A hydrophilic-hydrophobic dual-phase Bi2WO6-C3N4 heterojunction catalyst and a preparation method and application thereof

Abstract

This invention belongs to the field of new materials, specifically disclosing a hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst, its preparation method, and its application. Hydrophilic C3N4 powder is prepared by calcining melamine, and then hexadecyltrimethylammonium bromide (CTAB), bismuth nitrate pentahydrate, and sodium tungstate dihydrate are simultaneously added. The hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst is obtained using a hydrothermal method. This catalyst can be used as a photocatalyst for the photocatalytic reduction of CO2 in water vapor to CO and CH4. The hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst prepared in this invention has a hydrophobic Bi2WO6 surface that can directly transfer high concentrations of gaseous CO2 molecules to the catalyst, while the hydrophilic C3N4 surface can efficiently adsorb H2O molecules. This results in the biphase photocatalyst exhibiting high CO2 photocatalytic reduction efficiency in water vapor. It also exhibits higher photocatalytic activity in water vapor than the hydrophilic Bi2WO6-C3N4 monophase catalyst, and the photocatalytic reduction rate of CO2 to CO and CH4 is higher.

Description

Technical Field

[0001] This invention relates to the field of new materials, and in particular to a hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst, its preparation method, and its application. Background Technology

[0002] As one of the most attractive approaches to solving the energy and environmental crisis, solar-driven photocatalysis, which can reduce carbon dioxide into value-added chemicals, has attracted considerable attention in the scientific community. In recent years, researchers have focused on developing highly efficient photocatalysts, primarily through modifications related to morphology, interface or defect engineering, semiconductor heterojunctions, and dye sensitization. However, achieving carbon neutrality through photocatalysis still faces significant fundamental scientific challenges. For example, compared to the dominant photocatalytic hydrogen evolution reaction, CO2 reduction is kinetically slower due to its multi-step proton-coupled electron transfer pathway, requiring a larger reaction overpotential. Therefore, suppressing the competing hydrogen evolution reaction rate is crucial for improving CO2 conversion efficiency and selectivity.

[0003] Photocatalytic CO2 reduction is a rather complex reaction, beginning with the adsorption of CO2 molecules on the catalyst surface. CO2 adsorption is the most easily overlooked step, but it is actually fundamental to improving the efficiency of artificial CO2 conversion. High CO2 concentration and good CO2 trapping ability are crucial for the diffusion and adsorption kinetics of CO2 gas on the photocatalyst surface. A slow CO2 supply rate, i.e., slow diffusion and adsorption kinetics, results in less reactant adsorbed on the catalyst surface. The continuous accumulation of photogenerated electrons leads to recombination with holes, resulting in a high charge recombination rate. Three-dimensional hollow Bi2WO6 quantum dots prepared by Huang et al. exhibit high CO2 adsorption capacity and a wider band gap, demonstrating highly efficient solar CO2 reduction performance. Spherical Bi2WO6 prepared by Wang et al. significantly reduced the recombination rate, providing more stable alkaline sites for CO2 adsorption. Zou et al. reported ultrathin, uniform Bi2WO6 square nanoplates with high photogenerated support separation rate and high CO2 reduction photocatalytic activity. While the above photocatalysts enhance CO2 adsorption, they inevitably also enhance H2O adsorption. Due to the hydrophilicity of the catalyst surface, the concentration of H2O molecules is higher on hydrophilic surfaces, putting CO2 molecules at a disadvantage in the CO2 / H2O competitive adsorption. Antonietti et al. demonstrated that hydrophobic surfaces can overcome the mass transfer limitation of CO2 and increase the CO2 concentration on the catalyst surface. Although hydrophobic surfaces facilitate CO2 mass transfer, they significantly inhibit H2O adsorption. The rates of the CO2 reduction half-reaction and the H2O oxidation half-reaction simultaneously affect the conversion rate of photocatalytic CO2 reduction.

[0004] Chinese patent application CN201710115031.5 discloses a bismuth tungstate / carbon nitride composite photocatalyst, its preparation method, and its applications. Using Bi₂WO₆ synthesized by microwave hydrothermal synthesis and C₃N₄ obtained by co-firing melamine and urea as raw materials, and methanol as solvent, the bismuth tungstate / carbon nitride composite photocatalyst is synthesized by ultrasonic stirring. The bismuth tungstate / carbon nitride composite powder prepared by this method has high crystallinity, forms a heterojunction structure between components, and the composite process is carried out at room temperature under mild reaction conditions. The photocatalytic performance of the composite powder is significantly improved compared to Bi₂WO₆ and C₃N₄ powders, showing broad application prospects in the photocatalytic degradation of organic pollutants. However, this bismuth tungstate / carbon nitride composite photocatalyst does not reveal its ability to photocatalyze the reduction of CO₂ to CO and CH₄, nor can it solve the mass transfer problem of CO₂ and H₂O on the photocatalyst surface. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0007] The first objective of this invention is to provide a method for preparing a hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst, comprising the following steps:

[0008] S1. Hydrophilic C3N4 powder was prepared by calcining melamine.

[0009] S2. Take hydrophilic C3N4 powder, hexadecyltrimethylammonium bromide (CTAB), and bismuth nitrate pentahydrate in a mass ratio of 50–200:0–20:150 and add them together to an aqueous solution. After ultrasonic dispersion, a mixed solution A is obtained.

[0010] S3. Add sodium tungstate dihydrate to mixed solution A, wherein the mass ratio of sodium tungstate dihydrate to bismuth nitrate pentahydrate is 102:150, and stir until homogeneous to obtain mixed solution B;

[0011] S4. Pour the mixed solution B into a corrosion-resistant stainless steel reactor, heat it to 100-120℃, and react it in a sealed manner for 18-30 hours. After centrifugation, collect the solid, wash and dry the solid to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst.

[0012] Further, step S1 specifically includes:

[0013] Melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550°C for 4 hours, then allowed to cool naturally to room temperature. It was then poured into an open crucible and calcined again in a muffle furnace at 500°C for 1–3 hours to obtain hydrophilic C3N4 powder.

[0014] Preferably, the heating rate in the muffle furnace is 2 to 10 °C / min.

[0015] Preferably, in step S2, the mass ratio of hydrophilic C3N4 powder, hexadecyltrimethylammonium bromide (CTAB), and bismuth nitrate pentahydrate is 100:15:150.

[0016] Preferably, in step S2, ultrasonic dispersion is performed for 30 minutes, followed by magnetic stirring for 1 to 2 hours.

[0017] Preferably, the stirring in step S3 is magnetic stirring for 1 to 2 hours.

[0018] Preferably, in step S4, the collected solid is washed with distilled water and then vacuum dried at 60°C for 12 hours.

[0019] The second objective of this invention is to provide a hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst prepared by the above method.

[0020] The third objective of this invention is to provide an application of a hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst as a photocatalyst for the photocatalytic reduction of CO2 in water vapor to CO and CH4.

[0021] The principle of this invention is as follows: This invention ensures the directional migration of photogenerated charges by precisely controlling the band structure of the Bi2WO6-C3N4 heterojunction: electrons flow to the hydrophobic surface of Bi2WO6, and holes flow to the hydrophilic surface of C3N4, thereby achieving efficient carrier separation; the prepared hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst can simultaneously solve the mass transfer problem of CO2 and H2O on the catalyst surface during the photocatalytic reduction of CO2 in water vapor to CO and CH4. The hydrophobic Bi2WO6 transports high concentrations of CO2 to the catalyst surface, accelerating the reaction of CO2 with photogenerated electrons; while the hydrophilic C3N4 can efficiently adsorb H2O and undergo photooxidation with holes.

[0022] Compared with existing technologies, the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst prepared in this invention has the ability to directly transfer high concentrations of gaseous CO2 molecules to the catalyst via the hydrophobic surface of Bi2WO6, and the ability to efficiently adsorb H2O molecules via the hydrophilic surface of C3N4. This results in the biphase photocatalyst exhibiting high CO2 photocatalytic reduction efficiency in water vapor. It also exhibits higher photocatalytic activity in water vapor than the hydrophilic Bi2WO6-C3N4 monophase catalyst, and the photocatalytic reduction rate of CO2 to CO and CH4 is higher. Attached Figure Description

[0023] Figure 1 TEM images of C3N4 (a) prepared in Example 1 and Comparative Example 1 of the present invention and hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst (b, c, d) prepared in Example 1.

[0024] Figure 2 The UV-Vis diffuse reflectance spectrum (a), UPS diagram (b), VB-XPS diagram (c), and band structure diagram (d) of the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst prepared in Example 1 of this invention are shown.

[0025] Figure 3 The XRD pattern (a) and infrared spectrum (b) of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown.

[0026] Figure 4 The water contact angle diagrams are for the catalysts prepared in Examples 1, 2, 3, 4, Comparative Example 1, and Comparative Example 2 of this invention.

[0027] Figure 5 This is a CO2 reduction activity diagram of the catalysts prepared in Examples 1-5, Comparative Example 1, and Comparative Example 2 of the present invention during the CO2 reduction to CO and CH4 process in water vapor. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0029] Example 1

[0030] 8g of melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550℃ for 4 hours, with a heating rate of 4℃ / min. After cooling to room temperature, the obtained powder was placed in an open crucible and heated to 500℃ at 4℃ / min, and annealed for 2 hours to obtain hydrophilic C3N4 powder.

[0031] Add 40 ml of deionized water, 100 mg of hydrophilic C3N4 powder, 15 mg of CTAB, and 150 mg of bismuth nitrate pentahydrate (mass ratio of hydrophilic C3N4 powder:CTAB:bismuth nitrate pentahydrate: 100:15:150) to a beaker, sonicate for 30 min, and stir magnetically for 1 h; then add 102 mg of sodium tungstate dihydrate and stir magnetically for 1 h; pour the above mixture into a 100 ml corrosion-resistant stainless steel hydrothermal reactor at room temperature, heat to 120 °C, and react in a sealed container for 24 h; centrifuge the suspension, wash the solid with distilled water, and finally vacuum dry at 60 °C for 12 h to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst, denoted as BWO-CN-100.

[0032] Example 2

[0033] 8g of melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550℃ for 4 hours, with a heating rate of 4℃ / min. After cooling to room temperature, the obtained powder was placed in an open crucible and heated to 500℃ at 4℃ / min, and annealed for 2 hours to obtain hydrophilic C3N4. 40ml of deionized water, 50mg of hydrophilic C3N4 powder, 15mg of CTAB, and 150mg of bismuth nitrate pentahydrate (mass ratio of hydrophilic C3N4 powder:CTAB:bismuth nitrate pentahydrate: 50:15:150) were added to a beaker, and the mixture was sonicated for 30 minutes and magnetically stirred for 1 hour. Then, 102mg of sodium tungstate dihydrate was added, and the mixture was magnetically stirred for 1 hour. The mixture was then poured into a 100ml corrosion-resistant stainless steel hydrothermal reactor at room temperature, heated to 120℃, and reacted in a sealed environment for 24 hours. The suspension was centrifuged, the solid was washed with distilled water, and finally vacuum dried at 60°C for 12 hours to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction photocatalyst of the present invention, denoted as BWO-CN-50.

[0034] Example 3

[0035] 8g of melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550℃ for 4 hours, with a heating rate of 4℃ / min. After cooling to room temperature, the obtained powder was placed in an open crucible and heated to 500℃ at 4℃ / min, and annealed for 2 hours to obtain hydrophilic C3N4. 40ml of deionized water, 150mg of hydrophilic C3N4 powder, 15mg of CTAB, and 150mg of bismuth nitrate pentahydrate (mass ratio of hydrophilic C3N4 powder:CTAB:bismuth nitrate pentahydrate:150:150) were added to a beaker, and the mixture was sonicated for 30 minutes and magnetically stirred for 1 hour. Then, 102mg of sodium tungstate dihydrate was added, and the mixture was magnetically stirred for 1 hour. The mixture was then poured into a 100ml corrosion-resistant stainless steel hydrothermal reactor at room temperature, heated to 120℃, and reacted in a sealed environment for 24 hours. The suspension was centrifuged, the solid was washed with distilled water, and finally vacuum dried at 60°C for 12 hours to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction photocatalyst of the present invention, denoted as BWO-CN-150.

[0036] Example 4

[0037] 8g of melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550℃ for 4 hours, with a heating rate of 4℃ / min. After cooling to room temperature, the obtained powder was placed in an open crucible and heated to 500℃ at 4℃ / min, and annealed for 2 hours to obtain hydrophilic C3N4. 40ml of deionized water, 200mg of hydrophilic C3N4 powder, 15mg of CTAB, and 150mg of bismuth nitrate pentahydrate (mass ratio of hydrophilic C3N4 powder:CTAB:bismuth nitrate pentahydrate:200:15:150) were added to a beaker, and the mixture was sonicated for 30 minutes and magnetically stirred for 1 hour. Then, 102mg of sodium tungstate dihydrate was added, and the mixture was magnetically stirred for 1 hour. The mixture was then poured into a 100ml corrosion-resistant stainless steel hydrothermal reactor at room temperature, heated to 120℃, and reacted in a sealed environment for 24 hours. The suspension was centrifuged, the solid was washed with distilled water, and finally vacuum dried at 60°C for 12 hours to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction photocatalyst of the present invention, denoted as BWO-CN-200.

[0038] Example 5

[0039] 8g of melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550℃ for 4 hours, with a heating rate of 4℃ / min. After cooling to room temperature, the obtained powder was placed in an open crucible and heated to 500℃ at 4℃ / min for annealing for 2 hours to obtain hydrophilic C3N4. 40ml of deionized water, 150mg of hydrophilic C3N4 powder, 0mg of CTAB, and 150mg of bismuth nitrate pentahydrate (mass ratio of hydrophilic C3N4 powder:CTAB:bismuth nitrate pentahydrate:100:0:150) were added to a beaker, and the mixture was sonicated for 30 minutes and magnetically stirred for 1 hour. Then, 102mg of sodium tungstate dihydrate was added, and the mixture was sonicated for 30 minutes and magnetically stirred for 1 hour. The mixture was then poured into a 100ml corrosion-resistant stainless steel hydrothermal reactor at room temperature, heated to 120℃, and reacted in a sealed container for 24 hours. The suspension was centrifuged, the solid was washed with distilled water, and finally vacuum dried at 60°C for 12 hours to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction photocatalyst of the present invention, denoted as BWO-CN-S.

[0040] Comparative Example 1

[0041] 8g of melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550℃ for 4 hours, with a heating rate of 4℃ / min. After cooling to room temperature, the obtained powder was placed in an open crucible and heated to 500℃ at 4℃ / min, and annealed for 2 hours to obtain hydrophilic C3N4 powder.

[0042] Comparative Example 2

[0043] Add 40 ml of deionized water, 15 mg of CTAB, and 150 mg of bismuth nitrate pentahydrate (CTAB:bismuth nitrate pentahydrate mass ratio: 15:150) to a beaker, sonicate for 30 min, and magnetically stir for 1 h. Then add 102 mg of sodium tungstate dihydrate and magnetically stir for 1 h. Pour the mixture into a 100 ml corrosion-resistant stainless steel hydrothermal reactor at room temperature, heat to 120 °C, and react under sealed conditions for 24 h. Centrifuge the suspension, wash the solid with distilled water, and finally vacuum dry at 60 °C for 12 h to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction photocatalyst of this invention, denoted as BWO.

[0044] See Figure 1 TEM images of C3N4 (a) prepared in Example 1 of this invention and the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalysts (b, c, d) prepared in Example 1 are shown. Figure 1 It can be seen that the prepared C3N4 has a nanosheet structure, while Bi2WO6 nanoparticles are uniformly loaded on the C3N4 nanosheets, forming a Bi2WO6-C3N4 heterojunction. (Continue reading...) Figure 2The XRD pattern (a) and infrared spectrum (b) of the catalyst prepared in Example 1 of this invention are shown below. Figure 2 It can be seen that the prepared Bi2WO6-C3N4 heterojunction is a type II structure. Furthermore, refer to... Figure 3 , Figure 3 The XRD pattern (a) and infrared spectrum (b) of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown below. Figure 3 It can be seen that the Bi2WO6-C3N4 heterojunction was successfully prepared, and CTAB was successfully adsorbed on Bi2WO6.

[0045] Continue reading Figure 4 The water contact angle diagrams of the catalysts prepared in Examples 1, 2, 3, 4, Comparative Example 1, and Comparative Example 2 are shown. The diagrams show that the water contact angle of BWO-CN-100 is initially 91°, which decreases to 46° after 10 minutes; the water contact angle of BWO-CN-50 is initially 112°, which decreases to 71° after 10 minutes; the water contact angle of BWO-CN-150 is initially 59°, which decreases to 0° after 1 minute; the water contact angle of BWO-CN-200 is initially 49°, which decreases to 0° after 1 minute; the water contact angle of BWO-CN-S is initially 0°; the water contact angle of hydrophilic C3N4 is initially 0°; and the water contact angle of BWO is initially 124°, which decreases to 119° after 10 minutes.

[0046] Depend on Figure 4 It is evident that the original BWO is hydrophobic, while the original CN is completely hydrophilic. The hydrophobic-hydrophilic phase BWO-CN initially exhibits hydrophobic properties, but its water contact angle gradually decreases over time. The nonpolar long carbon chain adsorption of CTAB on Bi2WO6 leads to a larger contact angle. Meanwhile, H2O gradually forms hydrogen bonds with polar groups in C3N4, causing water droplets to be absorbed over time. With increasing hydrophilic CN content, the contact angle disappears more rapidly, indicating the existence of a hydrophobic-hydrophilic dual phase within BWO-CN.

[0047] Furthermore, the catalysts prepared in Examples 1-5, as well as Comparative Documents 1 and 2, were evaluated for their photocatalytic CO2 reduction activity in water splitting under steam. The specific experimental procedures are as follows:

[0048] Photocatalytic CO2 reduction was carried out in a 250 ml Pyrex glass reactor: 20 mg of photocatalyst was mixed with 5 ml of deionized water and ultrasonically dispersed in a solution with an area of ​​23.75 cm². 2The CO and CH4 were placed in a petri dish, and water was evaporated at 60°C to form a uniform thin film. The petri dish was placed at the bottom of the reactor, and the air in the reactor was removed using a vacuum pump. Subsequently, a mixture of CO2 gas and water vapor was introduced into the reactor through a bubbler, using a 300W xenon lamp as the light source. A circulating cooling water system was used to maintain the reaction temperature at 25°C. CO and CH4 were analyzed using a gas chromatograph equipped with a thermal conductivity detector and a flame ionization detector. The rates of CO and CH4 production are shown in Table 1. Figure 5 As shown.

[0049] Table 1

[0050] catalyst CO production rate (μmol / g / h) <![CDATA[CH4 production rate (μmol / g / h)]]> BWO-CN-100 25.54 7.96 BWO-CN-50 14.33 2.46 BWO-CN-150 15.99 3.40 BWO-CN-200 11.52 2.13 BWO-CN-S 2.42 0.38 <![CDATA[C3N4]]> 1.43 0.20 BWO 4.82 0.69

[0051] From Table 1 and Figure 5 It can be seen that the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst prepared when the mass ratio of hydrophilic C3N4 powder:CTAB:bismuth nitrate pentahydrate is 100:15:150 has the highest photocatalytic activity, with a maximum CO production rate of 25.54 μmol / g / h and a maximum CH4 production rate of 7.96 μmol / g / h. The reason for this is that the hydrophobic Bi2WO6 transports high-concentration CO2 to the surface of the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst, accelerating the reaction between CO2 and photogenerated electrons; while the hydrophilic C3N4 can efficiently adsorb H2O and undergo photooxidation with holes. Compared with the hydrophilic Bi2WO6-C3N4 single-phase catalyst, it has higher photocatalytic activity and a higher rate of photocatalytic CO2 reduction to CO and CH4.

[0052] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst, characterized in that, Includes the following steps: S1. Preparation of hydrophilic C3N4 powder by calcination of melamine: Melamine was placed in a semi-enclosed crucible and calcined in a muffle furnace at 550°C for 4 hours, then allowed to cool naturally to room temperature. It was then poured into an open crucible and calcined in a muffle furnace at 500°C for a second annealing process of 1–3 hours to obtain hydrophilic C3N4 powder. S2. Hydrophilic C3N4 powder, hexadecyltrimethylammonium bromide (CTAB), and bismuth nitrate pentahydrate were added to an aqueous solution at a mass ratio of 100:15:150 and dispersed by ultrasonication to obtain mixed solution A. S3. Add sodium tungstate dihydrate to mixed solution A, wherein the mass ratio of sodium tungstate dihydrate to bismuth nitrate pentahydrate is 102:150, and stir until homogeneous to obtain mixed solution B; S4. Pour the mixed solution B into a corrosion-resistant stainless steel reactor, heat it to 100-120 ℃, and react it in a sealed manner for 18-30 h. After centrifugation, collect the solid, wash and dry the solid to obtain the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst.

2. The preparation method of the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction photocatalyst according to claim 1, characterized in that, The heating rate in the muffle furnace is 2–10 °C / min.

3. The preparation method of the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst according to claim 1, characterized in that, In step S2, ultrasonic dispersion is performed for 30 minutes, followed by magnetic stirring for 1–2 hours.

4. The preparation method of the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst according to claim 1, characterized in that, The stirring in step S3 is magnetic stirring for 1 to 2 hours.

5. The preparation method of the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst according to claim 1, characterized in that, In step S4, the collected solid is washed with distilled water and then vacuum dried at 60 °C for 12 h.

6. A hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst prepared by the method according to any one of claims 1-5.

7. The application of the hydrophilic-hydrophobic biphase Bi2WO6-C3N4 heterojunction catalyst as described in claim 6 as a photocatalyst for the photocatalytic reduction of CO2 in water vapor to CO and CH4.

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