Application of BiVO4 photoanode modified with cobalt-binaphthylene (Salen) molecular catalyst

Abstract

The application of binaphthyl Salen cobalt molecular catalyst modified BiVO4 photoanode belongs to the field of photoelectrocatalysis technology and organic synthesis cross. BiOI film is deposited on FTO conductive glass by electrochemical deposition method, and then is converted into BiVO4 photoanode substrate by calcination; 3-hydroxy substituted binaphthyl Salen cobalt molecular catalyst CoL is synthesized; CoL is loaded on the surface of BiVO4 by cyclic voltammetry electrodeposition to obtain a hybrid photoanode. The photoanode is applied to the photoelectrocatalytic olefin epoxidation reaction, water is used as oxygen source, and acetone-water is used as electrolyte. The strong interface coupling between the catalyst and BiVO4 is strengthened by the electrodeposition of the molecular catalyst strategy, and the interface charge transport efficiency, reaction conversion rate and selectivity are improved. The conversion rate of styrene reaches 99%, the selectivity of epoxide reaches more than 90%, and the stability is excellent. The application provides a new way for green and efficient synthesis of epoxide, and has wide application prospect.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of photoelectrocatalysis and organic synthesis, specifically relating to a method for preparing a BiVO4 hybrid photoanode modified with an electrodeposited Salen cobalt molecular catalyst, and the application of this photoanode in photoelectrocatalytic olefin epoxidation using water as an oxygen source. Background Technology

[0002] Epoxides are an important class of chemical intermediates, widely used in the synthesis of plastics, pharmaceuticals, and agrochemicals. Traditional methods for synthesizing epoxides mainly include the chlorohydrin process, the Halcon process, the hydrogen peroxide process, and the direct oxidation process. However, these traditional processes have significant drawbacks: the chlorohydrin process generates chlorine-containing waste, posing a high environmental risk; the Halcon process produces large amounts of peroxycarboxylate byproducts; the hydrogen peroxide process is costly and carries decomposition safety risks; and the direct oxidation process typically requires high temperature and pressure conditions, which can easily lead to over-oxidation.

[0003] In recent years, photoelectrocatalysis (PEC) technology has attracted attention due to its ability to drive reactions using solar energy, its mild operating conditions (room temperature and pressure), and its environmental friendliness. BiVO4, as a visible-light-responsive semiconductor, possesses good chemical stability and a suitable band structure, making it an ideal photoanode material. However, pure BiVO4 photoanodes suffer from severe photogenerated carrier recombination, sluggish surface reaction kinetics, and poor selectivity for organic substrates, and are prone to photocorrosion in aqueous electrolytes. Furthermore, in photoelectrocatalytic organic synthesis, the oxygen evolution reaction (OER) often occurs as a competing reaction, reducing the Faradaic efficiency of the target product. Therefore, developing a modified BiVO4 photoanode that can suppress carrier recombination, accelerate interfacial charge transport, improve reaction conversion and selectivity, and effectively suppress side reactions is of great significance for achieving green and efficient olefin epoxidation.

[0004] Existing modification methods mainly include metal doping, heterojunction construction, and supported catalysts. However, inorganic catalysts often have unclear active sites, making molecular-level regulation difficult. While molecular catalysts possess ideal characteristics such as clear mechanisms, strong tunability, high selectivity, and atom economy, they face challenges in application, including low photocurrent and long reaction times. Furthermore, molecular catalysts lack stability on photoelectrode surfaces, easily detaching or degrading. Therefore, how to stably and efficiently support molecular catalysts on semiconductor photoanode surfaces and achieve highly selective catalysis and synergistic rate enhancement in organic synthesis reactions is a pressing technical challenge. Summary of the Invention

[0005] This invention aims to address the problems of high carrier recombination rate, slow surface reaction kinetics, and low product selectivity in the photoelectrocatalytic epoxidation of olefins using existing BiVO4 photoanodes. It provides a method for preparing a cobalt Schiff base and loading it onto a BiVO4 photoanodeposition. This composite photoanode can improve the conversion rate and selectivity of the olefin epoxidation catalyzed by the blank bismuth vanadate photoelectrochemical system, exhibiting excellent photoelectric performance in organic-water mixed electrolytes and good stability. This reaction pathway replaces the use of strong oxidants, and the entire process is green and pollution-free, providing an important strategy for the research of green organic synthesis.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The technical solution adopted in this invention is the application of BiVO4 photoanode modified with a binaphthyl Salen cobalt molecular catalyst, the specific solution of which is as follows:

[0008] (1) Preparation of BiVO4 photoanode substrate: BiOI thin film was deposited on FTO conductive glass by electrochemical deposition, and then converted into BiVO4 by calcination;

[0009] (2) Synthesis of CoL complex molecular catalyst: Schiff base ligand H2L was synthesized from 2,3-dihydroxybenzaldehyde and 1,1'-bi-2,2'-diaminonaphthalene as raw materials, and then coordinated with cobalt salt to obtain CoL complex;

[0010] (3) Construction of hybrid photoanode: CoL molecular catalyst was loaded onto the surface of BiVO4 photoanode by cyclic voltammetric electrodeposition to obtain CoL / BiVO4 hybrid photoanode.

[0011] (4) Application of CoL / BiVO4 hybrid photoanode: Using CoL / BiVO4 hybrid photoanode as working electrode, platinum wire as counter electrode, and Ag / AgCl as reference electrode, an external bias voltage is applied and light is applied in an organic-water mixed electrolyte containing olefin substrate, and water is used as oxygen source to achieve olefin epoxidation.

[0012] The BiOI thin film was prepared by using FTO as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode, and performing constant potential deposition to achieve a cumulative charge of 0.17 C / cm. 2 The calcination was terminated at 450℃ for 2 hours, with a heating rate of 2℃ / min. -1 After calcination, the electrode needs to be immersed in 1 M NaOH solution to remove excess V2O5, and then washed and dried to obtain BiVO4 photoanode.

[0013] The synthesis process of the cobalt complex molecular catalyst CoL is mainly divided into two steps.

[0014] (1) The synthesis method of ligand H2L is as follows: 2,3-dihydroxybenzaldehyde and 1,1'-bi-2,2'-diaminonaphthalene are dissolved in anhydrous methanol, heated under nitrogen protection for a period of time, and after the reaction is completed, filtered, washed and dried to obtain H2L ligand.

[0015] The molar ratio of 2,3-dihydroxybenzaldehyde to 1,1'-bi-2,2'-diaminonaphthalene is 2:1.

[0016] (2) The synthesis method of CoL complex is as follows: under anhydrous and oxygen-free conditions, the ligand H2L is dissolved in ultra-dry methanol, and a methanol solution of cobalt acetate tetrahydrate and lithium hydroxide monohydrate is added. After heating and reacting for a period of time, the mixture is filtered, washed, and dried to obtain CoL complex.

[0017] The molar ratio of the ligand H2L, cobalt acetate tetrahydrate, and lithium hydroxide monohydrate is 1:1.1:2.2.

[0018] Construction of the hybrid photoanode: CoL molecular catalyst was loaded onto the surface of BiVO4 photoanode by cyclic voltammetry (CV) electrodeposition to obtain CoL / BiVO4 hybrid photoanode.

[0019] The organic-water mixed electrolyte refers to a mixed solution of acetone and water in a ratio of 4:1, with tetrabutylammonium tetrafluoroborate as the electrolyte.

[0020] The light emitted by a 300 W xenon lamp under AM1.5 illumination conditions simulates sunlight, with an incident light intensity of 100 Wcm². -2 .

[0021] A method for preparing a BiVO4 photoanode modified with a binaphthyl Salen cobalt molecular catalyst and its application, comprising the following steps:

[0022] 1. Preparation of BiVO4 photoanode substrate: A BiOI thin film was deposited on FTO conductive glass using electrochemical deposition, followed by calcination to convert it to BiVO4. Specifically, FTO was used as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode. Deposition was carried out at a constant potential at -0.1 V vs. Ag / AgCl and 29℃, achieving a cumulative charge of 0.17 C / cm³. 2 The calcination was stopped at a certain time; the calcination conditions were as follows: 40 μL of a 0.2 M DMSO solution of acetylacetonate vanadium oxyacetate (VO(acac)2) was dropped onto the surface of the BiOI electrode, and calcined at 450 °C for 2 h with a heating rate of 2 °C / min. -1 After calcination, the electrode needs to be immersed in 1 M NaOH solution to remove excess V2O5, and then washed and dried to obtain BiVO4 photoanode.

[0023] 2. Synthesis of Cobalt Complex Molecular Catalyst (CoL): Schiff base ligand H2L was synthesized from 2,3-dihydroxybenzaldehyde and 1,1'-bi-2,2'-diaminonaphthalene, and then coordinated with cobalt salt to obtain CoL complex.

[0024] 4 mmol of 2,3-dihydroxybenzaldehyde was dissolved in 30 mL of anhydrous methanol and stirred at room temperature until completely dissolved. Then, 2 mmol of 1,1'-bi-2,2'-diaminonaphthalene was added in portions, and the mixture was heated under reflux for 4 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, rapidly filtered, and the solid product was collected. The precipitate was washed successively with anhydrous methanol and anhydrous diethyl ether to remove unreacted starting materials. The resulting orange-red crystals were dried in a vacuum drying oven to obtain the target ligand H2L.

[0025] Under anhydrous and oxygen-free conditions, a methanol solution of cobalt acetate tetrahydrate (0.136 g, 0.55 mmol) and lithium hydroxide monohydrate (0.262 g, 1.10 mmol) was added dropwise to 20 mL of ultra-dry methanol containing ligand H₂L (0.262 g, 0.50 mmol), and the mixture was heated under reflux for 8 h. After the reaction was complete, the system was cooled to room temperature, and the solvent was removed by rotary evaporation. The resulting residue was filtered through a microporous membrane, and a dark reddish-brown solid crude product was collected. The crude product was washed successively with methanol and anhydrous diethyl ether to remove unreacted starting materials and byproducts. The resulting solid was dried in a vacuum drying oven to obtain the target complex CoL.

[0026] 3. Construction of hybrid photoanode: CoL molecular catalyst was loaded onto the surface of BiVO4 photoanode by cyclic voltammetry (CV) electrodeposition to obtain CoL / BiVO4 hybrid photoanode.

[0027] The conditions for the cyclic voltammetric electrodeposition method are as follows: CoL and Bu4NPF6 are added to DMF and dissolved by ultrasonication to obtain an electrolyte. The concentration of CoL is 0.02 mmol / 20 mL and the concentration of Bu4NPF6 is 0.03 mmol / 20 mL. BiVO4 is used as the working electrode, Pt is used as the counter electrode, and Ag / AgCl is used as the reference electrode. Cyclic voltammetry is performed 5 times in the potential range of -0.5 V to 2.5 V vs. Ag / AgCl at a scan rate of 0.05 V / s.

[0028] 4. Application of CoL / BiVO4 hybrid photoanode: Using a CoL / BiVO4 hybrid photoanode as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, an external bias voltage is applied and the substrate is irradiated in an organic-water mixed electrolyte containing olefin substrates, with water as the oxygen source, to achieve olefin epoxidation.

[0029] The olefin substrate is styrene; the organic-water mixed electrolyte is 10 mL of a mixed solution of acetone and water at a volume ratio of 4:1; the supporting electrolyte is 0.1 M TBABF4; and the substrate concentration is 5 mM.

[0030] The applied bias voltage is preferably 1.6 V vs. Ag / AgCl, and the reaction time is preferably 3 h, at which point the conversion rate of styrene is ≥ 99% and the selectivity of epoxide is ≥ 98%.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. High selectivity and high conversion rate: The CoL / BiVO4 photoanode constructed in this invention can achieve a styrene conversion rate of up to 99% and an epoxide selectivity of over 90% in the photoelectrocatalytic styrene epoxidation reaction.

[0033] 2. Increased reaction rate and photocurrent: Near-complete conversion of olefins can be achieved within 3 h in the acetone / water system, while the photocurrent density of this system remains stable at 3 mA cm⁻¹. -2 The above represents an improvement of over 50% compared to bare BiVO4 photoanodes. This performance enhancement is attributed to the acetone / water mixed solvent system, which significantly reduces interfacial charge transfer resistance, improves the separation and utilization of photogenerated carriers, and simultaneously enhances the solubilization and dispersion of the substrate styrene on the electrode surface, promoting effective contact between the substrate and active sites. This results in a synergistic improvement in reaction rate and photocurrent density.

[0034] 3. Green oxygen source and mild conditions: The reaction uses water molecules as the only oxygen source, avoiding the use of toxic and harmful chemical oxidants. Moreover, the reaction is carried out at normal temperature and pressure, with low energy consumption and high safety, thus realizing green synthesis.

[0035] 4. Suppression of side reactions: The molecular catalyst CoL acts as a hole relay, promoting the transfer of photogenerated holes to the interface and stabilizing the active intermediate through ligand field regulation, effectively suppressing the competitive oxygen evolution reaction (OER) and the excessive oxidation of the substrate.

[0036] 5. Good stability: The chemical bonds formed at the Bi-O-Co interface by electrodeposition enhance the binding force between the catalyst and the substrate, and the photoanode exhibits excellent electrochemical stability under continuous illumination. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the synthesis process of the molecular catalyst CoL in an embodiment of the present invention.

[0038] Figure 2 This is a cyclic voltammogram during the preparation of the CoL / BiVO4 hybrid photoanode in an embodiment of the present invention.

[0039] Figure 3 This is a SEM image of the CoL / BiVO4 photoanode in an embodiment of the present invention.

[0040] Figure 4 This is an EDS elemental distribution diagram of the CoL / BiVO4 photoanode in an embodiment of the present invention.

[0041] Figure 5 The XRD patterns of BiVO4, H2L / BiVO4, and CoL / BiVO4 are shown in the embodiments of the present invention.

[0042] Figure 6 The UV-Vis diffuse reflectance spectra and Tauc diagrams of BiVO4, H2L / BiVO4, and CoL / BiVO4 in the embodiments of the present invention are shown.

[0043] Figure 7 This is the XPS spectrum of the CoL / BiVO4 photoanode in an embodiment of the present invention.

[0044] Figure 8 This is the Raman spectrum of the CoL / BiVO4 photoanode in an embodiment of the present invention.

[0045] Figure 9 The LSV curves for the photoelectrochemical epoxidation of styrene by the ML / BiVO4 photoanode are shown in the embodiments of the present invention.

[0046] Figure 10 The figures show the photoelectrochemical performance curves of CoL / BiVO4 photoanode for styrene epoxidation at different times and voltages in embodiments of the present invention.

[0047] Figure 11 The figures show the photoelectrochemical performance curves of different semiconductor materials used in the comparative examples of this invention for the photoelectrochemical oxidation of styrene.

[0048] Figure 12 This is a schematic diagram illustrating the effect of different solvent systems on the performance of the CoL / BiVO4 photoelectrocatalytic styrene epoxidation reaction in the comparative examples of this invention.

[0049] Figure 13 This is a schematic diagram illustrating the effect of different catalyst loading methods on the performance of photoelectrocatalytic styrene epoxidation reaction in this invention. Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. In the following embodiments, unless otherwise specified, the specific operating methods and testing methods are conventional techniques, and the reagents, medicines, materials and instruments used can all be obtained commercially.

[0051] Example 1: Preparation of BiVO4 photoanode substrate

[0052] (1) FTO cleaning: Clean the FTO conductive glass (resistance <15Ω cm) -2 Soak the product in detergent, water, acetone, and ethanol in sequence for 30 minutes each, then dry it for later use.

[0053] (2) BiOI thin film deposition: Prepare 50 mL of nitric acid aqueous solution with pH 1.7 containing Bi(NO3)3·5H2O (0.97 g) and KI (3.32 g), and add 20 mL of ethanol solution containing p-benzoquinone (0.487 g) to obtain the electrodeposition precursor solution. The water temperature must be below 25℃ during all ultrasonic processes. Use FTO as the working electrode (size 1×2 cm). 2 Using Ag / AgCl as the reference electrode and platinum wire as the counter electrode, a constant potential deposition was performed at -0.1 V (vs. Ag / AgCl), achieving a cumulative charge of 0.17 C / cm². 2 The process is terminated at a certain time, resulting in a BiOI thin film.

[0054] (3) Calcination conversion: 40 μL of 0.2 M VO(acac)2 DMSO solution was dropped onto the surface of the BiOI electrode and calcined at 450℃ for 2 h (heating rate 2 ℃ / min). After cooling, it was immersed in 1 M NaOH solution for 30 minutes to remove excess V2O5, washed and dried to obtain BiVO4 photoanode.

[0055] Example 2: Synthesis of CoL molecular catalyst

[0056] (1) Synthesis of ligand H2L: 2,3-dihydroxybenzaldehyde (0.610 g, 4 mmol) was dissolved in 30 mL of anhydrous methanol, and 1,1'-bi-2,2'-diaminonaphthalene (0.568 g, 2 mmol) was added. The mixture was refluxed at 80 °C for 4 h under nitrogen protection. After cooling and filtration, the mixture was washed successively with anhydrous methanol and anhydrous diethyl ether, and dried under vacuum for 12 h to obtain the orange-red ligand H2L.

[0057] (2) Synthesis of the CoL complex: Ligand H2L (0.262 g, 0.5 mmol) was dissolved in 20 mL of ultradry methanol. Cobalt acetate tetrahydrate (0.136 g, 0.55 mmol) and lithium hydroxide monohydrate (0.262 g, 1.1 mmol) were separately dissolved in 10 mL of ultradry methanol. The metal salt solution was added dropwise to the ligand solution under nitrogen protection, and the mixture was refluxed at 80 °C for 8 h. The mixture was then rotary evaporated, filtered, washed, and dried to obtain a dark reddish-brown CoL complex solid.

[0058] Example 3: Preparation of CoL / BiVO4 hybrid photoanode

[0059] CoL (0.0116 g, 0.02 mmol) and Bu4NPF6 (0.0116 g, 0.03 mmol) were dissolved in 20 mL DMF by sonication for 20 min to obtain the electrolyte. Using BiVO4 prepared in Example 1 as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode, cyclic voltammetry was performed 5 times at a scan rate of 0.05 V / s within a potential range of -0.5 V to 2.5 V (vs. Ag / AgCl). CoL was loaded onto the BiVO4 surface by electrodeposition to obtain a CoL / BiVO4 hybrid photoanode. ICP-OES testing showed that the CoL loading was approximately 2.06 × 10⁻⁶ g / mL. -4 mg cm -2 .

[0060] Example 4: Photocatalytic epoxidation of styrene (optimal conditions)

[0061] (1) Reaction system: A three-electrode system was used. The working electrode was the CoL / BiVO4 photoanode prepared in Example 3 (effective area of ​​10 mm × 10 mm), the counter electrode was platinum wire, and the reference electrode was Ag / AgCl. The electrolyte was a mixed solution of acetone and water (volume ratio 4:1), the electrolyte was 0.1 M tetrabutylammonium tetrafluoroborate (TBABF4), and the substrate was 5 mM styrene.

[0062] (2) Reaction conditions: The light source was a 300 W xenon lamp (AM 1.5G filter, 100 mW / cm²). 2 The external bias voltage was 1.6 V (vs. Ag / AgCl), the reaction time was 3 h, and the mixture was magnetically stirred at room temperature.

[0063] (3) Product analysis: The reaction solution was analyzed by high performance liquid chromatography (HPLC). The mobile phase was acetonitrile / water (v / v = 5:5), the equilibration time was 30 minutes, and the injection volume was 5 μL. The conversion and selectivity were calculated using the external standard method.

[0064] Example 5: Photoelectrocatalytic performance testing under different bias voltages

[0065] Except for the applied bias voltages being set to 0.8 V, 1.0 V, 1.2 V, 1.4 V, and 1.6 V versus Ag / AgCl, the reaction conditions were the same as in Example 4. The results showed that as the potential increased from 0.8 V to 1.6 V, the conversion rate increased from 45% to 99%, and the selectivity reached a peak of 98% at 1.6 V.

[0066] Example 6: Photoelectrocatalytic performance test at different reaction times.

[0067] Except for the reaction times, which were set to 0.5 h, 2 h, 4 h, and 12 h, the other preparation and reaction conditions were the same as in Example 4. The results showed that the conversion rate and selectivity increased to 99% and 98% simultaneously after 3 h of reaction; the selectivity decreased to 75% after 12 h, indicating that prolonged reaction may lead to secondary oxidation of the product.

[0068] Comparative Example 1: Pure BiVO4 photoanode

[0069] Except for omitting the CoL electrodeposition step, the preparation and reaction conditions were the same as in Examples 1 and 4.

[0070] Comparative Example 2: Modification with different metal complexes (FeL / MnL / BiVO4).

[0071] Except for replacing CoL with FeL or MnL complexes synthesized by a similar method as in Example 2, the other preparation methods and reaction conditions are the same as in Examples 3 and 4.

[0072] Comparative Example 3: No light conditions

[0073] Except for turning off the light source, the preparation and reaction conditions are the same as in Example 4.

[0074] Comparative Example 4: Comparison of photoanodes of different semiconductor materials (TiO2, WO3, Fe2O3).

[0075] BiVO4 was replaced with TiO2, WO3, and Fe2O3, respectively, while the remaining preparation methods and reaction conditions were the same as in Examples 3 and 4. The results showed that the CoL / BiVO4 system had the best performance.

[0076] Comparative Example 5: Supported by different electrolytes.

[0077] Tetrabutylammonium tetrafluoroborate was replaced with tetrabutylammonium hexafluorophosphate, and the reaction conditions were the same as in Example 3.

[0078] Comparative Example 6: Different electrolyte solvent ratios.

[0079] Except for the volume ratios of acetone to water being 2:1 and acetonitrile to water being 4:1 and 9:1 respectively, the preparation and reaction conditions were the same as in Example 4. The results showed that the solvent ratio of acetone / water at 4:1 was most favorable for the reaction to achieve the highest selectivity and conversion rate.

[0080] Comparative Example 7: Different load conditions.

[0081] Photoelectrocatalytic olefin epoxidation was carried out in CV-supported CoL / BiVO4, drop-coated CoL / BiVO4, and homogeneous systems (BiVO4 as the photoanode, with 10% wt CoL catalyst added to the solution), under the same reaction conditions as in Example 4. The results showed that the CV-supported CoL / BiVO4 system achieved the highest reaction conversion and selectivity.

[0082] Performance analysis was performed on the BiVO4 photoelectrocatalytic system modified with the molecular catalyst constructed in the examples:

[0083] Figure 2 This is the cyclic voltammogram of the CoL catalyst supported in Example 3. Figure 2 Two peaks were observed at 0.7 V and 1.2 V vs. Ag / AgCl. The peak at 0.7 V vs. Ag / AgCl corresponds to Co in the molecule. Ⅱ / Co Ⅲ The oxidation peak was observed, while the peak at 1.2V vs. Ag / AgCl was related to the chemical bonding between CoL molecules and BiVO4. The peak intensity gradually decreased with increasing cycle number, indicating that the adsorption of CoL molecules on the BiVO4 surface reached saturation.

[0084] Figure 3 , Figure 4 The images shown are SEM morphology and EDS elemental distribution diagrams of the CoL / BiVO4 photoanode in Example 3. Figure 3 The dense worm-like structure of CoL / BiVO4 on the FTO substrate shown in (a) is identical to that of the BiVO4 photoanode, indicating that the catalyst loading did not alter the structure of BiVO4. The thickness of the BiVO4 film is approximately 5.2 μm. Figure 3 As shown in (b), energy-dispersive X-ray spectroscopy (EDS) analysis reveals that Bi, V, O, and Co are uniformly distributed on the electrode surface, as shown in (b). Figure 4 This indicates that the photoanode modified with the molecular catalyst was successfully synthesized.

[0085] Figure 5The XRD patterns of BiVO4, H2L / BiVO4, and CoL / BiVO4 in embodiments of the present invention are shown. The XRD patterns of H2L / BiVO4 and CoL / BiVO4 are not significantly different from those of BiVO4. The 2θ diffraction peaks of BiVO4 at 17.6°, 28.5°, 30.2°, 35.1°, and 42.3° correspond to the (001), (121), (040), (002), and (051) planes, respectively. Peaks of the FTO film were observed, which are different from those of the pure BiVO4 film. In particular, the sharp peak at 18.5° corresponds to the pure monoclinic crystal plane (121) of FTO, while the peak at 28.9° corresponds to the characteristic scheelite peak of the BiVO4 monoclinic crystal system. This indicates that the BiVO4 photoanode with the addition of the co-catalyst maintains its monoclinic crystal structure. Importantly, no characteristic diffraction peaks of the co-catalyst were observed.

[0086] Figure 6 In Figures (a) and (b), the UV-Vis diffuse reflectance spectra and Tauc diagrams of BiVO4, H2L / BiVO4, and CoL / BiVO4 in the examples are shown. The band gap of the modified photoanode is slightly reduced, and a slight red shift is observed, indicating that the introduction of the catalyst is beneficial to enhancing the visible light capture capability of the photoanode. Figure 6 (b) shows the Tauc plot of the prepared photoanode. Analysis indicates that the optical bandgap of BiVO4 is 2.48 eV; after modification with ligand H2L, the bandgap decreases to 2.42 eV; further loading with CoL further reduces the bandgap to 2.38 eV. This systematic redshift confirms that the introduction of ligands and Co centers effectively broadens the visible light response range of the material and enhances the generation efficiency of photogenerated carriers.

[0087] Figure 7 The image shows the XPS spectrum of the CoL / BiVO4 photoanode in this example. The Bi4f spectrum of BiVO4 has two distinct peaks: 159.2 eV and 164.5 eV, which are attributed to Bi4f, respectively. 7 / 4 and Bi 4f 5 / 2 In the high-resolution V 2p spectrum, V 2p 3 / 2 and V 2p 1 / 2 The peaks appear at approximately 524.3 eV and 516.7 eV, with a spin-orbit spacing of 7.6 eV. Notably, the O 1s peaks at 529–530 eV and 532.2 eV can be attributed to lattice oxygen and surface-adsorbed oxygen species, while the peak at 531.5–532 eV may be Co-O. Overall, the slight positive shifts observed in the O 1s and V 2p spectra indicate an effective electronic interaction between BiVO4 and CoL, suggesting the successful synthesis of a photoanode.

[0088] Figure 8The image shows the Raman spectrum of the CoL / BiVO4 photoanode in this example. VO4 3- The ν1 symmetric stretching vibration of the VO bond in the tetrahedron, after material modification, increases from 828 cm⁻¹. -1 Displaced to 830 cm -1 This indicates that the VO bond strength is weakened due to the coordination effect between the ligand and the interface. The CoL complex maintained its structural integrity after loading and formed Bi-O-Co interfacial chemical bonds, interacting with the Co 2p bonds of XPS. 2 / 3 The peak at 781 eV is consistent, and the Bi 4f peak shows a slight positive shift, such as... Figure 8 As shown in (c), the successful synthesis of the photoanode was further verified. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis revealed that the CoL catalyst loading on the BiVO4 photoanode surface was approximately 2.06 × 10⁻⁶. -4 mg cm -2 .

[0089] Figure 9 These are the JV curves for the photoelectrochemical epoxidation of styrene using an ML / BiVO4 photoanode in this embodiment of the invention. (a) is the JV curve under styrene-free substrate conditions, and (b) is the JV curve under conditions containing 5 mM styrene substrate. Figure 9 As shown in (a), under substrate-free conditions, all ML-modified BiVO4 photoanodes (CoL / BiVO4, FeL / BiVO4, MnL / BiVO4) exhibited higher photocurrent densities than pure BiVO4, with CoL / BiVO4 showing a current density of 2.1 mA cm⁻¹ at 1.23 V vs. RHE. -2 Pure BiVO4 (1.4 mA cm⁻¹) -2 The increase was approximately 50%, slightly lower than MnL / BiVO4. In Figure 9 In (b), the photocurrent density of the CoL-modified BiVO4 photoanode system at the same potential increased from 2.6 mA cm⁻¹. -2 Significantly improved to 3.9 mAcm -2 The increase reached 50% (1.5 times), while the increases for FeL / BiVO4 and MnL / BiVO4 were less significant. This indicates that CoL modification has the most significant enhancement effect on the photoelectrocatalytic activity of BiVO4 photoanode, exhibiting the best catalytic performance, demonstrating the highly efficient catalytic effect of CoL catalyst on styrene oxidation reaction.

[0090] Figure 10 The figures show the catalytic performance curves of the CoL / BiVO4 photoanode photocatalytic styrene epoxidation under different times and voltages in embodiments of the present invention. Figure 10As shown in (a), the epoxidation performance of styrene changes significantly with reaction time. At 0.5 h, the conversion rate reaches 52%, but the selectivity is only 23%, resulting in a low yield of 2-phenylethylene oxide (12%), indicating that side reactions (such as the 2-phenylethylene oxide intermediate) dominate in the initial stage. With the reaction time extended to 3 h, the conversion rate and selectivity simultaneously increase to 99% and 98%, respectively, with a yield of 98%, confirming that the active sites on the catalyst surface are gradually activated and effectively suppress side reaction pathways. At 12 h, the yield slightly decreases to 90%, and the selectivity drops to 75%, indicating that the target product may undergo secondary oxidation during long-term reactions (such as ring-opening of the epoxide to form a diol, which is further oxidized to benzaldehyde, etc.). (b) shows the photoelectrochemical epoxidation performance curves of styrene at different voltages using the CoL / BiVO4 photoanode in this embodiment. As the potential increases from 0.8 V to 1.6 V vs. Ag / AgCl, the conversion rate continuously increases (from 45% to 99%), indicating that higher potentials enhance the photogenerated hole-driven oxidation kinetics. The selectivity exhibits a non-linear change: in the 0.8-1.2 V range, the selectivity slowly increases from 35% to 65%; when the potential is further increased to 1.4 V, the selectivity jumps significantly to 88%; and it reaches a peak of 98% at 1.6 V, while the yield reaches 95%.

[0091] Figure 11 The performance and product breakdown of photoelectrocatalysis of styrene using different semiconductor photoanode materials are presented. For example... Figure 11 As shown in the LSV curves in (a), the CoL / BiVO4 composite photoanode exhibits the best photoelectric response, with a photocurrent density as high as approximately 3.9 mA cm⁻¹ at a potential of 1.5 V (vs. Ag / AgCl). -2 It is significantly superior to a single BiVO4 photoanode (approximately 2.6 mA cm⁻¹). -2 In contrast, the photocurrent density of the CoL / WO3 system is only about 0.9 mA cm⁻¹. -2 The CoL / TiO2 and CoL / Fe2O3 systems showed almost no detectable photocurrent signal, reflecting the significant differences in interfacial charge dynamics between different semiconductor-molecular catalyst combinations. The excessively wide band gap of TiO2 (~3.2 eV) resulted in extremely poor visible light absorption, while Fe2O3 exhibited low photogenerated carrier mobility, severe bulk recombination, and low activity in neutral to slightly acidic solutions. These characteristics indicate that BiVO4 possesses irreplaceable advantages in visible light absorption and band structure matching. Figure 11The product distribution statistics in (b) further reveal the key differences in catalytic selectivity. The CoL / BiVO4 system achieved over 90% styrene conversion, epoxide yield, and selectivity, demonstrating superior catalytic performance. In contrast, while the single BiVO4 photoanode possesses some photoelectric activity, its epoxide selectivity is only around 25%, and its yield is less than 10%, indicating that in the absence of a molecular catalyst, photogenerated holes may tend to trigger non-selective deep oxidation side reactions (such as the formation of benzaldehyde). Although the CoL / WO3 system exhibits some selectivity (approximately 37%), its conversion and yield are unsatisfactory due to its low photocurrent density. The CoL / TiO2 and CoL / Fe2O3 systems showed almost no detection of the target product.

[0092] Figure 12 This is a schematic diagram showing the effect of different solvent systems on the photoelectrocatalytic epoxidation performance of CoL / BiVO4 on styrene. Figure 12 Figure (a) shows the JV curves of the CoL / BiVO4 system under different solvents, and Figure (b) shows the bar charts of styrene conversion, selectivity, and epoxide yield under different solvents and ratios. Figure (a) shows that in the acetone / water 2:1 system with a high water content, the photocurrent density is the highest and the peak potential is the earliest, indicating the best photoelectrochemical reaction kinetics. However, high electrochemical activity does not directly translate into optimal product selectivity. Combined with the product distribution statistics in Figure (b), it can be seen that although the acetone / water (2:1) system achieves complete styrene conversion, its epoxide selectivity and yield are lower than those of the acetone / water (4:1) system. This may be because the excessively high reactivity leads to an increase in side reactions. Furthermore, the photocurrent density decreases with decreasing water ratio, reaching its lowest in the acetonitrile:water 9:1 system. Although the acetone / water (4:1) system had a slightly lower current density than the 2:1 system in LSV testing, it achieved a styrene conversion rate of nearly 100%, an epoxide yield of over 90%, and selectivity, demonstrating the best overall catalytic performance.

[0093] Figure 13 This is a schematic diagram illustrating the effect of different catalyst loading methods on the performance of photoelectrocatalytic styrene epoxidation reaction, as shown below. Figure 13 As shown in (a) the LSV curves, both CV drop-coating and Nafion embedding immobilization strategies significantly outperformed the homogeneous system. Among them, the CV loading method achieved the highest photocurrent density (approximately 4 mA cm⁻¹) at 1.5 V (vs. Ag / AgCl). -2 Nafion embedding was the second most effective (approximately 3.2 mA cm⁻¹). -2 The current density of a homogeneous system is only about 1 mA cm⁻¹. -2 This trend is in Figure 13Further verification was obtained in the stability test of (b) in the middle section. The CV load system maintained a value of approximately 3.0 mAcm throughout the 3-hour test. -2 The stable current output exhibits excellent photoelectrochemical stability and charge separation efficiency, while the current density of both the Nafion-embedded and homogeneous systems remains at 1.5 mA cm⁻¹. -2 and 1.3 mA cm -2 The CV-supported system exhibits the best overall performance. Homogeneous systems suffer from high charge transfer resistance and numerous side reactions due to light shielding and free diffusion, resulting in the worst performance (yield approximately 68%). While the Nafion-embedded system avoids light loss, its performance is second best due to limitations in mass transfer resistance caused by the dense film and catalyst leaching. CV-supported systems stabilize CoL on the BiVO4 surface, eliminating light shielding, optimizing interfacial charge transport and mass transfer, regulating the microenvironment to suppress side reactions, and significantly improving the selectivity (over 90%) and yield (nearly 99%) of the target product.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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; and these 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.

Claims

1. The application of CoL / BiVO4 hybrid photoanode in photoelectrocatalytic olefin epoxidation, characterized by: Using a CoL / BiVO4 hybrid photoanode as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode, an external bias voltage was applied and the mixture was irradiated in an organic-water mixed electrolyte containing olefin substrates, with water as the oxygen source for olefin epoxidation. The preparation method of CoL / BiVO4 hybrid photoanode includes the following steps: (1) Preparation of BiVO4 photoanode substrate: BiOI thin film was deposited on FTO conductive glass by electrochemical deposition, and then converted into BiVO4 by calcination; (2) Synthesis of the CoL molecular catalyst Salen: N,N'-bis(2,3-dihydroxybenzaldehyde)-1,1'-binaphthyl-2,2'-diamine (abbreviated as H2L) was synthesized from 2,3-dihydroxybenzaldehyde and 1,1'-bi-2,2'-diaminonaphthalene as raw materials, and then coordinated with cobalt salt to obtain [N,N'-bis(2,3-dihydroxybenzyl)-1,1'-binaphthyl-2,2'-diamine]cobalt; (3) Construction of hybrid photoanode: CoL molecular catalyst was loaded onto the surface of BiVO4 photoanode by cyclic voltammetric electrodeposition to obtain CoL / BiVO4 hybrid photoanode.

2. The application according to claim 1, characterized in that: In step (1), the deposition conditions for the BiOI thin film are as follows: using FTO as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode, deposition is carried out at a constant potential of -0.1 V vs. Ag / AgCl, with a cumulative charge of 0.17 C / cm. 2 End at time; The calcination conditions were as follows: a DMSO solution of acetylacetone vanadium oxide was dropped onto the surface of the BiOI electrode, and calcined at 400℃-500℃ for 1-3 h with a heating rate of 1-3℃ / min. -1 .

3. The application according to claim 1, characterized in that: In step (2), the synthesis method of ligand H2L is as follows: 2,3-dihydroxybenzaldehyde and 1,1'-bi-2,2'-diaminonaphthalene are dissolved in anhydrous methanol at a molar ratio of 2:1 and refluxed under nitrogen protection for 3-5 h. The synthesis method of CoL complex is as follows: dissolve the ligand H2L in ultradry methanol, add a methanol solution of cobalt acetate tetrahydrate and lithium hydroxide monohydrate in a molar ratio of 1:1.1:2.2, and reflux for 7-9 h under nitrogen protection.

4. The application according to claim 1, characterized in that: In step (3), the conditions for cyclic voltammetric electrodeposition are as follows: CoL and Bu4NPF6 are added to DMF and dissolved by ultrasonication to obtain the electrolyte, with a CoL concentration of 0.02 mmol / 20 mL and a Bu4NPF6 concentration of 0.03 mmol / 20 mL; BiVO4 is used as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode; within the potential range of -0.5 V to 2.5 V vs. Ag / AgCl, the cyclic voltammetric electrodeposition is performed at a voltage of 0.05 V s⁻¹. -1 Perform 5 cyclic voltammetric scans at the scan rate.

5. The application according to claim 1, characterized in that: The olefin substrate is styrene; the organic-water mixed electrolyte is a mixture of acetone and water in a volume ratio of 4:1; the supporting electrolyte is 0.1 M TBABF4; and the substrate concentration is 3-7 mM.

6. The application according to claim 5, characterized in that: The applied bias voltage is 0.8 V~1.6 V vs. Ag / AgCl; the light source is a 300 W xenon lamp equipped with an AM 1.5G filter, and the incident light intensity is 100 mW cm⁻¹. -2 The reaction time is 0.5 h to 12 h.

7. The application according to claim 6, characterized in that: The reaction is carried out at room temperature, and the reaction system needs to be continuously magnetically stirred. During the reaction, water molecules are oxidized on the surface of the photoanode to generate active oxygen species, which directly participate in the epoxidation of olefins without the need for additional chemical oxidants.

8. A CoL / BiVO4 hybrid photoanode, characterized in that: The photoanode is prepared by the method for preparing the CoL / BiVO4 hybrid photoanode of claim 1, and the surface of the photoanode is loaded with a CoL molecular catalyst at a loading of approximately 2 × 10 mg cm⁻¹. -2 -2.2×10 mg cm -2 The CoL molecular catalyst is anchored to the BiVO4 surface through Bi-O-Co interfacial chemical bonds.

9. A CoL / BiVO4 hybrid photoanode according to claim 8, characterized in that: The photocurrent density of the photoanode at 1.23 V vs. Ag / AgCl is ≥ 2.1 mA cm⁻¹. -2 Under styrene substrate conditions, the photocurrent density is ≥ 3.9 mA cm⁻¹. -2 Furthermore, the photocurrent retention rate is ≥ 98% during a 3-hour continuous illumination test.

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