A bismuth-based semiconductor heterojunction photocatalyst and a preparation method thereof

Abstract

The application belongs to the technical field of photocatalyst preparation, and discloses a preparation method of a bismuth-based semiconductor heterojunction photocatalyst. The catalyst contains the following components in mass fraction: active component 5-50%, oxide carrier 50-95%; wherein the active component contains bismuth-based metal oxides (Bi x MO y , M is a transition metal); and the carrier is bismuth trioxide (Bi2O3). The obtained Bi x MO y / Bi2O3 heterojunction photocatalyst has a unique electronic structure, high light spectrum response, high carrier separation efficiency, simple preparation method and the like, and exhibits excellent selectivity, stability and solar energy conversion efficiency in photocatalysis such as carbon dioxide reduction, and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials, photocatalysis, and optoelectronics, and particularly to a method for preparing a novel bismuth-based semiconductor heterojunction photocatalyst. Background Technology

[0002] With the development of human society, excessive carbon dioxide emissions and the use of fossil fuels have led to serious environmental problems and energy crises. Therefore, researchers worldwide are dedicated to studying how to efficiently develop and utilize renewable and green energy sources, especially solar energy. Among these, the green and efficient technology of using photocatalysis to convert carbon dioxide into renewable hydrocarbon fuels and utilizing solar energy to achieve carbon resource recycling has attracted widespread attention. However, common photocatalytic materials such as TiO2 have limited applications in the field of photocatalysis due to their wide bandgap (3.2 eV) and low utilization of visible light.

[0003] In recent decades, bismuth-based materials (including bismuth oxides, bismuth sulfides, bismuth-based halide oxides, and bismuth metal oxides) have been found to exhibit unique electronic structures, tunable band gaps, and excellent catalytic performance, making them popular materials in the field of photocatalysis. However, during the preparation process, it is difficult to effectively control the crystal phase, morphology, size, and structural stability of these materials. Therefore, these materials generally face the problem of high photogenerated electron-hole recombination rates, resulting in low photoelectric conversion efficiency. Secondly, the absorption capacity of some bismuth-based semiconductors for visible light remains limited, and the light absorption range needs to be further expanded. Although various preparation methods have been tried, such as solid-state reaction methods and hydrothermal / solvothermal methods, the bismuth-based materials prepared by these methods have drawbacks such as large size, irregular morphology, small specific surface area, and impure crystal structure, which cannot meet the requirements of photocatalysis for band gap control and high solar energy utilization. In addition, in the industrial field, how to prepare bismuth-based semiconductors with excellent photoelectric properties simply, on a large scale, and with high yield remains a major obstacle.

[0004] To address these issues, this invention applies modification methods such as metal ion doping, morphology control, and heterostructure construction to the study of bismuth-based semiconductor heterojunctions, thereby optimizing the band structure, enhancing light absorption, and improving carrier separation efficiency, thus improving photoelectric performance and photoelectric conversion efficiency. Summary of the Invention

[0005] Technical Problem: To address the shortcomings of existing technologies, this invention aims to provide a bismuth-based semiconductor heterojunction photocatalyst and its preparation method, solving the problem of the difficulty in systematically controlling the morphology, photoelectric properties, and photocatalytic characteristics of bismuth-based materials.

[0006] Technical solution: A heterojunction photocatalyst composed of bismuth-based semiconductors, consisting of bismuth-based oxide Bi...x MO y It is composed of bismuth trioxide (Bi₂O₃) as a support, wherein M is a transition metal, x is 0.5–2, y is 1–8, and the mass fraction of each component is 5–50% Bi. x MO y 50-95% Bi2O3.

[0007] The transition metal is any one of vanadium, chromium, manganese, iron, cobalt, nickel, and bismuth.

[0008] The preparation method of the bismuth-based semiconductor heterojunction photocatalyst includes the following steps:

[0009] Step 1. Calcine the Bi2O3 support in air atmosphere;

[0010] Step 2. Mix the active component precursors: Dissolve the bismuth salt and transition metal salt in a small amount of solvent, mix and heat to dissolve;

[0011] Step 3. Mix the active component precursor mixture from Step 2 with the Bi2O3 support treated in Step 1 and stir until homogeneous;

[0012] Step 4. After drying the mixture obtained in Step 3 in a vacuum drying oven, a mixture of hydrogen and argon is introduced to carry out a reduction reaction under heating conditions. Then, a mixture of oxygen and argon is introduced to carry out an oxidation reaction under heating conditions, thereby obtaining Bi. x MO y A bismuth-based semiconductor heterojunction photocatalyst composed of a Bi2O3 support.

[0013] The transition metal salts mentioned in step 2) are ammonium metavanadate, chromium nitrate, chromium chloride, chromium acetate, manganese nitrate, manganese chloride, manganese acetate, ferric nitrate, ferric chloride, ferric acetate, cobalt nitrate, cobalt chloride, cobalt acetate, nickel nitrate, nickel chloride, nickel acetate, bismuth nitrate, bismuth chloride, and bismuth acetate.

[0014] The solvent mentioned in step 2) is any one of water, ethanol, nitric acid aqueous solution with a concentration of 0.1-4 mol / L, hydrochloric acid aqueous solution with a concentration of 0.1-4 mol / L, or ethylene glycol.

[0015] The reduction and oxidation reactions in step 4 are both carried out at 100–700 °C for 1–24 h.

[0016] The hydrogen concentration mentioned in step 4 is 2% to 100% by volume in argon, and the oxygen concentration is 2% to 100% by volume in argon.

[0017] The calcination temperature in step 1 is 200–600℃, and the time is 2–8 hours.

[0018] In step 2, the molar ratio of bismuth salt to transition metal salt is 0.5 to 2.

[0019] The temperature for mixing and heating in step 2 is 30–90°C.

[0020] Beneficial effects:

[0021] 1. The bismuth-based semiconductor heterojunction preparation method of the present invention has simple equipment, simple preparation steps, good repeatability, inexpensive raw materials, and can be mass-produced.

[0022] 2. The bismuth-based semiconductor heterojunction obtained in this invention achieves high visible light absorption, wide spectral response, high carrier mobility and high CO2 photocatalytic reduction efficiency. Detailed Implementation

[0023] The present invention discloses a method for preparing a heterojunction photocatalyst composed of bismuth-based semiconductors, characterized in that the catalyst is a bismuth-based oxide (Bi x MO y The composition consists of a transition metal (M) and a bismuth trioxide (Bi₂O₃) support, with each component having a mass fraction of 5–50% Bi. x MO y The preparation method of this bismuth-based semiconductor heterojunction photocatalyst includes the following steps: 50-95% Bi2O3.

[0024] Step 1. Calcine the Bi2O3 support in air at 200–600°C for 2–8 hours;

[0025] Step 2. Mix the active component precursors: Weigh out bismuth salt and transition metal salt in a molar ratio of 0.5 to 2, dissolve them in a small amount of solvent, mix and heat to 30 to 90°C;

[0026] Step 3. Mix the active component precursor mixture from Step 2 with the Bi2O3 support treated in Step 1 and stir until homogeneous;

[0027] Step 4. After drying the mixture obtained in Step 3 in a vacuum drying oven for 12 hours, a mixture of hydrogen and argon is introduced and reduced at 100–700°C for 1–24 hours. Then, a mixture of oxygen and argon is introduced and oxidized at 100–700°C for 1–24 hours to obtain the product composed of Bi. x MO y Bismuth-based heterojunction catalyst composed of Bi2O3 support.

[0028] in,

[0029] The transition metal salts mentioned in step 2 are ammonium metavanadate, chromium nitrate, chromium chloride, chromium acetate, manganese nitrate, manganese chloride, manganese acetate, ferric nitrate, ferric chloride, ferric acetate, cobalt nitrate, cobalt chloride, cobalt acetate, nickel nitrate, nickel chloride, nickel acetate, bismuth nitrate, bismuth chloride, and bismuth acetate.

[0030] The solvents mentioned in step 2 are water, ethanol, nitric acid aqueous solution with a concentration of 0.1-4 mol / L, hydrochloric acid aqueous solution with a concentration of 0.1-4 mol / L, and ethylene glycol.

[0031] The hydrogen concentration mentioned in step 4 is 2% to 100% by volume in argon, and the oxygen concentration is 2% to 100% by volume in argon.

[0032] The present invention is further illustrated by the following examples, but these are not intended to limit the invention. Specific experimental conditions and methods not specified in the following examples are generally conventional methods well known to those skilled in the art.

[0033] Example 1:

[0034] A bismuth-based semiconductor heterojunction photocatalyst contains the following components by mass fraction: 50% active component and 50% bismuth trioxide support; wherein the active component is bismuth vanadate with a Bi / V molar ratio of 1.

[0035] The catalyst preparation method described in this embodiment is the impregnation method, which specifically includes the following steps:

[0036] 500 mg of bismuth trioxide was weighed and calcined at 200 °C for 2 h in a pre-processor under air. 933 mg of bismuth nitrate pentahydrate and 225 mg of ammonium metavanadate were weighed and dissolved in a small amount of ethylene glycol. The mixture was heated to 80 °C, and the treated bismuth trioxide support was added simultaneously. After stirring until homogeneous, the mixture was dried in a vacuum drying oven for 12 h. Then, it was reduced at 400 °C for 2 h by introducing 50% hydrogen gas in argon atmosphere, and finally oxidized at 400 °C for 2 h by introducing 50% oxygen gas in argon atmosphere.

[0037] Example 2:

[0038] A bismuth-based semiconductor heterojunction photocatalyst contains the following components by mass fraction: 20% active component and 80% bismuth trioxide support; wherein the active component is bismuth chromate with a Bi / Cr molar ratio of 1.

[0039] The catalyst preparation method described in this embodiment is the impregnation method, which specifically includes the following steps:

[0040] (1) Weigh 800 mg of bismuth trioxide and calcine it at 500 °C for 2 h by passing air through it in the preprocessor. Weigh 377 mg of anhydrous bismuth chloride and 393 mg of anhydrous chromium chloride and dissolve them in a small amount of 1 mol / L hydrochloric acid aqueous solution.

[0041] The mixture was heated to 60°C, and the treated bismuth trioxide support was added. After stirring evenly, the mixture was dried in a vacuum drying oven for 12 hours. Then, hydrogen gas with a volume fraction of 75% in argon was introduced and the mixture was reduced at 600°C for 12 hours. Finally, oxygen gas with a volume fraction of 10% in argon was introduced and the mixture was oxidized at 700°C for 4 hours.

[0042] Example 3:

[0043] A bismuth-based semiconductor heterojunction photocatalyst contains the following components by mass fraction: 10% active component and 90% bismuth trioxide support; wherein the active component is bismuth manganate with a Bi / Mn molar ratio of 1.

[0044] The catalyst preparation method described in this embodiment is the impregnation method, which specifically includes the following steps:

[0045] (1) Weigh 900 mg of bismuth trioxide and calcine it at 100 °C for 2 hours in a pre-processor by introducing air. Weigh 185 mg of bismuth trioxide...

[0046] mg of anhydrous bismuth acetate and 149 mg of manganese acetate dihydrate were dissolved in a small amount of deionized water. The mixture was heated to 70°C, and the treated bismuth trioxide support was added simultaneously. After stirring until homogeneous, the mixture was dried in a vacuum drying oven for 12 h. Then, it was reduced at 500°C for 12 h by introducing 100% hydrogen gas in argon atmosphere. Finally, it was oxidized at 600°C for 12 h by introducing 30% oxygen gas in argon atmosphere.

[0047] Example 4:

[0048] A bismuth-based semiconductor heterojunction photocatalyst contains the following components by mass fraction: 60% active component and 40% bismuth trioxide support; wherein the active component is bismuth cobaltate with a Bi / Co molar ratio of 1.

[0049] The catalyst preparation method described in this embodiment is the impregnation method, which specifically includes the following steps:

[0050] 400 mg of bismuth trioxide was weighed and calcined at 400 °C for 2 h in a pre-processor under air. 378 mg of bismuth nitrate pentahydrate and 297 mg of cobalt nitrate hexahydrate were weighed and dissolved in a small amount of 1.5 mol / L nitric acid aqueous solution. The mixture was heated to 60 °C, and the treated bismuth trioxide support was added simultaneously. After stirring until homogeneous, the mixture was dried in a vacuum drying oven for 12 h. Then, it was reduced at 300 °C for 1 h by introducing hydrogen gas with a volume fraction of 25% in argon, and finally oxidized at 100 °C for 1 h by introducing oxygen gas with a volume fraction of 40% in argon.

[0051] Example 5:

[0052] A bismuth-based semiconductor heterojunction photocatalyst contains the following components by mass fraction: 90% active component and 10% bismuth trioxide support; wherein the active component is bismuth ferrite with a Bi / Fe molar ratio of 1.

[0053] The catalyst preparation method described in this embodiment is the impregnation method, which specifically includes the following steps:

[0054] 100 mg of bismuth trioxide was weighed and calcined at 300 °C for 2 h in a pre-processor under air. 1647 mg of bismuth nitrate pentahydrate and 1372 mg of ferric chloride hexahydrate were weighed and dissolved in a small amount of 0.5 mol / L hydrochloric acid aqueous solution. The mixture was heated to 80 °C, and the treated bismuth trioxide support was added simultaneously. After stirring until homogeneous, the mixture was dried in a vacuum drying oven for 12 h. Then, it was reduced at 500 °C for 1 h by introducing 5% hydrogen gas in argon atmosphere, and finally oxidized at 200 °C for 1 h by introducing 2% oxygen gas in argon atmosphere.

[0055] Example 6:

[0056] A bismuth-based semiconductor heterojunction photocatalyst contains the following components by mass fraction: 50% active component and 50% bismuth trioxide support; wherein the active component is bismuth nickelate with a Bi / Ni molar ratio of 1.

[0057] The catalyst preparation method described in this embodiment is the impregnation method, which specifically includes the following steps:

[0058] 500 mg of bismuth trioxide was weighed and calcined at 300 °C for 2 h in a pre-processor under air. 916 mg of bismuth nitrate pentahydrate and 765 mg of nickel nitrate hexahydrate were weighed and dissolved in a small amount of 1 mol / L nitric acid aqueous solution. The mixture was heated to 80 °C, and the treated bismuth trioxide support was added simultaneously. After stirring until homogeneous, the mixture was dried in a vacuum drying oven for 12 h. Then, it was reduced at 400 °C for 1 h by introducing 50% hydrogen gas in argon atmosphere, and finally oxidized at 400 °C for 1 h by introducing 10% oxygen gas in argon atmosphere.

[0059] Catalysts were prepared according to the methods described in Examples 1-6, and their light absorption range was detected using a microscopic spectroscopy system. These catalysts were then applied to a CO2 reduction photocatalytic reaction using a 300W xenon lamp, a CO2 to water molar ratio of 1:10, and a reaction time of 12 h. The methanol formation rate in the product was quantitatively analyzed using gas chromatography. Specific results are shown in Table 1.

[0060] Table 1. Spectral absorption range of the catalyst and methanol production rate in the CO2 reduction photocatalytic reaction.

[0061]

[0062] The preferred embodiments of the present invention have been described in detail above, but are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A heterojunction photocatalyst consisting of a bismuth-based semiconductor, characterized by, consisting of bismuth-based oxide Bi x MO y and bismuth trioxide (Bi2O3) carrier, wherein M is a transition metal, x is 0.5-2, y is 1-8, and the mass fraction of each component is: 5-50% of Bi x MO y , 50-95% of Bi2O3; the transition metal is any one of vanadium, chromium, manganese, iron, cobalt, nickel, bismuth; the preparation of the heterojunction photocatalyst composed of the bismuth-based semiconductor comprises the following steps: Step 1. Calcining treatment of Bi2O3 carrier in air atmosphere; Step 2. Mixing of active component precursors: dissolving bismuth salt and transition metal salt in a small amount of solvent, mixing and heating to dissolve; Step 3. Mixing the active component precursor mixture of step 2 with the Bi2O3 carrier treated in step 1, and stirring uniformly; Step 4. After drying the mixture obtained in Step 3 in a vacuum drying oven, a reduction reaction is performed under heating conditions by introducing a mixed gas of hydrogen and argon, and then an oxidation reaction is performed under heating conditions by introducing a mixed gas of oxygen and argon, and the reduction and oxidation reactions are performed at 100 to 700°C for 1 to 24 hours, thereby obtaining a bismuth-based semiconductor heterojunction photocatalyst composed of Bi x MO y and Bi2O3 support.

2. The Bi-based semiconductor heterojunction photocatalyst according to claim 1, wherein The transition metal salt in step 2 is ammonium metavanadate, chromium nitrate, chromium chloride, chromium acetate, manganese nitrate, manganese chloride, manganese acetate, iron nitrate, iron chloride, iron acetate, cobalt nitrate, cobalt chloride, cobalt acetate, nickel nitrate, nickel chloride, nickel acetate, bismuth nitrate, bismuth chloride, bismuth acetate.

3. The Bi-based semiconductor heterojunction photocatalyst according to claim 1, wherein The solvent in step 2 is any one of water, ethanol, 0.1-4 mol / L nitric acid aqueous solution, 0.1-4 mol / L hydrochloric acid aqueous solution, ethylene glycol.

4. The Bi-based semiconductor heterojunction photocatalyst according to claim 1, wherein The hydrogen concentration in step 4 is 2%-100% by volume in argon, and the oxygen concentration is 2%-100% by volume in argon.

5. The Bi-based semiconductor heterojunction photocatalyst according to claim 1, wherein The calcination temperature in step 1 is 200-600℃, 2-8 h.

6. The Bi-based semiconductor heterojunction photocatalyst according to claim 1, wherein The molar ratio of bismuth salt to transition metal salt in step 2 is 0.5-2.

7. The Bi-based semiconductor heterojunction photocatalyst according to claim 1, wherein The temperature of mixing and heating in step 2 is 30-90℃.

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