A flexible conjugated microporous polymer photocatalytic material with "induced fitting" function and a preparation method and application thereof

Abstract

This invention discloses a flexible conjugated microporous polymer photocatalytic material with "induced fit" function, its preparation method, and its application. The material uses bipyridine as the dynamic catalytic center, and alkynyl-containing porphyrin units as a broadband-response light-harvesting antenna and electron pump. The bipyridine derivative and porphyrin linking units are covalently linked by alkyne bonds to form a three-dimensional network conjugated polymer. The preparation method involves dissolving porphyrin, bipyridine derivative, and catalyst 1 in a solvent to obtain precursor solution A; dissolving catalyst 2 in a solvent to obtain precursor solution B; and mixing precursor solutions A and B for polymerization. This invention successfully introduces the dynamic intelligent mechanism of "induced fit" into solid-state photocatalytic materials for the first time, thus possessing a dynamic "induced fit" function, capable of actively optimizing the reaction pathway to achieve high activity and high selectivity in a one-step process. ‑ ORR produces hydrogen peroxide.

Description

Technical Field

[0001] This invention relates to the field of semiconductor photocatalytic materials technology, and in particular to a flexible conjugated microporous polymer photocatalytic material with "induced fitting" function, its preparation method and application. Background Technology

[0002] Hydrogen peroxide (H₂O₂) is a green oxidant with broad application prospects. However, its traditional anthraquinone oxidation process faces severe challenges such as high energy consumption and environmental pollution. Photocatalytic oxygen reduction reaction (ORR), as an ideal strategy, can directly convert O₂ to H₂O₂, offering high atom economy, mild reaction conditions, and an extremely low carbon footprint. However, the traditional two-step, two-electron (2e⁻²) process... - ) path (O2 + e - → O2 •- + e - + 2H⁺ → H₂O₂) will generate highly oxidizing superoxide radicals (O₂). •- This free radical promotes the secondary reduction / decomposition of H2O2 and accelerates catalyst degradation, thus severely affecting product selectivity and catalyst stability. In contrast, the direct one-step two-electron pathway (O2 + 2e) - + 2H⁺ → H₂O₂) then through the simultaneous transfer of 2e - The O2 is reduced to H2O2. From a thermodynamic perspective, the direct one-step method 2e - ORR (O2 / H2O2 0.68 V vs. NHE) is better than the two-step method 2e - ORR (O2 / O2) •- -0.33 V vs. NHE) is more advantageous. Therefore, for a step 2e - Designing appropriate photocatalysts for the ORR pathway is a promising strategy for achieving efficient and selective hydrogen peroxide production.

[0003] To achieve efficient one-step 2e - In the ORR pathway, O2 molecules must simultaneously adsorb onto the atom pairs in a bridging mode (Yeager type) to synchronously accept 2e. - To generate H2O2. Recent research has focused on designing adjacent active sites (e.g., a single pyridine-imine unit formed between a pyridine ring and an imine bond, or two adjacent nitrogen atoms in a pyrazine unit) in nitrogen-rich conjugated polymers to facilitate the generation of H2O2. -The ORR pathway. This type of dual-active-site configuration largely follows the enzyme's "lock and key" model, where the geometrically fixed dinitrogen sites act as rigid "locks," essentially pre-defining a match with O2, which acts as the "key." However, rigid conjugated polymers cannot dynamically adapt to the variable adsorption geometry of the O2 molecule, resulting in suboptimal active site coverage and thus limiting catalytic efficiency. Therefore, the rational design and efficient screening of polymers with suitable flexible units are urgently needed. Summary of the Invention

[0004] Objectives of the Invention: The first objective of this invention is to provide a conjugated microporous polymer photocatalytic material with dynamic "induced fit" function, capable of actively optimizing the reaction pathway to achieve highly active and selective ORR hydrogen peroxide production; the second objective of this invention is to provide a method for preparing the conjugated microporous polymer photocatalytic material; the third objective of this invention is to provide the application of the conjugated microporous polymer photocatalytic material in the photocatalytic synthesis of hydrogen peroxide, particularly for the efficient and highly selective synthesis of hydrogen peroxide via a one-step two-electron pathway without the need for sacrificial agents.

[0005] Technical Solution: The flexible conjugated microporous polymer photocatalytic material with "induced fit" function described in this invention is characterized in that the material uses bipyridine as the dynamic catalytic center, and alkynyl-containing porphyrin units as broadband-response light-harvesting antennas and electron pumps. The bipyridine derivative and porphyrin linking units are covalently linked by alkyne bonds to form a three-dimensional network conjugated polymer. Before and after oxygen adsorption, the dihedral angle of the core bipyridine linking unit can undergo a dynamic change of greater than 5°.

[0006] The bipyridine unit has a designable, rotatable dihedral angle in the polymer backbone, and its conformational flexibility is the structural basis for the material to achieve the "induced fit" function.

[0007] The porphyrin unit is responsible for broadband absorption and generating photogenerated electrons, while the rigid triple bond spacer arm serves to fix the relative orientation, prevent adverse interactions, and provide an efficient electron transport channel. This ensures that photogenerated electrons can be directionally and rapidly injected into the dynamically adjusted bipyridine active site, achieving efficient synergy between light capture, charge transport, and catalytic conversion.

[0008] The core design principle of this invention lies in breaking through the limitations of the traditional static "lock-key" model of rigid catalysts. In the photocatalytic oxygen reduction reaction, when oxygen molecules approach each other, their interaction with the lone pair electrons on the nitrogen atom of the bipyridine unit induces a significant dihedral twist in this flexible connecting unit. This dynamic conformational change causes the originally geometrically fixed dinitrogen active sites to undergo adaptive rearrangement, thereby optimizing the oxygen adsorption mode from single-site, weakly bound end-joint adsorption to two-site, strongly bound bridge adsorption. This optimized adsorption configuration directly changes the energy barrier of the reaction pathway, effectively suppressing the formation of harmful superoxide radical intermediates in the traditional two-step single-electron transfer pathway, and instead specifically promoting a highly efficient and clean one-step two-electron transfer pathway, thus simultaneously achieving high activity and high selectivity in hydrogen peroxide synthesis.

[0009] The bipyridine unit serves as the active center for the ORR reaction. Bipyridine derivatives with different halogenated positions (ortho, meta, and para) can be selected as reaction precursors. By changing the spatial position or steric hindrance of the substituents in the bipyridine unit, the dihedral angle and rotational degree of freedom of the bipyridine linker in the final material can be directly controlled during the polymerization process, thereby achieving precise programming of the material's "induced fit" strength.

[0010] Preferably, the structural formula of the bipyridine derivative is as follows:

[0011]

[0012] Where R is a halogen.

[0013] Preferably, when the bipyridine derivative is 4,4'-dibromo-2,2'-bipyridine, the dihedral angle of the core bipyridine linking unit of the material changes by more than 5° before and after oxygen adsorption, for example, it can be adjusted from about 32.8° to about 20.8°. This significant conformational adjustment creates optimal geometric conditions for the bridging adsorption of oxygen molecules.

[0014] Preferably, the alkynyl-containing porphyrin unit is tetrakis(4-ethynylphenyl)porphyrin.

[0015] Preferably, the molar ratio of bipyridine to tetra(4-ethynylphenyl)porphyrin is 1 to 2:1.

[0016] The preparation method of the flexible conjugated microporous polymer photocatalytic material of the present invention includes the following steps:

[0017] Step 1: Dissolve porphyrin, bipyridine derivative and catalyst 1 in solvent and stir until homogeneous to obtain precursor solution A;

[0018] Step 2: Dissolve catalyst 2 in a solvent and stir until homogeneous to obtain precursor solution B;

[0019] Step 3: Mix precursor solutions A and B to allow polymerization to occur. Finally, wash and dry to obtain the flexible conjugated microporous polymer photocatalytic material.

[0020] Preferably, the polymerization reaction is carried out at a temperature of 90-110°C for 40-48 hours.

[0021] Preferably, the catalyst 1 is bis(triphenylphosphine)palladium dichloride, and the solvent is N,N-dimethylformamide. Preferably, the amount of bis(triphenylphosphine)palladium dichloride used is 0.8 to 1 equivalent of the bipyridine derivative.

[0022] Preferably, the catalyst 2 is cuprous iodide, and the solvent is triethylamine. Preferably, the amount of cuprous iodide used is 1 to 1.5 equivalents of the bipyridine derivative.

[0023] The polymerization reaction is carried out in an Ar or N2 atmosphere.

[0024] The application of the flexible conjugated microporous polymer photocatalytic material described in this invention in the photocatalytic synthesis of hydrogen peroxide.

[0025] The application is as follows: under visible light irradiation, using the material as a catalyst and water and oxygen as raw materials, the oxygen reduction reaction is catalyzed to selectively generate hydrogen peroxide.

[0026] Mechanism of Invention: This invention uses a bipyridine derivative with intrinsic conformational flexibility as the key catalytic building block. Through covalent coupling reactions such as Sonogashira, it copolymerizes with a porphyrin light-harvesting unit and a rigid acetylene linker to construct a three-dimensional, fully conjugated microporous network framework. In this design, each unit has a clear function and works synergistically: the porphyrin unit acts as a broadband-response light-harvesting antenna and electron pump, responsible for efficiently absorbing visible light and generating photoelectrons; the rigid acetylene linker acts as an untwistable structural spacer and molecular wire, fixing the relative spatial orientation of porphyrin and bipyridine to prevent unfavorable electron coupling quenching, and establishing an efficient, directional electron transport channel; the flexible bipyridine unit acts as a dynamic catalytic center, and its rotatable dihedral angle is the structural source that endows the entire material with "induced fit" capabilities. This integrated "antenna-wire-intelligent center" design achieves full-chain functional integration from light energy harvesting and directional charge transport to substrate intelligent activation.

[0027] The core innovation of this invention lies in the dynamic response mechanism of the bipyridine unit. In photocatalytic ORR, when an O2 molecule approaches, its π antibonding orbital interacts with the electron-rich lone pair electrons on the nitrogen atom of the bipyridine. This interaction induces the flexible bipyridine linker to overcome a relatively small rotational energy barrier, resulting in a significant dihedral torsion (e.g., adjusted from ~32.8° to ~20.8° in the preferred embodiment CMP-B4). This dynamic conformational change is not a passive response, but an active optimization of the active sites. It causes an adaptive rearrangement of the spatial geometry of the two nitrogen active sites, thereby optimizing the O2 adsorption mode from a single-site, weakly bound end-joined (Pauling type) to a two-site, strongly bound bridging (Yeager type). This optimized adsorption configuration significantly reduces the energy barrier of the subsequent reduction reaction.

[0028] The mechanism of this invention possesses high designability and predictability. By altering the position and steric hindrance of the substituents in the bipyridine building blocks, their rotational degrees of freedom can be directly programmed at the molecular level, thereby precisely controlling the strength of their "induced fit" ability on a macroscopic scale. For example, increasing the steric hindrance of the substituents can limit the range of dihedral angle changes and weaken the dynamic response; conversely, it can enhance dynamic adaptability. This allows catalytic performance (such as activity and selectivity) to be rationally regulated through pre-designed molecules, providing a clear physical model and universal strategy for customizing high-performance catalysts on demand.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention breaks the traditional "lock-key" design paradigm of heterogeneous catalysts that rely on static active centers, and for the first time successfully introduces the dynamic intelligent mechanism of "induced fit" into solid photocatalytic materials, thereby having a dynamic "induced fit" function and being able to actively optimize the reaction path to achieve high activity and high selectivity in one step 2e - ORR produces hydrogen peroxide; (2) By optimizing the coupling position of the bipyridine unit, it has the best catalytic performance in the photocatalytic reaction. When the bipyridine is 4,4'-dibromo-2,2'-bipyridine, the dihedral angle of the core bipyridine connecting unit of the material changes by more than 5° before and after oxygen adsorption, and oxygen is adsorbed in the optimal adsorption configuration (Yeager type); (3) The preparation method has mild process conditions, simple operation, and low cost, and can be used for large-scale production; (4) The catalyst of the present invention exhibits excellent catalytic performance under sacrificial agent-free conditions, and the hydrogen peroxide generation rate of catalyst CMP-B4 reaches 5.27 mmol g. -1 h -1 It is approximately twice that of the rigid contrast material CMP-PhN in the same series, and exhibits extremely high selectivity. Attached Figure Description

[0030] Figure 1This is a flowchart illustrating the preparation process of the photocatalytic material of the present invention;

[0031] Figure 2 (a) Fourier transform infrared spectra of the photocatalytic materials obtained in Examples 1-3 and Comparative Example 1; Figure 2 (b) Raman spectra of the photocatalytic materials obtained in Examples 1-3 and Comparative Example 1; Figure 2 (c) Solid state of the photocatalytic materials obtained in Examples 1-3 and Comparative Example 1 13 C NMR spectrum; Figure 2 (d) are the X-ray diffraction spectra of the photocatalytic materials obtained in Examples 1-3 and Comparative Example 1;

[0032] Figure 3 (a), (b), and (c) are the nitrogen adsorption-desorption isotherms and pore size distribution diagrams of the photocatalytic materials prepared in Examples 1, 2, and 3, respectively.

[0033] Figure 4 The diagram shows the torsion angle of the bipyridine unit in the photocatalytic materials of Examples 1-3;

[0034] Figure 5 The figures show the photocatalytic activity test results of the catalytic materials obtained in Examples 1-4 and Comparative Example 1.

[0035] Figure 6 The above graph shows the apparent quantum yield of the photocatalytic material in Example 1.

[0036] Figure 7 This is a photocatalytic cycle test diagram of the photocatalytic material in Example 1. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to the embodiments.

[0038] Example 1

[0039] The flexible conjugated microporous polymer photocatalytic material with "induced fitting" function described in this invention is prepared by the following steps:

[0040] Step 1: Dissolve 21 mg (0.03 mmol) of 5,10,15,20-tetrakis(4-ethynylsilylphenyl)porphyrin, 14 mg (0.03 mmol) of 4,4'-dibromo-2,2'-bipyridine and 20 mg (0.03 mmol) of bis(triphenylphosphine)palladium dichloride in 15 mL of N,N-dimethylformamide and stir until homogeneous to obtain precursor solution A;

[0041] Step 2: Dissolve 10 mg (0.05 mmol) of cuprous iodide in 15 mL of triethylamine and stir well to obtain precursor solution B;

[0042] Step 3: Mix precursor solutions A and B in a glass reaction flask, degas with Ar for 10 minutes, alternate between double-row vacuum and Ar gas three times, and reflux at 100 °C for 48 hours in an Ar atmosphere in a sealed glass reaction flask. After the reaction is complete, cool the reaction system to room temperature, then wash the obtained product sequentially with tetrahydrofuran, water, and methanol, and finally dry the product to obtain the CMP-B4 flexible conjugated microporous polymer.

[0043] Example 2

[0044] Based on Example 1, the 4,4'-dibromo-2,2'-bipyridine was changed to 5,5'-dibromo-2,2'-bipyridine, while the other conditions remained unchanged, thus obtaining the CMP-B5 flexible conjugated microporous polymer.

[0045] Example 3

[0046] Based on Example 1, the 4,4'-dibromo-2,2'-bipyridine was changed to 6,6'-dibromo-2,2'-bipyridine, while the other conditions remained unchanged, thus obtaining the CMP-B6 flexible conjugated microporous polymer.

[0047] Example 4

[0048] Based on Example 1, the molar amount of 4,4'-dibromo-2,2'-bipyridine was changed to 0.06 mmol, while other conditions remained unchanged, thus obtaining the CMP-B4' flexible conjugated microporous polymer.

[0049] Comparative Example 1

[0050] Based on Example 1, the 14 mg (0.03 mmol) of 4,4'-dibromo-2,2'-bipyridine was changed to 20 mg (0.03 mmol) of 3,8-dibromo-1,10-phenanthridine, while keeping the other conditions unchanged, to obtain the CMP-B6 flexible conjugated microporous polymer.

[0051] Structural characterization

[0052] The structures of the samples prepared in Examples 1-3 and Comparative Example 1 were characterized, and the results are as follows: Figures 2-4 As shown.

[0053] Depend on Figure 2 The Fourier transform infrared spectra of all four polymers did not contain the characteristic peak of alkynyl CH stretching vibration (3287 cm⁻¹). -1 ) and C-Br stretching vibration peak (1087 cm⁻¹) -1 This indicates the success of the polymerization reaction; by Figure 2 b indicates that the Raman spectrum at 2203 cm⁻¹ -1The presence of characteristic stretching vibration peaks of the alkynyl C≡C bond at the position confirms that the alkynyl unit was not oxidized or reduced during the reaction. Figure 2 From c, we can know that solid state 13 In the C NMR spectrum, the signal at 120-140 ppm is attributed to the aromatic ring carbon skeleton, and the peak at 80 ppm corresponds to the sp hybrid carbon atom in the alkynyl C≡C bond, further confirming the construction of the conjugated skeleton. Figure 2 As can be seen from d, the X-ray diffraction patterns do not show any obvious sharp characteristic peaks in the 2θ range, indicating that Examples 1-3 and Comparative Example 1 are all amorphous materials.

[0054] Depend on Figure 3 As can be seen, the specific surface area of ​​CMP-B4 prepared in Example 1 is 328.61 m². 2 g -1 The pore size is 1.60 nm. (From...) Figure 3 b. It can be seen that the specific surface area of ​​CMP-B5 prepared in Example 2 is 412.62 m². 2 g -1 The pore size is 1.56 nm. (From...) Figure 3 c. The specific surface area of ​​CMP-B6 prepared in Example 3 is 378.37 m². 2 g -1 The pore size is 1.56 nm.

[0055] Structural optimization and energy calculations were performed on the embodiment using the DMol3 software package. A 1×1×1 k-point grid was used based on the Monkhorst–Pack scheme. The energy convergence criterion, maximum force, self-consistent field (SCF), and maximum displacement were all set to 2.0×10⁻⁶. -5 Ha, 4.0×10 -3 Ha / Å, 1×10 -5 Ha and 5.0×10 -3 Å. The calculation results are as follows: Figure 4 As shown.

[0056] Depend on Figure 4 The simulations showed that the dihedral angle of the bipyridine unit in CMP-B4 prepared in Example 1 was 32.8°, which decreased to 20.8° after oxygen adsorption, and the torsion angle was 12°. The simulations also showed that the dihedral angle of the bipyridine unit in CMP-B5 prepared in Example 2 was 177.2°, which decreased to 171.0° after oxygen adsorption, and the torsion angle was 6.2°. Finally, the simulations showed that the dihedral angle of the bipyridine unit in CMP-B6 prepared in Example 3 was 176.0°, which decreased to 178.9° after oxygen adsorption, and the torsion angle was 2.9°.

[0057] Performance testing

[0058] Xenon lamp irradiation (λ≥420 nm, 100 mW cm⁻¹) -2 Under the following conditions, 5 mg of the materials synthesized in Examples 1-3 and Comparative Example 1 were used as catalysts and added to 50 mL of pure water. O2 was continuously bubbled into the water, and sample solutions were taken every 15 min for detection using a UV spectrophotometer. The test results are as follows: Figure 4 As shown.

[0059] Depend on Figure 5 The photocatalytic hydrogen peroxide production performance of Examples 1-4 and Comparative Example 1 were found to be 5.27, 4.16, 2.29, 4.25, and 1.98 mmol g, respectively. -1 h -1 Among them, CMP-B4 and CMP-B4' prepared in Examples 1 and 4 showed the best photocatalytic hydrogen peroxide production effect, followed by CMP-B5, while CMP-B6 and CMP-PhN were almost identical. This is because oxygen induces torsion of the bipyridine unit, allowing oxygen to be adsorbed in the optimal adsorption configuration (Yeager type). Calculation simulations revealed that CMP-B4 prepared in Example 1 exhibited the greatest torsion of the bipyridine unit after oxygen adsorption (from 32.8° to 20.8°), demonstrating the strongest "induced fit" ability and best performance. CMP-B6 prepared in Example 3 only showed a slight change (from 176.0° to 178.9°), thus its performance was similar to that of CMP-PhN (with fixed dinitrogen sites) prepared in Comparative Example 1.

[0060] The apparent quantum yield (AQY) of CMP-B4 was obtained by using filters of different wavelengths (420, 450, 500, 550, and 600 nm). This normalizes the reactivity to the number of incident photons, eliminating differences in experimental conditions and directly reflecting the efficiency of the catalyst in converting photons into chemical reactions. The results are as follows: Figure 6 As shown.

[0061] Depend on Figure 6 The AQY values ​​of CMP-B4 prepared in Example 1 at wavelengths of 420, 450, 500, 550, and 600 nm were 2.15%, 2.21%, 1.44%, 4.12%, and 1.02%, respectively, demonstrating excellent catalytic performance under 550 nm light excitation. Furthermore, the measured AQY trend was consistent with the visible light absorption intensity, verifying the bandgap excitation mechanism and reflecting the catalyst's light absorption characteristics.

[0062] CMP-B4 catalytic efficiency after 5 cycles is as follows: Figure 7 As shown.

[0063] Depend on Figure 7 It can be seen that after 5 cycles, the hydrogen peroxide generation efficiency of CMP-B4 hardly decreased, showing that the catalyst has good stability.

Claims

1. A flexible conjugated microporous polymer photocatalytic material with "induced fit" function, characterized in that, The material uses bipyridine as the dynamic catalytic center, and alkynyl-containing porphyrin units as a broadband-response light-harvesting antenna and electron pump. The bipyridine derivative and porphyrin linking units are covalently linked by alkyne bonds to form a three-dimensional network conjugated polymer.

2. The flexible conjugated microporous polymer photocatalytic material according to claim 1, wherein, The structural formula of the bipyridine derivative is as follows: ； Where R is a halogen.

3. The flexible conjugated microporous polymer photocatalytic material according to claim 1, characterized in that, The alkynyl-containing porphyrin unit is tetrakis(4-ethynylphenyl)porphyrin.

4. The flexible conjugated microporous polymer photocatalytic material according to claim 1, wherein, The molar ratio of bipyridine to tetra(4-ethynylphenyl)porphyrin is 1~2:

1.

5. A method for producing the flexible conjugated microporous polymer photocatalytic material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Dissolve porphyrin, bipyridine derivative and catalyst 1 in solvent and stir until homogeneous to obtain precursor solution A; Step 2: Dissolve catalyst 2 in a solvent and stir until homogeneous to obtain precursor solution B; Step 3: Mix precursor solutions A and B to allow polymerization to occur. Finally, wash and dry to obtain the flexible conjugated microporous polymer photocatalytic material.

6. The method for preparing the flexible conjugated microporous polymer photocatalytic material according to claim 5, characterized in that, The polymerization reaction is carried out at a temperature of 90-110°C for 40-48 hours.

7. The method for preparing the flexible conjugated microporous polymer photocatalytic material according to claim 5, characterized in that, The catalyst 1 is bis(triphenylphosphine)palladium dichloride, and the solvent is N,N-dimethylformamide.

8. The method of claim 5, wherein the flexible conjugated microporous polymer photocatalytic material is prepared by the reaction of a compound represented by the following formula 1 and a compound represented by the following formula 2: ###0002### ###0003### 1 2 The catalyst 2 is cuprous iodide, and the solvent is triethylamine.

9. The application of the flexible conjugated microporous polymer photocatalytic material according to any one of claims 1 to 4 in the photocatalytic synthesis of hydrogen peroxide.

10. Use according to claim 9, characterized in that, The application is as follows: under visible light irradiation, using the material as a catalyst and water and oxygen as raw materials, the oxygen reduction reaction is catalyzed to selectively generate hydrogen peroxide.

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