) was tested using a D8 Advance X-ray diffractometer. The specific experimental conditions were as follows: a Cu Kα diffraction target was used, and the X-ray wavelength was The scanning range is 2θ = 10° to 60°; the operating voltage is 40kV, the current is 40mA; the scanning speed is 10°min -1 .

[0055] Scanning electron microscopy (SEM) A JSM-5610LV scanning electron microscope was used to characterize the morphology of the samples in order to deeply explore their microstructural characteristics.

[0056] Fourier transform infrared spectroscopy (FT-IR) uses a Nicoleti S50 Fourier transform infrared spectrometer to accurately analyze the chemical and physical properties of samples. Its high resolution and sensitivity can also accurately provide detailed information on the molecular structure of materials, providing strong support for a deeper understanding of the chemical nature and physical behavior of samples.

[0057] Raman spectroscopy uses the ATR3000 Raman spectrometer to quantitatively analyze specific components in the sample and assist in identifying key information such as the chemical composition and functional groups in the sample, providing accurate spectral data support for research.

[0058] Thermogravimetric analysis (TGA) uses a Pyris Diamond TGA thermogravimetric analyzer to evaluate the thermal stability of the synthesized polymers in order to accurately characterize their thermal behavior and performance under different temperature conditions.

[0059] X-ray photoelectron spectroscopy (XPS) uses a Nexsa X-ray photoelectron spectrometer. With its excellent performance, it conducts in-depth analysis of the chemical composition, valence state and electronic structure of the material surface, and further explores the catalytic activity of the material, providing key information for understanding its surface chemical behavior.

[0060] The BET surface area and pore size of the samples were measured using a 3H-2000PS1 surface area and pore size analyzer. The test conditions included pre-treating the samples in a high vacuum environment at 120°C for 8 hours to remove surface impurities. Subsequently, N2 physical adsorption-desorption measurements were performed at 77K. This analysis provided strong support for a deeper understanding of the sample's microstructure.

[0061] Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) uses a U-3900 UV-Vis DRS spectrometer to accurately analyze the UV and visible light absorption characteristics of samples. This instrument not only determines the photocatalytic activity of samples but also uses the DRS data to calculate the band gap of semiconductor materials, providing a theoretical basis for optimizing the photocatalytic performance of the materials.

[0062] Ultraviolet-visible spectrophotometer (UV) was used to characterize the absorbance of the samples using a UH4150 UV-visible spectrophotometer with a test wavelength range of 300-500 nm.

[0063] The FLS980 steady-state transient fluorescence spectrometer was used to measure and analyze the excitation and emission spectra of the samples in detail.

[0064] Electron paramagnetic resonance spectrometer (EPR) was used to detect superoxide free radicals (·O2 - The free radical scavenger used in the experiment was 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), which reacts with superoxide radicals to form a stable adduct, thereby achieving efficient detection of superoxide radicals.

[0065] The electrochemical test was performed using a CHI660E electrochemical workstation with a three-electrode system. 2 mg of the catalyst was dispersed by ultrasound (30 min) in 1 mL of ethanol solution containing Nafion perfluorinated resin (5 wt%, 50 μL). Subsequently, 100 μL of the mixed solution was evenly drop-coated on a fluorine-doped tin oxide (FTO, 1 cm × 1 cm) glass electrode and dried at room temperature as a working electrode. In the experiment, a Hg / HgCl2 electrode was used as a reference electrode, and a platinum sheet electrode was used as a comparison electrode. The electrolyte was 0.1 mol·L -1 The light source was a 300W xenon lamp (equipped with a 400nm cut-off filter).

[0066] Determination of H2O2 concentration: The H2O2 concentration was detected by iodine titration. The specific operation is as follows: 1 mL of the reaction solution was mixed with 0.5 mL of 0.4 mol·L-1 KI solution and 0.5 mL of 0.1 mol·L -1 The solution was mixed with potassium hydrogen phthalate and allowed to stand for 30 minutes. Under acidic conditions, H₂O₂ molecules react with iodide ions to form triiodide ions, which exhibit significant absorption at 350 nm. The concentration of triiodide ions was measured by UV-visible spectroscopy, from which the amount of H₂O₂ generated during the photocatalytic process could be calculated.

[0067] In addition, a series of H2O2 standard solutions with known concentrations were tested using iodine titration, and a standard curve of H2O2 concentration and absorbance was drawn based on this. A good linear relationship was shown between H2O2 concentration and absorbance, as shown in the following figure:

[0068] Y=144.66319X-2.9272

[0069] Where X is the absorbance at 350 nm, Y is the H2O2 concentration (μmolL -1 Based on this standard curve, the concentration of H2O2 in the sample solution can be accurately calculated by measuring the absorbance of the sample solution.

[0070] The cyclic stability test of H2O2 was carried out under the same photocatalytic reaction conditions. First, 10 mg of catalyst was accurately weighed and added to a glass photocatalytic reactor containing 30 mL of deionized water, and the experiment was repeated according to the experimental method for photocatalytic generation of H2O2. After each round of photocatalytic reaction, the reaction solution was transferred to a clean centrifuge tube and centrifuged at 10,000 rpm for 5 minutes. Subsequently, the catalyst obtained by centrifugation was placed in a vacuum drying oven at 70°C and dried overnight. After drying, an appropriate amount of new catalyst was added to restore the total amount to 10 mg. The above operation was repeated 4 times to obtain a series of photocatalytic reaction solutions. Finally, the H2O2 concentration in these photocatalytic reaction solutions was detected by iodine titration.

[0071] H2O2 degradation experiment: 500μmol·L -1 The H2O2 solution was prepared and the H2O2 degradation performance of the catalyst under visible light irradiation was studied in depth. In the experiment, 10 mg of catalyst was added to 30 mL of 500 μmol·L -1 The reaction system was then illuminated using a 300W xenon lamp equipped with a 400nm filter. During the illumination process, 1mL of the reaction solution was sampled every 20min for a total of 4 times. Finally, the iodine titration method was used to accurately detect the H2O2 concentration in the photocatalytic reaction solution to evaluate the degradation efficiency of the catalyst.

[0072] Quenching experiment: Before the photocatalytic reaction, different types of quenchers (concentration of 0.1 mmol·L -1 ) to conduct systematic quenching experiments. Among them, p-benzoquinone (p-BQ) was used to quench superoxide radicals, while potassium bromate (KBrO3) was used to quench electrons (e-).

[0073] 2. Structure and characterization of materials.

[0074] The crystal structures of K-PPc-n, Li-PPc-n and Li-K-PPc-n were characterized in detail using XRD technology. Figure 1 As shown in (a). XRD analysis shows that all three materials exhibit good crystallinity. K-PPc-n, Li-PPc-n and Li-K-PPc-n did not destroy the original π-π stacking crystal structure of polyphthalocyanine, and the characteristic diffraction peaks corresponding to their macrocyclic framework structures still exist. In addition, the strong diffraction peak of K-PPc-n near 41° confirms the successful synthesis of polyphthalocyanine assisted by potassium molten salt. Similarly, the three smaller diffraction peaks of Li-PPc-n near 21°, 26° and 34° also demonstrate the effectiveness of the lithium molten salt assisted synthesis strategy. The XRD spectrum of Li-K-PPc-n clearly shows the characteristic diffraction peaks of potassium molten salt and lithium molten salt, proving the successful synthesis of the catalyst.

[0075] The structures of K-PPc-n and Li-K-PPc-n were characterized and analyzed by FT-IR technology, and compared with the infrared spectrum of PPc-n. Figure 1 As shown in (b). The infrared spectra of these materials show highly similar absorption peaks, indicating that neither potassium molten salt-assisted synthesis nor lithium potassium mixed molten salt-assisted synthesis destroys the original macrocyclic framework structure of polyphthalocyanine. Specifically, 1610 cm -1 、1510cm -1 and 1330cm -1 The absorption peaks at 1290 cm and 1290 cm are respectively attributed to the characteristic vibration of the polyphthalocyanine macrocyclic framework, and -1 and 1170cm -1 The absorption peak at is attributed to the stretching vibration of the C-N bond. In addition, no obvious characteristic absorption peaks of potassium molten salt or lithium molten salt appear in the spectrum, which indicates that the molten salt-assisted synthesis strategy does not have a significant impact on the polyphthalocyanine network itself as it does on other composite materials.

[0076] In addition, Raman characterization further verified the above conclusions ( Figure 1(c)). K-PPc-n, Li-PPc-n and Li-K-PPc-n at 685 cm -1 、1130cm -1 and 1335cm -1 Similar A 1g Characteristic peak at 747cm -1 A similar B is shown nearby 1g characteristic peaks, and at 1450 cm -1 A similar B is shown nearby 2g Characteristic peaks. These characteristic peaks all originate from the in-plane vibration of the phthalocyanine macrocyclic structure, indicating that K-PPc-n, Li-PPc-n, and Li-K-PPc-n, like PPc-n, retain the complete phthalocyanine macrocyclic framework structure.

[0077] Figure 2 SEM images of K-PPc-n, Li-PPc-n, and Li-K-PPc-n are shown. It can be clearly observed from the figure that all three materials exhibit a large-scale flake stacking structure similar to PPc-n, similar to the graphene-like morphology. Specifically, no obvious agglomerated particles were observed on the surface of K-PPc-n, a small number of agglomerated particles existed on Li-PPc-n, and a large number of agglomerated particles appeared on Li-K-PPc-n. This phenomenon indicates that the introduction of molten salt did not destroy the original structure of the polyphthalocyanine material. Further analysis shows that due to the high melting point of potassium molten salt, the amount of potassium salt ultimately coated on the surface of polyphthalocyanine is relatively small; while the melting point of lithium molten salt is relatively low, and mixing with potassium salt can significantly lower the overall melting point, resulting in more molten salt coated on the surface of polyphthalocyanine. This is the reason why more agglomerated particles appear on Li-PPc-n and Li-K-PPc-n. Furthermore, similar to PPc-n, K-PPc-n, Li-PPc-n, and Li-K-PPc-n all exhibited low thickness. This suggests that ball milling and ultrasonic treatment significantly reduced the thickness of these three materials during synthesis. This treatment effectively exposed the active sites of the catalysts, significantly enhancing the photocatalytic activity of K-PPc-n, Li-PPc-n, and Li-K-PPc-n.

[0078] The BET surface area and pore size distribution of K-PPc-n, Li-PPc-n and Li-K-PPc-n were determined by N2 adsorption-desorption isotherm analysis. Figure 3 As shown in Figure 2, the adsorption isotherms of these three materials all show typical IV type curves, indicating that they are all mesoporous materials. The BET specific surface areas of Li-PPc-n, K-PPc-n and Li-K-PPc-n are calculated to be 7.15 m 2 g -1 4.44m2 g -1 and 7.7m 2 g -1 . Further analysis of the pore size distribution diagram shows that their average pore sizes are 24.74nm, 30nm, and 23.2nm, respectively. Compared with PPc-n, the BET specific surface area of ​​Li-K-PPc-n is smaller, which may be due to the blockage of some of the original pores of PPc-n during the molten salt-assisted synthesis process. However, the average pore size of Li-K-PPc-n is larger, which may be due to the formation of new channels during the synthesis process by the introduction of molten salt, thereby expanding the pore size of the catalyst.

[0079] The material compositions of K-PPc-n and Li-K-PPc-n were characterized in detail by XPS analysis. Figure 4 As shown. It is clear that the molten salt-assisted synthesis did not destroy the original polyphthalocyanine network, nor did it affect its core structure. Furthermore, the carbon spectra of K-PPc-n and Li-K-PPc-n were separated ( Figure 4 (a) and (d)). The comparison results show that compared with K-PPc-n, the bond energies of C=C, C-NHx, NC=N and π-π* of Li-K-PPc-n have all undergone significant negative shifts, indicating that the polyphthalocyanine network has a strong electron affinity. Similarly, the nitrogen spectra of K-PPc-n and Li-K-PPc-n were separated by peak processing ( Figure 4 The results show that the bond energies of the C=N and N-C bonds of Li-K-PPc-n are lower than those of K-PPc-n, which further proves that the potassium-lithium molten salt-assisted synthesis of polyphthalocyanine networks can attract more electrons.

[0080] The potassium spectra of K-PPc-n and Li-K-PPc-n were separated by peak processing ( Figure 4 (b) and (e)). Comparison of K 2p of the two materials 3 / 2 bond energy, and found that it increased from 292.96eV to 292.96eV, and their K 2p 1 / 2 The bond energy of the two species was found to increase from 295.63 eV to 295.86 eV. This result indicates that the introduction of lithium salt can further promote the electron transfer of potassium molten salt to the polyphthalocyanine network, thereby improving the photocatalytic activity of the catalyst.

[0081] The thermal stability and decomposition characteristics of K-PPc-n, Li-PPc-n and Li-K-PPc-n were evaluated by TGA analysis. Figure 5As shown, all three materials exhibited good thermal stability when heated to 350°C under a nitrogen atmosphere. Specifically, the weight loss rate of K-PPc-n at 350°C was 5.95%, the weight loss rate of Li-PPc-n at 350°C was 4.67%, and the weight loss rate of Li-K-PPc-n at the same temperature was 10.15%. Although the weight loss rate of Li-K-PPc-n was slightly higher than that of K-PPc-n and Li-PPc-n, the material still exhibited high thermal stability at 350°C. This excellent thermal stability is crucial for the photocatalytic process because it ensures that Li-K-PPc-n does not undergo photothermal decomposition under xenon lamp irradiation, thereby avoiding the reduction of photocatalytic efficiency due to material decomposition.

[0082] The light-harvesting capabilities and band gap characteristics of K-PPc-n, Li-PPc-n, and Li-K-PPc-n were clarified through calculation and analysis of UV-vis DRS and Tauc plots. Figure 6 As shown in (a), these three materials all exhibit a wide range of light absorption. Further, based on the Kubelka-Munk equation (αhv=A(hv-E g ) 2 ) calculated Tauc plot ( Figure 6 Figures (b), (c), and (d) clearly reveal their band gap characteristics. The band gap energy (Eg) of K-PPc-n is 2.13 eV, that of Li-PPc-n is 2.14 eV, and that of Li-K-PPc-n is 2.17 eV. Compared with polyphthalocyanine (PPc-n), these materials have smaller band gap energies, making them more conducive to the transfer of photogenerated electrons. This characteristic greatly promotes the photocatalytic synthesis of H2O2 and significantly improves the photocatalytic yields of K-PPc-n, Li-PPc-n, and Li-K-PPc-n.

[0083] The photogenerated electron-hole pair separation efficiency of K-PPc-n, Li-PPc-n and Li-K-PPc-n was investigated by PL spectroscopy analysis and compared with the PL spectroscopy data of PPc-n. Figure 7As shown, the PL signal peak intensities of K-PPc-n, Li-PPc-n, and Li-K-PPc-n are significantly reduced compared to PPc-n. The intensity of the PL signal peak is closely related to the recombination rate of photogenerated carriers in the catalyst: a stronger signal peak indicates a greater ease of recombination of photogenerated carriers; a weaker signal peak indicates suppressed recombination and higher separation efficiency. Therefore, K-PPc-n, Li-PPc-n, and Li-K-PPc-n exhibit higher photogenerated electron-hole pair separation efficiency compared to PPc-n. Notably, K-PPc-n and Li-PPc-n exhibit the lowest PL signal peak intensities compared to Li-K-PPc-n, likely attributable to the π-π stacking interaction between the single molten salt-assisted synthesized polyphthalocyanine molecules. These results demonstrate that polyphthalocyanine materials synthesized with the assistance of molten salts can significantly suppress the recombination of photogenerated carriers, thereby effectively improving their efficiency in photocatalytic H2O2 synthesis.

[0084] like Figure 8 As shown in (a) and (b), the photogenerated carrier separation efficiency of K-PPc-n, Li-PPc-n, and Li-K-PPc-n was deeply explored by using EIS and TPC, and the activity of these three materials in the photocatalytic synthesis of H2O2 was further evaluated. The EIS test results show that Li-K-PPc-n exhibits a smaller arc radius than Li-PPc-n, indicating that Li-K-PPc-n has a lower charge transfer resistance. Therefore, the interfacial electron transfer rate of Li-K-PPc-n is significantly higher than that of Li-PPc-n. In addition, K-PPc-n has the lowest arc radius, which is also attributed to the orderly π-π stacking between catalyst molecules. However, K-PPc-n has low water solubility and tends to agglomerate, which hinders the photocatalytic production of H2O2. Therefore, Li-K-PPc-n is more suitable for the photocatalytic synthesis of H2O2 than K-PPc-n. The TPC test results also clearly show that the photocurrent intensity of Li-K-PPc-n is significantly higher than that of K-PPc-n and Li-PPc-n, which further confirms that Li-K-PPc-n has a lower recombination rate of photogenerated electron-hole pairs. Based on the above results, it can be clearly concluded that the polyphthalocyanine material Li-K-PPc-n synthesized with the assistance of molten salt can significantly inhibit the recombination of photogenerated carriers, thereby effectively improving its efficiency in photocatalytic synthesis of H2O2. This result reveals that the strategy of lithium potassium molten salt assisted synthesis of polyphthalocyanine can effectively improve the photocatalytic performance of polyphthalocyanine materials and exhibit excellent photocatalytic activity.

[0085] Figure 9(a), (b) and (c) are the Mott-Schottky spectra of K-PPc-n, Li-PPc-n and Li-K-PPc-n respectively. Based on these curves, the flat band potentials of K-PPc-n, Li-PPc-n and Li-K-PPc-n were determined to be -0.49V, -0.57V and -0.54V respectively. Since a saturated calomel electrode (SCE) was used, the electrode potential conversion formula (E NHE =E SCE +0.2V, NHE is a general hydrogen electrode) to estimate the CB positions of PPc-p and PPc-n, which are -0.29V, -0.37V and -0.34V respectively. g =E VB -E CB , we can calculate the VB positions of K-PPc-n, Li-PPc-n and Li-K-PPc-n, which are 1.84V, 1.77V and 1.83V respectively. Figure 10 As shown, the band structure of K-PPc-n cannot satisfy the conversion of O2 into ·O2 - The band structures of both Li-PPc-n and Li-K-PPc-n materials meet the thermodynamic conditions of ORR (E O2 / H2O2 =0.68V vs.NHE), so Li-PPc-n and Li-K-PPc-n can achieve photocatalytic synthesis of H2O2 through ORR process. In addition, the band structures of K-PPc-n and Li-K-PPc-n meet the thermodynamic conditions (E H2O / H2O2 =1.78 V vs. NHE), which makes it possible for K-PPc-n and Li-K-PPc-n to achieve photocatalytic synthesis of H2O2 via the WOR pathway. In particular, using ethanol as a sacrificial agent, the redox potential of ethanol oxidation (E C2H5OH / CH3CHO =-0.21 V vs. NHE).

[0086] Three sets of photocatalytic experiments were designed and implemented. Figure 11 As shown in (a) and (d), the photocatalytic H2O2 synthesis performance of K-PPc-n, Li-PPc-n, and Li-K-PPc-n was first investigated in pure water. The experimental results showed that the photocatalytic H2O2 yields of these three catalysts in pure water were relatively low. After 100 minutes of illumination, the yields were 51.5 μmol g -1 h -1 、37.17μmol g -1 h -1 and 27.29 μmol g -1 h-1 This result indicates that the strategy of molten salt-assisted synthesis of polyphthalocyanine is not effective in a reaction environment without sacrificial agents. In particular, Li-K-PPc-n has the lowest yield of photocatalytic synthesis of H2O2, which may be related to the particles formed by the agglomeration of molten salt, thereby affecting the exposure of active sites of the catalyst and the separation efficiency of photogenerated carriers.

[0087] Ethanol was introduced as a sacrificial agent, and experiments on photocatalytic synthesis of H2O2 were carried out on K-PPc-n, Li-PPc-n and Li-K-PPc-n. Figure 11 As shown in (b) and (d), compared with the pure water environment, the photocatalytic synthesis of H2O2 by these three materials under the condition of ethanol as a sacrificial agent is significantly improved. After 100 minutes of illumination, the yields are 157.73 μmol g -1 h -1 , 119.99 μmol g -1 h -1 and 152.26 μmol g -1 h -1 . Compared with the results in pure water environment, the yields increased by 2.06 times, 2.66 times and 4.58 times, respectively, among which the improvement of Li-K-PPc-n was particularly significant. Based on the above experimental results, under the condition of ethanol as a sacrificial agent, it was not only successfully verified that the strategy of lithium potassium molten salt assisted synthesis of polyphthalocyanine can significantly improve the photocatalytic performance of the catalyst, but also further proved the feasibility of enhancing its photocatalytic activity through the synthesis method of modified polyphthalocyanine.

[0088] The effects of pH 3 on the photocatalytic performance of K-PPc-n, Li-PPc-n and Li-K-PPc-n in the synthesis of H2O2 were further studied. Figure 11 As shown in (c) and (d), a solution with a pH value of 3 was prepared with ethanol as a sacrificial agent, and experiments on the photocatalytic synthesis of H2O2 were carried out. The experimental results showed that when the pH value was 3, the photocatalytic activity of K-PPc-n and Li-PPc-n was significantly inhibited. After 100 minutes of illumination, their H2O2 yields were only 49.93 μmol g -1 h -1 and 67.12 μmol g -1 h -1. In particular, the yield of K-PPc-n was even lower than that in a pure water environment, indicating that the catalyst exhibited poor photocatalytic performance under acidic conditions. This may be because a single molten salt cannot effectively promote electron transfer in an acidic environment, thereby limiting the progress of the photocatalytic reaction. In contrast, Li-K-PPc-n showed significantly enhanced photocatalytic activity at a pH of 3. After 100 min of illumination, its H2O2 yield reached 194.18 μmol g -1 h -1 , which is 27.53% higher than when only ethanol is used as a sacrificial agent. This result shows that the photocatalytic performance of Li-K-PPc-n is significantly improved under acidic conditions. This enhancement may be attributed to the synergistic effect between potassium molten salt and lithium molten salt. This synergistic effect can further promote the separation and migration of photogenerated carriers, thereby improving the photocatalytic synthesis of H2O2 efficiency of Li-K-PPc-n. This discovery reveals the unique advantages of the bimetallic molten salt system under specific conditions and provides new ideas and directions for the design of efficient photocatalytic polyphthalocyanine catalysts.

[0089] The photocatalytic degradation performance of Li-K-PPc-n on H2O2 under light and oxygen-free (argon) conditions was investigated and compared with that of PPc-n. Figure 12 As shown in (a). As can be seen from the figure, after 80 minutes of illumination, the degradation rates of H2O2 by Li-K-PPc-n and PPc-n are low, both less than 20%. This result shows that in the process of photocatalytic synthesis of H2O2, the degradation effect of Li-K-PPc-n on H2O2 is basically the same as that of PPc-n, so the synthesis of polyphthalocyanine assisted by molten salt will not significantly affect the photocatalytic yield of H2O2. Further, the cyclic stability of Li-K-PPc-n was investigated, and the results are shown in Figure 2. Figure 12 As shown in (b). A total of four sets of cycle experiments were carried out, and each set of experiments lasted for 100 minutes of illumination. The results showed that the H2O2 yield did not decrease much after four sets of cycle experiments. The H2O2 yield of the fourth set of experiments only decreased by 8.51% compared with the first set of experiments. This result fully demonstrates that Li-K-PPc-n has high photocatalytic stability and can maintain efficient H2O2 yield in multiple cycles. Subsequently, a series of quenching experiments were carried out on the Li-K-PPc-n catalyst to further explore the ORR pathway involved in its photocatalytic synthesis of H2O2. The results are shown in Figure 2. Figure 12As shown in (c). In the experiment, when KBrO3 (electron quencher) and p-BQ (superoxide radical quencher) were added to the reaction system, the photocatalytic synthesis of H2O2 yields of Li-K-PPc-n decreased by 29.57% and 19.65%, respectively. This phenomenon shows that photoexcited electrons and play a vital role in the photocatalytic synthesis of H2O2. In addition, when ethanol was not added as a sacrificial agent, the photocatalytic synthesis of H2O2 yield of Li-K-PPc-n decreased significantly by 82.08%, which further highlights the importance of ethanol as a sacrificial agent in the photocatalytic synthesis of H2O2. Based on the above results, it can be clearly seen that Li-K-PPc-n mainly realizes the photocatalytic synthesis of H2O2 through the ORR pathway.

[0090] The EPR spectroscopy of Li-K-PPc-n was performed using the spin trap DMPO to investigate the reactive oxygen species generated under light conditions. Figure 13 As shown in Figure 2, no obvious EPR signal peak was detected in the dark condition for Li-K-PPc-n, but after 5 minutes of illumination, its EPR spectrum showed DMPO-·O2 - The typical characteristic peaks of Li-K-PPc-n are in the order of 2:2:1:2:1:2. This result indicates that Li-K-PPc-n successfully captured key intermediates during the photocatalytic process. This discovery not only fully confirms that Li-K-PPc-n photocatalytically generates H2O2 through the ORR pathway, but also further proves that the strategy of using molten salt to assist the synthesis of polyphthalocyanine can significantly improve its efficiency in photocatalytic synthesis of H2O2. In addition, the intermediates detected in the EPR spectrum can effectively promote the formation of peroxyl radicals (·OOH), which is a key step in the photocatalytic synthesis of H2O2.

[0091] The present invention adopts the strategy of potassium-lithium blended molten salt-assisted synthesis of edge-functionalized polyphthalocyanine to successfully prepare the catalyst Li-K-PPc-n and a series of comparative materials. Subsequently, the photocatalytic performance of the material was further optimized by treatment methods such as ball milling and cell crushing. In order to comprehensively characterize and analyze the synthesized materials, a variety of test methods were adopted, including XRD, FT-IR, SEM, Raman, BET, TGA, XPS, EPR and some photoelectrochemical tests. In terms of performance, not only the performance of the synthesized Li-K-PPc-n in the photocatalytic synthesis of H2O2 was systematically studied, but also the influence of different reaction conditions (pure water environment, ethanol as a sacrificial agent, and ethanol as a sacrificial agent and the pH value of the solution is 3) on the photocatalytic synthesis of H2O2 activity of the catalyst Li-K-PPc-n was deeply explored, and the mechanism of the material's photocatalytic synthesis of H2O2 was further analyzed. The main conclusions obtained are as follows:

[0092] (1) Li-K-PPc-n and a series of comparative materials were successfully synthesized using a modified synthesis strategy of molten salt-assisted synthesis of edge-functionalized polyphthalocyanine. A series of characterization methods not only confirmed the success of these synthetic strategies but also ensured that the synthesized Li-K-PPc-n met the requirements for photocatalytic H2O2 synthesis. These results indicate that the synthesized materials achieved the desired goals in terms of structure and function, laying a solid foundation for subsequent photocatalytic performance testing.

[0093] (2) The performance of Li-K-PPc-n photocatalytic synthesis of H2O2 was tested. In pure water environment, the yield of Li-K-PPc-n photocatalytic synthesis of H2O2 was only 27.29 μmol g -1 h -1 When ethanol was used as a sacrificial agent, the photocatalytic H2O2 yield of Li-K-PPc-n reached 152.26 μmol g -1 h -1 The photocatalytic performance of Li-K-PPc-n in the synthesis of H2O2 in an acidic environment was also tested. At pH = 3, the photocatalytic H2O2 yield of Li-K-PPc-n reached 194.18 μmol g -1 h -1 , the photocatalytic performance was further improved by 27.53%. These results not only demonstrate that ethanol as a sacrificial agent and the pH value of the photocatalytic reaction solution have a significant impact on the performance of the Li-K-PPc-n catalyst for the photocatalytic synthesis of H2O2, but also prove that the modification strategy of molten salt-assisted synthesis of edge-functionalized polyphthalocyanine can successfully improve its photocatalytic synthesis of H2O2 yield.

[0094] (3) Li-K-PPc-n has a low degradation rate for H2O2 and good cyclic stability. Through the analysis of the results of the quenching experiment, EPR analysis, and band structure analysis, it is clear that the catalyst Li-K-PPc-n has an ORR pathway in the process of photocatalytic generation of H2O2.

[0095] Therefore, the present invention adopts the above-mentioned molten salt-assisted polyphthalocyanine photocatalyst preparation and its method for synthesizing hydrogen peroxide, and adopts the strategy of potassium-lithium blended molten salt-assisted synthesis of edge-functionalized polyphthalocyanine to successfully prepare the catalyst Li-K-PPc-n. Through treatment methods such as ball milling and cell disruption, the photocatalytic performance of the material is further optimized and the yield of its photocatalytic synthesis of H2O2 is improved.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a molten salt-assisted polyphthalocyanine photocatalyst, characterized in that: The steps include: S1. Weigh pyromellitic anhydride, 2,3-naphthalene dicarboxylic anhydride, ammonium chloride, alkali metal chloride, urea, and ammonium molybdate tetrahydrate, mix them evenly in a mortar and grind them for 30 minutes, then transfer the mixture into a ceramic crucible; S2. Place the ceramic crucible in a muffle furnace, heat to 220°C at a heating rate of 5°C / min, and maintain at this temperature for 7 hours to obtain a crude product; S3. The crude product was placed in a Soxhlet extractor and extracted with a mixed solvent at a temperature of 120° C. for 48 hours. S4. After the extraction is completed, the product is placed in a vacuum drying oven to dry overnight, and the dried sample is placed in a ball mill filled with zirconium dioxide balls and ball milled at a speed of 500 rpm for 6 h; S5. Weigh the sample and disperse it in deionized water. Use an ultrasonic cell disruptor to treat it for 1 hour to achieve uniform dispersion of the sample. Centrifuge and wash the ultrasonically treated solution three times. Place the washed sample in a vacuum drying oven again and dry it overnight to obtain the final product.

2. The method for preparing a molten salt-assisted polyphthalocyanine photocatalyst according to claim 1, wherein: In step S1, the alkali metal chloride includes potassium chloride and lithium chloride.

3. The method for preparing a molten salt-assisted polyphthalocyanine photocatalyst according to claim 1, wherein: In step S3, the mixed solvent is a mixed solvent of water, ethanol and tetrahydrofuran, and the volume ratio of water, ethanol and tetrahydrofuran is 1:1:

1.

4. The method for preparing a molten salt-assisted polyphthalocyanine photocatalyst according to claim 1, wherein: In step S5, an acetone solution is used for centrifugal washing.

5. Molten salt-assisted polyphthalocyanine photocatalyst, characterized by: It is prepared by the preparation method according to any one of claims 1 to 4.

6. A method for synthesizing hydrogen peroxide using a molten salt-assisted polyphthalocyanine photocatalyst, characterized in that: The method is achieved by the photocatalyst according to claim 5, comprising the following steps: At room temperature, the photocatalyst, deionized water and sacrificial agent were evenly dispersed in a glass photocatalytic reactor. In the dark, O2 was introduced into the solution at a flow rate of 300 mL / min and stirred for 30 minutes to achieve O2 adsorption-desorption equilibrium. The solution was illuminated by a 300W xenon lamp equipped with a 400nm filter to generate hydrogen peroxide.

7. The method for synthesizing hydrogen peroxide using a molten salt-assisted polyphthalocyanine photocatalyst according to claim 6, wherein: The sacrificial agent is ethanol.

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