Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation and application of Bi / Bi2S3 / TiO2 heterojunction composite material in photo-thermal catalytic reduction of carbon dioxide

Abstract

The invention discloses a Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation and application of the Bi / Bi2S3 / TiO2 heterojunction composite material in photo-thermal catalytic reduction of carbon dioxide. The preparation method of the composite material comprises the following steps: performing in-situ growth of petal-shaped H2Ti2O5.H2O on the surface of a metal titanium sheet by adopting a hydrothermal method, then performing in-situ growth of rod-shaped Bi2S3 on the H2Ti2O5.H2O by adopting a secondary hydrothermal method, and finally annealing in a tubular furnace inert or N2 atmosphere at 400-600 DEG C to obtain the Bi / Bi2S3 / TiO2 heterojunction composite material. Two strategies of built-in electric field and S-type heterojunction construction are combined into the material through one-step calcination, so that the material has full-spectrum absorption and short carrier transmission distance, photo-generated carriers can be effectively separated, and due to the internal electric field action of Bi and the strong thermal effect of Bi2S3, the material has a high photothermal effect, so that the photothermal catalysis CO2 conversion efficiency is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and specifically relates to a Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation and its application in photothermal catalytic reduction of carbon dioxide. Background Art

[0002] In today's rapidly developing science, technology, and economy, excessive fossil fuel consumption has exacerbated the energy crisis, and the greenhouse effect caused by excessive CO2 emissions has become increasingly severe, posing a serious threat to the sustainable development of human society. In light of this, photocatalytic conversion technology has emerged as a promising technology. It can convert CO2 into chemical energy sources such as carbon monoxide, methanol, and methane under the action of visible light at room temperature and pressure using semiconductor catalysts. Its environmentally friendly and efficient properties make it a key technology with great potential and application prospects in the field of CO2 conversion. Its significant significance in alleviating energy and environmental challenges is attracting global research efforts to explore pathways for its optimization and large-scale application. While traditional photocatalysis has established a solid foundation in the exploration of CO2 conversion technology, its development is severely hampered by its low sunlight utilization efficiency. In stark contrast, photothermal catalysis, with its innovative integration of photocatalysis and thermal catalysis, has rapidly emerged in recent years, attracting significant research investment and becoming a key technology with great potential for addressing energy and environmental challenges, continuously propelling related research to new heights. Photothermal catalysis (PTC) offers a novel strategy that leverages the full spectrum of sunlight to stimulate the synergistic effects between photocatalysis (PC) and thermocatalysis (TC). This not only achieves high solar energy utilization efficiency but also minimizes solar energy use. Across the entire solar spectrum, PTC demonstrates superior solar energy utilization efficiency compared to both photocatalysis and thermocatalysis. This is due to the synergistic effect of light and heat during the PTC process, significantly boosting PTC activity and making it a key advantage in this research field. The light mechanism excites charge carriers and high-energy hot electrons, modulating adsorption sites and promoting a reduction in activation energy and reaction temperature, effectively addressing the high energy consumption and high pollution associated with thermocatalysis. The heat mechanism, on the other hand, accelerates material transport, adsorption, and charge transfer, overcoming kinetic limitations, promoting thermal activation and cracking, and providing activation energy, effectively addressing the low catalytic efficiency associated with photocatalysis. PTC not only saves energy but also leverages the thermal effects of sunlight through the coupling of thermocatalysis and photocatalysis, improving the utilization of solar energy. Therefore, it is highly necessary to develop novel photothermal catalysts with high efficiency and full-spectrum light response. Summary of the Invention

[0003] The present invention aims to provide a Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation and its preparation method, and to apply it to the photothermal catalytic reduction of carbon dioxide. This invention uses a simple strategy to construct a Bi / Bi2S3 heterostructure with a strong internal electric field. The excellent electrical conductivity of metallic bismuth (Bi), the resulting internal electric field, and the strong coupling between Bi and Bi2S3 significantly enhance charge transfer, thereby improving photothermal catalytic efficiency.

[0004] The preparation method of the Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation is as follows: first, H2Ti2O5·H2O is in situ grown on the surface of a metal titanium sheet by a hydrothermal method, then Bi2S3 is in situ grown on H2Ti2O5·H2O by a secondary hydrothermal method, and finally, the Bi / Bi2S3 / TiO2 heterojunction composite material is annealed at 400-600°C for 0.5-4 h in an inert atmosphere or N2 atmosphere in a tubular furnace.

[0005] The specific operation of the hydrothermal method for in-situ growth of H2Ti2O5·H2O on the surface of a metal titanium sheet is as follows: the titanium sheet is ultrasonically cleaned with deionized water and anhydrous ethanol in sequence, dried, placed in an alkaline solution, and then transferred to a polytetrafluoroethylene liner of a high-pressure reactor, and sealed for hydrothermal reaction at 160-200°C for 10-48 hours; after the reaction is completed, the titanium sheet is cooled to room temperature, taken out, first washed with deionized water, then soaked in an acidic solution for 0.5-20 hours, taken out, washed with deionized water and anhydrous ethanol, and dried to obtain a titanium sheet with in-situ growth of H2Ti2O5·H2O on the surface.

[0006] The specific operation of the secondary hydrothermal method for in-situ growth of Bi2S3 on H2Ti2O5·H2O is as follows: first, a mixed solution of Bi(NO3)3 and Na2S2O3 is prepared, and then a titanium sheet with H2Ti2O5·H2O grown in situ on the surface is added, and then the solution is transferred to the polytetrafluoroethylene liner of a high-pressure reactor, the amount of the solution covering the titanium sheet, and a sealed hydrothermal reaction is carried out at 80-120°C for 10-48 hours. After the reaction is completed, the titanium sheet is removed after cooling to room temperature, washed with deionized water and anhydrous ethanol, and dried.

[0007] The alkaline solution is one or more of sodium hydroxide, lithium hydroxide and potassium hydroxide solutions.

[0008] The concentration of the alkaline solution is 2-5 mol / L.

[0009] The acidic solution is one or more of nitric acid, hydrochloric acid and sulfuric acid.

[0010] The concentration of the acidic solution is 0.1-0.5 mol / L.

[0011] The concentration of Bi(NO3)3 in the mixed solution is 1-4 mmol / L, and the concentration of Na2S2O3 is 1.5-6 mmol / L.

[0012] The above-prepared Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation is used for photothermal catalytic reduction of carbon dioxide.

[0013] The specific operation of the photothermal catalytic reduction of carbon dioxide is as follows: a Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation is placed in a reactor, carbon dioxide mixed with water vapor is introduced into the reactor, and after removing the air, light is irradiated at room temperature to 70°C for reaction.

[0014] The present invention has the following beneficial effects: 1) The raw materials used in the present invention are cheap and easily available, and the experimental operation is simple, the cycle is short, and the product can be easily recycled and reused.

[0015] 2) The prepared composite material combines two strategies (built-in electric field and heterojunction) into the material through a one-step calcination process, resulting in full-spectrum absorption and short carrier transport distance. This effectively separates photogenerated carriers and exhibits a high photothermal effect, significantly improving the photothermal catalytic CO2 conversion efficiency. The catalytic performance of the catalyst reaches its peak when the reduction temperature reaches 70°C. The maximum total CO production of the BST-2 catalyst within 5 hours is 380.2 μmol·g -1 ·h -1 At the same time, the average CO yield of BST-2 reached 76.04569 μmol·g -1 ·h -1 , respectively pure TiO2 (21.516 μmol·g -1 ·h -1 ) and Bi2S3 / TiO2 powder (40.34175 μmol·g -1 ·h -1 ) are 3.5 and 1.9 times.

[0016] 3) The prepared composite material exhibited a photothermal effect. The temperature of the catalyst rose rapidly after illumination, reaching its maximum temperature within 9.6 minutes. In particular, the surface plasmon resonance effect of Bi metal extended the light response to the near-infrared region, endowing the BST-2 catalyst with a more effective thermal effect. Its temperature rose rapidly from room temperature to 107.7°C, resulting in a significant CO generation rate of the BST-2 catalyst, which could be further increased to 76.04569 μmol·g -1 ·h -1 .

[0017] 4) The photocatalytic CO2 reduction rate of the present invention is high, and the composite material provides a new strategy for designing effective solar energy utilization solutions, which can be used to alleviate global energy shortages and anthropogenic climate change. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 SEM images of Bi2S3, TiO2, and BST-2; Figure 2 XRD characterization patterns of TiO2, Bi2S3, BST-1, BST-2 and BST-3; Figure 3 EPR diagrams of TiO2 and BST-2; Figure 4 Bi 4f and S 2p XPS spectra of Bi2S3 and BST-2; Figure 5 UV diffuse reflectance spectra of TiO2, Bi2S3, BST-1, BST-2 and BST-3; Figure 6 (a) CO2 photoreduction CO production rate of Bi2S3 / TiO2, TiO2, BST-1, BST-2 and BST-3, (b) CO production rate of TiO2 and BST-2 catalysts at different temperatures; Figure 7 (a) Photothermal images and (b) temperature curves of TiO2, Bi2S3 / TiO2, BST-1, BST-2 and BST-3 under xenon lamp. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it. Example 1

[0020] (1) In situ growth of H2Ti2O5·H2O on the surface of titanium sheet by hydrothermal method: 2×4.5 cm 2 A rectangular titanium sheet was ultrasonically cleaned with deionized water and anhydrous ethanol and placed in a 50 mL polytetrafluoroethylene reactor containing 35 mL of 3 mol / L NaOH solution. The reaction was hydrothermally reacted at 180°C for 20 h. After the reactor was cooled to room temperature, the titanium sheet was removed, rinsed with deionized water, and immersed in 0.1 mol / L HCl solution for 2 h. After removal, it was washed with deionized water and anhydrous ethanol and dried to obtain H2Ti2O5·H2O nanoflowers in situ grown on the surface of the titanium sheet.

[0021] (2) First, a mixed solution of Bi(NO3)3 and Na2S2O3 was prepared. The titanium sheet obtained in step (1) was then inserted into the solution. The solution was then transferred to a 50 ml sealed polytetrafluoroethylene-lined stainless steel autoclave. The amount of the solution covered the titanium sheet. The solution was hydrothermally reacted at 100°C for 24 h and then cooled to room temperature. The sample was washed with deionized water and anhydrous ethanol and then dried in an oven at 60°C. Next, the sample was placed in a porcelain boat in a tube furnace and heated to 500°C for annealing for 2 h under a N2 atmosphere to obtain a Bi / Bi2S3 / TiO2 heterojunction composite material supported on the titanium sheet based on internal electric field regulation. In the above mixed solution, the concentration of Bi(NO3)3 is 1mmol / L, the concentration of Na2S2O3 is 1.5mmol / L, and the obtained composite material is recorded as BST-1; the concentration of Bi(NO3)3 is 2mmol / L, the concentration of Na2S2O3 is 3mmol / L, and the obtained composite material is recorded as BST-2; the concentration of Bi(NO3)3 is 4mmol / L, the concentration of Na2S2O3 is 6mmol / L, and the obtained composite material is recorded as BST-3.

[0022] A piece of BST-1 was used as a catalyst (1×1 cm 2 ) was placed on a quartz tripod in a photocatalytic reactor (200 mL). High-purity CO2 was mixed with water vapor through a bubbler and introduced into the reactor. This process lasted for 1 hour to ensure CO2 adsorption-desorption equilibrium on the catalyst. A 300 W xenon lamp was used as the light source for the photocatalytic reaction for 5 hours. Throughout the reaction, the reaction products were quantitatively analyzed using gas chromatography (Agilent 7890B). Figure 6 As shown in Figure 2, the CO production rate of the BST-1 composite material is 60.8039 μmol·g -1 ·h -1 .

[0023] BST-2 was used as a catalyst (1×1 cm 2 ) was placed on a quartz tripod in a photocatalytic reactor (200 mL), and high-purity CO2 was mixed with water vapor through a bubbler and introduced into the reactor. The process lasted for 1 hour to ensure the CO2 adsorption-desorption equilibrium of the catalyst. A 300 W xenon lamp was used as the light source for the photocatalytic reaction for 5 hours. During the entire reaction process, the circulating water in the reaction system was maintained at 25°C, 50°C, and 70°C for three parallel tests. The reaction products were quantitatively analyzed by gas chromatography (Agilent 7890B), and no external light source was used as a comparative example. Figure 6 As shown in (b), the CO production rate of BST-2 material is 76.04569 μmol·g -1 ·h -1 、84.63654 μmol·g -1·h -1 、175.94459 μmol·g -1 ·h -1 .

[0024] A piece of BST-3 was used as a catalyst (1×1 cm 2 ) was placed on a quartz tripod in a photocatalytic reactor (200 mL). High-purity CO2 was mixed with water vapor through a bubbler and introduced into the reactor. This process lasted for 1 hour to ensure CO2 adsorption-desorption equilibrium on the catalyst. A 300 W xenon lamp was used as the light source for 5 hours of photocatalytic illumination. Throughout the reaction, the reaction products were quantitatively analyzed using gas chromatography (Agilent 7890B). Figure 6 As shown in Figure 2, the CO production rate of the BST-3 composite material is 44.44729 μmol·g -1 ·h -1 .

[0025] Comparative Example 1: First, a titanium sheet was ultrasonically cleaned with deionized water and anhydrous ethanol. The cleaned sheet was then oven-dried and placed in a sealed, polytetrafluoroethylene-lined stainless steel autoclave filled with 3 mol / L NaOH solution for a hydrothermal reaction at 180°C for 20 hours. After the autoclave cooled to room temperature, the titanium sheet was removed and rinsed with deionized water. The sample was then soaked in 0.1 mol / L hydrochloric acid for 2 hours, removed, rinsed with deionized water and anhydrous ethanol, and oven-dried at 60°C. Next, the sample was annealed at 500°C for 2 hours in a tube furnace under a nitrogen atmosphere to obtain in situ TiO2 growth on the titanium sheet.

[0026] The titanium sheet with in situ growth of TiO2 on the surface obtained above (denoted as TiO2) was directly used as a catalyst (1×1 cm 2 ) was placed on a quartz tripod in a photocatalytic reactor (200 mL), and high-purity CO2 was mixed with water vapor through a bubbler and introduced into the reactor. The process lasted for 1 hour to ensure the CO2 adsorption-desorption equilibrium of the catalyst. A 300 W xenon lamp was used as the light source for the photocatalytic reaction for 5 hours. During the entire reaction process, the circulating water in the reaction system was maintained at 25°C, 50°C, and 70°C for three parallel tests. The reaction products were quantitatively analyzed by gas chromatography (Agilent 7890B), and no external light source was used as a comparative example. Figure 6 As shown in (b), the CO generation rate of TiO2 / Ti foil material is 21.516 μmol·g -1 ·h -1 , 24.58 μmol·g -1 ·h -1 、27.018 μmol·g-1 ·h -1 .

[0027] Comparative Example 2: A mixed solution of Bi(NO3)3 and Na2S2O3 was prepared, with the concentration of Bi(NO3)3 being 1 mmol / L and the concentration of Na2S2O3 being 1.5 mmol / L; the solution was then poured into a sealed polytetrafluoroethylene-lined stainless steel high-pressure reactor containing a titanium sheet with surface in-situ grown TiO2 prepared in Control Example 1, with the amount of solution covering the titanium sheet, and the solution was hydrothermally reacted at 100°C for 24 hours to obtain Bi2S3 / TiO2 in situ grown on the titanium sheet.

[0028] A titanium sheet with in situ growth of Bi2S3 / TiO2 on its surface was placed on a quartz tripod in a photocatalytic reactor (200 mL). High-purity CO2 was mixed with water vapor through a bubbler and introduced into the reactor. This process lasted for 1 hour to ensure the CO2 adsorption-desorption equilibrium of the catalyst. A 300 W xenon lamp was used as the light source for the photocatalytic reaction for 5 hours. During the entire reaction process, the reaction products were quantitatively analyzed by gas chromatography (Agilent 7890B). Figure 6 As shown in Figure 2, the CO production rate of Bi2S3 / TiO2 material is 40.342 μmol·g -1 ·h -1 .

[0029] Experimental verification: Experiment 1: SEM and TEM images The BST-2 of the present invention and the comparative example TiO2 were photographed by field emission scanning electron microscope. Figure 1 The SEM picture shown. Figure 1 and Figure 7 The in situ grown H2Ti2O5·H2O on the titanium sheet exhibits a nanoflower structure. After a secondary hydrothermal treatment, Bi2S3 with an ultrathin nanosheet structure is deposited on the surface of the H2Ti2O5·H2O. After high-temperature calcination, Bi attaches to the Bi2S3 / TiO2, creating an internal electric field. The structure of the H2Ti2O5·H2O remains largely unchanged, with uniform distribution of elements. The nanosheet-based structure and built-in electric field enhance light utilization, reactant adsorption, and photogenerated charge carrier separation, exposing more active sites and improving photothermal catalytic efficiency.

[0030] Experiment 2: XRD Pattern The X-ray powder diffraction of the present invention's examples BST-1, BST-2 and BST-3 and the comparative example TiO2 was obtained as follows Figure 2 The XRD pattern shown by Figure 2It can be seen that the characteristic diffraction peaks of pure TiO2 at 25.3°, 37.8°, 48.1°, 53.9° and 55.1° correspond to the anatase (1 0 1), (0 0 4), (2 0 0), (1 0 5) and (2 1 1) crystal planes of TiO2. For pure Bi2S3, its main characteristic diffraction peaks are located at 24.9° and 28.6°, respectively, which are attributed to its (1 3 0) and (2 1 1) crystal planes (JCPDS No.17-0320). For Bi, its main characteristic diffraction peaks are located at 27.16° and 39.62°, respectively, which are attributed to its (0 1 2) and (1 10) crystal planes (JCPDS No.44-1246). However, the XRD pattern of the composite material shows diffraction peaks that are almost the same as those of pure TiO2. This is due to the low content and high dispersion of Bi2S3 and elemental Bi in the composite. In fact, as the Bi2S3 content in the composite increases, the intensity of the characteristic peak of TiO2 in the composite gradually weakens, which indeed confirms the successful hybridization of TiO2 and Bi2S3.

[0031] Experiment 3: UV-Vis Diffuse Reflectance Spectroscopy The catalysts BST-1, BST-2 and BST-3 of the present invention and the comparative example TiO2 were tested and obtained as follows: Figure 5 UV-Vis diffuse reflectance spectrum shown. Figure 5 It can be seen that TiO2 powder has strong absorption in the ultraviolet region. After being compounded with bismuth sulfide, the light absorption range of the BST composite material is expanded to the visible light region.

[0032] Experiment 4: Photothermal catalytic activity and temperature rise measurement The catalysts BST-1, BST-2 and BBST-3 of the present invention and TiO2 and Bi2S3 / TiO2 of the comparative examples were tested and obtained as follows: Figure 7 Different result graphs are shown. No obvious reduction products were detected in the pure heat reaction experiment of the comparative example pure TiO2 and the example BST-2 catalyst, while the CO production increased significantly after the introduction of light in the pure light and photothermal synergistic control experiments. At the same time, the production of CO increased significantly with the increase of temperature, proving that the photothermal synergistic effect helps to further improve the photocatalytic reduction performance. In addition Figure 7 The real-time photothermal images of the catalysts BST-1, BST-2 and BBST-3 and the comparative examples TiO2 and Bi2S3 / TiO2 under illumination were recorded. Figure 7It can be seen that the temperature of the catalyst rises rapidly after illumination and reaches the maximum temperature within 9.6 minutes. In particular, the surface plasmon resonance effect of Bi metal extends the light response to the near-infrared region, giving the BST-2 catalyst a more effective thermal effect, and its temperature rises rapidly from room temperature to 107.7 ° C. However, once the Bi2S3 content exceeds a certain amount, the TiO2 surface will be over-covered by Bi2S3. However, although the increase in Bi2S3 content is conducive to the absorption of light, the over-coverage of the surface Bi2S3 layer will hinder the transfer of photogenerated holes to the TiO2 catalyst, which is not conducive to the photothermal effect, thereby reducing the photothermal activity.

[0033] Experiment 5: Electron Paramagnetic Resonance Spectroscopy The electron paramagnetic resonance spectroscopy (EPR) of the present invention's BST-2 and comparative example TiO2 was used to obtain the following results: Figure 3 The EPR diagram shown by Figure 3 It can be seen that no signal peak was detected for TiO2, while a single Lorentz force signal was detected for the BST-2 composite material, indicating that BST-2 has unpaired electrons, that is, the formation of oxygen vacancies, thereby improving the CO2 conversion efficiency.

Claims

1. A method for preparing a Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation, characterized in that: The preparation method is specifically as follows: first, H2Ti2O5·H2O is in situ grown on the surface of a metal titanium sheet by a hydrothermal method, then Bi2S3 is in situ grown on the H2Ti2O5·H2O by a secondary hydrothermal method, and finally, the Bi / Bi2S3 / TiO2 heterojunction composite material is annealed at 400-600°C for 0.5-4 h in an inert atmosphere or N2 atmosphere in a tubular furnace.

2. The preparation method according to claim 1, characterized in that The specific operation of the hydrothermal method for in-situ growth of H2Ti2O5·H2O on the surface of a metal titanium sheet is as follows: the titanium sheet is ultrasonically cleaned with deionized water and anhydrous ethanol in sequence, dried, placed in an alkaline solution, and then transferred to a polytetrafluoroethylene liner of a high-pressure reactor, and sealed for hydrothermal reaction at 160-200°C for 10-48 hours; after the reaction is completed, the titanium sheet is cooled to room temperature, taken out, first washed with deionized water, then soaked in an acidic solution for 0.5-20 hours, taken out, washed with deionized water and anhydrous ethanol, and dried to obtain a titanium sheet with in-situ growth of H2Ti2O5·H2O on the surface.

3. The preparation method according to claim 2, characterized in that The specific operation of the secondary hydrothermal method for in-situ growth of Bi2S3 on H2Ti2O5·H2O is as follows: first, a mixed solution of Bi(NO3)3 and Na2S2O3 is prepared, and then a titanium sheet with H2Ti2O5·H2O grown in situ on the surface is added, and then the solution is transferred to the polytetrafluoroethylene liner of a high-pressure reactor, the amount of the solution covering the titanium sheet, and a sealed hydrothermal reaction is carried out at 80-120°C for 10-48 hours. After the reaction is completed, the titanium sheet is removed after cooling to room temperature, washed with deionized water and anhydrous ethanol, and dried.

4. The preparation method according to claim 2, characterized in that The alkaline solution is one or more of sodium hydroxide, lithium hydroxide and potassium hydroxide solutions.

5. The preparation method according to claim 2, characterized in that The concentration of the alkaline solution is 2-5 mol / L.

6. The preparation method according to claim 2, characterized in that The acidic solution is one or more of nitric acid, hydrochloric acid and sulfuric acid.

7. The preparation method according to claim 2, characterized in that The concentration of the acidic solution is 0.1-0.5 mol / L.

8. The preparation method according to claim 3, characterized in that The concentration of Bi(NO3)3 in the mixed solution is 1-4 mmol / L, and the concentration of Na2S2O3 is 1.5-6 mmol / L.

9. Application of the Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation prepared by the method according to any one of claims 1 to 8 in photothermal catalytic reduction of carbon dioxide.

10. The use according to claim 9, characterized in that The specific operation of the photothermal catalytic reduction of carbon dioxide is as follows: a Bi / Bi2S3 / TiO2 heterojunction composite material based on internal electric field regulation is placed in a reactor, carbon dioxide mixed with water vapor is introduced into the reactor, and after removing the air, light is irradiated at room temperature to 70°C for reaction.

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