A method for preparing a BiOI / InVO4 heterojunction composite photocatalyst and its application in photocatalytic degradation of methylene blue and hydrogen production.

Abstract

The application discloses a preparation method of a BiOI / InVO4 heterojunction composite photocatalyst and application of the BiOI / InVO4 heterojunction composite photocatalyst in photocatalytic degradation of methylene blue and hydrogen production, and belongs to the technical field of semiconductor photocatalytic materials. The two-step hydrothermal method is adopted to prepare InVO4 microspheres, and then two-dimensional BiOI nanosheets are compounded with the InVO4 microspheres to controllably construct a BiOI / InVO4 heterojunction structure, wherein the BV-1 sample with a BiOI / InVO4 molar ratio of 1:1 has the optimal catalytic performance. The heterojunction can effectively broaden the visible light response range, promote the separation and migration of photoinduced carriers, inhibit the recombination of electron-hole pairs, and provide abundant active sites. Performance tests show that under visible light, the BV-1 has a highest degradation rate of 99.3% on a 10mg / L methylene blue solution within 180min, and still has an activity of 84.1% after 5 cycles; and the 4h photocatalytic hydrogen production amount is as high as 2278muol.g ‑1 , and the performance does not obviously attenuate after 4 cycles. The preparation process is simple, the conditions are mild, the cost is low, and the catalyst has high activity and high stability.

Description

Technical Field

[0001] This invention relates to the field of semiconductor photocatalytic materials technology, specifically to a method for preparing a BiOI / InVO4 heterojunction composite photocatalyst and its application in photocatalytic degradation of methylene blue and hydrogen production. Background Technology

[0002] Against the backdrop of continuous global industrialization, energy shortages and water pollution have become two core issues restricting the sustainable development of human society.

[0003] Hydrogen energy boasts significant advantages such as high energy density, pollution-free combustion products, and recyclability, and is widely recognized as the most promising clean energy source. Utilizing solar energy to drive semiconductor photocatalytic water splitting to produce hydrogen eliminates the need for fossil fuels and electricity, making it an ideal pathway for achieving green, low-carbon, and large-scale hydrogen production.

[0004] Meanwhile, wastewater from organic dyes such as methylene blue discharged from industries such as textiles, dyeing, and chemicals is characterized by its complex composition, high toxicity, difficulty in biodegradation, and tendency to accumulate in water bodies. This severely disrupts the aquatic ecosystem and harms the health of plants, animals, and humans. Traditional treatment technologies, such as physical adsorption, chemical oxidation, and biodegradation, generally suffer from low efficiency, high cost, susceptibility to secondary pollution, and difficulty in deep mineralization, failing to meet the demands for efficient and harmless treatment.

[0005] Semiconductor photocatalysis technology can directly utilize solar energy at room temperature and pressure to simultaneously achieve deep degradation of organic pollutants and clean energy production, combining the dual functions of environmental governance and energy production, and has become a research hotspot in the fields of environment and energy in recent years.

[0006] However, single semiconductor photocatalysts generally suffer from the following bottlenecks:

[0007] Narrow visible light response range and low solar energy utilization rate;

[0008] Photogenerated electron-hole pairs recombine rapidly, but carrier utilization is low.

[0009] Insufficient surface active sites lead to slow catalytic reaction kinetics.

[0010] It has poor structural stability and is prone to leakage and deactivation.

[0011] Constructing heterojunction composite materials is the most effective strategy to overcome the aforementioned bottlenecks. By tightly combining two semiconductors with matching band structures, a built-in electric field can be formed at the interface, enabling efficient separation and migration of photogenerated carriers, suppressing recombination, and simultaneously broadening the light absorption range, increasing active sites, and improving stability.

[0012] BiOI is a typical bismuth-based semiconductor with advantages such as layered structure, strong visible light response, large specific surface area, and simple preparation; InVO4 is a vanadium-based semiconductor with suitable band structure, strong redox ability, and stable structure. The high band structure matching between the two allows them to form a highly efficient heterojunction after recombination, achieving band complementarity and rapid charge transfer, thereby significantly improving photocatalytic degradation and hydrogen production performance.

[0013] Currently, research on the controllable synthesis, morphology regulation, optimal ratio screening, bifunctional catalytic mechanism, and industrial application conditions of BiOI / InVO4 heterojunctions is still insufficient. The reported catalysts generally suffer from problems such as low degradation efficiency, low hydrogen production, poor cycle stability, and complex preparation processes, making it difficult to meet the needs of practical applications.

[0014] Therefore, developing a BiOI / InVO4 heterojunction photocatalyst with simple preparation process, controllable morphology, high activity, strong stability, and the ability to simultaneously achieve efficient degradation of methylene blue and high hydrogen production has important theoretical value and practical application significance. Summary of the Invention

[0015] This invention provides a method for preparing a BiOI / InVO4 heterojunction composite photocatalyst and its application in photocatalytic degradation of methylene blue and hydrogen production, overcoming the problem that the recombination of photogenerated carriers in a single semiconductor is too fast, resulting in low degradation and hydrogen production efficiency.

[0016] To achieve the above objectives, the present invention adopts the following technical solution:

[0017] A method for preparing a BiOI / InVO4 heterojunction composite photocatalyst includes the following two hydrothermal steps:

[0018] Preparation of S1 and InVO4: 2.0 mmol of indium nitrate was dissolved in 20 mL of deionized water to obtain solution A; 2.0 mmol of sodium vanadate was dissolved in 40 mL of deionized water to obtain solution B; solution B was slowly added dropwise to solution A, and the pH was adjusted to <2 with dilute nitric acid and stirred for 1 h; the solution was transferred to a high-pressure reactor and hydrothermally heated at 180 °C for 18 h; the solution was centrifuged, washed alternately with deionized water and anhydrous ethanol at least 6 times, and dried at 60 °C for 12 h to obtain InVO4 powder;

[0019] S2, BiOI / InVO4 composite: Prepare 30 mL of 0.05 mol / L bismuth nitrate ethanol solution and 30 mL of 0.05 mol / L potassium iodide aqueous solution, mix and stir; add measured InVO4 powder and continue stirring for 2 h; hydrothermally heat at 180℃ for 12 h; centrifuge, wash 3 times each with deionized water and anhydrous ethanol, and dry at 80℃ for 12 h to obtain BiOI / InVO4 heterojunction composite photocatalyst.

[0020] Preferably, in step S1, the acceleration rate of solution B drops is 1-2 mL / min, the centrifugation speed is 8000 r / min, and the time is 5 min.

[0021] Preferably, the molar ratio of bismuth nitrate to potassium iodide in step S2 is 1:1.

[0022] Preferably, the molar ratio of BiOI to InVO4 in step S2 is 1:0.5, 1:1, or 1:2.

[0023] Preferably, the molar ratio of BiOI to InVO4 is 1:1, denoted as BV-1, corresponding to an InVO4 addition amount of 0.35g.

[0024] Application of BiOI / InVO4 heterojunction composite photocatalyst in photocatalytic degradation of methylene blue: using a 300W xenon lamp with a λ≥420nm filter as the light source, methylene blue concentration 10mg / L, pH=7~11, catalyst dosage 30mg / 100mL, dark adsorption for 60min, and light irradiation for 180min; BV-1 degradation rate ≥99.3%, and retaining more than 84.1% of the activity after 5 cycles.

[0025] Application of BiOI / InVO4 heterojunction composite photocatalyst in the photocatalytic degradation of methylene blue: using 10 vol% triethanolamine as a sacrificial agent, catalyst dosage 30 mg / 100 mL, nitrogen replacement for oxygen removal, reaction temperature 5℃, visible light irradiation for 4 h; BV-1 hydrogen production ≥2278 μmol·g -1 After four cycles, more than 90% of the performance is retained.

[0026] This invention precisely constructs a BiOI / InVO4 heterojunction composite photocatalyst via a two-step hydrothermal method, which has the following outstanding advantages compared with existing single semiconductors and traditional composite photocatalytic materials:

[0027] The BiOI / InVO4 heterojunction constructed in this invention can effectively broaden the visible light response range and enhance the ability to capture and convert sunlight. It solves the technical defects of traditional single-component photocatalysts, such as narrow response range and low light energy utilization, and provides a more sufficient energy supply for photocatalytic reactions.

[0028] In this invention, BiOI and InVO4 form a closely contacted heterojunction interface and construct a built-in electric field, which can drive the directional and rapid migration and efficient separation of photogenerated electrons and holes, significantly reduce the carrier recombination rate, extend the carrier lifetime, and enable more active carriers to participate in the surface redox reaction, thereby improving the catalytic efficiency from the root.

[0029] The InVO4 prepared by this invention has a hierarchical microsphere structure, and BiOI has a two-dimensional nanosheet structure. When the two are combined, they form a sheet-sphere composite heterojunction with a large specific surface area, high interfacial contact area, and rich pore structure. This provides a large number of catalytic active sites, enhances substrate adsorption and interfacial reaction kinetics, and significantly improves the catalytic reaction rate.

[0030] In this invention, under visible light, the optimal BV-1 ratio achieves a degradation rate of up to 99.3% for 10 mg / L methylene blue over 180 min, and a photocatalytic hydrogen production of up to 2278 μmol·g over 4 h. -1 It is far superior to pure BiOI, pure InVO4 and other composite materials, achieving synergistic effects of "pollution control + clean energy preparation".

[0031] The BV-1 catalyst in this invention retains more than 84.1% of its activity after 5 degradation cycles and has a performance retention rate of more than 90% after 4 hydrogen production cycles. It is structurally stable, not easily lost or deactivated, and can be reused multiple times, which greatly reduces the application cost.

[0032] This invention employs a two-step hydrothermal method, which uses readily available raw materials, is simple to operate, has mild reaction conditions, and is highly reproducible. It requires no complex equipment or harsh environment, making it suitable for laboratory preparation and large-scale production, and has good potential for industrial application.

[0033] The catalyst in this invention is non-toxic and harmless, has mild reaction conditions, and produces no secondary pollution. It can be used simultaneously for the treatment of dyeing and printing wastewater, the degradation of organic pollutants, and photocatalytic green hydrogen production. It has extremely high practical value and promising prospects in the fields of environmental remediation and energy production. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0035] Figure 1 X-ray diffraction (XRD) patterns of InVO4, BiOI, BV-0.5, BV-1, and BV-2 prepared for embodiments of the present invention;

[0036] Figure 2 Scanning electron microscope (SEM) images of InVO4, BiOI, and BV-1 prepared for embodiments of the present invention;

[0037] Figure 3 The figures show the photocatalytic degradation curves of methylene blue, first-order kinetic fitting, rate constants, and cycle stability of each sample in this invention.

[0038] Figure 4 The performance curves and kinetic diagrams of the BV-1 sample degrading different concentrations of methylene blue are shown in the figure.

[0039] Figure 5 The following are the performance curves and kinetic diagrams of the BV-1 sample of this invention degrading methylene blue under different pH conditions;

[0040] Figure 6 The figures show the photocatalytic hydrogen production performance of each sample in this invention and the stability of hydrogen production during BV-1 cycles. Detailed Implementation

[0041] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0042] Preparation of InVO4:

[0043] Weigh out 2.0 mmol of indium nitrate Dissolve 2.0 mmol of sodium vanadate (NaVO3) in 20 mL of deionized water and stir vigorously for 15 min until completely dissolved to obtain solution A. Weigh 2.0 mmol of sodium vanadate (NaVO3) and dissolve it in 40 mL of deionized water, stirring for 30 min until dissolved to obtain solution B. While continuously stirring, slowly add solution B to solution A at a rate of 1–2 mL / min, and continue stirring for 10 min after the addition is complete. Add dilute nitric acid dropwise to the mixture to adjust the pH to below 2, and continue stirring for 1 h. Transfer the mixture to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and hydrothermally react at 180 °C for 18 h. Allow it to cool naturally to room temperature, centrifuge at 8000 r / min for 5 min, and collect the precipitate. Wash the precipitate alternately with deionized water and anhydrous ethanol 3 times each, for a total of 6 washes. Dry the precipitate at 60 °C for 12 h and grind it to obtain a pale yellow InVO4 powder.

[0044] Preparation of BiOI / InVO4 heterojunction:

[0045] Prepare 30 mL of a 0.05 mol / L solution. The ethanol solution was magnetically stirred for 30 min. 30 mL of a 0.05 mol / L KI aqueous solution was prepared and slowly added dropwise to the bismuth nitrate ethanol solution under vigorous stirring, with stirring continued for 10 min. 0.35 g of InVO4 powder was added to the mixture, and the mixture was stirred for 2 h until uniformly dispersed. The suspension was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 180 °C for 12 h. After cooling, the mixture was centrifuged, washed three times with deionized water, and three times with anhydrous ethanol. It was dried at 80 °C for 12 h to obtain a composite photocatalyst with a BiOI to InVO4 molar ratio of 1:1, labeled BV-1.

[0046] Following the same method, 0.175 g and 0.7 g of InVO4 were added respectively to prepare BV-0.5 (1:0.5) and BV-2 (1:2).

[0047] The crystal structure of the sample was characterized using X-ray diffraction (XRD), and the results are shown in the attached figure. Figure 1 As shown.

[0048] InVO4 exhibits characteristic diffraction peaks at 2θ = 18.6°, 20.8°, 31.1°, 33.1°, and 35.2°, which correspond perfectly to the orthorhombic InVO4 standard card PDF#48-0898.

[0049] BiOI exhibits characteristic diffraction peaks at 29.7°, 31.7°, 45.5°, and 55.3°, which highly match the tetragonal BiOI standard card PDF#73-2062.

[0050] The XRD patterns of the BV-0.5, BV-1, and BV-2 composite materials show characteristic peaks of both BiOI and InVO4 phases, with no impurity phase diffraction peaks, indicating that the present invention has successfully prepared a high-purity BiOI / InVO4 heterojunction composite photocatalyst.

[0051] The microstructure of the samples was characterized using scanning electron microscopy (SEM), and the results are shown in the attached figure. Figure 2 As shown.

[0052] Pure-phase InVO4 exhibits a hierarchical microsphere structure with self-assembled nanoparticles. The microspheres are approximately 3 μm in diameter, with a rough surface and abundant pores. Pure-phase BiOI is a two-dimensional layered nanosheet structure with clear and uniformly distributed layers. In the optimal sample BV-1, BiOI nanosheets are uniformly and tightly attached to the surface of InVO4 microspheres, and the two-phase interface has good contact, successfully constructing a sheet-sphere type BiOI / InVO4 heterojunction structure.

[0053] Photocatalytic degradation performance of methylene blue:

[0054] The photocatalytic degradation performance of each sample under visible light was tested, and the results are attached. Figure 3 As shown.

[0055] From the appendix Figure 3 (a) It can be seen that the degradation rate of pure BiOI at 180 min is only 35.5%, and that of pure InVO4 is only 49.3%; the degradation rates of BV-0.5, BV-1 and BV-2 are 58.0%, 90.9% and 64.3% respectively, among which BV-1 has the best performance.

[0056] Appendix Figure 3 (b) and appendix Figure 3The first-order kinetics and rate constant results in (c) show that BV-1 has the largest reaction rate constant k and the fastest catalytic kinetics.

[0057] Appendix Figure 3 (d) Cyclic stability tests showed that BV-1 maintained a degradation rate of 84.1% after 5 cycles, demonstrating excellent stability.

[0058] The effect of different initial concentrations of methylene blue on the degradation effect was further investigated, and the results are attached. Figure 4 As shown.

[0059] As the substrate concentration increases, the degradation efficiency gradually decreases; the degradation effect is best at 10 mg / L, with a degradation rate of 90.9% after 180 min, indicating that the low concentration system is more conducive to the full utilization of active sites and efficient photon absorption.

[0060] The effect of initial solution pH on degradation performance was investigated, and the results are shown in the appendix. Figure 5 As shown.

[0061] Under acidic conditions, the catalyst and dye exhibit electrostatic repulsion, resulting in low degradation efficiency. Under neutral to alkaline conditions, adsorption is enhanced, and degradation efficiency is significantly improved, reaching a maximum of 99.3% at pH 9. (See attached image) Figure 5 The kinetic results (b) and (c) further demonstrate that alkaline conditions are more favorable for photocatalytic reactions.

[0062] Photocatalytic hydrogen production performance:

[0063] Photocatalytic water splitting for hydrogen production under visible light was tested on each sample, and the results are attached. Figure 6 As shown.

[0064] Appendix Figure 6 (a) shows that pure BiOI and pure InVO4 have extremely low hydrogen production activity, but the hydrogen production performance is significantly improved after constructing a heterojunction; the hydrogen production of the BV-1 sample is as high as 4h. It is significantly superior to BV-0.5 and BV-2.

[0065] Appendix Figure 6 (b) Cyclic test results show that after four hydrogen production cycles, BV-1 still achieves a hydrogen production capacity of up to [percentage missing]. With a performance retention rate of over 90%, it possesses excellent structural stability and recyclability.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a BiOI / InVO4 heterojunction composite photocatalyst, characterized in that, It includes the following two hydrothermal steps: Preparation of S1 and InVO4: Dissolve 2.0 mmol of indium nitrate in 20 mL of deionized water to obtain solution A; 2.0 mmol sodium vanadate was dissolved in 40 mL of deionized water to obtain solution B; solution B was slowly added dropwise to solution A, and the pH was adjusted to <2 with dilute nitric acid and stirred for 1 h; it was then transferred to a high-pressure reactor and hydrothermally heated at 180 °C for 18 h; after centrifugation, the mixture was washed with deionized water and anhydrous ethanol at least 6 times alternately, and dried at 60 °C for 12 h to obtain InVO4 powder. S2, BiOI / InVO4 composite: Prepare 30 mL of 0.05 mol / L bismuth nitrate ethanol solution and 30 mL of 0.05 mol / L potassium iodide aqueous solution, mix and stir; add measured InVO4 powder and continue stirring for 2 h; hydrothermally heat at 180℃ for 12 h; centrifuge, wash 3 times each with deionized water and anhydrous ethanol, and dry at 80℃ for 12 h to obtain BiOI / InVO4 heterojunction composite photocatalyst.

2. The preparation method of the BiOI / InVO4 heterojunction composite photocatalyst according to claim 1, characterized in that, In step S1, the acceleration rate of solution B drop is 1-2 mL / min, the centrifugation speed is 8000 r / min, and the time is 5 min.

3. The preparation method of the BiOI / InVO4 heterojunction composite photocatalyst according to claim 1, characterized in that, In step S2, the molar ratio of bismuth nitrate to potassium iodide is 1:

1.

4. The preparation method of the BiOI / InVO4 heterojunction composite photocatalyst according to claim 1, characterized in that, In step S2, the molar ratio of BiOI to InVO4 is 1:0.5, 1:1, or 1:

2.

5. The preparation method of the BiOI / InVO4 heterojunction composite photocatalyst according to claim 4, characterized in that, The molar ratio of BiOI to InVO4 is 1:1, denoted as BV-1, corresponding to an InVO4 addition amount of 0.35g.

6. A BiOI / InVO4 heterojunction composite photocatalyst prepared by any one of claims 1 to 5, characterized in that, This is a heterojunction structure in which BiOI nanosheets are uniformly loaded onto the surface of InVO4 microspheres.

7. The application of the catalyst according to claim 6 in the photocatalytic degradation of methylene blue, characterized in that: Using a 300W xenon lamp with a λ≥420nm filter as the light source, a methylene blue concentration of 10mg / L, pH=7~11, a catalyst dosage of 30mg / 100mL, dark adsorption for 60min, and light irradiation for 180min, the BV-1 degradation rate was ≥99.3%, and more than 84.1% of the activity was retained after 5 cycles.

8. The application of the catalyst according to claim 6 in photocatalytic hydrogen production, characterized in that: Using 10 vol% triethanolamine as a sacrificial agent, with a catalyst dosage of 30 mg / 100 mL, nitrogen purging for oxygen removal, a reaction temperature of 5 °C, and visible light irradiation for 4 h; BV-1 hydrogen production ≥ After four cycles, more than 90% of the performance is retained.

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