Zif-8 porphyrin self-assembly s-type heterojunction photocatalyst and preparation method and application thereof

Abstract

The application discloses a preparation method of a ZIF-8 porphyrin self-assembly S-type heterojunction photocatalyst, and comprises the following steps: 1) dissolving PdTCPP powder in an N,N-dimethylformamide solution, and ultrasonically forming a precursor solution; 2) rapidly injecting the precursor solution into an aqueous solution containing a surfactant, stirring and reacting, and obtaining SPT nanopowder through centrifugation, washing and drying; and 3) adding the SPT nanopowder into a precursor solution of ZIF-8, stirring and reacting at room temperature, and obtaining the ZIF-8 porphyrin self-assembly S-type heterojunction photocatalyst through washing, centrifugation and drying. The ZIF-8 porphyrin self-assembly S-type heterojunction photocatalyst prepared by the method has a D-A structure S-type heterojunction composite material, can efficiently separate charges and maximize the redox capacity of carriers, and simultaneously realizes excellent photocatalytic hydrogen production and hydrogen peroxide production under visible light irradiation, with a hydrogen production rate of 4956.82 µmol·g ‑1 ·h ‑1 and a hydrogen peroxide production rate of 1120 µmol·g ‑1 ·h ‑1 .

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst and its preparation method, as well as its application in photocatalytic decomposition for hydrogen production and synthesis of hydrogen peroxide. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Currently, developing efficient and clean solar energy conversion technologies is an important way to solve energy shortages and environmental problems. Photocatalysis technology has attracted widespread attention because it can directly utilize solar energy to drive chemical reactions, with photocatalytic water splitting for hydrogen production and photocatalytic synthesis of hydrogen peroxide being two important directions. In existing technologies, commonly used photocatalysts are mostly single materials, such as metal-organic frameworks (MOFs) or organic supramolecular self-assemblies.

[0004] ZIF-8 possesses an ultra-high specific surface area, tunable pore structure, and good chemical stability; however, its wide band gap limits its absorption of visible light, resulting in low solar energy utilization and photocatalytic activity. Porphyrin-based supramolecular self-assemblies, on the other hand, exhibit a large π-conjugated structure, strong visible light absorption, and good semiconductor properties. However, single supramolecular self-assemblies suffer from high recombination rates of photogenerated electron-hole pairs, severely restricting their quantum efficiency and practical application performance. While existing heterojunctions can separate charges to some extent, they often weaken the redox capabilities of photogenerated electrons and holes, hindering reactions requiring strong reducing electrons and strong oxidizing holes. Currently, there is a lack of composite materials and their construction methods that can simultaneously achieve efficient charge separation, retain strong redox capabilities, and be used for bifunctional photocatalysis. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the main objective of this invention is to provide a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst capable of simultaneously achieving efficient charge separation and retaining strong redox capabilities, as well as a method for its preparation.

[0006] This invention also provides the application of the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst in photocatalytic decomposition for hydrogen production and synthesis of hydrogen peroxide.

[0007] The objective of this invention is achieved through the following technical solution: A method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst includes the following steps: 1) Dissolve PdTCPP powder in N,N-dimethylformamide solution and sonicate to form a precursor solution; 2) The precursor solution obtained in step 1) is rapidly injected into an aqueous solution containing a surfactant, the reaction is stirred, and the product is centrifuged, washed, and dried to obtain SPT nanopowder. 3) The SPT nanopowder obtained in step 2) was added to the precursor solution of ZIF-8 and stirred at room temperature. The product was washed, centrifuged and dried to obtain ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst.

[0008] In some specific embodiments, the mass concentration of PdTCPP powder in the precursor solution in step 1) is 5-15 mg / mL.

[0009] In some specific embodiments, the surfactant described in step 2) includes, but is not limited to, hexadecyltrimethylammonium bromide.

[0010] In some specific embodiments, the mass concentration of the surfactant in the aqueous solution in step 2) is 1-3 mg / mL.

[0011] In some specific embodiments, the volume ratio of the precursor solution to the aqueous solution in step 2) is 1:(5-15). In some specific embodiments, the process parameters for the stirring reaction in step 2) are: stirring at 70-90°C for 20-30 hours.

[0012] In some specific embodiments, the precursor solution of ZIF-8 in step 3) is composed of Zn(NO3)2·6H2O and 2-methylimidazole dissolved in anhydrous methanol solution.

[0013] The molar ratio of Zn(NO3)2·6H2O to 2-methylimidazole is 1:(3-10). In some specific embodiments, the solid-liquid ratio of the SPT nanopowder to the ZIF-8 precursor solution in step 3) is (0.2-0.6):1.

[0014] In some specific embodiments, the process parameters for the stirring reaction in step 3) are: stirring reaction at room temperature for 4-8 hours.

[0015] As part of the same inventive concept, the present invention also provides a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst prepared by the aforementioned preparation method, wherein the photocatalyst is an S-type heterojunction composite material with a DA structure.

[0016] As part of the same inventive concept, this invention also provides an application of the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst in photocatalytic decomposition for hydrogen production and synthesis of hydrogen peroxide.

[0017] Compared with the prior art, the present invention has at least the following advantages: 1) The ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst provided by this invention is an S-type heterojunction composite material with a DA structure, which can efficiently separate charges and maximize the redox ability of retaining charge carriers. Experimental testing showed that it simultaneously achieved excellent photocatalytic hydrogen production and hydrogen peroxide production performance under visible light irradiation, with a hydrogen production rate as high as 4956.82 µmol·g⁻¹. -1 ·h -1 The hydrogen peroxide production rate is as high as 1120 µmol·g -1 ·h -1 It is far superior to pure ZIF-8 and pure SPT.

[0018] 2) The ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst provided by this invention simultaneously induces oxygen reduction reaction (ORR, O2 → ·O2) during the photocatalytic production of hydrogen peroxide. - The process proceeds through two pathways: (H2O → H2O2) and water oxidation (WOR, H2O → ·OH → H2O2), achieving full utilization of electrons and holes. Furthermore, after multiple cycles of photocatalytic hydrogen peroxide production tests, its activity did not show a significant decrease, demonstrating good photochemical stability.

[0019] 3) The preparation method of this invention, through the electrostatic self-assembly of a donor-acceptor DA structure, forms an interfacial built-in electric field (IEF) pointing from SPT to ZIF-8 at the ZIF-8 and SPT interface. This IEF drives photogenerated carrier transfer following an S-type mechanism, i.e., weakly reducing electrons in the ZIF-8 conduction band recombine with weakly oxidizing holes in the SPT valence band, thereby retaining strongly reducing electrons in the SPT conduction band and strongly oxidizing holes in the ZIF-8 valence band. Both photoelectric response and impedance measurements confirm that the charge separation efficiency and carrier lifetime of the composite material of this invention are far superior to those of a single component. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0021] Figure 1 SEM images of SPT nanopowder, ZIF-8 / SPT-8 photocatalyst in Example 1 of the present invention, and ZIF-8 photocatalyst in Comparative Example 1; Figure 2The XRD spectrum (2A) and FT-IR infrared spectrum (2B) of the PdTCPP and / or SPT nanopowder in Example 1 of the present invention, the photocatalyst ZIF-8 / SPT-X in Examples 1-5 (where X represents the amount of SPT nanopowder added), and the ZIF-8 photocatalyst in Comparative Example 1 are shown. Figure 3 XPS spectra of SPT nanopowder, ZIF-8 / SPT-8 photocatalyst in Example 1 of the present invention, and ZIF-8 photocatalyst in Comparative Example 1. Figure 4 These are TEM images of the SPT nanopowder, the ZIF-8 / SPT-8 photocatalyst in Example 1 of this invention, and the ZIF-8 photocatalyst in Comparative Example 1; where A represents ZIF-8, B represents SPT, C represents ZIF-8 / SPT-8; D represents the overall elemental EDS image of ZIF-8 / SPT-8, E represents the elemental EDS image of C, F represents N, G represents O, H represents Zn, and I represents Pd. Figure 5 The photocatalytic hydrogen production performance and photocatalytic hydrogen peroxide production performance of SPT nanopowder, photocatalyst ZIF-8 / SPT-8, and ZIF-8 photocatalyst in Comparative Example 1 of this invention are shown below; where A is the hydrogen evolution amount of SPT, ZIF-8, and ZIF-8 / SPT-X; B is the corresponding H2 generation rate; C is the AQY and STH values ​​of ZIF-8 / SPT-8 at specific wavelengths (365, 420, and 500 nm); D is the H2O2 generation amount of ZIF-8, SPT, and ZIF-8 / SPT-8; and E is the cycle stability of ZIF-8 / SPT-8 for H2O2 generation. Figure 6 This describes the free radical trapping experiment and electron spin resonance (ESR) of the photocatalyst ZIF-8 / SPT-8 in Example 1 of this invention; Figure 7 Density functional theory (DFT) calculations are shown for SPT nanopowder, photocatalyst ZIF-8 / SPT-8 in Example 1 of the present invention, and ZIF-8 photocatalyst in Comparative Example 1. Figure 8 Kelvin probe force microscopy (KPFM) and in-situ XPS were used to examine the photocatalyst ZIF-8 / SPT-8 in Example 1 of this invention. Figure 8Test results; KPFM surface potential diagrams of SPT (A) and ZIF-8 / SPT-8 (B), c is the corresponding potential curve (corresponding to the black dashed line in the potential diagram), in-situ XPS spectra of ZIF-8 / SPT-8: (D) survey, (E) C 1s spectrum, (F) N 1s spectrum, (G) O 1s spectrum, (H) Pd 3d spectrum, (I) Zn 2p spectrum; Figure 9 The UV-vis test results of SPT nanopowder, photocatalyst ZIF-8 / SPT-8 in Example 1 of the present invention and ZIF-8 photocatalyst in Comparative Example 1 are shown. Figure 10 The images show the visible light response and impedance spectra of SPT nanopowder, ZIF-8 / SPT-8 photocatalyst in Example 1 of this invention, and ZIF-8 photocatalyst in Comparative Example 1. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0023] When a quantity, concentration, or other value or parameter is described as a range, preferred range, or preferred upper and lower limits, it should be understood that it is equivalent to specifically disclosing any range by combining any pair of upper or preferred values ​​with any lower or preferred values, regardless of whether the range is specifically disclosed. Unless otherwise stated, the numerical range values ​​listed herein include the endpoints of the range and all integers and fractions within that range.

[0024] Unless otherwise stated, all percentages, parts, ratios, etc. in this document are by weight.

[0025] The materials, methods, and embodiments described herein are exemplary and should not be construed as limiting unless otherwise stated.

[0026] This invention provides a method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, specifically including the following steps: 1) Dissolve PdTCPP powder in N,N-dimethylformamide solution and sonicate to form a precursor solution with a mass concentration of 5-15 mg / mL; 2) The precursor solution obtained in step 1) is rapidly injected into an aqueous solution containing surfactant (1-3 mg / mL) (the volume ratio of precursor solution to aqueous solution is 1: (5-15), the reaction is stirred, and the product is centrifuged, washed and dried to obtain SPT nanopowder. 3) The SPT nanopowder obtained in step 2) is added to the ZIF-8 precursor solution (the solid-liquid ratio of SPT nanopowder to ZIF-8 precursor solution is 0.2-0.6:1), and the mixture is stirred at room temperature. The product is washed, centrifuged, and dried to obtain the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst.

[0027] Example 1

[0028] This embodiment provides a method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, which includes the following steps: 1) Dissolve PdTCPP powder in DMF and sonicate for 10 min to prepare a 10 mg / mL PdTCPP / DMF precursor solution; 2) Under continuous stirring, 1 mL of PdTCPP / DMF precursor solution was rapidly injected into 9 mL of an aqueous solution containing 1.36 mg / mL CTAB. The mixture was stirred continuously at 80 °C for 24 hours. After the reaction was completed, the cooled solution was centrifuged at 6000 rpm to collect the self-assembled porphyrin nanocrystals, which were then washed with ultrapure water to remove free surfactants and unassembled porphyrin molecules. Finally, the product was dried overnight in a vacuum drying oven at 70 °C to obtain SPT nanopowder (denoted as SPT). 3) Dissolve 59.5 mg Zn(NO3)2·6H2O in 10 mL of anhydrous methanol and label it as solution A; dissolve 181.15 mg 2-methylimidazole in 10 mL of anhydrous methanol and sonicate for 30 min and label it as solution B; add 8 mg of SPT nanoparticles from step 1) to solution A and sonicate for 30 min. 4) Slowly add the solution A (10 ml) containing SPT nanopowder (8 mg) prepared in step 3) to the solution B (10 ml) in step 3) and stir at room temperature for 6 hours; wash the product with anhydrous methanol, centrifuge three times, and dry it in a vacuum drying oven at 65°C to obtain the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst (denoted as ZIF-8 / SPT-8).

[0029] Example 2

[0030] This embodiment provides a method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, which is basically the same as that in Example 1, except that the ratio of SPT nanoparticles in step 3) is different, specifically: 3) Dissolve 59.5 mg Zn(NO3)2·6H2O in 10 mL of anhydrous methanol and label it as solution A; dissolve 181.15 mg 2-methylimidazole in 10 mL of anhydrous methanol and sonicate for 30 min and label it as solution B; add 4 mg of SPT nanoparticles from step 1) to solution A and sonicate for 30 min. The remaining steps 1), 2), and 4) are the same as in Example 1, and the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst (denoted as ZIF-8 / SPT-4) is prepared.

[0031] Example 3

[0032] This embodiment provides a method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, which is basically the same as that in Example 1, except that the ratio of SPT nanoparticles in step 3) is different, specifically: 3) Dissolve 59.5 mg Zn(NO3)2·6H2O in 10 mL of anhydrous methanol and label it as solution A; dissolve 181.15 mg 2-methylimidazole in 10 mL of anhydrous methanol and sonicate for 30 min and label it as solution B; add 6 mg of SPT nanoparticles from step 1) to solution A and sonicate for 30 min. The remaining steps 1), 2), and 4) are the same as in Example 1, and the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst (denoted as ZIF-8 / SPT-6) is prepared.

[0033] Example 4

[0034] This embodiment provides a method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, which is basically the same as that in Example 1, except that the ratio of SPT nanoparticles in step 3) is different, specifically: 3) Dissolve 59.5 mg Zn(NO3)2·6H2O in 10 mL of anhydrous methanol and label it as solution A; dissolve 181.15 mg 2-methylimidazole in 10 mL of anhydrous methanol and sonicate for 30 min and label it as solution B; add 10 mg of SPT nanoparticles from step 1) to solution A and sonicate for 30 min. The remaining steps 1), 2), and 4) are the same as in Example 1, and the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst (denoted as ZIF-8 / SPT-10) is prepared.

[0035] Example 5

[0036] This embodiment provides a method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, which is basically the same as that in Example 1, except that the ratio of SPT nanoparticles in step 3) is different, specifically: 3) Dissolve 59.5 mg Zn(NO3)2·6H2O in 10 mL of anhydrous methanol and label it as solution A; dissolve 181.15 mg 2-methylimidazole in 10 mL of anhydrous methanol and sonicate for 30 min and label it as solution B; add 12 mg of SPT nanoparticles from step 1) to solution A and sonicate for 30 min. The remaining steps 1), 2), and 4) are the same as in Example 1, and the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst (denoted as ZIF-8 / SPT-12) is prepared.

[0037] Comparative Example 1 This comparative example provides a method for preparing ZIF-8 photocatalyst, which includes the following steps: 59.5 mg of Zn(NO3)2·6H2O was dissolved in 10 mL of anhydrous methanol to form solution A; 181.15 mg of 2-methylimidazole was dissolved in 10 mL of anhydrous methanol to form solution B; solution A was slowly added dropwise to solution B at room temperature, and the mixture was stirred at room temperature for 6 hours. Finally, the product was washed with anhydrous methanol and centrifuged three times. The resulting white sample was dried to obtain the ZIF-8 photocatalyst (denoted as ZIF-8).

[0038] Performance characterization: The present invention conducts performance tests on the photocatalysts prepared in Examples 1-5 and Comparative Example 1, specifically as follows: 1) Appearance and morphology test This application performs morphology testing on the SPT nanopowder prepared in Example 1, and its SEM image is shown below. Figure 1 As shown in the figure, the SPT nanopowder prepared in this application has a morphology of smooth, uniform nanorods. Figure 1 A).

[0039] The appearance morphology of the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst prepared in Example 1 was tested, and its SEM image is shown below. Figure 1 As shown in the figure, the photocatalyst ZIF-8 / SPT-8 prepared in this application has ZIF-8 nanoparticles that grow densely and uniformly on the surface of SPT nanorods. Figure 1 C).

[0040] This application presents an morphological test on the ZIF-8 photocatalyst prepared in Comparative Example 1, and its SEM image is shown below. Figure 1As shown in the figure, the ZIF-8 photocatalyst prepared in Comparative Example 1 has a morphology of nanoparticles (…). Figure 1 B).

[0041] Furthermore, taking Example 1 as an example, the SPT nanopowder, the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, and the ZIF-8 photocatalyst in Comparative Example 1 were subjected to TEM lens testing, and their TEM morphologies are as follows: Figure 4 As shown in (AI), the figure clearly shows that ZIF-8 is attached to the surface of SPT, and the C, N, O, Zn and Pd elements are evenly distributed. The coexistence of Zn (from ZIF-8) and Pd (from SPT) further verifies the formation of the composite structure.

[0042] 2) Organizational Structure The present invention performed XRD spectroscopy tests on PdTCPP and SPT in Example 1, as well as the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalysts prepared in Examples 1-5 and the ZIF photocatalyst in Comparative Example 1. The XRD spectra are shown below. Figure 2 As shown in Figure A, the photocatalyst prepared in this application contains characteristic diffraction peaks of both ZIF-8 and SPT, proving that the two have been successfully combined. The present invention also performed FT-IR infrared spectroscopy tests on the SPT nanopowder in Example 1, the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalysts prepared in Examples 1-5, and the ZIF photocatalyst in Comparative Example 1. The FT-IR infrared spectra are shown below. Figure 2 As shown in Figure B, pure ZIF-8 and pure SPT exhibit their respective characteristic functional group absorption peaks, with clear peak shapes and significant characteristics. In contrast, the infrared spectrum of the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst prepared in this application simultaneously detects the characteristic peaks of the imidazole ring stretching vibration of ZIF-8 and the characteristic absorption peaks of the porphyrin ring and functional groups of SPT, with no obvious impurity peaks appearing, and none of the main characteristic peaks disappearing or shifting significantly. This fully demonstrates that ZIF-8 and SPT were successfully composited without damaging the basic molecular structure of each component during the composite process, and the heterojunction composite material was successfully prepared, further confirming the successful construction of the material.

[0043] The present invention also performed XPS tests on the SPT nanopowder in Example 1, the photocatalyst ZIF-8 / SPT-8, and the ZIF-8 photocatalyst in Comparative Example 1, and their XPS spectra are shown below. Figure 3As shown in the figure, compared with pure SPT nanopowder (3A), the Pd 3d peak in ZIF-8 / SPT-8 shifts towards higher binding energy; compared with pure ZIF-8 (3B), the Zn 2p peak shifts towards lower binding energy. This indicates that electrons have been transferred from SPT to ZIF-8, providing evidence for the formation of an interface built-in electric field. 3) Photocatalytic hydrogen production performance test Test Method: Photocatalytic hydrogen production experiments were conducted in a 100 mL optical reaction vessel at room temperature. Specifically, 5 mg of the test sample was dispersed in 50 mL of deionized water containing ascorbic acid (AA, 0.2 M), with ascorbic acid used as a sacrificial agent. Subsequently, the solution was bubbled with nitrogen for 15 min to remove air. The experimental temperature was maintained at 6 ± 0.5 °C using a constant-temperature cooling circulating water system; the experiment was conducted with a 420 nm cutoff filter and an optical density of 520 mW·cm⁻¹. -2 Under irradiation with a 300W Xe lamp, the solution was continuously stirred for 4 hours to carry out photocatalytic water removal and hydrogen desorption reaction; the generation of H2 was detected online every 30 minutes using a gas chromatograph equipped with nitrogen as a carrier. Test results ( Figure 5 (A, 5B), the hydrogen production rate of the ZIF-8 photocatalyst in Comparative Example 1 was 71.65 µmol·g. -1 ·h -1 The hydrogen production rate of the SPT nanopowder in Example 1 was 1703.00 µmol·g. -1 ·h -1 The prepared photocatalyst ZIF-8 / SPT-8 exhibited a hydrogen production rate as high as 4956.82 µmol·g⁻¹. -1 ·h -1 The concentrations are approximately 69 times and 2.9 times that of pure ZIF-8 and SPT nanopowder, respectively.

[0044] The apparent quantum yield (AQY) of ZIF-8 / SPT-8 under different monochromatic lights is highest at 365 nm, reaching 5.484%. Figure 5 C).

[0045] 4) Photocatalytic hydrogen peroxide production performance test Test method: 5 mg of photocatalyst powder was dispersed in a quartz reactor containing 50 mL of aqueous solution. The mixture was then sonicated for 5 min, followed by magnetic stirring in the dark for 30 min to dissolve sufficient air and achieve adsorption-desorption equilibrium. The reactor was fixed 2 cm below a 300 W xenon lamp equipped with a 420 nm cutoff filter. The temperature of the reaction solution was maintained at 25 ± 2 °C using a cold water circulation system. All mixed solutions were continuously stirred to ensure thorough mixing. During the illumination process, 2 mL of the reaction solution was taken every 15 min and filtered through a 0.22 μm disposable filter to remove catalyst particles. Simultaneously, 1 mL of potassium hydrogen phthalate (0.1 M) and 1 mL of potassium iodide (0.4 M) were mixed with the taken reaction solution and allowed to stand for 30 min for color development. The experiment lasted for 60 min. Finally, the absorbance at 350 nm was set using a visible spectrophotometer as the wavelength for determining the H2O2 concentration.

[0046] result( Figure 5 D): The H2O2 yield of the ZIF-8 photocatalyst in Comparative Example 1 was only 45 µmol·g. -1 ·h -1 The H2O2 yield of the SPT nanopowder in Example 1 was 217 µmol·g. -1 ·h -1 The H2O2 yield of the photocatalyst ZIF-8 / SPT-8 prepared in the examples reached 1120 µmol·g. -1 ·h -1 These figures are 24.9 times and 5.2 times that of ZIF-8 photocatalyst and SPT nanopowder, respectively.

[0047] Cyclic stability tests were performed on the samples. The test method involved reacting the sample that had completed the photocatalytic hydrogen peroxide production test for 4 hours, then adding the sacrificial agent again and continuing the photocatalytic reaction. This process was repeated 4 times. The cyclic stability test results showed that ( Figure 5 E), ZIF-8 / SPT-8 maintained a high yield (1079 µmol·g) even after 4 cycles. -1 ·h -1 ).

[0048] 5) Reaction mechanism To explore the reaction pathway for the photocatalytic synthesis of hydrogen peroxide, this application conducted free radical capture experiments and electron spin resonance tests on the photocatalyst ZIF-8 / SPT-8 prepared in Example 1. Results of free radical trapping experiments and electron spin resonance (ESR) are as follows: Figure 6 As shown in A-6B, it is confirmed that ·O2 is generated during the photocatalytic production of H2O2. -The presence of (6A) and ·OH (6B) radicals indicates that the reaction follows both oxygen reduction (ORR) and water oxidation (WOR) pathways.

[0049] Density functional theory (DFT) calculations: To gain a deeper understanding of the relationship between optical, photoelectrochemical properties and photocatalytic activity, this application uses the Vienna First Principles Simulation Software (VASP) to perform all density functional theory (DFT) calculations; in Figure 7 Theoretical calculations of the frontier molecular orbital distribution of A show that the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of ZIF-8 / SPT-8 are located in the ZIF-8 and SPT regions, respectively. This distribution directly confirms the characteristics of the DA structure. Figure 7 B and 7C show that the Eg value for ZIF-8 is 5.03 eV and the Eg value for SPT is 1.98 eV, which are within the error range compared to the Eg value obtained by the Tauc-plot method.

[0050] Analysis of the TDOS and PDOS of ZIF-8, SPT, and ZIF-8 / SPT-8 shows that the VB and CB of ZIF-8 and SPT are both located at high symmetry points, indicating that both materials are direct bandgap semiconductors. The CBM of ZIF-8 is mainly composed of C, N, and Zn, while the VBM below the Fermi level is also composed of C and N, such as... Figure 7 As shown in Figure D; for SPT, CBM is mainly contributed by C, N, and Pd orbitals, while VBM mainly contains C (7E); to better confirm the direction of electron movement in ZIF-8 / SPT-8, the work function (WF) was also calculated; the work function values ​​of ZIF-8 and SPT are 5.92 eV (7F) and 5.10 eV (7G), respectively, with ZIF-8 having a larger WF value than SPT. The Fermi level (Ef) is usually negatively correlated with the work function. Obviously, the Fermi level of SPT (-4.45 eV) is higher than that of ZIF-8 (-5.01 eV). When ZIF-8 and SPT are in close contact, in order to achieve equilibrium of the Fermi level of the entire system, electrons will spontaneously flow from the SPT side with the higher Fermi level to the ZIF-8 side with the lower Fermi level until equilibrium is reached. Electrons flow out at the SPT interface, causing positive charge to accumulate on that side and the energy band to bend upwards. Electrons are gained at the ZIF-8 interface, and the influx of electrons accumulates negative charge, causing the energy band to bend downwards. Due to the redistribution of charge on both sides of the interface, an IEF is formed at the contact surface, with the electric field direction pointing from the positively charged side to the negatively charged side, i.e., from the SPT to the ZIF-8.

[0051] In addition, this application also studies the H* adsorption energy and ΔG of the hydrogen evolution reaction of ZIF-8, SPT, and ZIF-8 / SPT-8. H*Calculations were performed to assess the differences in activity. Figure 7 The H* adsorption energies of ZIF-8, SPT, and ZIF-8 / SPT-8 in H are -2.37, -2.73, and -2.95 eV, respectively. Figure 7 ΔG of ZIF-8, SPT, and ZIF-8 / SPT-8 in I H* The values ​​were 1.31, 0.98, and 0.77 eV, respectively. The more negative the H* adsorption energy, the stronger the bonding ability between H and the catalyst surface, and the easier it is to capture H. + An adsorbed state is formed. ΔG H* The smaller the value, the lower the adsorption energy for H atoms, and the more H atoms can be adsorbed during the reaction, thus exhibiting better catalytic activity.

[0052] The photocatalyst ZIF-8 / SPT-8 prepared in Example 1 was subjected to Kelvin probe force microscopy (KPFM) and in-situ XPS tests. Figure 8 AI): KPFM showed that the surface potential of ZIF-8 / SPT-8 decreased under illumination, indicating that holes accumulated on the surface; while in-situ XPS showed that the Zn 2p peak shifted to a higher binding energy (reduced electron density) under illumination, while the Pd 3d peak shifted to a lower binding energy (increased electron density), directly proving that photogenerated electrons transferred from ZIF-8 to SPT under illumination, which is completely consistent with the charge transfer mechanism of S-type heterojunction.

[0053] 6) Electrochemical performance testing Test method: First, 3 mg of photocatalyst sample was dispersed in 250 μL of deionized water, then 10 μL of Nafion solution and 250 μL of anhydrous ethanol were added. After the mixed solution was ultrasonically dispersed evenly, 200 μL of photocatalyst sample solution was dropped onto an ITO slide (1.5 × 1.5 cm) in the middle of the sample tube to ensure that the photocatalyst was evenly covered on the ITO. Finally, it was dried at 60 °C for further characterization. The electrolyte used in the test was a 0.2M sodium sulfate aqueous solution, and a three-electrode test was conducted. The reference electrode was a saturated calomel electrode, the working electrode was a clip with a metal sheet, and the counter electrode was a 1cm*1cm platinum sheet electrode. To investigate the response of the photocatalyst to visible light, UV-vis testing was performed on the sample. The results are as follows: Figure 9 As shown in Figure A, ZIF-8 has a narrower visible light absorption range, while SPT and ZIF-8 / SPT-X have wider visible light absorption ranges, with an observation at a wavelength of approximately 420 nm. 1u (π)→e* g The Soret band caused by the (π) transition contains two Q-band absorptions in the 450-550 nm range, which is due to the α-transition in the porphyrin nucleus. 2u(π)→e* g This is generated by (π) transitions. When SPT is combined with ZIF-8, the excellent photosensitivity of the porphyrin structure can effectively broaden the response range of the monomer material to visible light and enhance the absorption intensity. According to the Tauc-plot ( Figure 9 According to calculations (B and 9C), the Eg values ​​of ZIF-8 and SPT are 5.11 and 2.06 eV, respectively. Figure 9 Figures D and 9E show the MS curves of ZIF-8 and SPT at 500, 1000, and 1500 Hz. It can be clearly observed that both ZIF-8 and SPT have positive slopes, typical of n-type semiconductors. The Efb values ​​measured by SCE are -1.62 and -1.88 eV, respectively (relative to E...). NHE The values ​​are -1.38 and -1.64 eV, respectively. NHE =E SCE +0.241). Generally speaking, for n-type semiconductors, their E CB Usually more than E fb -0.1-0.3V (0.2V is used in this application), the E of ZIF-8 and SPT is calculated. CB They are -1.58 and -1.84 eV, respectively. VB According to formula E VB =E CB +E g The obtained values ​​were 3.53 and 0.22 eV, respectively. To facilitate subsequent research on the catalytic mechanism, the specific band structures of the two monomer materials are shown here, as follows: Figure 9 As shown in F.

[0054] like Figure 10 As shown in Figure A, the it responses of ZIF-8 and SPT to visible light are relatively weak, while the it responses of ZIF-8 / SPT-X to visible light gradually increase. This may be because the combination of ZIF-8 and SPT promotes the separation of photogenerated electron-hole pairs. Furthermore, the electron transfer rate is also represented by the diameter of the Nyquist semicircle; generally, the smaller the radius, the lower the resistance, and the faster the transfer rate of photogenerated carriers. From... Figure 10 The Nyquist plot of ZIF-8 / SPT-X in section B shows that its arc radius is smaller compared to the original ZIF-8 or SPT, with ZIF-8 / SPT-8 having the smallest radius. This indicates that it has the lowest resistance and the fastest charge transfer rate, which is beneficial for the separation of photogenerated electron-hole pairs. These results confirm that the combination of ZIF-8 and SPT can effectively promote charge transfer and improve carrier separation efficiency.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing a ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst, characterized in that, Includes the following steps: 1) Dissolve PdTCPP powder in N,N-dimethylformamide solution and sonicate to form a precursor solution; 2) The precursor solution obtained in step 1) is rapidly injected into an aqueous solution containing a surfactant, the reaction is stirred, and the product is centrifuged, washed, and dried to obtain SPT nanopowder. 3) The SPT nanopowder obtained in step 2) was added to the precursor solution of ZIF-8 and stirred at room temperature. The product was washed, centrifuged and dried to obtain ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst.

2. The method for preparing the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 1, characterized in that, The mass concentration of PdTCPP powder in the precursor solution described in step 1) is 5-15 mg / mL.

3. The method for preparing the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 1, characterized in that, The surfactants mentioned in step 2) include, but are not limited to, hexadecyltrimethylammonium bromide.

4. The method for preparing the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 1, characterized in that, The mass concentration of the surfactant in the aqueous solution described in step 2) is 1-3 mg / mL.

5. The method for preparing the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 1, characterized in that, The process parameters for the stirring reaction described in step 2) are: stirring at 70-90℃ for 20-30 hours.

6. The method for preparing the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 4, characterized in that, In step 3), the precursor solution of ZIF-8 is composed of Zn(NO3)2·6H2O and 2-methylimidazole dissolved in anhydrous methanol solution.

7. The method for preparing the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 4, characterized in that, In step 3), the solid-liquid ratio of the SPT nanopowder to the ZIF-8 precursor solution is (0.2-0.6):

1.

8. The method for preparing the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 4, characterized in that, The process parameters for the stirring reaction described in step 3) are: stirring reaction at room temperature for 4-8 hours.

9. A ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst prepared by the preparation method according to any one of claims 1-8, characterized in that, The photocatalyst is an S-type heterojunction composite material with a DA structure.

10. The application of the ZIF-8 porphyrin self-assembled S-type heterojunction photocatalyst according to claim 9 in photocatalytic decomposition for hydrogen production and synthesis of hydrogen peroxide.

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