Bi2O2S / N-BiVO4 photo-anode as well as preparation method and application thereof

Abstract

The invention relates to the technical field of preparation of photoelectric catalytic materials, in particular to a Bi2O2S / N-BiVO4 photo-anode as well as a preparation method and application of the Bi2O2S / N-BiVO4 photo-anode. Comprising the following steps: (1) preparing Bi2O2S; (2) preparation of BiVO4; (3) preparation of N-BiVO4: placing the BiVO4 photo-anode prepared in the step (2) in an ammonia gas protection atmosphere, and carrying out calcination treatment; (4) preparation of a Bi2O2S / N-BiVO4 photo-anode: dropwise adding an ethanol solution of Bi2O2S to the surface of the N-BiVO4 prepared in the step (3), carrying out spin coating on the N-BiVO4 loaded with the solution, and then carrying out heat treatment on the electrode to prepare the Bi2O2S / N-BiVO4 photo-anode; in an experiment of photoelectrocatalytic degradation of methyl orange, the Bi2O2S / N-BiVO4 photo-anode disclosed by the invention shows an efficient degradation rate of 99.62%.

Description

Technical Field

[0001] This invention relates to the field of photoelectrocatalytic material preparation technology, specifically to a Bi2O2S / N-BiVO4 photoanode and its preparation method and application. Background Technology

[0002] With the rapid development of my country's economy, water pollution has become increasingly serious, posing a significant threat to human and animal health. Advanced oxidation processes (AOPs) have attracted considerable attention due to their high efficiency in degrading recalcitrant pollutants. AOPs generate strong oxidizing agents, such as hydroxyl radicals and superoxide radicals, to completely oxidize pollutants into CO2 and water. Among these, photoelectrocatalysis shows broad application prospects due to its high efficiency and environmental friendliness. This method combines the advantages of electrochemical catalysis and photocatalysis, effectively separating electrons and holes within a semiconductor through an applied electric field, improving quantum efficiency, while avoiding the re-reduction of oxidation intermediates and eliminating the need for additional electron trapping agents. Numerous studies have demonstrated the significant effectiveness of photoelectrocatalysis in treating recalcitrant pollutants.

[0003] Despite the numerous advantages of photoelectrochemical degradation technology, further improving the light absorption efficiency and photogenerated carrier separation efficiency of photoelectrode materials remains a key challenge in enhancing the efficiency of photoelectrochemical synergistic catalysis in practical applications. BiVO4, as a material with excellent light absorption performance, high photogenerated electron-hole pair separation efficiency, good stability, and non-toxicity, has shown significant advantages in photoelectrochemical synergistic catalysis. To further improve the photoelectrochemical performance of BiVO4, researchers have employed various modification methods, such as noble metal deposition, ion doping, and semiconductor composites. These methods can optimize the crystal structure of BiVO4, improve its light absorption and photogenerated carrier separation efficiency, thereby achieving more efficient degradation of pollutants. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a Bi2O2S / N-BiVO4 photoanode, its preparation method and application, promoting the application and development of photoelectrocatalysis technology in the fields of energy conversion and environmental pollution control.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing a Bi2O2S / N-BiVO4 photoanode, comprising the following steps: (1) Preparation of Bi2O2S Bi(NO3)3·5H2O, CH4N2S and LiOH·H2O were added sequentially to an aqueous solution of hexadecyltrimethylammonium bromide and stirred to obtain a mixture. The mixture was then reacted in a high-pressure reactor lined with polytetrafluoroethylene. The reaction product was repeatedly washed with deionized water and ethanol and dried under vacuum to obtain Bi2O2S powder. (2) Preparation of BiVO4 A DMSO solution containing VO(acac)2 was uniformly drop-coated onto the surface of a dry BiOI electrode, and the electrode was placed in a muffle furnace for calcination. After the electrode cooled naturally to room temperature, it was immersed in NaOH solution for 30 minutes, then rinsed with distilled water and dried to obtain BiVO4. (3) Preparation of N-BiVO4 The BiVO4 prepared in step (2) was placed in an ammonia protective atmosphere and calcined to obtain N-BiVO4; (4) Preparation of Bi2O2S / N-BiVO4 photoanode Bi2O2S powder was dissolved in anhydrous ethanol to obtain an ethanol solution of Bi2O2S. The ethanol solution of Bi2O2S was then dropped onto the surface of N-BiVO4 obtained in step (3). The N-BiVO4 loaded with the solution was then spin-coated. After spin-coating, heat treatment was performed to obtain a Bi2O2S / N-BiVO4 photoanode.

[0006] As a further limitation of the technical solution of the present invention, the mass-volume ratio of hexadecyltrimethylammonium bromide to water in step (1) is 6g:875mL; the mass ratio of hexadecyltrimethylammonium bromide, Bi(NO3)3·5H2O, CH4N2S and LiOH·H2O is 1600:776:61:9600.

[0007] As a further limitation of the technical solution of the present invention, the reaction temperature of the high-pressure reactor in step (1) is 200°C and the reaction time is 2 hours.

[0008] As a further limitation of the technical solution of the present invention, the preparation method of the BiOI electrode in step (2) includes the following steps: S1. Preparation of electrolyte KI was dissolved in distilled water, the pH was adjusted to 1.7 with HNO3 solution, and Bi(NO3)3·5H2O was added to the solution. The mixture was stirred vigorously until it was completely dissolved to obtain a mixture. Then the mixture was thoroughly mixed with anhydrous ethanol solution containing p-benzoquinone to obtain the electrolyte. S2. Electrodeposition preparation of BiOI electrode Electrodeposition was performed using a typical three-electrode system. A 1.0 cm × 2.0 cm FTO conductive glass was used as the working electrode, a platinum electrode as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode. The mixed solution prepared in S1 was used as the electrolyte. Deposition was performed for 4 minutes at a constant voltage of -0.1 V vs. Ag / AgCl. After deposition, the resulting BiOI electrode was rinsed with deionized water.

[0009] As a further limitation of the technical solution of the present invention, in step S1, the mass-to-volume ratio of KI to distilled water is 83g:1250mL, the concentration of the anhydrous ethanol solution containing p-benzoquinone is 0.23M, and the volume ratio of the mixture to the anhydrous ethanol solution containing p-benzoquinone is 5:2.

[0010] As a further limitation of the technical solution of the present invention, the concentration of the DMSO solution containing VO(acac)2 in step (2) is 0.2M; the electrode is placed in a muffle furnace and calcined at a temperature of 450°C for 2 hours.

[0011] As a further limitation of the technical solution of the present invention, the calcination temperature in step (3) is 400°C and the calcination time is 1 hour.

[0012] As a further limitation of the technical solution of the present invention, the concentration of the ethanol solution of Bi2O2S in step (4) is 0.04 g / mL; during spin coating, first spin coating at a low speed of 500 rpm for 10 seconds, and then increase the speed to 1500 rpm for 50 seconds; the temperature of electrode heat treatment is 250℃ and the time is 30 minutes.

[0013] The present invention also provides a Bi2O2S / N-BiVO4 photoanode prepared by the above preparation method.

[0014] In addition, the present invention also provides the application of the Bi2O2S / N-BiVO4 photoanode prepared by the above preparation method in the photoelectrocatalytic degradation of pollutants.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention uses BiVO4 as the anode material and modifies it by treating it in an ammonia atmosphere and forming an S-type heterojunction with a Bi2O2S semiconductor, thereby conducting in-depth research on its photoelectrocatalytic performance. Under simulated sunlight irradiation, the Bi2O2S / N-BiVO4 photoanode exhibited a photocurrent density of 5.39 mA / cm² at 1.23 V vs. RHE, approximately 1.35 times that of BiVO4 (4.01 mA / cm²). In experiments on the photoelectrocatalytic degradation of methyl orange, the Bi2O2S / N-BiVO4 photoanode of this invention demonstrated a high degradation rate of 99.62%. This invention provides new ideas and methods for the modification of BiVO4-based composite photoanodes, promoting the application and development of photoelectrocatalysis technology in the fields of energy conversion and environmental pollution control. Attached Figure Description

[0016] Figure 1 The image shows the XRD patterns of Bi2O2S prepared for different hydrothermal times in Example 1.

[0017] Figure 2 The images show the XRD patterns of the samples obtained in Examples 1-4.

[0018] Figure 3 SEM images of the samples prepared in Examples 1-4; (where a is the sample prepared in Example 2, b is the sample prepared in Example 1, c is the sample prepared in Example 3, and d is the sample prepared in Example 4).

[0019] Figure 4 The images shown are TEM and HRTEM images of the Bi2O2S / N-BiVO4 photoanode prepared in Example 4.

[0020] Figure 5 The image shows the Bi 4f spectrum of the Bi2O2S / N-BiVO4 photoanode prepared in Example 4.

[0021] Figure 6 The image shows the V 2p spectrum of the Bi2O2S / N-BiVO4 photoanode prepared in Example 4.

[0022] Figure 7 The image shows the O 1s spectrum of the Bi2O2S / N-BiVO4 photoanode prepared in Example 4.

[0023] Figure 8 The S 2s spectrum of the Bi2O2S / N-BiVO4 photoanode prepared in Example 4 is shown.

[0024] Figure 9 The N 1s spectrum of the Bi2O2S / N-BiVO4 photoanode prepared in Example 4 is shown.

[0025] Figure 10 The LSV curves are for the samples obtained in Examples 2-4.

[0026] Figure 11 The ABPE curves are for the samples obtained in Examples 2-4.

[0027] Figure 12 The image shows the EIS curves of the samples obtained in Examples 2-4.

[0028] Figure 13 The LSV curves of the samples obtained in Examples 2-4 in the presence of Na2SO3 are shown.

[0029] Figure 14 The diagram shows the charge injection efficiency of the samples prepared in Examples 2-4.

[0030] Figure 15 The diagram shows the charge separation efficiency of the samples prepared in Examples 2-4.

[0031] Figure 16 The graph shows the effect of different Bi2O2S layer numbers on the photoelectrode degradation performance of the photoanode in Examples 4 and 5.

[0032] Figure 17 The images show the photoelectric degradation test results of the samples obtained in Examples 2-4.

[0033] Figure 18 The images show the Bi2O2S / N-BiVO4 photoanode prepared in Example 4 under electrocatalysis, photocatalysis, and photoelectrocatalysis.

[0034] Figure 19 The image shows the photoelectric degradation free radical scavenging test results of the Bi2O2S / N-BiVO4 photoanode prepared in Example 4.

[0035] Figure 20 The images show the UV-Vis diffuse reflectance spectra of the samples prepared in Examples 1-4.

[0036] Figure 21 This is a bandgap diagram of the samples obtained in Examples 1-4.

[0037] Figure 22 MS test images of the samples obtained in Examples 2-4.

[0038] Figure 23 MS test results for Bi2O2S (hydrothermal reaction time 2h).

[0039] Figure 24 This is a diagram illustrating the photoelectrocatalytic mechanism of the Bi2O2S / N-BiVO4 photoanode in Example 4. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments.

[0041] Example 1 Preparation of Bi2O2S 0.48 g of hexadecyltrimethylammonium bromide (CTAB) was dissolved in 70 mL of deionized water and sonicated to form a transparent solution. 0.2328 g of Bi(NO3)3·5H2O was added to this solution under continuous vigorous stirring for 30 min. Subsequently, 0.0183 g of CH4N2S was added, and stirring continued for several tens of minutes. Immediately afterwards, 2.88 g of LiOH·H2O was added, and the mixture was stirred for 60 min. The mixture was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and subjected to hydrothermal reactions at 200 °C for different durations (2 h, 4 h, 8 h, 12 h, 16 h). After the reaction, the product was repeatedly washed with deionized water and ethanol, and then vacuum dried at 60 °C to obtain Bi2O2S powder.

[0042] Example 2 Preparation of BiVO4 First, 3.32 g KI was dissolved in 50 mL of distilled water, and the pH was adjusted to 1.7 with 1 M HNO3 solution. Then, 0.970 g Bi(NO3)3·5H2O was added to this solution, and the mixture was stirred vigorously for 15 minutes until completely dissolved. Next, this solution was thoroughly mixed with 20 mL of anhydrous ethanol solution containing 0.23 M p-benzoquinone. Electrodeposition was performed using a typical three-electrode system, with a 1.0 cm × 2.0 cm FTO conductive glass as the working electrode, a platinum electrode as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode. Using the above mixed solution as the electrolyte, deposition was performed at a constant voltage of -0.1 V vs. Ag / AgCl for 4 minutes. After deposition, the resulting BiOI electrode was rinsed with deionized water. Subsequently, 100 μL of DMSO solution containing 0.2 M VO(acac)2 was uniformly drop-coated onto the dried BiOI electrode surface. The electrode was placed in a muffle furnace and calcined at 450°C for 2 hours. After the electrode cooled naturally to room temperature, it was immersed in 1M NaOH solution for 30 minutes to remove residual V₂O₅. Finally, the electrode was rinsed three times with distilled water and dried in ambient air to obtain BiVO₄.

[0043] Example 3 Preparation of N-BiVO4 The BiVO4 prepared in Example 2 was placed in an ammonia protective atmosphere at 400°C and calcined for 1 hour to obtain N-BiVO4.

[0044] Example 4 Preparation of Bi2O2S / N-BiVO4 photoanode The Bi₂O₂S powder prepared in Example 1 (hydrothermal reaction time 2 h) was dissolved in anhydrous ethanol to prepare a Bi₂O₂S solution with a concentration of 0.04 g / mL. Then, 0.1 mL of this solution was pipetted onto the pre-prepared N-BiVO₄ surface. The electrode loaded with the solution was placed on a spin coater and initially spin-coated at 500 rpm for 10 seconds to allow the solution to spread initially; then the speed was increased to 1500 rpm for 50 seconds to obtain a uniform and smooth film. Ten layers were spin-coated. After spin-coating, the electrode was heat-treated at 250 °C for 30 min to finally obtain the Bi₂O₂S / N-BiVO₄ photoanode.

[0045] Example 5 Preparation of Bi2O2S / N-BiVO4 photoanodes with different numbers of Bi2O2S layers The preparation method is the same as in Example 4, except that the number of Bi2O2S layers is 5 and 15, respectively.

[0046] The products prepared in Examples 1-4 were analyzed as follows: I. Characterization Analysis The crystal structure of the sample was systematically characterized using X-ray diffraction (XRD). For example... Figure 1 As shown, Bi₂O₂S samples prepared with different hydrothermal reaction times all exhibited a series of characteristic diffraction peaks. The positions of all diffraction peaks were completely consistent with the standard card (JCPDS No. 34-1493) of orthorhombic Bi₂O₂S, and no diffraction signals of other impurity phases were detected. This result confirms that the prepared sample is pure phase Bi₂O₂S, and also indicates that when the hydrothermal reaction time is 2 h, the Bi₂O₂S crystal has formed a complete crystal lattice structure.

[0047] Figure 2 The XRD patterns showed that the diffraction peaks of the BiVO4 and N-BiVO4 samples were completely matched with the characteristic peaks of the standard card (JCPDS No. 14-0688) of the monoclinic scheelite structure BiVO4, indicating that the prepared BiVO4 has a pure phase monoclinic scheelite structure and good crystallinity. For the Bi2O2S / N-BiVO4 photoanode, in addition to the characteristic diffraction peaks of monoclinic BiVO4, new characteristic diffraction peaks were also detected at 24.20°, 27.43°, 29.88°, 32.28°, 32.81°, 45.47° and 47.19°. These peaks correspond to the (110), (120), (040), (130), (101), (141) and (002) crystal planes of orthorhombic Bi2O2S (JCPDS No. 34-1493), respectively, which strongly confirms that Bi2O2S was successfully loaded on the N-BiVO4 surface and formed a composite structure.

[0048] The microstructure of the samples was observed using scanning electron microscopy (SEM). Figure 3 As shown in a and 3c, both BiVO4 and N-BiVO4 exhibit typical worm-like porous network structures. This loose three-dimensional channel structure facilitates multiple reflections and scatterings of photons within the material, thereby effectively enhancing the light-harvesting capability of the electrode. Figure 3 b. Cubic Bi₂O₂S particles (hydrothermal reaction time 2 hours) were found to exhibit a regular geometric morphology and a complete surface structure. Further observation of the morphology of the Bi₂O₂S / N-BiVO₄ photoanode revealed ( Figure 3 d) Bulk Bi2O2S is loaded on the surface of N-BiVO4, and the two form a closely contacted heterojunction structure. This morphological feature is conducive to promoting the effective transfer of interfacial charges.

[0049] To further investigate the microstructure and crystal characteristics of the Bi2O2S / N-BiVO4 photoanode, transmission electron microscopy (TEM) analysis was performed. Figure 4Results a and 4b indicate that a tight interfacial contact is formed between Bi₂O₂S and N-BiVO₄, and this heterojunction structure helps to improve the carrier transport efficiency in the composite system. Clear lattice fringes were observed in the high-resolution TEM (HRTEM) images, with interplanar spacings of 0.31 nm and 0.298 nm, corresponding to the (-121) plane of monoclinic BiVO₄ and the (040) plane of orthorhombic Bi₂O₂S, respectively, further confirming the coexistence of the BiVO₄ and Bi₂O₂S phases. Furthermore, EDS elemental mapping analysis showed that ( Figure 4 (cg) The elements Bi, O, V, N, and S are uniformly distributed in the Bi2O2S / N-BiVO4 photoanode.

[0050] The surface chemical composition of the Bi₂O₂S / N-BiVO₄ photoanode was analyzed using X-ray photoelectron spectroscopy (XPS). The Bi₄f spectra of the Bi₂O₂S / N-BiVO₄ samples show (…). Figure 5 ), Bi 4f 3 / 2 and Bi 4f 1 / 2 The binding energies of the peaks are located at 158.3 eV and 163.6 eV, respectively, indicating that Bi is bound in the form of Bi. 3+ Valence state exists. In the V 2p spectrum ( Figure 6 The characteristic peaks at 524.2 eV and 516.7 eV can be attributed to V 2p, respectively. 1 / 2 and V 2p 3 / 2 The binding energy. O 1s spectrum ( Figure 7 After peak fitting, three characteristic peaks appeared at 529.8 eV, 531.3 eV, and 533.0 eV: the main peak at 529.8 eV is attributed to lattice oxygen, while the peaks at 531.3 eV and 533.0 eV correspond to surface hydroxyl / hydrogen-containing groups and adsorbed water species, respectively. Furthermore, the S 2s spectrum ( Figure 8 The characteristic peak observed at 224.3 eV confirms the presence of S in Bi2O2S. 2- The existence of species. Figure 9 The N 1s spectrum shows that element N can be detected, indicating that N has been successfully doped into BiVO4. The above XPS analysis results confirm the successful preparation of the Bi2O2S / N-BiVO4 photoanode and are consistent with the XRD results.

[0051] II. Photoelectrochemical Performance Analysis The PEC performance of BiVO4-based samples was evaluated using a three-electrode system under simulated AM1.5G sunlight. At 1.23V vs. RHE, Figure 10 The photocurrent density of BiVO4 in the sample is only 1.57 mA / cm². -2The photocurrent density of BiVO4 after calcination in an ammonia atmosphere was further increased to 2.53 mA / cm². -2 This indicates that N-ion doping can improve the photoelectrocatalytic performance of BiVO4. Furthermore, the Bi2O2S / N-BiVO4 photoanode achieved a photocurrent density of 3.68 mA / cm² at 1.23 V vs. RHE. -2 Compared to BiVO4 and N-BiVO4, it achieves an enhancement of 2.3 times and 1.5 times, respectively. The significant improvement in PEC performance on the Bi2O2S / N-BiVO4 photoanode is attributed to the expansion of the light absorption range and the enhancement of charge separation efficiency.

[0052] The photoelectric conversion efficiency of the photoanode was further evaluated by measuring the bias photon-to-current conversion efficiency (ABPE). Figure 11 The Bi₂O₂S / N-BiVO₄ photoanode achieved a maximum ABPE value of 1.14% at 0.73 V vs. RHE, which is 4.4 times the maximum ABPE value of BiVO₄ (0.26%) at 0.87 V vs. RHE. This result demonstrates that constructing Bi₂O₂S / N-BiVO₄ heterojunctions can achieve more efficient photon energy conversion under lower thermodynamic driving forces.

[0053] To investigate the reasons for the enhanced PEC performance of the Bi₂O₂S / N-BiVO₄ photoanode, the reaction kinetics of charge carriers at the interface were studied using electrochemical impedance spectroscopy (EIS). In the EIS test, the radius of the arc in the Nyquist plot reflects the magnitude of the interfacial charge transfer resistance. Figure 12 As shown, the Bi2O2S / N-BiVO4 photoanode exhibits the smallest Nyquist radius, confirming that the construction of the heterojunction structure significantly reduces the interfacial charge transfer resistance.

[0054] To investigate the charge recombination behavior on the photoanode surface, sodium sulfite (Na₂SO₃) was used as a hole scavenger to consume photogenerated holes and promote their participation in the PEC reaction. Under the action of Na₂SO₃, Figure 13 The photocurrent density of BiVO4 at 1.23 V vs. RHE increased from 1.57 mA / cm². -2 Significantly improved to 4.01 mAcm -2 This directly reflects the severe charge recombination phenomenon in BiVO4. Under the same conditions, the photocurrent density of N-BiVO4 increased to 4.46 mA / cm². -2 This improvement can be attributed to N doping optimizing the electronic structure of BiVO4 and partially suppressing charge recombination. In contrast, the Bi2O2S / N-BiVO4 photoanode exhibits the best performance in the presence of a hole scavenger, achieving a photocurrent density of 5.39 mA / cm² at 1.23 V vs. RHE. -2This indicates that the construction of heterojunction structures can effectively suppress the charge recombination process on the BiVO4 surface.

[0055] Charge separation efficiency reflects the ability of photogenerated holes to overcome bulk recombination losses and migrate to the electrode-electrolyte interface. At 1.23 V vs. RHE, the charge separation efficiencies of BiVO4, N-BiVO4, and Bi2O2S / N-BiVO4 photoanodes were 51.31%, 55.76%, and 67.32%, respectively. Figure 14 It is worth noting that the charge separation efficiency values ​​of N-BiVO4 and BiVO4 are quite similar, indicating that N doping has a limited effect on improving the bulk charge separation of BiVO4. Therefore, the significantly improved photocurrent response of Bi2O2S / N-BiVO4 mainly stems from interface modification rather than the enhancement of bulk separation efficiency.

[0056] Charge injection efficiency is a key parameter for evaluating the kinetics of water oxidation on the photoanode surface, characterizing the proportion of holes reaching the interface that participate in the water oxidation reaction. For example... Figure 15 As shown, at 1.23 V vs. RHE, the Bi2O2S / N-BiVO4 photoanode exhibits a charge injection efficiency of 68.23%, and the N-BiVO4 charge transfer efficiency reaches 61.59%, both significantly higher than the original BiVO4 charge injection efficiency of 35.21%. This result confirms that Bi2O2S modification and the heterojunction constructed therein effectively promote the transfer of photogenerated holes to the electrolyte solution. Furthermore, it is speculated that optimizing the electronic structure of BiVO4 through N doping reduces carrier transport resistance, thereby improving overall performance.

[0057] PEC degradation experiments were conducted using a standard three-electrode system with boric acid solution as the electrolyte and 50 mL of 10 ppm methyl orange (MO) solution as the target degradation product. Prior to the formal experiments, the effect of the number of Bi₂O₂S spin-coating layers on the degradation performance of the Bi₂O₂S / N-BiVO₄ photoanode was investigated. Figure 16 The results showed that the Bi2O2S / N-BiVO4 photoanode exhibited the best degradation performance for MO when the number of spin-coated layers was 10. Excessive or insufficient Bi2O2S loading both led to increased charge transfer resistance, promoted the recombination of photogenerated electron-hole pairs, and thus reduced photoelectrochemical degradation efficiency. Figure 17As shown, after 60 min of reaction, the MO degradation rate of BiVO4 was 65.84%, while that of N-BiVO4 increased to 81.23%. In contrast, the optimized Bi2O2S / N-BiVO4 photoanode achieved a MO degradation rate of 99.62% within 45 min. This indicates that the effective loading of Bi2O2S on the BiVO4 surface promotes the separation and transfer of photogenerated charge carriers, which is conducive to the generation of more active species and plays a positive role in the degradation of MO molecules.

[0058] To gain a deeper understanding of the PEC process and mechanism, the degradation performance of the Bi2O2S / N-BiVO4 photoanode under the synergistic effects of electrocatalysis (EC), photocatalysis (PC), and photoelectrocatalysis (PEC) was further investigated. The results showed that ( Figure 18 The degradation efficiency of MO by this photoanode was low under both PC and EC conditions, with degradation rates of 4.43% and 63.63% within 45 min, respectively. However, when photocatalysis and electrocatalysis synergistically constituted a photoelectrocatalytic system, the degradation rate of MO reached 99.62%, demonstrating the synergistic effect of photocatalysis and electrocatalysis in the photoelectrocatalytic process.

[0059] To elucidate the reaction mechanism of MO degradation by PEC at a Bi₂O₂S / N-BiVO₄ photoanode, the role of key active species was investigated through a free radical quenching experiment. Isopropanol (IPA), ammonium oxalate (AO), and methanol (MeOH) were used as hydroxyl radicals (·OH) and holes (h₂O₂S / N-BiVO₄ photoanodes, respectively. + ) and superoxide radicals (·O2) - Quenchers. For example, ... Figure 19 As shown, the addition of IPA did not significantly change the removal rate of MO, indicating that ·OH is not the main active substance in this reaction process. Conversely, the addition of AO and MeOH reduced the degradation rate from 99.62% to 20.52% and 55.21%, respectively. This result demonstrates that cavitation (h + ) is the main active species in the photoelectrocatalytic degradation of MO by Bi2O2S / N-BiVO4 photoanode, while superoxide radicals (·O2) are the main active species. - (Then it plays a secondary role.)

[0060] III. Analysis of Photoelectrocatalytic Mechanism The light absorption properties of the prepared samples were evaluated using ultraviolet-visible diffuse reflectance spectroscopy (UV-VisDRS). Figure 20 As shown, all photoanodes exhibit good light absorption in both the ultraviolet and visible light regions. Notably, the absorption edge of the Bi₂O₂S / N-BiVO₄ photoanode shows a significant red shift, indicating a significantly broadened absorption range, enabling it to capture more visible light and induce more photogenerated electron-hole pairs. Based on the classical Tauc method (… Figure 21The calculated band gaps (Eg) of the samples are: BiVO4 2.39eV, N-BiVO4 2.36eV, Bi2O2S / N-BiVO4 photoanode 2.08eV and Bi2O2S 1.42eV.

[0061] The flat band potential (E) of the sample in boric acid solution was determined using the Mott-Schottky method. fb Furthermore, the band structure of each material was determined. Figure 22 and 23 As shown, the slopes of the Mott-Schottky curves for all samples are positive, consistent with the characteristics of n-type semiconductors. The E0 values ​​for BiVO4, N-BiVO4, and Bi2O2S were obtained from the curve intercepts. fb The values ​​are 0.35V, 0.66V, and 0.39V vs. RHE, respectively. For an n-type semiconductor, its conduction band potential (E... CB ) is usually more than E fb The E values ​​are approximately 0.1~0.3 eV lower, therefore the E values ​​of BiVO4, N-BiVO4, and Bi2O2S are... CB These can be estimated as 0.15V, 0.46V, and 0.19V vs. RHE. Based on the conversion relationship between RHE and NHE (E... RHE =E NHE +0.0591×pH, pH=9.5), E of BiVO4, N-BiVO4 and Bi2O2S CB The values ​​were -0.41V, -0.10V, and -0.37V vs. RHE, respectively. This was combined with E measured by UV-VisDRS. g Through formula E VB = E CB + E g The valence band potential (E) of each material can be calculated. VB E of BiVO4, N-BiVO4 and Bi2O2S VB The values ​​were 1.98 eV, 2.26 eV, and 1.05 eV respectively, compared to NHE.

[0062] Based on the above results, the band structure diagrams of BiVO4, N-BiVO4, and Bi2O2S are shown below. Figure 24 As shown, the band structure of N-BiVO4 is more favorable for the adsorption of oxygen molecules (O2), thereby promoting the adsorption of superoxide radicals (·O2). - The generation of ). For n-type semiconductors, E fb Approximately equal to its Fermi level (E f When N-BiVO4 and Bi2O2S come into contact to form a heterojunction, electrons from Bi2O2S will spontaneously transfer to N-BiVO4 until the Fermi level E of both is reached. fEquilibrium is reached. During this process, Bi₂O₂S accumulates positive charge at the interface due to electron loss, causing its energy band to bend upwards; while N-BiVO₄ accumulates negative charge at the interface due to electron accumulation, causing its energy band to bend downwards. This creates a built-in electric field at the interface pointing from Bi₂O₂S to N-BiVO₄. Under illumination, under the combined effect of the interface energy band bending and the built-in electric field: photogenerated electrons in the conduction band (CB) of N-BiVO₄ rapidly transfer to the conduction band (VB) of Bi₂O₂S under the influence of the built-in electric field, and recombine with holes therein; this process effectively retains the holes in the conduction band of N-BiVO₄ and the photogenerated electrons in the CB of Bi₂O₂S, thus forming an S-type heterojunction between N-BiVO₄ and Bi₂O₂S. Electrons accumulated in the conduction band of Bi₂O₂S can effectively participate in the reduction reaction of O₂, generating ·O₂. - Subsequently, O2 - With H in the solution + The reaction produces H₂O₂, which is further converted into hydroxyl radicals (·OH) with higher oxidizing activity. Simultaneously, holes (h₂O₂) in the N-BiVO₄ valence band... + The potential is higher than the standard oxidation potential (E) of ·OH. θ (·OH / OH - () = +1.99 eV vs. NHE), therefore it can directly oxidize OH. - ·OH is generated. Finally, ·O2 is produced. - ·OH and h + The combined effect of these factors degrades MO into smaller molecule products.

Claims

1. A method for preparing a Bi2O2S / N-BiVO4 photoanode, characterized in that, Includes the following steps: (1) Preparation of Bi2O2S Bi(NO3)3·5H2O, CH4N2S and LiOH·H2O were added sequentially to an aqueous solution of hexadecyltrimethylammonium bromide and stirred to obtain a mixture. The mixture was then reacted in a high-pressure reactor lined with polytetrafluoroethylene. The reaction product was repeatedly washed with deionized water and ethanol and dried under vacuum to obtain Bi2O2S powder. (2) Preparation of BiVO4 A DMSO solution containing VO(acac)2 was uniformly drop-coated onto the surface of a dry BiOI electrode, and the electrode was placed in a muffle furnace for calcination. After the electrode cooled naturally to room temperature, it was immersed in NaOH solution for 30 minutes, then rinsed with distilled water and dried to obtain BiVO4. (3) Preparation of N-BiVO4 The BiVO4 prepared in step (2) was placed in an ammonia protective atmosphere and calcined to obtain N-BiVO4; (4) Preparation of Bi2O2S / N-BiVO4 photoanode Bi2O2S powder was dissolved in anhydrous ethanol to obtain an ethanol solution of Bi2O2S. The ethanol solution of Bi2O2S was then dropped onto the surface of N-BiVO4 obtained in step (3). The N-BiVO4 loaded with the solution was then spin-coated. After spin-coating, heat treatment was performed to obtain a Bi2O2S / N-BiVO4 photoanode.

2. The method for preparing a Bi2O2S / N-BiVO4 photoanode according to claim 1, characterized in that, In step (1), the mass-to-volume ratio of hexadecyltrimethylammonium bromide to water is 6 g: 875 mL; the mass ratio of hexadecyltrimethylammonium bromide, Bi(NO3)3·5H2O, CH4N2S and LiOH·H2O is 1600:776:61:9600.

3. The method for preparing a Bi2O2S / N-BiVO4 photoanode according to claim 1, characterized in that, In step (1), the reaction temperature of the high-pressure reactor is 200℃ and the reaction time is 2 hours.

4. The method for preparing a Bi2O2S / N-BiVO4 photoanode according to claim 1, characterized in that, The preparation method of the BiOI electrode in step (2) includes the following steps: S1. Preparation of electrolyte KI was dissolved in distilled water, the pH was adjusted to 1.7 with HNO3 solution, and Bi(NO3)3·5H2O was added to the solution. The mixture was stirred vigorously until it was completely dissolved to obtain a mixture. Then the mixture was thoroughly mixed with anhydrous ethanol solution containing p-benzoquinone to obtain the electrolyte. S2. Electrodeposition preparation of BiOI electrode Electrodeposition was performed using a typical three-electrode system. A 1.0 cm × 2.0 cm FTO conductive glass was used as the working electrode, a platinum electrode as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode. The mixed solution prepared in S1 was used as the electrolyte. Deposition was performed for 4 minutes at a constant voltage of -0.1 V vs. Ag / AgCl. After deposition, the resulting BiOI electrode was rinsed with deionized water.

5. The method for preparing a Bi2O2S / N-BiVO4 photoanode according to claim 4, characterized in that, In step S1, the mass-to-volume ratio of KI to distilled water is 83g:1250mL, the concentration of the anhydrous ethanol solution containing p-benzoquinone is 0.23M, and the volume ratio of the mixture to the anhydrous ethanol solution containing p-benzoquinone is 5:

2.

6. The method for preparing a Bi2O2S / N-BiVO4 photoanode according to claim 1, characterized in that, In step (2), the concentration of the DMSO solution containing VO(acac)2 is 0.2M; the electrode is placed in a muffle furnace and calcined at 450℃ for 2 hours.

7. The method for preparing a Bi₂O₂S / N-BiVO₄ photoanode according to claim 1, characterized in that, In step (3), the calcination temperature is 400℃ and the calcination time is 1 hour.

8. The method for preparing a Bi2O2S / N-BiVO4 photoanode according to claim 1, characterized in that, In step (4), the concentration of the ethanol solution of Bi2O2S is 0.04 g / mL. During spin coating, spin coating is first performed at a low speed of 500 rpm for 10 seconds, and then the speed is increased to 1500 rpm for 50 seconds. The temperature of the electrode heat treatment is 250℃ and the time is 30 minutes.

9. The Bi2O2S / N-BiVO4 photoanode prepared by the preparation method according to any one of claims 1-8.

10. The application of the Bi2O2S / N-BiVO4 photoanode prepared by the preparation method according to any one of claims 1-8 in the photoelectrocatalytic degradation of pollutants.

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