A silver-supported bismuth vanadate composite material, its preparation method and application

Abstract

This invention provides a silver-supported bismuth vanadate composite material, its preparation method, and its application, belonging to the field of photoelectrocatalysis technology. This invention utilizes Bacillus-based extracellular polymeric substances to reduce silver ions, obtaining silver nanoparticles, which are then used as co-catalysts to modify bismuth vanadate, resulting in a composite photoanode material for photoelectrochemical water splitting under natural light. The prepared silver-supported bismuth vanadate composite material exhibits excellent catalytic activity and stability. Compared to bismuth-based composite photoanode materials prepared using inorganic methods, the photoanode modified with microbial silver nanoparticles in this invention demonstrates superior OER performance under simulated sunlight, exhibiting better stability.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalysis technology, specifically relating to a silver-supported bismuth vanadate composite material, its preparation method, and its application. Background Technology

[0002] Photoelectrochemical water splitting is a clean energy conversion technology that utilizes solar energy to produce hydrogen. Bismuth vanadate has been extensively studied due to its suitable band gap, good chemical stability, and visible light response. However, bismuth vanadate suffers from problems such as high photogenerated carrier recombination rate and slow surface reaction kinetics, which limit its further application in the field of photoelectrocatalysis.

[0003] To improve their performance, noble metal nanoparticles (such as Ag and Au) are often introduced as co-catalysts to enhance electron-hole separation efficiency and accelerate the oxygen evolution reaction. However, traditional noble metal nanoparticle preparation processes mostly employ chemical reduction methods, which require strong reducing agents (such as sodium borohydride and hydrazine hydrate) and high-temperature conditions (590~740℃), resulting in problems such as high energy consumption, high reagent toxicity, and environmental pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a silver-supported bismuth vanadate composite material, its preparation method, and its application. This invention uses Bacillus-binding extracellular polymeric substances to reduce silver nanoparticles and load them onto the surface of bismuth vanadate, eliminating the need for strong reducing agents and high-temperature conditions, resulting in low energy consumption and no environmental pollution problems.

[0005] To achieve the objectives of this invention, the following technical solutions are provided: A method for preparing a silver-supported bismuth vanadate composite material includes the following steps: Bismuth vanadate was chemically etched to obtain a bismuth vanadate precursor with oxygen vacancies on its surface. Bacillus-binding extracellular polymeric substances and silver ion solutions were mixed and subjected to a reduction reaction to obtain elemental silver; the reduction reaction was carried out at a temperature of 25-40°C for 48-72 hours. The elemental silver and bismuth vanadate precursor were mixed and annealed to obtain a silver-supported bismuth vanadate composite material.

[0006] Preferably, the method for preparing the Bacillus-binding extracellular polymeric polymer includes the following steps: Bacillus was cultured periodically to obtain soluble extracellular polymers of Bacillus. The cultivation period for the Bacillus is 1-5 days; the cultivation temperature is 37℃; the culture medium is Luria-Bertani liquid medium; and the culture medium volume is 100mL / bottle.

[0007] Preferably, the method for preparing bismuth vanadate includes the following steps: A BiOI film was obtained on the surface of a conductive substrate by electrodeposition in a bismuth deposition solution. A vanadium solution was coated onto the surface of the BiOI film, and after calcination, bismuth vanadate was obtained on the surface of a conductive substrate.

[0008] Preferably, the bismuth deposition solution comprises a soluble bismuth source, a soluble iodine source, p-benzoquinone, and ethanol; the pH value of the bismuth deposition solution is 1.7~2.0; The vanadium solution is a soluble vanadium source and dimethyl sulfoxide.

[0009] Preferably, the electrodeposition potential is 0.1~0.5V, and the deposition time is 5~10min; The roasting temperature is 450~500℃, and the holding time is 1~3h.

[0010] Preferably, the chemical etching includes a first etching and a second etching performed sequentially; The etching solution used for the first etching is an alkali metal hydroxide; The second etching is an electrochemical etching, and the electrolyte is a borate.

[0011] Preferably, the calcination temperature is 100~120℃, and the calcination is carried out in a reducing atmosphere.

[0012] The present invention also provides a silver-supported bismuth vanadate composite material prepared by the preparation method described above, comprising bismuth vanadate and elemental silver nanoparticles supported on the surface of the bismuth vanadate; The surface of the bismuth vanadate contains Ov vacancies. The surface of the elemental silver nanoparticles contains CO groups of amino acid residues; The Ov vacancy and CO group are bonded by VOC bonds.

[0013] Preferably, the particle size of the elemental silver nanoparticles is 10~20 nm.

[0014] This invention also provides the application of the silver-supported bismuth vanadate composite material described above in photoelectrocatalytic water splitting.

[0015] This invention provides a method for preparing a silver-supported bismuth vanadate composite material, comprising the following steps: chemically etching bismuth vanadate to obtain a bismuth vanadate precursor with oxygen vacancies on its surface; mixing a Bacillus-bound extracellular polymeric material with a silver ion solution and performing a reduction reaction to obtain elemental silver; the reduction reaction is carried out at a temperature of 25-40°C for 48-72 hours; the elemental silver and the bismuth vanadate precursor are mixed and annealed to obtain the silver-supported bismuth vanadate composite material. Compared with existing methods for reducing silver ions in wastewater, this invention utilizes a Bacillus-bound extracellular polymeric material to reduce silver ions to obtain silver nanoparticles, which serve as a co-catalyst to modify the bismuth vanadate photoanode, and has the following advantages in photoelectrochemical water splitting under natural light conditions: 1) Bacillus is readily available and easy to cultivate, and Bacillus-bound extracellular polymers are easily extracted. 2) Using Bacillus-bound extracellular polymers to directly reduce silver ions in wastewater to silver nanoparticles achieves green recycling of precious metal resources, with advantages of bioreduction, low energy consumption, and no pollution, combining the dual benefits of precious metal recycling and pollution reduction. 3) The surface of the elemental silver nanoparticles bioreduced by Bacillus is coated with a layer of natural organic matter, and the CO groups of amino acid residues help improve the dispersibility and chemical stability of elemental silver. Specifically, the CO groups of amino acid residues can interact with the Ov vacancies on bismuth vanadate to form VOC bonds, thereby enhancing the interfacial bonding ability between elemental silver and bismuth vanadate. The results of the embodiments of this invention show that the silver-supported bismuth vanadate composite material has excellent catalytic activity and stability. Compared with other composite bismuth-based photoanodes prepared by inorganic methods, the photoanode modified with microbially reduced silver nanoparticles exhibits a higher OER (current density of 6.92 mA cm⁻¹ at 1.23 V vs. RHE) under simulated sunlight. -2 It exhibits superior performance compared to most bismuth-based composite photoanodes synthesized by inorganic methods, and also demonstrates good stability (at 1.23V vs. RHE for 25 hours).

[0016] Meanwhile, this invention enables the direct preparation of high-performance photocatalytic materials from wastewater, which has multiple advantages such as resource recycling, environmental pollution reduction and efficient energy conversion, opening up new ideas for the preparation of green and efficient photoanodes. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1This is a flowchart illustrating the preparation process of the silver-supported bismuth vanadate composite material (Ov-BiVO4 / bio-Ag) of the present invention. Figure 2 This is a scanning electron microscope image of the surface of the Ov-BiVO4 / bio-Ag photoanode prepared in Example 5 of the present invention; Figure 3 The ultraviolet spectrum of bio-Ag nanoparticles prepared in Example 1 of this invention; Figure 4 Raman spectra of Ov-BiVO4 / bio-Ag, BiVO4, and Ov-BiVO4 prepared in Example 1; Figure 5 LSV curves of OER for Ov-BiVO4 / bio-Ag, BiVO4 and Ov-BiVO4 prepared in Examples 1-6 under simulated natural light and 1.0 M potassium borate solution; Figure 6 The LSV curves of OER for Ov-BiVO4 / bio-Ag, Ov-BiVO4 / Ag-1, and Ov-BiVO4 / Ag-2 prepared in Example 5 and Comparative Examples 1-2, respectively, under simulated natural light and in 1.0 M potassium borate solution are shown. Figure 7 Photoelectric conversion efficiency of Ov-BiVO4 / bio-Ag, BiVO4 and Ov-BiVO4 prepared in Example 1 under simulated natural light irradiation; Figure 8 EIS curves of OER of Ov-BiVO4 / bio-Ag, BiVO4 and Ov-BiVO4 prepared in Example 1 in 1.0M potassium borate solution; Figure 9 The results of the OER stability test of Ov-BiVO4 / bio-Ag prepared in Example 1 under simulated natural light and 1.0 M potassium borate solution; Figure 10 The surface scanning electron microscope image of Ov-BiVO4 / bio-Ag prepared in Example 1 after OER stability testing under simulated natural light and 1.0 M potassium borate solution. Detailed Implementation

[0019] This invention provides a method for preparing a silver-supported bismuth vanadate composite material, comprising the following steps: Bismuth vanadate was chemically etched to obtain a bismuth vanadate precursor with oxygen vacancies on its surface. The binding extracellular polymer of Bacillus was mixed with a silver ion solution and a reduction reaction was carried out to obtain elemental silver; the reduction reaction was carried out at a temperature of 25~40℃ for 48~72h. The elemental silver and bismuth vanadate precursor were mixed and annealed to obtain a silver-supported bismuth vanadate composite material.

[0020] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0021] This invention involves chemically etching bismuth vanadate to obtain a bismuth vanadate precursor (Ov-BiVO4) with oxygen vacancies on its surface. The preparation method of bismuth vanadate described in this invention includes the following steps: A BiOI film was obtained on the surface of a conductive substrate by electrodeposition in a bismuth deposition solution. A vanadium solution was coated onto the surface of the BiOI film, and after calcination, bismuth vanadate was obtained on the surface of a conductive substrate.

[0022] In this invention, the conductive substrate can be FTO glass; the bismuth deposition solution includes a soluble bismuth source, a soluble iodine source, p-benzoquinone, and ethanol; the soluble bismuth source can be bismuth nitrate, hydrochloride, or sulfate, and in a specific embodiment, it can be Bi(NO3)3·5H2O; the soluble iodine source is potassium iodide; the pH value of the bismuth deposition solution is 1.7~2.0; the mass ratio of the soluble bismuth source to the soluble iodine source in the bismuth deposition solution is 1:3~5, and in a specific embodiment, it can be 1:4.5.

[0023] In this invention, the electrodeposition potential is 0.1~0.5V, and in specific embodiments it can be 0.2 or 0.3V; the deposition time is 5~10 min, and in specific embodiments it can be 7 or 9 min. This invention electrodeposits on Bi-containing substrates... 3+ I - The process is carried out in an electrolyte solution containing p-benzoquinone, where p-benzoquinone acts as an electron shuttle to indirectly reduce Bi. 3+ A BiOI precursor film is formed by electrodeposition on the surface of a conductive substrate, and the reaction formula is: BiO + +I - +2e - →BiOI.

[0024] In this invention, the vanadium solution comprises a soluble vanadium source and dimethyl sulfoxide; the soluble vanadium source may be vanadium acetylacetonate; the concentration of the soluble vanadium source in the vanadium solution is 0.5~1.0 mmol / L, and in a specific embodiment it may be 0.053 g / mL.

[0025] In this invention, the calcination temperature is 450~500℃, and in specific embodiments it can be 470 or 480℃; the holding time is 1~3h. After calcination, the obtained substrate is washed with alkali, water, and dried; the reagent used for alkali washing is a 0.5mol / L NaOH solution, and there are no special limitations on the drying process. This invention removes excess V2O5 formed on the surface through alkali washing and water washing. During the calcination process, BiOI undergoes a solid-phase reaction with vanadium oxide, and iodine volatilizes in the form of I2, transforming into monoclinic BiVO4.

[0026] In this invention, the chemical etching includes a first etching and a second etching performed sequentially. The etching solution used for the first etching is an alkali metal hydroxide, specifically sodium hydroxide, with a concentration of 0.5~1.0 mol / L. The first etching time is 2~6 min, and the temperature is 25~40℃. The second etching is an electrochemical etching, using borate as the electrolyte, specifically borate buffer, with a concentration of 1~2 mol / L and a pH of 9.0±0.1. The electrochemical etching is performed in a three-electrode cell, with bismuth vanadate as the working electrode, Pt as the counter electrode, and Ag / AgCl as the reference electrode. The electrochemical etching potential is 0.5~1.0 V, and the time is 7~13 min, which can be 8, 9, 10, or 11 min in specific embodiments. By controlling the time of the first and second etching, this invention can effectively control the concentration of oxygen vacancies on the surface of the bismuth vanadate photoanode. EPR measurements of oxygen vacancy concentration revealed that increased oxygen vacancy concentration can improve the performance of the photoanode, but excessive etching may cause bismuth vanadate to dissolve, which in turn reduces the photocurrent density of the material.

[0027] In this invention, the method for preparing the Bacillus-bound extracellular polymer includes the following steps: periodically culturing Bacillus to obtain the Bacillus-bound extracellular polymer; In this invention, the cultivation period of the Bacillus is 1-5 days; the cultivation temperature is 37°C; the culture medium is Luria-Bertani liquid medium (LB liquid medium); and the culture medium volume is 100 mL / bottle.

[0028] In a specific embodiment of the present invention, the preparation method of LB liquid culture medium includes the following steps: LB liquid medium was prepared by dissolving 10 g / L tryptone, 5 g / L yeast extract, and 10 g / L sodium chloride in deionized water and then sterilizing it at high temperature. In this example, the specific dosage was 10 g tryptone, 5 g yeast extract, and 10 g sodium chloride in 1000 mL of deionized water, followed by high-temperature sterilization.

[0029] In a specific embodiment of the present invention, the periodic cultivation of Bacillus includes the following steps: Bacillus hainese was cultured in a mixture of LB liquid medium at 37°C and 180 rpm for 1 day. The cultured Bacillus hainese was then centrifuged at 4500 rpm for 15 min to obtain solid bacterial cells. The cells were washed with 0.9 wt% NaCl to remove the culture medium. 40 mL of 2 mmol / L Na₂EDTA solution was added to the resulting cells, and the mixture was incubated at 4°C for 4 h. After incubation, the cells were centrifuged at 4500 rpm for 10 min, and the supernatant was collected. The bacteria were washed with sterile ultrapure water, and the supernatant was collected to obtain the Bacillus hainese conjugated extracellular polymeric substance.

[0030] After obtaining the Bacillus-bound extracellular polymeric substance, this invention mixes the Bacillus-bound extracellular polymeric substance with a silver ion solution and performs a reduction reaction to obtain elemental silver (bio-Ag). In this invention, the reduction reaction temperature is 25~40℃, and in specific embodiments it can be 30 or 35℃, and the time is 48~72h, and in specific embodiments it can be 50 or 60h; Ag in the silver ion solution... + The concentration of the silver ion solution is 10-20 g / L, and the volume of the bound extracellular polymer is 100-200 mL. After the reduction reaction is completed, the resulting system is centrifuged at a frequency of 6000-8000 rpm for 10-15 min.

[0031] This invention involves mixing elemental silver and a bismuth vanadate precursor, followed by annealing to obtain a silver-supported bismuth vanadate composite material. Specifically, mixing the elemental silver and bismuth vanadate precursor involves coating the surface of the bismuth vanadate precursor with an elemental silver solution, drying, and then annealing. The concentration of the elemental silver solution is 4-5 μg / mL, and in specific embodiments, it can be 4.05, 4.3, 4.5, or 4.7 μg / mL. Drying is performed in air; annealing is performed in a reducing atmosphere, which can be N2; the annealing temperature is 100-120°C, and in specific embodiments, it can be 110 or 115°C; the annealing time is 0.5-3 h, and in specific embodiments, it can be 1 or 1.5 h; the heating rate from room temperature to the required annealing temperature is 1-5°C / min, and in specific embodiments, it can be 2 or 3°C / min. The annealing process of this invention mainly involves the reducing pyrolytic carbonization of the bound extracellular polymers remaining on the surface of elemental silver, and the directional anchoring of elemental silver nanoparticles on oxygen vacancies on the surface of bismuth vanadate. Furthermore, this invention utilizes a reducing atmosphere to prevent silver from oxidizing to silver oxide and to inhibit the filling of oxygen vacancies by oxygen.

[0032] The present invention also provides a silver-supported bismuth vanadate composite material prepared by the preparation method described above, comprising bismuth vanadate and elemental silver nanoparticles supported on the surface of the bismuth vanadate; the surface of the bismuth vanadate contains Ov vacancies; the surface of the elemental silver nanoparticles contains CO groups of amino acid residues; the Ov vacancies and CO groups are VOC bonds.

[0033] In this invention, the particle size of the elemental silver nanoparticles is 10~20nm, and in specific embodiments it can be 10.5, 11.9, 12.6, 13.5, 15.7, 17.0 or 18.9nm.

[0034] This invention also provides the application of the silver-supported bismuth vanadate composite material described above in photoelectrocatalytic water splitting.

[0035] In this invention, the photoelectrocatalytic water splitting is performed using a three-electrode system. The silver-supported bismuth vanadate composite material (Ov-BiVO4 / bio-Ag) described above serves as the working electrode, a platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. The exposed area of ​​the silver-supported bismuth vanadate composite material is 1.00~3 cm². 2 .

[0036] The photoelectrocatalytic water splitting process of this invention consists of two steps: the photoanode (working electrode) absorbs visible light to generate electron-hole pairs; the electrons are transferred to the cathode to carry out the hydrogen evolution reaction, and the holes oxidize water on the surface of the photoanode to generate oxygen.

[0037] To further illustrate the present invention, the silver-supported bismuth vanadate composite material, its preparation method, and its application provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0038] Example 1 according to Figure 1 The flowchart shown illustrates the preparation of silver-supported bismuth vanadate composite materials. The specific steps are as follows: 1) Cultivation of Bacillus haenes-binding extracellular polymers: Activated *Bacillus hainese* was scraped from a sterile 200 μL pipette tip and placed in 100 mL of LB broth. The LB broth was incubated at 37°C and 180 rpm for one day. After the *Bacillus hainese* culture was complete, it was transferred to a sterile 50 mL centrifuge tube and centrifuged at 4500 rpm for 15 min to collect the bacterial cells. The cells were then washed three times with 0.9 wt% NaCl (to maintain bacterial integrity) to remove the culture medium. 40 mL of 2 mmol / L Na₂EDTA solution was added to the cells, mixed thoroughly to ensure complete dispersion, and then incubated at 4°C for 4 h. After incubation, the cells were centrifuged at 4500 rpm for 10 min, the supernatant was collected, and the bacteria were washed with sterile ultrapure water. All supernatants were collected to obtain the *Bacillus hainese*-bound extracellular polymer.

[0039] 2) Bacillus haenes-binding extracellular polymeric reduced silver nanoparticles: Add 10 g / L Ag to 100 mL of the above-mentioned Bacillus hainanensis conjugated extracellular polymeric polymer solution. + The solution was left at room temperature for 3 days, and the entire reaction system turned reddish-brown, yielding elemental silver nanoparticles. The reactants were removed, and the UV absorption peaks of the reaction solution in the range of 200–800 nm were recorded using a UV-Vis spectrophotometer. The resulting reaction solution was centrifuged at 8000 rpm for 10 min, the precipitate was collected, washed twice with ultrapure water, and 10 mL of ultrapure water was added to obtain a bio-Ag solution for later use.

[0040] 3) Preparation of bismuth vanadate photoanodes by electrodeposition and calcination: BiOI was first electrodeposited onto FTO glass using a three-electrode system. The counter electrode was a platinum wire electrode, the working electrode was a photoanode, and the reference electrode was an Ag / AgCl electrode. The deposition solution consisted of two components, A and B. Component A: 0.9071 g of Bi(NO3)3·5H2O was dissolved in 50 mL of 0.4 mol / L KI aqueous solution, and the pH was adjusted to 1.7 with dilute HNO3. Component B: 0.4973 g of p-benzoquinone was added to 20 mL of anhydrous ethanol. The two components A and B were mixed and stirred for 40 min to obtain the Bi deposition solution.

[0041] The sample was transferred to an electrochemical cell, immersed in three electrodes, and subjected to a constant potential of -0.1 V for 5 min to deposit nanosheet-like BiOI on the FTO surface, thus obtaining a BiOI film. 0.1060 g of vanadium acetylacetonate was dissolved in 2 mL of dimethyl sulfoxide (DMSO) and sonicated at 20 °C for 20–30 min. 100 μL of the resulting vanadium acetylacetonate solution was uniformly transferred onto the BiOI film, and the temperature was increased to 450 °C at a heating rate of 1 °C / min. The film was then calcined in a muffle furnace at 450 °C for 2 h to obtain BiVO4.

[0042] 4) Preparation of BiVO4 photoanodes with oxygen vacancies on their surface: The calcined BiVO4 film from step 3) was immersed in a 0.5 mol / L NaOH solution for 2 min to partially remove surface V2O5, followed by electrochemical etching to eliminate residual V2O5. Electrochemical etching was performed in a three-electrode cell with a Pt wire pair electrode, an Ag / AgCl reference electrode, and a BiVO4 working electrode. The electrolyte was a 1 mol / L borate buffer solution, and the pH was adjusted to 9.0 ± 0.1 using KOH. A constant potential of 0.5 V and RHE was applied to the working electrode for 11 min, followed by rinsing with deionized water. The resulting Ov-BiVO4 film was dried under an airflow to obtain a bismuth vanadate photoanode with oxygen vacancies on its surface.

[0043] 5) Silver nanoparticle-supported bismuth vanadate composite photoanode: Take 40 μL of the bio-Ag solution obtained in step 2) and uniformly drop it onto the surface of the Ov-BiVO4 photoanode in step 4). Dry it in air at 60°C for 30 min. Then place the resulting film in a tube furnace and heat it to 120°C in N2 at a heating rate of 2°C / min. Hold it for annealing for 1 h to obtain a silver-supported bismuth vanadate composite photoanode, denoted as Ov-BiVO4 / bio-Ag photoanode.

[0044] Example 2 The Ov-BiVO4 / bio-Ag photoanode was prepared according to the method described in Example 1, except that in step 5), 10 μL of the bio-Ag solution obtained in step 2) was taken.

[0045] Example 3 The Ov-BiVO4 / bio-Ag photoanode was prepared according to the method described in Example 1, except that in step 5), 20 μL of the bio-Ag solution obtained in step 2) was taken.

[0046] Example 4 The Ov-BiVO4 / bio-Ag photoanode was prepared according to the method described in Example 1, except that in step 5), 30 μL of the bio-Ag solution obtained in step 2) was taken.

[0047] Example 5 The Ov-BiVO4 / bio-Ag photoanode was prepared according to the method described in Example 1, except that in step 5), 45 μL of the bio-Ag solution obtained in step 2) was taken.

[0048] Example 6 The Ov-BiVO4 / bio-Ag photoanode was prepared according to the method described in Example 1, except that in step 5), 80 μL of the bio-Ag solution obtained in step 2) was taken.

[0049] Comparative Example 1 The Ov-BiVO4 / bio-Ag photoanode was prepared according to the method described in Example 1, with the only difference being that the preparation method of the bio-Ag solution was as follows: Silver nitrate (13 mM) and polyvinylpyrrolidone (50 mM) were dissolved in 18 mL of N-N-dimethylformamide and reduced in an oil bath at 140 °C for 10 h. The resulting solution was centrifuged at 4500 rpm for 10 min, the precipitate was collected, and washed three times with deionized water to obtain silver nanoparticles. The obtained silver nanoparticles were dispersed in ethanol for later use. Quantification was performed using ultraviolet light to ensure that the absorbance of the silver / ethanol dispersion at 400 nm was 2.13 A.

[0050] Comparative Example 2 The Ov-BiVO4 / bio-Ag photoanode was prepared according to the method described in Example 1, with the only difference being that the preparation method of the bio-Ag solution was as follows: 30 mL of 0.1 M sodium borohydride was stirred in an ice bath for 20 min. Then, 2 mL of 0.05 M silver nitrate was added dropwise to the solution, and the mixture was stirred for 20 min. The resulting solution was centrifuged at 4500 rpm for 10 min, the precipitate was collected, and washed three times with deionized water to obtain silver nanoparticles. The obtained silver nanoparticles were dispersed in ethanol for later use. Quantitative analysis was performed using UV light, ensuring that the absorbance of the silver / ethanol dispersion at 400 nm was 2.13 A.

[0051] Test case A three-electrode system was used, equipped with a CHI 660E electrochemical workstation for electrochemical testing. The Ov-BiVO4 / bio-Ag photoanode obtained in Examples 1-6 was used as the working electrode, platinum wire as the counter electrode, and Ag / AgCl as the reference electrode. A PL-X300 / PL-X300 DUV xenon lamp equipped with an AM 1.5G filter was used to simulate sunlight, and the light intensity at the working electrode was calibrated to 100 mW / cm². 2 The exposed area of ​​the photoanode is 1.00 cm².2 PEC tests were performed using back illumination through the fluorine-doped tin oxide (FTO) side, with 1 mol / L potassium borate buffer (pH=9) as the electrolyte.

[0052] All results in this test case were measured relative to a reversible hydrogen electrode (RHE) to facilitate comparison with the redox potentials of H2 and O2 and other studies using electrolytes under different pH conditions.

[0053] The OER performance of the Ov-BiVO4 / bio-Ag photoanode was evaluated using linear scanning voltammetry. For OER, the voltage was scanned from 0.2V to 1.3V vs. RHE at a scan rate of 20 mV / s. -1 .

[0054] The photoelectric conversion efficiency was measured using a xenon lamp system with a monochromator in the wavelength range of 400–700 nm at 10-minute intervals. The transient photocurrent under illumination and darkness was recorded at each wavelength, and the photoelectric conversion efficiency at each wavelength was calculated to evaluate the photogenerated carrier separation and transport characteristics of the electrode.

[0055] Electrochemical impedance spectroscopy (EIS) is used to evaluate charge transfer resistance, and its value is calibrated to RHE using the Nernst equation. Measurements are performed at AC voltages with a frequency resolution of 1.5 mHz over a frequency range of 0.1–100 kHz, and EIS is measured at 1.23 V (vs. RHE).

[0056] The OER stability of the photoanode was tested at 1.23 V vs. RHE for 25 h, and the results are shown below.

[0057] Figure 2 This is a scanning electron microscope (SEM) image of the surface of the Ov-BiVO4 / bio-Ag photoanode prepared in Example 5 of this invention. Figure 2 The results show that Ov-BiVO4 has a nanorod structure with a characteristic diameter of 200-500 nm. After annealing with bioreduced elemental silver, the morphology of Ov-BiVO4 remains unchanged. It is also noteworthy that a layer of bio-silver nanoparticles is clearly visible on its surface.

[0058] Figure 3 The image shows the ultraviolet spectrum of the bio-Ag nanoparticles prepared in Example 1 of this invention. Figure 3 The results showed that the UV-Vis spectrum of the bioreduced silver nanoparticles exhibited a surface plasmon resonance (SPR) peak at 400 nm, verifying the successful synthesis of the bioreduced silver nanoparticles.

[0059] Figure 4The Raman spectra of Ov-BiVO4 / bio-Ag, BiVO4, and Ov-BiVO4 prepared in Example 1 are shown below; Figure 4 The results show that after silver loading, the VO stretching vibration (VO) of Ov–BiVO4 decreases from 828 cm⁻¹. -1 Displaced to 831cm -1 This indicates that the VO bond is shortened in the Ov–BiVO4 / bio-Ag system, and this shift reflects the effect of biosilver on the VO4 bond. 3- The alteration of local structure and electronic environment enhances the rigidity of VO bonds. These phenomena indicate that bio-silver loading effectively improves the interfacial bonding between the two components by filling surface oxygen vacancies, shortening VO bonds, and altering their electronic structure.

[0060] Figure 5 The LSV curves of OER for Ov-BiVO4 / bio-Ag, BiVO4, and Ov-BiVO4 prepared in Examples 1-6 under simulated natural light and 1.0 M potassium borate solution are shown. Figure 5 The results show that the original BiVO4 only produces 2.04 mA cm⁻¹ at 1.23 V relative to RHE. -2 The photocurrent density was 4.04 mA cm⁻¹, while Ov-BiVO₄ reached 4.04 mA cm⁻¹. -2 This is 1.98 times higher. Notably, Ov-BiVO4 / bio-Ag achieved 6.92 mA cm⁻¹. -2 The photocurrent density of Ov-BiVO4 is far greater than that of BiVO4 and is 3.39 times that of BiVO4.

[0061] Figure 6 The LSV curves of OER for Ov-BiVO4 / bio-Ag, Ov-BiVO4 / Ag-1, and Ov-BiVO4 / Ag-2 prepared in Example 5 and Comparative Examples 1-2, respectively, under simulated natural light and in 1.0 M potassium borate solution are shown. Figure 6 The results showed that the silver nanoparticles prepared by the pure chemical reagent reduction method and loaded on Ov-BiVO4 in Comparative Examples 1 and 2 had a lower photocurrent than those on Ov-BiVO4 / bio-Ag, which confirmed that microbially reduced bio-silver can be more effectively loaded onto oxygen vacancies on the photoanode surface.

[0062] Figure 7 The photoelectric conversion efficiency of Ov-BiVO4 / bio-Ag, BiVO4, and Ov-BiVO4 prepared in Example 1 under simulated natural light irradiation; Figure 7The results show that the Ov-BiVO4 / bio-Ag photoanode achieves an IPCE of 96.5% at a wavelength of 400 nm at 1.23 V relative to the reference potential (RHE), which is significantly better than Ov-BiVO4 (76.2%) and BiVO4 (48.5%), indicating that it has excellent photoelectric conversion performance.

[0063] Figure 8 EIS curves of OER for Ov-BiVO4 / bio-Ag, BiVO4, and Ov-BiVO4 prepared in Example 1 in 1.0 M potassium borate solution; Figure 8 The results show that the bulk resistance of BiVO4 remained essentially unchanged after introducing oxygen vacancies and loading with bio-silver, indicating that this dual modification did not significantly alter the bulk carrier transport characteristics. In contrast, the loading of bio-silver established a close electronic contact with Ov-BiVO4, and the resulting built-in electric field promoted interfacial charge transfer, thereby significantly reducing Rct.

[0064] Figure 9 The results of the OER stability test of Ov-BiVO4 / bio-Ag prepared in Example 1 under simulated natural light and 1.0 M potassium borate solution are as follows; Figure 9 The results showed that after 25 hours of continuous illumination, the photocurrent density decreased by only 12.02%, indicating that it has excellent durability.

[0065] Figure 10 The images show surface scanning electron microscope (SEM) images of Ov-BiVO4 / bio-Ag prepared in Example 1 after OER stability testing under simulated natural light and in 1.0 M potassium borate solution. Images a and c are SEM images of Ov-BiVO4 / bio-Ag before stability testing with scale bars of 2.00 μm and 500 nm, respectively; images b and d are SEM images of Ov-BiVO4 / bio-Ag before stability testing with scale bars of 1.00 μm and 500 nm, respectively. Figure 10 The results showed that no significant morphological changes were found in the SEM analysis 25 hours after the PEC test, further confirming the excellent stability of the photoanode.

[0066] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a silver-supported bismuth vanadate composite material, characterized in that, Includes the following steps: Bismuth vanadate was chemically etched to obtain a bismuth vanadate precursor with oxygen vacancies on its surface. Bacillus-binding extracellular polymeric substances and silver ion solutions were mixed and subjected to a reduction reaction to obtain elemental silver; the reduction reaction was carried out at a temperature of 25-40°C for 48-72 hours. The elemental silver and bismuth vanadate precursor were mixed and annealed to obtain a silver-supported bismuth vanadate composite material.

2. The preparation method according to claim 1, characterized in that, The method for preparing the Bacillus-bound extracellular polymeric polymer includes the following steps: Bacillus was cultured periodically to obtain soluble extracellular polymers of Bacillus. The cultivation period for the Bacillus is 1-5 days; the cultivation temperature is 37℃; the culture medium is Luria-Bertani liquid medium; and the culture medium volume is 100mL / bottle.

3. The preparation method according to claim 1, characterized in that, The method for preparing bismuth vanadate includes the following steps: A BiOI film was obtained on the surface of a conductive substrate by electrodeposition in a bismuth deposition solution. A vanadium solution was coated onto the surface of the BiOI film, and after calcination, bismuth vanadate was obtained on the surface of a conductive substrate.

4. The preparation method according to claim 3, characterized in that, The bismuth deposition solution comprises a soluble bismuth source, a soluble iodine source, p-benzoquinone, and ethanol; the pH value of the bismuth deposition solution is 1.7~2.0; The vanadium solution is a soluble vanadium source and dimethyl sulfoxide.

5. The preparation method according to claim 3, characterized in that, The electrodeposition potential is 0.1~0.5V, and the deposition time is 5~10min; The roasting temperature is 450~500℃, and the holding time is 1~3h.

6. The preparation method according to claim 1, characterized in that, The chemical etching includes a first etching and a second etching performed sequentially. The etching solution used for the first etching is an alkali metal hydroxide; The second etching is an electrochemical etching, and the electrolyte is a borate.

7. The preparation method according to claim 1, characterized in that, The calcination temperature is 100~120℃, and the calcination is carried out in a reducing atmosphere.

8. The silver-supported bismuth vanadate composite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that, Includes bismuth vanadate and elemental silver nanoparticles supported on the surface of the bismuth vanadate; The surface of the bismuth vanadate contains Ov vacancies. The surface of the elemental silver nanoparticles contains CO groups of amino acid residues; The Ov vacancy and CO group are bonded by VOC bonds.

9. The silver-supported bismuth vanadate composite material according to claim 8, characterized in that, The particle size of the elemental silver nanoparticles is 10~20 nm.

10. The application of the silver-supported bismuth vanadate composite material according to claim 8 or 9 in photoelectrocatalytic water splitting.

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